Universe, 5th edition

Odenwald, S. The Astronomy Cafe. W. H. Freeman, 1998. This wonderful little book contains the answers to 365 common questions about astronomy. The accompanying web site http://www2.ari.net/home/odenwald/cafe.html has even more!

World Wide Web:

Astronomy Now! is the on-line version of Britain's best-selling astronomy magazine. This web site is an excellent source for the latest astronomical news.
Link: http://www.astronomynow.com/

Yahoo! (a well-known source for information on the Web) has a special page devoted to the latest discoveries in astronomy. It includes links to web pages with the original data and press releases, as well as links to articles about new discoveries written by the world's finest science journalists.
Link: http://headlines.yahoo.com/Full_Coverage/Tech/Astronomy_Discoveries/

Another excellent source for news about the latest developments in astronomy is NASA's Marshall Space Flight Center. Regular press releases from their web site will keep you up to date on a variety of branches of astronomy.
Link: http://science.msfc.nasa.gov/newhome/pad/padheadlines.htm

For the latest discoveries about our solar system, one of the best places to check is the "News Flashes" page of NASA's Jet Propulsion Laboratory web site.
Link: http://www.jpl.nasa.gov/news/

The European Space Agency (ESA) has a new web site with links to the latest discoveries made by ESA research projects. (1998 August 6)
Link: http://sci.esa.int/

Watch out for bad astronomy: Newspapers, television, and the movies often present incorrect ideas about astronomy. The entertaining "Bad Astronomy" web site can help you separate the science from the fiction. It also provides help with many common misconceptions about astronomy. (1998 June 20)
Link: http://www.badastronomy.com/

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Chapter 2 Knowing the Heavens

Books and magazine articles:

Rubincam, D. P., Chao, B. F., and Bills, B. G. "The Incredible Shrinking Tropics." Sky & Telescope, June 1998. The tilt of the Earth's axis is slowly decreasing. This brief article describes the reasons why, as well as the consequences of these subtle changes.

World Wide Web:

The motions of the Sun: If you were to note the Sun's position in the sky every day at the same time, you would find that the Sun appears to move north and south with the changing of the seasons, but also seems to move east and west. As a result, on some days the Sun is highest in the sky at noon, while on other days this happens before noon or after noon. The reasons for these curious changes are lucidly described at a new and richly illustrated web site. (1998 June 17)
Link: http://www.analemma.com/

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Chapter 3 Eclipses and the Motion of the Moon

Books and magazine articles:

Olson, D. W., Fienberg, R. T., and Sinnott, R. W. "What's a Blue Moon?" Sky & Telescope, May 1999.
Hiscock, P. "Once in a Blue Moon." Sky & Telescope, March 1999. When two full moons occur in a calendar month, the second one is called a "blue moon." But where did this phrase come from? In these articles, a folklorist and three astronomers search for the answer.

Stephenson, F. R. "Early Chinese Observations and Modern Astronomy." Sky & Telescope, February 1999. Skywatchers of ancient China left behind detailed astronomical records that extend back to the 7th century BC. This article describes this magnificent collection of data, and explains how modern scientists have used these data to help understand the nature of supernovae and how the rotation of the Earth changes over time.

Walker, C. B. F., ed. Astronomy Before the Telescope. St. Martin's, 1997. This remarkable collection of essays traces the history of astronomy before 1610, including the astronomical ideas of the native peoples of Africa, Asia, and the Americas as well of those of Europeans.

World Wide Web:

Java-based tutorial on the phases of the Moon: If your web browser supports Java, you can use a wonderful tutorial on lunar phases provided by Prof. Lawrence A. Molnar of the Physics and Astronomy Department at the University of Iowa. It includes sections on time of day, time of month and apparent direction of the moon. (1998 June 4)
Link: http://www-astro.physics.uiowa.edu/~lam/teaching/moon/

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Chapter 4 Gravitation and the Motions of the Planets

Books and magazine articles:

Moyer, A. E. "Simon Newcomb: Astronomer with an Attitude." Scientific American, October 1998. A century ago, the most acclaimed American scientist was the astronomer Simon Newcomb, who carried out detailed calculations of the motions of the inner planets and the Moon. As this entertaining article describes, Newcomb was also an investigator of psychic claims, a political economist, and a popular advocate of the scientific method.

White, R. J. "Weightlessness and the Human Body." Scientific American, September 1998. After almost four decades of human space flight, as this informative article describes, medical researchers have begun to understand the curious effects of long-term weightlessness on astronauts. An expanded version of this article is also available on the World Wide Web
( http://www.sciam.com/1998/0998issue/0998white.html).

Johnson, N. L. "Monitoring and Controlling Debris in Space." Scientific American, August 1998. Most of the objects orbiting the Earth are bits of debris left behind by forty years of satellites. As this article describes, such debris poses a real threat to manned and unmanned spacecraft.

Lucid, S. W. "Six Months on Mir." Scientific American, May 1998. A NASA astronaut recounts the experiences and sensations of spending half a year in weightlessness on board the Russian space station Mir. An expanded version of this article is also available on the World Wide Web
( http://www.sciam.com/1998/0598issue/0598lucid.html).

World Wide Web:

Calculate your weight on other worlds: Your weight depends on your mass, the mass of the planet on which you're standing, and the radius of the planet. A Java-based calculator provided by the Exploratorium in San Francisco makes it easy to explore how your weight would vary on different worlds of the solar system. (1998 August 10)
Link: http://www.exploratorium.edu/ronh/weight/index.html

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Chapter 5 The Nature of Light and Matter

Books and magazine articles:

Armbruster, P., and Hessberger, F. P. "Making New Elements." Scientific American, September 1998. There are several chemical elements whose existence has been predicted theoretically but which have never been found in nature. This article by two leading researchers explains how scientists attempt to synthesize these new elements in the laboratory.

Scerri, E. R. "The Evolution of the Periodic System." Scientific American, September 1998. This informative article describes how the periodic table of the elements (discussed in Box 5-4) came to be devised in the second half of the nineteenth century.

World Wide Web:

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Chapter 6 Optics and Telescopes

Books and magazine articles:

Stix, G. "A New Eye Opens on the Cosmos." Scientific American, April 1999. This beautifully illustrated article describes the challenges involved in building a modern state-of-the-art telescope, the 8.1-meter Gemini North, atop the summit of Mauna Kea.

Panek, R. Seeing and Believing: How the Telescope Opened Our Eyes and Minds to the Universe. Viking, 1998. In the four centuries since Galileo first trained his telescope on the heavens, telescopes have helped revolutionize our understanding of the natural world. This clearly-written book recounts the history of this revolution.

Dickinson, T., and Newton, J. Splendors of the Universe. Firefly, 1997. This copiously illustrated book is a practical guide to making images of the night sky. The authors explain how beginners armed with no more than a camera and a tripod can make wonderful photographs.

World Wide Web:

Chandra X-ray Observatory to be orbited in 1999: Formerly known as AXAF (Advanced X-ray Astrophysics Facility), the Chandra X-ray Observatory --- named for astrophysicist and Nobel laureate Subrahmanyan Chandrasekhar --- is to be placed in orbit no earlier than May 1999. Once operational, Chandra will observe X-rays from energetic regions of the universe, such as hot gas in the remnants of supernovae, with angular resolution far superior to any previous X-ray telescope. (1999 January 20)
Links: http://xrtpub.harvard.edu/ and http://snail.msfc.nasa.gov/axaf/axaf.html

ROSAT mission comes to an end: ROSAT, the X-ray telescope placed into Earth orbit in 1990, has ceased operation after the failure of its on-board detectors. During its eight years of operation, ROSAT --- a joint mission of Germany, the United Kingdom, and the United States --- discovered 150,000 X-ray sources, provided new insights into how stars are formed, and offered puzzling new data about the most distant galaxies (the first ones to form after the Big Bang). (1998 December 9)
Link: http://www.astronomynow.com/breaking/981216rosat/

The Hubble Heritage Project: A new web site from the Space Telescope Science Institute (STScI) is dedicated to presenting the finest images from the tens of thousands returned so far from the Hubble Space Telescope. The site also includes a wealth of background information on each selected image. (1998 October 22)
Link: http://heritage.stsci.edu/public/

