April DAS Focus

COMPUTERS IN ASTRONOMY by Don Shedrick

This month, we have the opportunity to view a comet that is bright enough to be easily visible with binoculars, and even with the naked eye under very good conditions. Comets, clumps of rock and ice, were made when the solar system formed 4.5 billion years ago from the same material that made the planets and Sun. When its orbit takes it far from the Sun, the low temperature of deep space keeps the comet frozen. As the comet comes close to the Sun, it heats up, emitting gases and the dust that reflects the Sun's rays and makes the comet visible from Earth.

Comet Ikeya-Zhang was discovered as a faint, telescopic object near the western horizon on the evening of February 1st independently by Kaoru Ikeya of Japan and Daqing Zhang in China. It has brightened significantly during March and April, and passed closest to the Sun (perihelion) on March 18 at a point roughly midway between the orbits of Mercury and Venus. It is now thought to be a comet that last visited the inner solar system in 1661. This month the comet will move from low in the northwest evening sky, where it is visible just after sunset, to the morning sky. It will slide past the W-shaped constellation Cassiopeia around April 10-15, and will become "circumpolar" -- it will never set. At this point the comet will be fading quickly as it moves farther from the Sun. Ikeya-Zhang will pass closest to Earth on April 28, at a distance of about 38 million miles.

The Space.com web site has a viewer’s guide for the comet at:

http://www.space.com/spacewatch/spacewatch_comet_020309.html

and week-by-week viewing details at:

http://www.space.com/spacewatch/ikeya_zhang_sidebar_020309.html

Ikeya-Zhang's faint blue color and turbulent tail have made it one of the most photogenic comets in years. To see a collection of recent amateur photographs, see the Spaceweather.com web site:

http://www.spaceweather.com/comets/gallery_iz.html

For additional info, observations and some of the best photographs of Ikeya-Zhang on the web, see Gary Kronk’s web site:

http://cometography.com/lcomets/2002c1.html

The best sky map I have found for Ikeya-Zhang on the web is at NASA’s JPL site:

http://encke.jpl.nasa.gov/images/02C1/c2002c1chart.jpg

The best printable sky map is from The Royal Observatory of Greenwich web site:

http://www.rog.nmm.ac.uk/leaflets/images/comets/ikeya_zhang/ikeya_zhang.gif

For the Orbital Elements and ephemeris of Ikeya-Zhang, see the International Astronomical Union comet web site at:

http://cfa-www.harvard.edu/iau/Ephemerides/Comets/2002C1.html

Another unusual event occurs in April and early May. Five planets are assembling toward a rare alignment later this month, when they will occupy a small portion of the sky together. This planetary alignment will not occur in such an easily visible display again during the remainder of this century. Already, Jupiter, Mars and Saturn have formed a nearly straight line in the west each night. By late April, Mercury and Venus will join them. In early May, Venus, Saturn and Mars will form a tight triangle in the west.

See more details and a sky map, see the Space.com Rare Planet Alignment page at:

http://www.space.com/scienceastronomy/solarsystem/planets_align_020402-1.html