Free Astronomy Software

There are many free astronomical programs available on the Internet.  Here we will list those found to be useful/interesting.  If you know of one (or more) not listed here, send an email to jroe at  Likewise, if you would like to comment/review any of these programs, send the email.  Please report broken links.

Astronomers Digital Clock (Windows)

This is a neat little utility that reports current time (as determined from your computer clock) in both hours:minutes: seconds and decimal hours, UTC (used to be called Greenwich Mean Time), the local sidereal time and the Julian Date.  The local time zone and longitude must be set to be accurate vis a vis the sidereal time.  Download it at

Stellarium (Windows, Mac OSX, Linux)

Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope.  Download it at

GIMP (Windows, Mac OSX, Linux)

GIMP is the GNU Image Manipulation Program. It is a freely distributed piece of software for such tasks as photo retouching, image composition and image authoring. It works on many operating systems, in many languages.  It has most, if not all, the functionality of Photoshop at a much reduced cost.  Download it at

The Ultimate Messier Object Log (TUMOL) (Windows)

The Ultimate Messier Object Log (TUMOL) is a FileMaker Pro 6.0 database that contains relevant information for all 110 Messier objects. It contains various layouts to assist amateur astronomers in documenting their search for deep sky objects.  Download it at

Planetary, Lunar and Stellar Visibility

This is one really neat program.  If you are familiar with the chart Sky & Telescope produces each January that shows the times of sunrise, sunset and has lots and lots of diagonal lines labeled with such things as "Mars Rises", "Saturn Transits", etc, then you will be at home with the display of this program.  It calculates most of the stuff shown on the S&T chart, but then adds some really nice flourishes.  To get maximum accuracy (estpecally with times of eclipses) you must set your location from a drop down menu (St. Louis is close enough for Eastern Missouri).  You would then select which object your are interested in (includes Sun, Moon, all major planets plus Pluto and most bright stars).  For the Sun selection, the program produces a graphic with the days of the year running down the vertical axis (you can change the year from -2999 to +6000, but only from 1600 for Jupiter) and the hour of the day running from 0 to 24 across the width of the chart.  Two curving lines represent sun rise and sun set, but twilight is shown in light colors.  Unfortunately, to my taste, this is somewhat wasteful of good graphics space in that daytime hours occupy the middle of the graph (unlike the S&T graph) and I have emailed the authors asking about this.  But the Solar graph is probably the least interesting.

Selecting another object, say the Moon, sends the program off for a few seconds calculating and then it displays the visibility of the Moon in the same format (Sunrise and Sunset lines are still shown) with color coding.  But you can get detailed times from the cursor position as digital read outs in a box.  Especially, neat is a short red line shows when an eclipse is visible.  Placing the cursor on this line causes a pop-up animation which shows the relative position of the Moon’s disk and the Earth’s shadow.  Moving the cursor causes the animation to shift to the correct orientation for the moment selected.  This is a very effective visualization tool.  Moving the cursor around the main graphic also shows, dynamically, the phase of the Moon at the selected instant.

Moving on to the planets, the phase, angular diameter, sub-earth point, etc are shown when the cursor is moved about the main display.  Those squiggly lines showing the positions of Jupiter’s moons that are published in S&T every month are shown but are interactive, ie, putting the cursor on the lines shows which moon is which, how far from Jupiter it is (in Jupiter diameters or arc sec), how bright it is, etc. and the whole display can be scrolled.  This program will be very useful for planning photographic sessions of the planets, especially Mars.

I give it 10 stars.  It is free and can be downloaded at .