First scientific results from space VLBI: In the first application of space VLBI (very long-range interferometry), an international consortium of astronomers has successfully combined observations made by an orbiting 8-meter radio telescope with simultaneous observations made by several radio telescopes at different locations on Earth. The resulting images of quasars billions of lightÐyears away reveal previously unseen details of these remote objects. (1998 September 17)
Links: http://www.jpl.nasa.gov/releases/98/spacevlbi.html and http://sgra.jpl.nasa.gov/

Very Large Telescope produces first images: The first of the four 8.2-meter telescopes that will make up the Very Large Telescope array in Chile has produced its first images. Among the razor-sharp images is a high-resolution view of the Butterfly Nebula (NGC 6302), an image of which (from the Hubble Space Telescope) appears on the cover of Universe. (1998 May 27)
Link: http://www.hq.eso.org/outreach/info-events/ut1fl/pr-pictures/ut1fl-set3.html

Infrared Space Telescope ceases observations: As had been anticipated, the Infrared Space Telescope (ISO) ran out of liquid helium coolant in April 1998. As the temperature of the image sensors rose, they became unusable (infrared telescopes require low temperatures) and were shut down. Many ISO observations remain to be analyzed. The next infrared telescope planned to go into orbit is NASA's Space Infrared Telescope Facility (SIRTF), scheduled for a December 2001 launch. (1998 April 8)
Links: http://isowww.estec.esa.nl/activities/info/iso_end.html and http://sirtf.jpl.nasa.gov/sirtf/home.html

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Chapter 7 Our Solar System

Books and magazine articles:

Wood, J. A.. "Forging the Planets." Sky & Telescope, January 1999. This copiously-illustrated article describes the present state of understanding of how our solar system came to be, and points out areas where more research still needs to be done.

LePage, A. J. "Habitable Moons." Sky & Telescope, December 1998. None of the extrasolar planets yet discovered are likely homes for life. But if these planets have moons comparable to those of our Jovian planets, such moons might support life forms. This fascinating article describes these intriguing possibilities.

Boss, A. Looking for Earths: The Race to Find New Solar Systems. John Wiley & Sons, 1998. This entertaining book tells the tale of how astronomers first discovered planets orbiting other stars, and provides a glimpse of how we may discover Earthlike worlds beyond our solar system.

World Wide Web:

New HST images of possible protoplanetary disks: Hubble Space Telescope observations of two young stars may provide new clues about the origin of planets. One of the stars is surrounded by a disk within which there is a gap some 6 x 10⁹ km wide. Such gaps are predicted by certain theories of planet formation. (1999 January 8)
Link: http://oposite.stsci.edu/pubinfo/pr/1999/03/

A binary star system with a massive planet: A team of Swiss astronomers (including Didier Queloz and Michel Mayor, who discovered the first extrasolar planet in 1995) have discovered a planet in the binary star system Gliese 86. The two stars in this system orbit each other at a distance of only about 10 AU, while the planet orbits the brighter star at a distance of only 0.11 AU. Explaining how such an unusual system of stars and planets came to be is a major challenge to current theories of planet formation. (1998 November 24)
Link: http://www.astronomynow.com/breaking/981124newplanet/

A solar system in the making?: Using NASA's Infrared Telescope Facility atop Mauna Kea, astronomers at the University of Arizona have discovered a dusty "debris disk" around the Sunlike star 55 Cancri. This star is already known to be orbited by a planet larger than Jupiter. The inner edge of this debris disk lies some 44 AU from the star, about the same as the distance from the Sun to Pluto. The 55 Cancri system may resemble our own solar system as it was early in its history, when planets were in the process of formation and a debris disk encircled the Sun --- a disk from which condensed a cloud of comets and other icy objects. (1998 October 22)
Link: http://science.opi.arizona.edu/lasso.acgi?-database=science.fp3&-layout=Fields&-response=%2f%7escience%2fcurrentdetails.htm&-recid=34267&-search

Two more extrasolar planets discovered: By using one of the giant 10-meter Keck telescopes in Hawaii, a team of astronomers have located two more planets orbiting other stars. In each case the planet is about the size of Jupiter and the star is similar to our Sun, though the distance from star to planet is much less than the Sun-Jupiter distance. (1998 September 30)
Link: http://www.astronomynow.com/breaking/980925planet/ and http://www.physics.sfsu.edu/~gmarcy/planetsearch/news.html

Protoplanetary disks spotted in binary star system: Astronomers using the Very Large Array in New Mexico have discovered a young binary star system with two protoplanetary disks, one around each star. These observations suggest that planets may form more often in binary systems than had heretofore been suspected. (1998 September 24)
Links: http://www.nrao.edu/pr/protodisks.html and http://antwrp.gsfc.nasa.gov/apod/ap980925.html

View the solar system in 3-D: A wonderful collection of three-dimensional images of geological features from across the solar system can be found at a web site maintained by the Lunar and Planetary Institute. To view these images, you will need a pair of glasses with one red lens and one blue lens. A more extensive collection of 160 such images is available on an inexpensive CD-ROM, which can be ordered through this site. (1998 September 6)
Link: http://cass.jsc.nasa.gov/research/stereo_atlas/START.HTM

Build a model of the solar system: An excellent way to get a feel for the immense distances between the planets is to build a scale model of the solar system. A Java-based calculator provided by the Exploratorium in San Francisco will help you with this easy and fun project. (1998 August 10)
Link: http://www.exploratorium.edu/ronh/solar_system/

Another extrasolar planet discovered: Astronomers have used the radial velocity method (described in Section 7-9) to reveal the presence of a planet orbiting the star Gliese 876. This star is only 15 light-years from the Sun. (1998 June 26)
Links: http://antwrp.gsfc.nasa.gov/apod/ap980626.html and http://cannon.sfsu.edu/~gmarcy/planetsearch/gl876/gl876.html

First direct view of a possible extrasolar planet: The Hubble Space Telescope has given astronomers their first direct look at what is possibly a planet outside our solar system -- one apparently that has been ejected into deep space by its parent stars. (1998 May 28)
Link: http://oposite.stsci.edu/pubinfo/pr/1998/19/

A possible early solar system: Astronomers have discovered that one of the stars in the binary system HR 4796 is surrounded by a protoplanetary disk --- at the center of which is a "hole" some 30 to 50 AU around the star. Could this be a region within which planets have already formed? (1998 April 21)
Links: http://www.noao.edu/outreach/press/pfdisk.html and http://www.jpl.nasa.gov/releases/98/hr4796.html

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Chapter 8 Our Living Earth

Books and magazine articles:

Bell, R. E. "Gravity Gradiometry." Scientific American, June 1998. By measuring tiny variations in the Earth's gravity from one place to another, geologists can probe beneath our planet's surface with unprecedented precision.

World Wide Web:

New insight into the Earth's dynamic environment: The region of space immediately surrounding the Earth continues to reveal new and surprising information. One recent discovery is that the Earth's magnetosphere acts like a gigantic particle accelerator, taking slow-moving particles from the solar wind and accelerating them to nearly the speed of light. Another is that eruptions on the Sun can cause oxygen and other gases from our atmosphere to gush into space. These findings come from the International Solar-Terrestrial Physics program, which uses a constellation of spacecraft from the United States, Russia, Europe, and Japan to study how the Sun affects the Earth's environment in space. (1998 December 8)
Links: http://www-istp.gsfc.nasa.gov/istp/news/9812/ and http://www-istp.gsfc.nasa.gov/istp/outreach/profile.html

Images of the Earth from orbit: Space Shuttle astronauts have taken over 250,000 photographs of the Earth from orbit. A NASA web site features the best 500 of these. (1998 June 6)
Link: http://earth.jsc.nasa.gov/

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Chapter 9 Our Barren Moon

Books and magazine articles:

Bean, A., and Chaikin, A. Apollo: An Eyewitness Account. The Greenwich Workshop Press, 1998. After becoming the fourth human to walk on the Moon, astronaut Alan Bean began a new career as an accomplished artist. This magnificent book includes more than 90 of Bean's paintings of the human exploration of the lunar surface.

Foust, J. A. "The Moon Rediscovered." Sky & Telescope, December 1998. Even more discoveries from Lunar Prospector --- including updates on the Moon's magnetic field and on the evidence for ice at the lunar poles --- are described in this informative article.

Foust, J. A. "NASA's New Moon." Sky & Telescope, September 1998. This article describes many of the remarkable discoveries made by the Lunar Prospector spacecraft. Besides confirming the existence of ice at the Moon's north and south poles, Lunar Prospector has provided new insights into the chemical makeup of the lunar surface.

World Wide Web:

"From the Earth to the Moon": The excellent TV miniseries of this name has an accompanying web site with much interesting information about the human exploration of the Moon. (1998 April 5)
Link: http://www.hbo.com/apollo/

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Chapter 10 Sun-Scorched Mercury

Books and magazine articles:

Sheehan, W., and Dobbins, T. "Le Verrier's Wild Geese." Sky & Telescope, October 1998. For several years during the middle of the nineteenth century, a number of astronomers felt certain that they had discovered a planet that orbited even closer to the Sun than Mercury. This entertaining article describes the rise and fall of this idea --- and proposes that rather than a planet, these astronomers may actually have been seeing birds flying in front of their telescopes!

World Wide Web:

New proposal for a mission to Mercury: The Japanese space agency is proposing a new unmanned mission to Mercury that would be carried out in collaboration with NASA. The proposed spacecraft would be launched in 2005. (1998 June 15)
Link: http://news.bbc.co.uk/hi/english/sci/tech/newsid_112000/112804.stm

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Chapter 11 Cloud-Covered Venus

Books and magazine articles:

Bullock, M. A., and Grinspoon, D. H. "Global Climate Change on Venus." Scientific American, March 1999. As little as 800 million (8 x 10⁸) years ago, the surface of Venus was a much more benign place than it is today. This article describes how massive volcanic activity resurfaced the planet and triggered the greenhouse effect that keeps present-day Venus so hot.

World Wide Web:

Cassini flies past Venus en route to Saturn: The Cassini spacecraft, which was launched in October 1997, made a close flyby of Venus on April 26, 1998. While gaining energy from Venus to propel it to a rendezvous with Saturn in 2004, Cassini made observations of Venus's atmosphere. (1998 April 26)
Link: http://www.jpl.nasa.gov/cassini/MoreInfo/pressrel/status980426.html

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Chapter 12 Red Planet Mars

Books and magazine articles:

Treiman, A. "Microbes in a Martian Meteorite?" Sky & Telescope, April 1999. This article describes the current status of a scientific controversy: Does the Martian meteorite ALH 84001 (Section 12-8 of UNIVERSE) contain fossil microbes from Mars?

Malin, M. C. "Visions of Mars." Sky & Telescope, April 1999. The designer of the camera on board Mars Global Surveyor (MGS), and a planetary scientist in his own right, describes the remarkable discoveries that MGS has made so far about Martian geology.

David, L. "A Master Plan for Mars." Sky & Telescope, April 1999. NASA's series of unmanned missions to Mars is planned to continue for the next several years. This article surveys current plans for the ongoing exploration of the red planet.

Dobbins, T., and Sheehan, W. "The Colors of Mars: Reality and Illusion" Sky &Telescope, April 1999. As seen through a telescope, the surface of Mars displays a variety of different colors. As this article describes, the true colors of the planet can be quite different.

Parker, S. "The Triumphant Turnaround of Mars Global Surveyor." Sky & Telescope, August 1998. This article describes how the Mars Global Surveyor spacecraft has overcome technical malfunctions to provide new insights into the nature of the Martian surface.

Bell, J. "Mars Pathfinder: Better Science?" Sky & Telescope, July 1998. A member of the Mars Pathfinder science team summarizes the remarkable scientific bounty from that brave little spacecraft.

Golombek, M. "The Mars Pathfinder Mission." Scientific American, July 1998. The project scientist for the Mars Pathfinder mission describes the evidence that Mars was once far warmer and wetter than it is today.

Gibson, E. K., McKay, D. S., Thomas-Keprta, K., and Romanek, C. S. "The Case for Relic Life on Mars." Scientific American, December 1997. This article --- written by the scientific team that first claimed to have found ancient Martian microbes within the meteorite ALH 84001 --- summarizes the evidence in favor of that conclusion. An expanded version of this article is also available on the World Wide Web
( http://www.sciam.com/1297issue/1297gibson.html).

World Wide Web:

Mars Climate Orbiter en route to the red planet: The Mars Climate Orbiter (MCO) spacecraft was launched successfully on December 11, 1998. MCO is scheduled to enter Martian orbit on September 23, 1999. Its mission is to observe variations in the Martian climate at close range over an entire Martian year (1.88 Earth years). It will also provide support for the Mars Polar Lander spacecraft, which is scheduled to land near the edge of the Martian north polar cap in December 1999. (1998 December 11)
Link: http://mars.jpl.nasa.gov/msp98/orbiter/

3-D views of the north pole of Mars: Using an on-board laser altimeter, the Mars Global Surveyor spacecraft has provided scientists with a detailed topographic map of the Martian north pole. The data reveals the presence of deep canyons and troughs utterly unlike anything found in the Earth's polar regions. (1998 December 6)
Links: http://www.msss.com/mars/global_surveyor/camera/images/MENUS/poles_list.html and http://www.astronomynow.com/breaking/981207marspole/

New images of Martian volcanoes and channels: Spectacular new images from Mars Global Surveyor reveal details on the giant volcano Olympus Mons and in Kasei Vallis, an extensive series of channels thought to have been carved out a billion years ago or more by catastrophic floods. (1998 October 13)
Links: http://www.astronomynow.com/breaking/981013mgs/index.html and http://mpfwww.jpl.nasa.gov/mgs/msss/camera/images/10_12_98_dps_release/

The powdered surface of Phobos: Infrared observations by Mars Global Surveyor show that the surface of Phobos, the inner and larger of the two Martian moons, cools off very rapidly as Phobos rotates and the surface moves from sunshine into shadow. To explain this rapid cooling, scientists at Arizona State University suggest that the surface of Phobos is covered with a meter-thick layer of dust particles. Such a layer, which can change its temperature much more readily than a solid, rocky surface, could have been produced by eons of meteorite impacts. (1998 September 12)
Links: http://www.jpl.nasa.gov/releases/98/mgsphobos.html and http://antwrp.gsfc.nasa.gov/apod/ap980914.html

Comprehensive list of Martian links: An especially comprehensive list of links to information about Mars exploration is maintained by the Mars Global Surveyor Thermal Emission Spectrometer project team at Arizona State University. (1998 September 6)
Link: http://emma.la.asu.edu/newsurveyormenu.html

Japanese spacecraft en route to Mars: The Japanese spacecraft Nozomi was launched toward Mars on July 3, 1998. When it enters Martian orbit in October 1999, it will devote most of its observations to studies of the planet's atmosphere and magnetic field. Formerly known as Planet-B, Nozomi (Japanese for "Hope") is Japan's first interplanetary spacecraft. (1998 September 4)
Links: http://nssdc.gsfc.nasa.gov/cgi-bin/database/www-nmc?98-041A,
http://www.planet-b.isas.ac.jp/index-e.html, and
http://antwrp.gsfc.nasa.gov/apod/ap980904.html

Mars Pathfinder anniversary: A year after Mars Pathfinder arrived at the red planet, research continues into understanding the history of the Martian surface. (1998 June 29)
Link:http://www.jpl.nasa.gov/releases/98/mpfanniv.html

A dried-up Martian pond(?): A newly-released image from Mars Global Surveyor shows what may be a dried-up pond where water once stood on the surface of Mars. Islands and bays can be seen within the pond. Further observations will be needed to determine whether these features were caused by liquid water or by lava. (1998 May 27)
Links: http://antwrp.gsfc.nasa.gov/apod/ap980603.html and http://www.msss.com/mars/global_surveyor/camera/images/5_27_98_agu_release/

The "Face" on Mars: Some people have claimed that a Viking Orbiter image shows a human face carved on the surface of Mars. In April 1998, Mars Global Surveyor made high-resolution images of this same part of the Martian surface. The new images show a region with interesting geology but with no sign of a face. (1998 April 7)
Links: http://antwrp.gsfc.nasa.gov/apod/ap980407.html and http://www.jpl.nasa.gov/marsnews/mgs/cydonia/

