Observation planning with JSkyCalc

JSkyCalc is an easy-to-install ephemeris tool that helps you plan your observing runs, then carry them out as efficiently as possible.  It’s a graphical revival of the venerable Skycalc by John Thorstensen of Dartmouth.

Airmass-plotting tools exist for ESO and Keck.  The advantage of JSkyCalc is that it calculates everything you’ll need for observing, and it knows all major observatories—one tool can plan all your runs.

There are 2 versions of JSkyCalc:  a web version, and a downloadable version.  I recommend downloading it, so that you can load lists of targets.  On my Mac (OS X 10.5),  a simple double-click of “JSkyCalc.jar” starts the program.

Here’s a simple demo.  Start JSkyCalc and select an observatory.  The main screen looks like this:

Enter a date & time (there’s a button for “now”).  Hit “Nightly Almanac” to see the times of sunset, sunrise, and twilight.  Hit “Object Lists” and load a set of objects; in this example I’ve loaded three standard stars.   (Hit “Help” to learn the catalog format.)

Select all targets with shift-click.  The “Sky Display” window shows you the positions of your objects with respect to the constellations and the moon.

At the telescope, hit “Set to Now” to show current conditions.  Even better, you can ask JSkyCalc to update in real time: try setting “sleep” to ~60 s, and hit “Auto Update.”   Select all targets, and check the airmass graph: a vertical bar shows you the current time.  This is a handy aid for deciding when to switch targets and observe standard stars.

That’s just a quick look.  JSkyCalc’s “Help” button has more details.

Two grumbles so far:  First, I can’t figure out how to PRINT!  I’m currently screen grabbing the airmass plot, and using “convert -negate” to make a printer-friendly version.  Anyone know a better way?  Second, since Keck has unique pointing constraints, you still need to use their tool to calculate how far down in elevation you can follow a given source.

JSkyCalc, free