August 20, 2019

Astro-event for October 6th-12th, 2008: Spot the Hubble Space Telescope!

I almost didn’t do this weeks’ event. The Hubble space telescope is in trouble. This past week, the failure of Hubble’s Control Unit- Side A has meant that the telescope is effectively crippled in space; engineers will attempt to transfer services to the Side -B backup, which hasn’t been used since the telescope was put in orbit in 1990.

All this means that STS-125 and its spectacular night launch has been postponed until sometime in 2009. The good news is that you can still spot the Hubble as it silently glides through the night sky… several sites abound to forecast its passage, but our favorite is Heavens-Above . Hubble will make early morning passages for most of the week over North America, and then starts a cycle of evening passages on the weekend, although it’ll be competing with a waxing Moon. Alas, there will be no space shuttle floating next to it, but it’s still a thrill to see one of the great technological achievements of man!

This weeks Astro-word is Cassegrain telescope. This is a reflecting telescope that folds the light path back on itself by use of a primary and secondary mirror along a central axis. Commercially, these have become very popular because they can pack a large aperture in a small package. The Hubble itself is a variant of Cassegrain, known as a Ritchey-Chretien. This utilizes a hyperbolic primary and secondary mirror, instead of the traditional parabolic primary. Hubble has a focal ratio of about f/24.


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