More on meteorite ALH 84001: Scientists have recently measured the amount of the carbon isotope ¹⁴C in the Martian meteorite ALH 84001. The results suggest that most of the carbon in the meteorite came from Earth, not Mars, weakening the notion that this meteorite harbors fossils of ancient Martian life. (1998 February 17)
Link: http://www.soest.hawaii.edu/PSRdiscoveries/Feb98/OrganicsALH84001.html

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Chapter 13 Jupiter: Lord of the Planets

Books and magazine articles:

World Wide Web:

A new giant Jovian storm: The Galileo spacecraft has seen two "white ovals" --- long-lasting storms in Jupiter's atmosphere --- merge to form a giant storm second in size only to the Great Red Spot. These new observations may provide clues to a better understanding of the atmospheric dynamics of the solar system's largest planet. (1998 October 15; updated 1998 December 7)
Links: http://www.jpl.nasa.gov/galileo/news31.html and http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01651

Lightning and thunderstorms on Jupiter: New images from the Galileo spacecraft give insights into Jupiter's dramatically active atmosphere. The images show multiple lightning strokes, a burst of lightning associated with a storm, and a water-bearing thundercloud 1000 km (620 miles) wide and 75 km (45 miles) high. (1998 October 12)
Links: http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01636 (multiple lightning strokes), http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01638 (lightning associated with a storm), and http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01639 (thunderstorm)

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Chapter 14 The Galilean Satellites of Jupiter

Books and magazine articles:

World Wide Web:

A "San Andreas fault" on Europa: Recent images from the Galileo spacecraft reveal a geologic fault line some 800 km (500 miles) in length. Like the similar-size San Andreas fault in California, crustal material on either side of the fault has slid in opposite directions over time. This fault line gives additional evidence for either liquid water or soft ice beneath Europa's solid, icy crust. (1998 December 7)
Links: http://www.jpl.nasa.gov/galileo/news33.html and http://www.astronomynow.com/breaking/981208europa/

A salty ocean beneath Callisto's surface?: Images from the Galileo spacecraft have provided compelling evidence of liquid water beneath the icy surface of Europa. Now scientists have the first indication that there may also be liquid water beneath the surface of Jupiter's moon Callisto. This conclusion comes from Galileo measurements of variations in Callisto's magnetic field. To explain the observed variations, scientists propose an electrically conducting ocean beneath the moon's icy surface. Pure water is a poor conductor, so such an ocean would have to contain dissolved salts. (1998 October 22)
Links: http://science.nasa.gov/newhome/headlines/ast22oct98_2.htm and http://www.jpl.nasa.gov/galileo/caption32.html

Io's aurora and hot spots: The Galileo spacecraft has made the first-ever observations of a glowing aurora surrounding Jupiter's moon Io. This aurora is caused by collisions between the tenuous gases that surround Io Io's atmospheric gases and fast-moving charged particles trapped in Jupiter's magnetic field. Another Galileo image, made with infrared light while Io was in Jupiter's shadow, shows glowing "hot spots" from Io's active volcanic vents. (1998 October 12)
Links: http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01637 (Io's aurora) and http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01635 (Io's hot spots)

Jupiter's rings are debris blasted off the planet's moons: Astronomers at Cornell University have discovered evidence that the faint rings of Jupiter are made up of dust particles knocked off Jupiter's four innermost satellites --- Metis, Adrastea, Amalthea, and Thebe --- by meteorite impacts. Observations made with the Galileo spacecraft show that the colors of the ring particles, as well as their orbits around Jupiter, are consistent with this picture of the particles' origin. (1998 September 15)
Links: http://www.news.cornell.edu/releases/sept98/jupiter_rings.html and http://antwrp.gsfc.nasa.gov/apod/ap980916.html

Ice volcanoes on Ganymede? Recent Galileo images provide strong evidence that Jupiter's moon Ganymede went through a period of volcanic activity. Several features on the surface appear to show ancient flows of icy "lava." Other images give new insights into Ganymede's complex history of fracturing and impacts. (1998 September 15)
Links: http://www.jpl.nasa.gov/galileo/ganymede/g8images.html and http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01614

High-temperature volcanoes on Io: Jupiter's moon Io, the most volcanically active world in the solar system, may also be the hottest. Recent observations from the Galileo spacecraft indicate that temperatures in Io's volcanoes can reach 2000 K (2300 degrees Celsius, or 3100 degrees Fahrenheit). This is far higher than the temperatures in volcanoes on the present-day Earth. These high temperatures suggest that volcanic action on Io may involve not only compounds of sulfur, but also silicates --- compounds containing silicon and oxygen. (Silicates have much higher melting temperatures than do sulfur compounds.) Silicate volcanism is thought to have been common on Earth in the distant past, so studies of Io may provide new insights into our own planet's ancient geological history. (1998 July 2)
Link: http://www.jpl.nasa.gov/galileo/news23.html

Mountain building on Io: In addition to its exotic volcanism, Io also shows other forms of dynamic geologic activity. At least one mountain on Io appears to have been formed by thrust faulting, a process that also takes place on Earth. An on-line article (with 3-D images) describes these recent discoveries. (1998 April 27)
Link: http://www.soest.hawaii.edu/PSRdiscoveries/April98/io.html

Jupiter's retrograde ring: A new ring of Jupiter has been discovered using Galileo data. It is much larger than the previously known ring of Jupiter. Furthermore, most of the particles that make up this ring orbit the planet in a retrograde direction (that is, opposite to Jupiter's rotation). (1998 April 3)
Link: http://galileo.ivv.nasa.gov/status980403.html

More evidence for subsurface water on Europa: New images from Galileo suggest even more strongly that a layer of liquid water or "slush" lies beneath Europa's icy surface. (1998 March 2)
Link: http://galileo.ivv.nasa.gov/news8.html

Interactive map of Europa: The Galileo project now has clickable maps of Europa on their web site. Clicking on different portions of the maps allows you to see the corresponding regions of the surface in close-up detail. (1998 February 2)
Link: http://galileo.ivv.nasa.gov/europa/clickmap/europa.html

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Chapter 15 The Spectacular Saturnian System

Books and magazine articles:

Dobbins, T., and Sheehan, W. "Saturn's Enigmatic Crepe Ring." Sky & Telescope, September 1998. This interesting article describes how the crepe ring, or C ring --- the faintest of Saturn's rings visible with a small telescope --- came to be discovered.

World Wide Web:

New Hubble Space Telescope image of Saturn: A new infrared image of Saturn from the Hubble Space Telescope is available. The image suggests differences in the heights and chemical compositions of Saturn's cloud layers. (1998 April 23)
Link: http://oposite.stsci.edu/pubinfo/pr/1998/18/

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Chapter 16 The Outer Worlds

Books and magazine articles:

Beatty, J. K. "Pluto Reconsidered." Sky & Telescope, May 1999. Is Pluto truly a planet, or is it just another of the small, icy bodies that orbit beyond Neptune? This article describes an ongoing controversy.

Elliot, J. L. "The Warming Wisps of Triton." Sky & Telescope, February 1999. Over the past decade, astronomers observing Neptune's large satellite Triton have noticed a small but significant temperature increase of 1 to 2 K in the satellite's atmosphere. This article by a long-term observer of Triton explains how these sensitive determinations of temperature are made, and suggests some possible explanations for this "global warming."

MacRobert, A. M. "The Moons of Uranus and Neptune." Sky & Telescope, September 1998. If you have access with a telescope whose objective is at least 25 cm (10 inches) in diameter, you may be able to spot some of the satellites of Uranus and Neptune. This article provides some useful tips.

Stern, A., and Mitton, J. Pluto and Charon. Wiley, 1997. This very accessible book describes how our understanding of the ninth planet has grown since its discovery in 1930. It also provides an excellent description of recent discoveries about the Kuiper Belt.

