Wednesday, March 5, 2014

Eye in the Sky!

I've certainly extolled the virtues of Heavens-Above - the website that predicts the location of virtually every satellite that is circling the Earth.  While the bright visual ones are easy to spot, if you have a particular little satellite you want to follow telescopically, you can find positions of those too.  And besides objects that circle the earth, you can also plot out sky maps for any time and date, as well as make finder charts for comets and asteroids and find out information about other solar system objects.  It is a great resource!  Just enter your location by city name or from Google Maps, make sure you enter your time zone correctly, and you should be ready to go.

Thanks to the heads-up provided by a TAAA member earlier today, I saw that the Hubble Space Telescope (HST) would be making a favorable pass over Tucson tonight shortly after 1900 (7pm).  Heavens-above provided a map where it would appear in the sky.  You can also print out a ground track, the positions on the globe that it passes over.  Interestingly, the HST's orbit is inclined 28 degrees to the equator, the same latitude of Cape Canaveral, Florida where it was launched.  It takes a lot of extra work to launch a satellite into an inclination different from your launch point's location.  As a result, it NEVER passes directly over Tucson, which has a latitude of 32 degrees.  The best you can do is a situation like tonight where it gets about 51 degrees high to the south - as reflected in the ground track, it passes us well to the south, but thanks to its relatively high orbit (550km, about 330 miles), it is still easily seen.  The circle on the ground track at right indicates where it would be visible.  I just checked, and if we had been observing from our home in Illinois, HST would only have been about 12 degrees over the southern horizon - a big difference in appearance!

Of course, to see it, it needs to be mostly dark at the observing location, but the HST needs to be still lit up by the sun and that was the circumstance tonight.  Looking at the sky plot at left, you can see where the track stops at the left side below the constellation Leo - that is where it enters the Earth's shadow.

I decided to try photographing it from the back yard with a tracking mount so at least the stars wouldn't be trailed.  Since the Hubble would be passing through Orion, not far from Rigel and the Orion Nebula, it was a natural to try getting those in the images too.  Of course, it always takes longer to set up gear than you think it does, and just about the time I finished focusing the lens I happened to look up and it was right there about to enter the field!  I quickly snapped the picture, but it was only set to 15 seconds - shown here at left is the cropped part of the image that shows the trail of HST with Rigel at lower right and the Orion Nebula at left center.  The focal length of the zoom lens was set to 85mm, and F/3.5.  Unfortunately there were some think clouds in the field, but that is nothing new - we've had at least thin clouds for seemingly months!

So spotting the Hubble was a great success!  It won't be many years that the Hubble will have another failing reaction wheel or something that will knock it out of commission.  While there have been several servicing missions over the decades, with the retirement of the Space Shuttle, the opportunity to repair or upgrade HST is over.  The 6.5 meter James Webb Space Telescope is not a direct replacement and is still years from launch, so it will be sad to see Hubble end, though it will likely continue to circle the Earth in its orbit for a long time.  In the meantime, hopefully some day it will clear again here in Arizona, without the moon, and with my schedule allowing me to get out to a dark site.  Until then, these little back yard excursions will have to do!

No comments: