Best Free Astronomy Software

Astronomy Software is a pretty broad spectrum, providing everything from simple mapping software (relative positions of the solar system), through detailed observation planning software to first-person planetarium software. I looked at several free astronomy programs for producing sky maps.

Unless otherwise stated all of the planetarium programs:

• Simulate a view or the stars as if the observer is looking at the horizon.
• Display the sun, moon, and major planets.
• Display or hide planet names or symbols.
• Display or hide constellation names.
• Display or hide names or designations of the brighter stars.
• Display deep space objects, e.g. Andromeda galaxy.
• Display lunar phases.
• Can vary the space time coordinates of the observer.
• Can zoom in on sections of the sky.

I didn't pick a best as I couldn't decide between the three contenders for the top spot.  The best for your purposes would depend on your needs.

Aladin could be thought of as an astronomy browser. Instead of the internet, Aladin browses through astronomy images, density maps, and other astronomy sources, e.g. Hubble images, the Simbad database, and the VizieR service. You select the item you wish to view and it automatically downloads a view of the item selected.

This program provides access to professional quality telescope images in several wavelengths.  In effect you are looking through a very large telescope. The images are downloaded from the internet so some displays take a few seconds to update—your results would depend of course on the connection speed and on how many databases are being utilized. One can apparently download files for offline viewing.

I could superimpose various views in to one and I could open up to 16 panels with images in each.

It was one of only two programs which indexed every star and deep space object in my test sample as well as showing several images of each item. You can also point at a specific location using the right ascension and declination coordinates.  You can bookmark views.

Since Aladin is a sky atlas image viewer and not a planetarium program it has no solar system objects in its index. Obviously there could be images of the solar objects in many of these images but it's beyond my ability to locate them.

Requires Java 1.5 and runs under Windows, Linux, and Mac.

Sky-Map.org (aka WikiSky) is an online viewer utilizing your browser. The images here are in color and come from several sources, e.g. DSS2 all Sky Survey, IRAS Infrared Sky Survey, and user uploaded photos.

The index also found every star and deep space object in my test sample.  Oddly it also indexed the location of the planets but no images were available.

The website allows one to upload an image for display in the catalog.  Some of the views have many layers of images each opaque to the ones beneath.  Left clicking on an area with one or more images opens a popup window where you can select the desired image for viewing.  When zoomed out a bit the layered images look a bit odd.

Requires an Internet connection and browser.

Cartes du Ciel (aka Skychart) is a very easy to use planetarium program.  Its in depth index found every object in my test sample with the exception of UGC 9128.  Additional catalogs for stars down to magnitude 16 (UCAC3) are available on the website, along with several specialty catalogs.  There are instructions for adding the entire PPMXL catalog (magnitude 20), which I didn't attempt as it required 148 GB of hard disk and 24 GB of ram.

Cartes du Ciel has a calendar calculating ephemerides for twilight, planets, sun, moon, comets, asteroids, and solar and lunar eclipses between any two dates.  And there is a variable star observer with the predictions of minima and maxima for many variable stars for the next couple of cycles.

Cartes du Ciel can control a computerized telescope mount.

The program includes images of many deep space objects right in the planetarium window.  I didn't notice any actual stellar images or planetary images.  However, the online documentation indicates that planetary images are available in the Linux version.  No bookmarks. 

Windows, Linux, and Mac versions.

Computer Aided Astronomy (aka C2A) was also fairly easy to use.  Its index is second only to Cartes du Ciel in thoroughness.  There are several additional catalogs for download.

There are a lot of images included with the program.  Unlike several of the other planetarium programs the images are viewed through a separate window in the image browser.  If there is an internet connection, the program can download images from either the ESO or the STScl sky surveys for display in either the image viewer or directly in the planetarium field of view.

I liked the data section to the left of the planetarium window with the details about the object on display.  I liked the ability to move forward or back through recent views and the ability to bookmark views.

Computer Aided Astronomy has an ephemeris generator which can generate tables for the sun, planets, moon, comets, and asteroids between any two dates. There are tools to generate trajectories of planets, asteroids, and comets between any two dates.  One tool shows the moon phases for the entire month.  The Ecliptic View tool displays an animated view of the solar system with comets and asteroids.

Computer Aided Astronomy can control a computerized telescope mount.

Windows only.

Stellarium creates fairly realistic views of the sky. The basic program has over 600,000 stars (roughly up to magnitude 9.9) with another 240 million available as add-ons.  This is the only free program that shows constellation groupings for other cultures. 

The zoom in shows actual images of planets and some deep space objects.

Stellarium provides many visual effects, including the Milky Way, twinkling stars, shooting stars, clouds, and light pollution. Several landscapes are included.

The telescope control plug in allows Stellarium to control a computerized telescope. The Satellites plug in calculates and renders satellites in Earth orbit from NORAD/TLE data.

Its catalog is weak in comets and asteroids.

Windows, Linux, and Mac versions.

WorldWide Telescope comes in two versions, Windows Client and Web Client. Both versions are very similar and work equally well. If connected to the Internet the Windows client automatically downloads images that aren't already in the catalog.

The Windows Client version can control a computerized telescope.

Its catalog is weak in comets, asteroids, and planetary moons, e.g. only Jupiter shows moons.

Home Planet excels at locating artificial satellites, comets, and asteroids. There are 256,000 stars in its catalog. Planetary moons such as Titan aren't shown.

The display isn't as realistic as others. The default sky display is a sky map display, e.g. as a circle with straight up as the center and the horizon as the circumference. There are smaller displays centered on the horizon and a telescope zoom window. There are no images. Solar system objects are indicated by symbols.

Home Planet is portable.

Celestia is a space travel simulator. You can travel throughout the solar system, to any of over 100,000 stars, or even beyond the galaxy.  There are add ins to expand the catalogs and images of comets, stars, solar system objects, and deep space objects. You can even add in fictional objects such as Star Wars, Star Trek, Babylon 5, etc.

I feel this is a fun way to view many of the objects themselves.  There are images of many solar system objects, e.g. Deimos and Ceres.

As this is a simulator and not a planetarium program, Celestia does not indicate constellations, have telescope controls, or have a method for pointing to a specific location, e.g. RA 02:31:49.09 dec +89:15:50.8.  (Not intended as a criticism—just an observation.)

Orbiter is a fun interplanetary space ship simulator which obeys the laws of physics.  You can launch from nearly anywhere in the solar system and fly to nearly anywhere else.

There are many ships available (both historical and fictional).  You select your ship, space port and destination.  There is a cockpit with three displays (an open screen view, instrumentation, and a heads up display projected on the forward view port.)  The ship can also be viewed externally as if you're in a chase ship.  The tutorials explain how to make a successful trip including how to match orbit with the destination.  Be careful, you can run out of fuel (or you can cheat with an unlimited fuel suply). 

You can make the trip in real time.  Fortunately, a time warp shortcut can speed time up by 100,000 if you don't want to wait the three days or so it would take for a Lunar mission or months in the case of a trip to the outer planets.

The best at artificial satelites and better than most at solar system objects.  However, interstellar is apparently not supported.  Consequently stars and deep space objects are shown but a method of directly locating these is out of scope.

• EarthSky Tonight
• Google Earth (View>Explore>Sky)
• Google Sky
• Hallo Northern Sky
• Home Planet
• KStars (Linux)
• Sky Map Online
• SkyORB 3D
• WinStars
• Your Sky

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