World Wide Web:

New molecule discovered in Neptune's atmosphere: Observations using the European Space Agency's Infrared Space Observatory (ISO) have revealed the presence of the short-lived molecule methyl (CH₃) in the upper atmosphere of Neptune. This discovery gives insight into the dynamic web of chemical reactions taking place in the eighth planet's atmosphere. (1998 November 30)
Link: http://www.astronomynow.com/breaking/981201neptune/

New views of Neptune: At its great distance from the Sun, Neptune receives so little solar energy that its atmosphere should be nearly devoid of activity. But in fact the planet is encircled by 1500-km/h (900-mi/h) winds and has frequent major storms. New images from the Hubble Space Telescope and NASA's Infrared Telescope Facility may help scientists understand this curious state of affairs. (1998 October 22)
Links: http://news.bbc.co.uk/hi/english/sci/tech/newsid_192000/192980.stm and http://news1.news.wisc.edu/photos/neptune.html

New cloud activity on Uranus: New Hubble Space Telescope images show 20 clouds in the atmosphere of Uranus --- nearly as many clouds as the previous total in the history of modern observations of the planet. The images also provide new insights into the dynamics of the Uranian rings. (1998 October 22)
Link: http://oposite.stsci.edu/pubinfo/pr/1998/35/

Global warming on Triton: Hubble Space Telescope observations of Neptune's large moon Triton show that this satellite's atmosphere has become noticeably denser and warmer over the past decade. The cause may be the approach of summer in Triton's southern hemisphere, which causes nitrogen ice on the satellite's surface to evaporate into the atmosphere. (1998 June 24)
Link: http://oposite.stsci.edu/pubinfo/pr/1998/23/

Useful Pluto web site: An excellent web site with lots of information about Pluto is maintained by Fran Bagenal at the University of Colorado, Boulder. (1998 June 2)
Link: http://dosxx.colorado.edu/plutohome.html

Two new satellites of Uranus discovered: A team of astronomers from the University of Toronto, Cornell University, and McMaster University has discovered two additional satellites of the planet Uranus. Unlike the 15 satellites of Uranus known previously, the two new satellites are relatively far from the planet and move in orbits that are not in the plane of the planet's equator. In this regard they resemble the outer satellites of Jupiter, Saturn, and Neptune. (1997 October 30)
Link: http://www.cita.utoronto.ca/~gladman/utpress.html

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Chapter 17 Vagabonds of the Solar System

Books and magazine articles:

Schaefer, B. E. "Meteors that Changed the World." Sky & Telescope, December 1998. Meteors have affected human history in many surprising ways. This interesting article traces the story from the end of the Cretaceous period through the Iron Age and Roman empire down to the present day.

Weissman, P. R. "The Oort Cloud." Scientific American, September 1998. This interesting article describes the latest findings about the Oort cloud --- the vast halo of icy comets that surrounds our solar system --- and presents evidence that our Earth will be bombarded by a swarm of such comets some 1.4 million (1.4 x 10⁶) years from now.

Scotti, J. V. "Fleeting Expectations: The Tale of an Asteroid." Sky & Telescope, July 1998. For a few days in March 1998, the world hung under the threat of an asteroid impact predicted for 2028. The discoverer of the asteroid in question, 1997 XF₁₁, explains how this threat proved to be illusory.

Verschuur, G. L. "Impact Hazards: Truth and Consequences." Sky & Telescope, June 1998. A well-known astronomer gives a well-reasoned analysis of the real danger from asteroid impact.

World Wide Web:

NEAR spacecraft flies past Eros: The NEAR (Near-Earth Asteroid Rendezvous) spacecraft had been targeted to go into orbit around the asteroid 433 Eros in December 1998. An on-board engine failure prevented this from taking place, but the spacecraft did return images of Eros --- which have been made into a movie --- as it flew past. A second attempt to enter orbit will be made in February 2000. (1999 January 22)
Link: http://near.jhuapl.edu/

Report from the 1998 Leonids meteor shower: One of the most impressive meteor showers of recent years was the November 17, 1998 Leonid shower. This web site describes some of the most impressive aspects of the shower, including meteors that exploded, meteors that could be seen in the daytime, and meteors bright enough to cast shadoes at night. (1998 November 29)
Link: http://science.nasa.gov/newhome/headlines/ast27nov98_1.htm

A "Kuiper Belt" around another star: Astronomers have discovered what appears to be a ring of dust particles some 60 AU in radius around Epsilon Eridani, a young, nearby, sunlike star. Observations at submillimeter wavelengths using the James Clerk Maxwell Telescope (JCMT) in Hawaii revealed this ring at roughly the same distance from Epsilon Eridani that the Kuiper Belt lies from our own Sun. The Kuiper Belt is thought to be very ancient and to date from the very beginnings of our solar system; by analogy, the presence of such a ring around Epsilon Eridani (which is known to be younger than our Sun) suggests that a system of planets may be under formation there. A bright spot in the ring may be caused by dust particles orbiting a young planet. (1998 July 9)
Link: http://www.jach.hawaii.edu/News/kbelt.html

Two comets disappear into the Sun's corona: The SOHO spacecraft has observed two comets whose orbits took them into the Sun's corona, or tenuous outer atmosphere. Neither one appears to have survived the plunge! The link to the SOHO web site, given below, includes movies of the comets. (1998 June 3)
Link: http://umbra.nascom.nasa.gov/comets/SOHO_sungrazers.html

Impact Hazards: Truth and Consequences: A web site from Sky & Telescope magazine presents Gerrit Verschuur's article of this title from the June 1998 issue, along with links to other sites on the World Wide Web with information about planetary impacts --- especially impacts on Earth. (1998 May 2)
Link: http://impact.skypub.com/

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Chapter 18 Our Star, the Sun

Books and magazine articles:

Yonas, G. "Fusion and the Z-Pinch" Scientific American, August 1998. A veteran of the effort to produce controlled thermonuclear fusion reactions on Earth describes recent progress on this challenging problem. An expanded version of this article is also available on the World Wide Web
( http://www.sciam.com/1998/0898issue/0898yonas.html).

World Wide Web:

SOHO spacecraft back in action: Ground controllers have successfully restored communication with and control of SOHO, the Solar and Heliosopheric Observatory spacecraft. The scientific instruments on board SOHO are being brought back on-line, and the prospects look good for a complete recovery. Contact with SOHO was lost suddenly on April 24, 1998. Since it was placed in orbit in 1995, SOHO has given astronomers many new insights into the workings of the Sun. (1998 October 15)
Links: http://science.nasa.gov/newhome/headlines/ast14oct98_1.htm and http://sohowww.nascom.nasa.gov/operations/Recovery/recovery.html

New web site about the sunspot cycle: NASA's Marshall Space Flight Center is sponsoring a web site dedicated to "Sunspots and the Solar Cycle." In addition to data on current sunspot activity on the Sun (including movies and still images), it provides a wealth of information about the history of the sunspot cycle and the effects of sunspots on Earth. (1998 October 5)
Link: http://www.sunspotcycle.com/

New images of the active Sun from TRACE: The Transition Region and Corona Explorer (TRACE) spacecraft, launched on April 2, 1998, has already provided some amazing, high-resolution images of magnetic activity in the solar atmosphere. (1998 June 10)
Link: http://vestige.lmsal.com/TRACE/

Neutrinos have mass: Scientists using the Super-Kamiokande neutrino detector in Japan have announced the discovery of neutrino oscillations. This is evidence that neutrinos have mass, and may provide a solution to the solar neutrino problem. (1998 June 4 --- updated 1998 September 24)
Links: http://www.phys.hawaii.edu/~jgl/neutrino_news.html and http://www.phys.hawaii.edu:80/~jgl/nuosc_story.html and http://publish.aps.org/FOCUS/v2/st10.html

Neutrino image of the Sun: Scientists have used data from the Super-Kamiokande neutrino detector in Japan to create a "neutrino image" of the Sun, just as an ordinary photograph can be thought of as a "photon image." (1998 June 1)
Links: http://beavis.phys.lsu.edu/~superk/ and http://antwrp.gsfc.nasa.gov/apod/ap980605.html

Giant convection cells found on the Sun: Scientists using the Michelson Doppler Interferometer aboard the Solar and Heliospheric Observatory (SOHO) have discovered giant convection cells that extend from the solar photosphere down to the bottom of the convective zone. These cells may help explain details of the Sun's rotation. (1998 May 28)
Link: http://science.msfc.nasa.gov/newhome/headlines/ast28may98_1.htm

Solar quakes: The Solar and Heliospheric Observatory (SOHO) has discovered that solar flares produce seismic waves, and gigantic seismic quakes, in the Sun's interior. (1998 May 27)
Link: http://soi.stanford.edu/press/ssu05-98/

