Don Shedrick

Sept, 2000

September DAS Focus

COMPUTERS IN ASTRONOMY by Don Shedrick

It has been a long dry spell for planetary observers, but we can now celebrate the return of Jupiter and Saturn to the evening skies. We have the added bonus of each being accompanied by a spectacular star cluster and the richly hued star Aldebaran.

Saturn rises first with the Pleiades (M45), often called The Seven Sisters after their mythological connection to the seven daughters of Atlas and Pleione. This is one of the most beautiful and easily observable star clusters in the skies, since it is easily seen with the unaided eye, and is at its best in binoculars. Tennyson described it well as a "swarm of fireflies tangled in a silver braid." Before focusing on Saturn, learn more about the Pleiades - its mythology, stars, reflection nebula, and other links at the web site of the Radio Astronomy Lab at the University of Calgary:

http://www.ras.ucalgary.ca/~gibson/pleiades/

Saturn’s famous rings are now in one of their most favorable positions for viewing in their 29 year cycle of tilting up and down, being within a couple of degrees of maximum tilt to the north, obscuring the north pole from view. In addition to the rings, there is the nightly dance of the moons of Saturn, four of which are readily observable in small telescopes. Two software programs are available on the Internet to aid in viewing these features of the planet, and to just have fun playing with.

 

SATSAT is an MS-DOS program that will use the time and date from your computer's clock to determine and display the locations of the moons of Saturn. It is available from Dan Bruton's astronomy software site:

http://www.physics.sfasu.edu/astro/dansoftware.html

The rings of Saturn are also displayed, showing their angle of tilt and the shadow they cast on the planet. Other orbital data on Saturn and its moons are given as well. There is an animation feature so you can set the moons in motion and observe the changing tilt of the rings. Can you find out when the rings will next be edge on to us?

 

Satview is an MS-DOS program that projects a mathematical model of a sunlit Saturn from any angle. It is available from:

http://www.bookcase.com/library/software/msdos.education.astronomy.html

You can select parameters resulting in views that would be unfamiliar and impossible to be viewed from Earth, such as from a spaceship flying over the poles of the planet. You enter three values to create the image - the altitude of the sun above the ring plane, the altitude of the viewpoint above the ring plane, and the difference in azimuth between Sun and the Observer as measured from Saturn. There are an infinite number of possibilities to try out.

Additional Saturn Observing Events and many links relative to Saturn can be found at the web site of the Stephen F. Austin State University Department of Physics and Astronomy:

http://www.physics.sfasu.edu/astro/saturn.html

Shortly after Saturn, Jupiter rises in the constellation Taurus near the Hyades open star cluster. Mythologically speaking, this name is appropriate, since the nearby Seven Sisters were half sisters of the Hyades, whose mother was Aethra. Like the Pleiades, the Hyades are most impressive in binoculars, where the field will hold the brilliant V of the cluster (the face of Taurus the Bull) along with 1st magnitude orange hued Aldebaran. Nearby, there are several small open clusters, a planetary nebula, and the famous remains of a 1054 supernova explosion, the Crab Nebula (M1).

JupSat, featured earlier in this column, is excellent for viewing the positions of the moons of Jupiter and the position of the Great Red Spot. This software is still vailable on the Internet at:

http://indigo.ie/~gnugent/JupSat95/

TRACKER is an MS-DOS program that uses the time and date from your computer's clock to determine and display the approximate locations of a few features on the southern or northern hemisphere of Jupiter as seen from Earth. It is available at Dan Bruton's astronomy software site:

http://www.physics.sfasu.edu/astro/dansoftware.html

In addition to the Great Red Spot, other features displayed include the major white spots, the smaller white ovals, and small red and dark spots and streaks. Impact sites of the fragments of comet Shoemaker-Levy 9 are displayed as dark spots if you set the time to late 1994. The actual positions of these features are constantly drifting with the Jovian clouds, so to keep this program accurate, the data base needs to be kept current with the latest longitude information for their location based on current observations. This is fairly easy to do with this program, but finding the data for features other than the GRS is more difficult. The GRS longitude is published in Sky and Telescope (currently 74 deg). Data for other features is usually available with varying promptness and detail on the Association of Lunar and Planetary Observers (ALPO) web site at :

http://www.lpl.arizona.edu/alpo/

JOVIAN MOON EVENTS is an MS-DOS program that computes the time for Transits, Shadows, Eclipses, and Occultations of Jupiter's Moons for one month accurate to within one minute. It is available at:

http://www.physics.sfasu.edu/astro/dansoftware.html

The table generated is similar to that offered in the Astronomical Almanac, and the output is printed to a file. A similar table is displayed on the Project Pluto web site:

http://www.projectpluto.com/jevent.htm#sep

and a table for the Great Red Spot transit times is at another of their web sites:

http://www.projectpluto.com/jeve_grs.htm

A unique Jupiter Strip Map of the surface cloud features of Jupiter is on the web site of an ALPO-Japan member Yuichi Iga:

http://www.kk-system.co.jp/Alpo/Jupiter00/Stripmap.htm

Additional Jupiter Observing Events can be found at the web site of the Stephen F. Austin State University Department of Physics and Astronomy:

http://www.physics.sfasu.edu/astro/jupiter.html

And now - this month’s Cool Web Site of the Month.

"Skynotes" at:

http://indigo.ie/~gnugent/dnso/skynotes.htm

This site is brought to you by the same amatuer from Ireland who wrote JupSat and Lunar Phase software programs featured earlier in this column. This site has a quick Java Script version of parts of these programs, and a wealth of other up to date observing information changing daily, weekly, or monthly, including sky events and notes, satellite predictions, star charts (from HomePlanet), images, and links to other resources. There is a lot of useful and functional information packed into this site.