Solar tornadoes: The Solar and Heliospheric Observatory (SOHO) has discovered tall gyrating storms on the Sun that are far larger and faster than tornadoes on the Earth. (1998 April 28)
Link: http://orpheus.nascom.nasa.gov/cds/home/tornado/tornado.html

Nuclear fusion on Earth: A major thrust of modern physics is the quest to produce controlled, sustained thermonuclear fusion reactions --- like those that take place in the Sun's core --- here on Earth. Such reactions could be the ultimate source of electrical energy for home and industry. A web site at the Princeton Plasma Physics Laboratory explains the challenges of fusion research. (1998 March 13)
Link: http://ippex.pppl.gov/ippex/

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Chapter 19 The Nature of Stars

Books and magazine articles:

World Wide Web:

Delving into the personalities of stars: The stars visible with the naked eye and with a small telescope are not all the same, but have a wide variety of physical attributes. A web site at the University of Illinois gives insights into a different "Star of the Week" every week. (1999 January 23)
Link: http://www.astro.uiuc.edu/~kaler/sow/sowlist.html

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Chapter 20 The Birth of Stars

Books and magazine articles:

Kaler, J. "Eyewitness to Stellar Evolution." Sky & Telescope, March 1999. Most stages in the birth, aging, and death of stars occur so slowly as to be unnoticeable. But as a stellar expert describes in this fascinating article, some stars are passing through dramatic transitional stages that allow us to see stellar evolution in action.

World Wide Web:

Protoplanetary disks spotted in binary star system: Astronomers using the Very Large Array in New Mexico have discovered a young binary star system with two protoplanetary disks, one around each star. These observations suggest that planets may form more often in binary systems than had heretofore been suspected. (1998 September 24)
Link: http://www.nrao.edu/pr/protodisks.html and http://antwrp.gsfc.nasa.gov/apod/ap980925.html

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Chapter 21 Stellar Evolution: After the Main Sequence

Books and magazine articles:

Djorgovski, S. G. "The Dynamic Lives of Globular Clusters." Sky & Telescope, October 1998. As this fascinating article describes, stars in globular clusters can lead dramatic lives. Because the stars in such clusters are closely spaced, some of them collide and merge; other stars that undergo near-misses can be ejected completely out of the cluster. Both of these phenomena have profound effects on the evolution of the cluster as a whole.

World Wide Web:

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Chapter 22 Stellar Evolution: The Death of Stars

Books and magazine articles:

Kahabka, P., van den Heuvel, E. P. J., and Rappaport, S. A. "Supersoft X-ray Stars and Supernovae." Scientific American, February 1999. When a white dwarf star is in a close orbit around a red giant star, material from the red giant can be drawn onto the white dwarf's surface and undergo nuclear fusion. This article describes how this scenario can explain an unusual class of objects called luminous supersoft x-ray sources, and how these objects provide insight into the nature of Type Ia supernovae.

Kwok, S. "Stellar Metamorphosis." Sky & Telescope, October 1998. The Hubble Space Telescope has provided astronomers with the finest images ever of planetary nebulae. This article by a planetary nebula specialist describes what we have learned from these images, as well as the most recent theories of how these beautiful objects acquire their exotic shapes.

Skiff, B. A. "Carbon Stars: Reddest of the Red." Sky & Telescope, May 1998. This article explains how you can observe carbon stars with either binoculars or telescopes, along with tips to help you see their dramatic red colors.

World Wide Web:

HST spots another oddly-shaped planetary nebula: Recent Hubble Space Telescope images of the planetary nebula NGC 6210 reveal an exotic and complex structure, with multiple jets and evidence of interactions between stellar winds of different speeds. (1998 October 22)
Link: http://oposite.stsci.edu/pubinfo/pr/1998/36/

An ultra-distant supernova: The Hubble Space Telescope has observed a Type Ia supernova in a galaxy some 8 billion (8 x 10⁹) light-years from Earth. Type Ia supernovae are of particular interest to astronomers because they share a standard maximum luminosity. By measuring the supernova's apparent brightness, astronomers can determine a Type Ia's distance from Earth. From such measurements they can measure not only the overall size of the universe, but also the rate at which it is expanding. (1998 August 20)
Link: http://oposite.stsci.edu/pubinfo/1998/26

Newly born planetary nebula: The Hubble Space Telescope has observed a brand-new planetary nebula that has only "turned on" within the last 20 years. (1998 April 1)
Link: http://oposite.stsci.edu/pubinfo/pr/1998/15/

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Chapter 23 Neutron Stars

Books and magazine articles:

World Wide Web:

Super-intense radiation burst from a super-magnetized neutron star: On August 27, 1998, several Earth-orbiting spacecraft detected an unusually powerful burst of gamma rays striking our planet. This radiation is thought to have been emitted from an accretion disk around a highly magnetized neutron star, or "magnetar." The magnetar lies some 20,000 light-years from Earth in the constellation Aquila. (1998 September 4; updated 1998 September 30)
Links: http://www.astronomynow.com/breaking/980929magnetar/ and http://antwrp.gsfc.nasa.gov/apod/ap980903.html

Discovery of a "missing link" in pulsar evolution: Astronomers have theorized that millisecond pulsars --- neutron stars that spin as fast as 1000 times per second --- acquire their rapid spin by being members of close binary star systems. In this model, the pulsar gains mass from its companion star by accretion, which also causes the pulsar to spin faster. Now scientists have used NASA's Rossi X-ray Timing Explorer to discover an X-ray-emitting neutron star that seems to be in the processing of "spinning up" in just this way. The discoverers estimate that the neutron star --- which spins at 400 times per second --- has been accreting material from its companion star for the last 10⁸ to 10⁹ years. (1998 July 22)
Link: FTP://PAO.GSFC.NASA.GOV/newsmedia/PULSAR/PULSAR.JPG

Neutron stars with ultra-strong magnetic fields: Astronomers have found evidence for neutron stars with magnetic fields a thousand times stronger than those on a typical neutron star, and 10¹⁵ times stronger than the Earth's field. These magnetic stars, or "magnetars," may provide an explanation for a class of exotic objects that emit repeating pulses of gamma rays. (1998 May 20)
Link: http://science.msfc.nasa.gov/newhome/headlines/ast20may98_1.htm

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Chapter 24 Black Holes

Books and magazine articles:

World Wide Web:

Answers to your questions about black holes: A web page by Ted Bunn at the Center for Particle Astrophysics (University of California, Berkeley) has clear explanations to many frequently-asked questions about the nature of black holes. (1998 June 20)
Link: http://physics7.berkeley.edu/BHfaq.html

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Chapter 25 Our Galaxy

Books and magazine articles:

Tarlé, G. and Swordy, S. P. "Cosmic Antimatter." Scientific American, April 1998. By studying what happens when protons and their antimatter equivalents --- negative particles called antiprotons --- meet and annihilate in intergalactic space, scientists may be gathering clues about the nature of the dark matter that pervades our galaxy.

World Wide Web:

Neutrinos have mass: Scientists using the Super-Kamiokande neutrino detector in Japan have announced the discovery of neutrino oscillations. This is evidence that neutrinos have mass, and may provide a partial solution to the dark matter problem. (1998 June 4 --- updated 1998 September 24)
Links: http://www.phys.hawaii.edu/~jgl/neutrino_news.html and http://www.phys.hawaii.edu:80/~jgl/nuosc_story.html and http://publish.aps.org/FOCUS/v2/st10.html

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Chapter 26 Galaxies

Books and magazine articles:

Martin, P., and Friedli, D. "At the Hearts of Barred Galaxies." Sky & Telescope, March 1999. The nuclei of many spiral galaxies have a prominent linear or bar shape. This article by two galactic astronomers describes our present understanding of how such bars might arise, as well as how the presence of a bar in a galaxy can affect the evolution of the galaxy as a whole.

Russell, D. "Island Universes from Wright to Hubble." Sky & Telescope, January 1999. This fascinating article relates the story of how astronomers came to understand that galaxies are objects that lie outside our Milky Way. Surprisingly, this idea was fashionable for a short period 50 years before Edwin Hubble's key observations.

Henry, J. P., Briel, U. G., and Böhringer, H. "The Evolution of Galaxy Clusters." Scientific American, December 1998. This article describes the state of current research into clusters of galaxies, including the remarkable new understanding that has been obtained using x-ray imaging.

Kraan-Kortweg, R. C., and Lahav, O. "Galaxies behind the Milky Way." Scientific American, October 1998. More than 20 percent of the universe is hidden from direct observation because it lies on the other side of the Milky Way's obscuring dust. This article relates how astronomers in recent years have used radio telescopes to explore this previously unknown region of the sky, and describes some of the remarkable discoveries they have made. An expanded version of this article is also available on the World Wide Web
( http://www.sciam.com/1998/1098issue/1098laham.html).

Dressler, A. "The Journey Back to the Source." Sky & Telescope, October 1998. This interesting article describes how astronomers' understanding of the nature and evolution of galaxies has developed over the past century, and suggests what more we may learn from the Next Generation Space Telescope (scheduled to be launched around 2007). An essay by the same author follows Chapter 26 of Universe.

Jayawardhana, R. "Our Galaxy's Nearest Neighbor." Sky & Telescope, May 1998. This entertaining article describes how the Sagittarius Dwarf was discovered --- and how tidal forces from the Milky Way are tearing this tiny galaxy apart.

World Wide Web:

New evidence that galaxies form before clusters: By using the ROSAT X-ray telescope to observe the hot gas trapped within clusters of galaxies, astronomers at the University of Birmingham have concluded that galaxies formed in the early universe before grouping into clusters. These observations are important for understanding the series of steps whereby galaxies and clusters of galaxies formed in the early universe. (1999 January 14)
Link: http://www.ras.org.uk/ras/press/pn99-02.htm

Combined visible-light and infrared images of distant galaxies: By combining visible and near-infrared observations made with the Hubble Space Telescope, astronomers have obtained new insights into ancient, distant (and hence highly redshifted) galaxies. A number of these galaxies appear to be ellipticals that contain many old, highly-evolved stars. The presence of such old stars in galaxies seen as they were billions of years ago helps to constrain models of how the first galaxies formed. (1999 January 7)
Link: http://oposite.stsci.edu/pubinfo/pr/1999/02/

Hubble Deep Field - South: In December 1995, the Hubble Space Telescope (HST) spent ten days observing a one-arcminute-wide piece of sky in the northern constellation Ursa Major. These observations yielded the Hubble Deep Field, an unprecendented look into extremely faint --- and extremely distant --- galaxies from near the edge of the observable universe. Now HST has made a similar set of observations of a patch of sky in the southern constellation Tucana. In combination with the 1995 observations in the northern sky, these new data will give astronomers new insights into the nature and evolution of the early universe. (1998 November 4)
Link: http://oposite.stsci.edu/pubinfo/pr/1998/41/

The fate of the Magellanic Clouds: As the Large and Small Magellanic Clouds orbit our Milky Way Galaxy, they trail behind them a cloud of gas called the Magellanic Stream that extends for tens of thousands of parsecs. Recent observations using the Parkes radio telescope in Australia have shown gas on both the leading and trailing sides of the Clouds --- as would be expected if the Magellanic Stream was the result of tidal forces exerted on the Magellanic Clouds by the gravity of the Milky Way. Over the next several hundred million (10⁸) years, these tidal forces may pull the Magellanic Clouds completely apart. (1998 September 4)
Links: http://www.csiro.au/news/mediarel/mr1998/mr98194.html
and http://antwrp.gsfc.nasa.gov/apod/ap980826.html

HST Catalog of Galaxies available on-line: The Medium Deep Survey (MDS) is an international project that uses the Hubble Space Telescope to study the nature of faint galaxies at great distances, and hence in the remote past of the universe. By studying such galaxies, astronomers hope to learn how galaxies form and evolve. A web site at Carnegie Mellon University includes the latest findings from the MDS, and provides access to the complete catalog of MDS images. (1998 August 27)
Link: http://astro.phys.cmu.edu/mds/

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Chapter 27 Quasars, Blazars, and Active Galaxies

Books and magazine articles:

MacRobert, A. M. "Gamma-Ray Burst Hunters Catch a Whopper." Sky & Telescope, May 1999. While more than 2,000 gamma-ray bursters have been observed, the burster seen on January 23, 1999 was truly unique: less than a minute after gamma rays were first detected, the burster was seen to be emitting visible light. As this article describes, for a few seconds this burster shone with the light of more than 10¹⁶ suns!

Voit, G. M. "The Rise and Fall of Quasars." Sky & Telescope, May 1999. There is increasing evidence that supermassive black holes lurk at the cores of quasars. This article discusses recent findings and suggests links between quasars and the evolution of galaxies.

Disney, M. "A New Look at Quasars." Scientific American, June 1998. This article, beautifully illustrated with Hubble Space Telescope images and artist's conceptions, summarizes the latest discoveries about the nature of quasars.

World Wide Web:

New wide-angle view of an active galaxy's central region: For several years, astronomers studying the active galaxy M87 have known about the energetic jet of material being ejected from what is presumably a supermassive black hole at the center of the galaxy. A recent wide-angle radio image of M87 shows that the center of the galaxy is also surrounded by two enormous radio-emitting regions spanning some 60 kiloparsecs (200,000 light-years). These regions may be "bubbles" of hot gas heated by material flowing outward from the galaxy's core. (1999 January 7)
Link: http://www.nrao.edu/pr/m87big.html

A quasar caused by interactions between galaxies: New radio images of three nearby quasars (within a few hundred megaparsecs) reveal that these quasars lie within galaxies that have recently interacted with other, adjoining galaxies. These observations reinforce the idea that nearby quasars occur in mature galaxies in which a central black hole is "fed" new material from another galaxy during a galactic interaction. By contrast, distant quasars (which are thousands of megaparsecs away) seem to lie within young galaxies. Such galaxies have enough interstellar gas and dust to "feed" their central black hole and produce a quasar. (1998 December 29)
Link: http://www.nrao.edu/pr/quasars.html

Are gamma-ray bursters "super-supernovae?": An unusually bright supernova in a distant spiral galaxy appeared in the same part of the sky, and at the same time, as a recent gamma-ray burster (GRB). Was this merely a remarkable coincidence, or could GRBs be caused by such unusual supernovae? (1998 October 22)
Link: http://science.nasa.gov/newhome/headlines/ast21oct98_1.htm

What gamma-ray bursters are NOT: One leading model that attempted to explain the origin of the mysterious gamma-ray bursters was the "synchrotron shock." In this model, a tremendous explosion generates a shock wave that accelerates charged particles, like electrons and protons, to velocities near the speed of light. But recent observations have shown that this model cannot explain the spectrum of radiation emitted by gamma-ray bursters. The true nature of these celestial cataclysms remains a mystery. (1998 October 13)
Link: http://science.nasa.gov/newhome/headlines/ast13oct98_1.htm

Viewing distant quasars with a telescope larger than the Earth: By using an orbiting 8-meter radio telescope in concert with radio telescopes on Earth, an international consortium of astronomers have been able to observe distant quasars with unprecedented resolution. These observations reveal heretofore unseen details in the fast-moving jets emanating from these quasars. (1998 September 17)
Links: http://www.jpl.nasa.gov/releases/98/spacevlbi.html and http://sgra.jpl.nasa.gov/

The most luminous quasar: The quasar APM 08279+5255 in the northern constellation Lynx has the highest continuous luminosity --- equivalent to 5 x 10¹⁵ Suns --- of any object known in the universe. (Supernovae and gamma-ray bursters are more luminous, but only for very brief periods.) This luminosity is so large that it conflicts with our present-day understanding of how quasars emit radiation. One possible explanation is that the quasar's radiation is "magnified" by gravitational lensing by an unseen massive galaxy that lies between APM 08279+5255 and Earth. More work needs to be done before astronomers can fully understand this remarkable object. (1998 September 4)
Link: http://antwrp.gsfc.nasa.gov/apod/ap980818.html

A dust disk around a supermassive black hole: The Hubble Space Telescope has been used to image a dusty disk some 3700 light-years in diameter at the core of the active elliptical galaxy NGC 7052. The disk appears to be orbiting around a black hole of some 300 million (3 x 10⁸) solar masses. The orientation of the disk suggests that it is the relic of another galaxy that long ago collided with NGC 7052. (1998 June 18)
Link: http://oposite.stsci.edu/pubinfo/pr/1998/22/

Gamma-ray burster news: A web site at the Marshall Space Flight Center lists all the latest developments in the study of gamma-ray bursters. A map shows the location in the sky of the previous week's gamma-ray bursts. (1998 June 15)
Link: http://www.batse.com/

A black hole in Centaurus A: Recent Hubble Space Telescope observations show a black hole at the center of NGC 5128, an active elliptical galaxy in Centaurus (see Figure 27-15), being "fed" by interstellar dust and gas. (1998 May 14)
Link: http://oposite.stsci.edu/pubinfo/pr/1998/14/

Gamma-ray bursters: The Hubble Space Telescope has helped confirm that a gamma-ray burster observed in December 1997 took place within a very distant galaxy some 370 megaparsecs (1.2 x 10⁹ light-years) away. During its brief duration, this gamma-ray burster was the most energetic object in the universe. (1998 May 6)
Link: http://oposite.stsci.edu/pubinfo/pr/1998/17/

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Chapter 28 Cosmology: The Creation and Fate of the Universe

Books and magazine articles:

Luminet, J.-P., Starkman, G. D., and Weeks, J. R. "Is Space Finite?" Scientific American, April 1999. The consensus among cosmologists is that our universe is infinite. But might it really be finite, and merely appear to be infinite because of the overall geometry of space and time? This article explores this intriguing possibility. An expanded version of this article is also available on the World Wide Web
( http://www.sciam.com/1999/0499issue/0499weeks.html).

Krauss, L. M. "Cosmological Antigravity." Scientific American, January 1999. Recent observations of the expansion of the universe contradict long-held ideas about the fundamental character of the universe as a whole. This fascinating article describes the new picture of a universe with a nonzero cosmological constant, and explains the challenges that this new picture presents to theoretical cosmologists.

Hogan, C. J., Kirshner, R. P., and Suntzeff, N. B. "Surveying Space-Time with Supernovae." Scientific American, January 1999. Complementing the article by A. K. Finkbeiner in the September 1998 Sky & Telescope, this piece by three leading astronomers describes how distant supernovae give insight into the nature of our expanding universe, and how they lead to the conclusion that the universe is expanding faster today than it was in the past.

Finkbeiner, A. K. "Cosmic Yardsticks: Supernovae and the Fate of the Universe." Sky & Telescope, September 1998. Measurements of the apparent brightnesses of distant supernovae give astronomers a way to determine both the rate at which the universe is expanding (given by the Hubble constant, H₀) and the rate at which the expansion is slowing (given by the deceleration parameter, q₀). This article explains how these measurements are made, and details the controversial conclusion that the expansion of the universe may actually be accelerating...

Adams, F. C. and Laughlin, G. "The Future of the Universe." Sky & Telescope, August 1998. Two astrophysicists describe how the universe may evolve over the next 10¹²⁰ years.

World Wide Web:

"Our Hierarchical Universe:" A beautiful and extensive web site at the National Center for Supercomputer Applications provides a multimedia look at the structure and origin of the universe as a whole. (1998 September 15)
Link: http://chico.ncsa.uiuc.edu/Cyberia/Cosmos/HierarchUni.html

Still more evidence for an open universe: A six-year survey of galaxies by the Hubble Space Telescope (HST) has revealed 10 or 20 clusters of galaxies which appear to lie more than 7 billion (7 x 10⁹) light-years from Earth. Thus we are seeing these clusters as they were some 7 billion years ago, when the universe was only about half its present age. If these distance estimates are confirmed by ground-based telescopes, they will give further evidence that clusters of galaxies formed rather early in the history of the universe --- which in turn implies that the average density of matter in the universe is quite low, and that our universe will continue to expand forever. (See the item below.) (1998 September 8)
Links: http://oposite.stsci.edu/pubinfo/pr/1998/27/
and http://antwrp.gsfc.nasa.gov/apod/ap980908.html

More evidence that we live in an open universe: A team of astronomers using the Hubble Space Telescope has discovered a massive cluster of galaxies --- the largest ever seen --- at a distance of some 8 billion (8 x 10⁹) light-years from Earth. This means that 8 billion years ago, the universe was dense enough for such a massive cluster to be able to form. If the average density of the universe were relatively large, then such clusters in the early universe should have continued to accumulate mass and massive clusters should be common in the present-day universe (that is, in the nearby universe). But in fact, we do not see such massive clusters at close distances. This implies that the average density of the universe is low --- and in particular, that the average density is less than the critical density. If this conclusion is correct, our low-density universe will keep expanding forever. (1998 August 20)
Link: http://oposite.stsci.edu/pubinfo/1998/26

The value of the Hubble constant: In 1996 a "Great Debate" about the value of the Hubble constant H₀ was held. (This commemorated the 1920 Shapley-Curtis debate concerning the size of the universe.) A transcript of the debate, as well as a great deal of background information about the Hubble constant, is available at a NASA web site. (1998 June 20)
Link: http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate96.html

Neutrinos have mass: Scientists using the Super-Kamiokande neutrino detector in Japan have announced the discovery of neutrino oscillations. This is evidence that neutrinos have mass, and may provide a partial solution to the dark matter problem. (1998 June 4 --- updated 1998 September 24)
Links: http://www.phys.hawaii.edu/~jgl/neutrino_news.html and http://www.phys.hawaii.edu:80/~jgl/nuosc_story.html and http://publish.aps.org/FOCUS/v2/st10.html

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Chapter 29 Exploring the Early Universe

Books and magazine articles:

Greene, B. The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory. W. W. Norton, 1999. Written by a researcher in the field, this lucid book tells the scientific and human story of superstring theory and the crusade to find the "theory of everything."

Mukerjee, M. "A Little Big Bang." Scientific American, March 1999. As this article describes, new experiments in which large atomic nuclei collide at nearly the speed of light may give insight into conditions in the early universe.

Bucher, M. A., and Spergel, D. N. "Inflation in a Low-Density Universe." Scientific American, January 1999. The notion of cosmic inflation resolves many problems in cosmology. However, the original inflationary model is not compatible with recent observations that indicate that the expansion of the universe is accelerating. This article describes recent efforts to refine the theory of inflation.

Quinn, H. R., and Witherell, M. S. "The Asymmetry between Matter and Antimatter." Scientific American, October 1998. Our universe is made almost entirely of matter, with only traces of antimatter. This state of affairs is thought to be caused by a subtle but fundamental difference between the behaviors of matter and antimatter. A new set of extraordinarily sensitive experiments is poised to measure these differences, and to thus provide new insights into conditions at the very beginning of the universe.

Liss, T. M., and Tipton, P. L. "The Discovery of the Top Quark." Scientific American, September 1997. Science now knows of the existence of a total of six different types, or "flavors," of quarks. This informative article explains how the sixth of these was discovered after a massive international research effort. An expanded version of this article is also available on the World Wide Web
( http://www.sciam.com/0997issue/0997tipton.html).

World Wide Web:

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Chapter 30 The Search for Extraterrestrial Intelligence

Books and magazine articles:

Schilling, G. "The Chances of Finding Aliens: Reevaluating the Drake Equation." Sky & Telescope, December 1998. The Drake equation, described in Section 30-2 of UNIVERSE, is a tool for estimating the number of advanced, communicative civilizations in the Galaxy. This articles relates how recent discoveries in astronomy are suggesting new values of the various terms in this equation.

LePage, A. J., and MacRobert, A. M. "SETI Searches Today." Sky & Telescope, December 1998. This article describes the current state of radio searches for extraterrestrial intelligence, as well as plans for the next generation of searches.

World Wide Web:

Web site for the movie "Contact": The 1997 film Contact, based on the Carl Sagan novel of the same name, has a web site with a good deal of information about the search for extraterrestrial intelligence. (1998 June 1)
Link: http://www.contact-themovie.com/main.html

Big Ear radio telescope torn down to build a golf course: The Big Ear radio telescope in Ohio, which had spent nearly four decades observing the sky and listening for signals from extraterrestrial civilizations, was demolished in early 1998. The land will be used to extend a golf course. (1998 May 8)
Link: http://www.bigear.org/press.htm

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Last updated 1999 March 31