Hubble Space Telescope has been orbiting Earth for more than 20 years. Or parts of it have. The telescope has changed dramatically over the years, as astronauts installed new and better instruments, better electronics, and other equipment.
For astronomers, that means that comparing Hubble observations made over the years requires some work. Different instruments may be sensitive to different wavelengths of light, for example, or have a different field of view. So astronomers must carefully compensate when they use observations from more than one instrument.
Texas astronomer Fritz Benedict and his colleagues have had to adjust several times over the years to changes in instruments known as the Fine Guidance Sensors.
BENEDICT: There are three Fine Guidance Sensors on the telescope. Two of them are used to guide the telescope — hold it steady so you can make those beautiful pictures. The third Fine Guidance Sensor can be used to do astrometry, which is measure star positions, which is what we do.
A decade ago, one of the sensors failed, so a new one took its place, requiring a recalibration. Another recalibration was needed just a few years ago.
BENEDICT: They decided to refocus the telescope and do a little tweak in the FGS-1R that we were using. And it turned out that, yeah, it now gives slightly better positions, but it basically destroyed our calibration in that we now had to bridge a gap.
Team member Barbara McArthur did just that — keeping the astronomers from losing years of observations of the stars.
Script by Damond Benningfield, Copyright 2013
Find out much more about Hubble Space Telescope and its role in this research on our special web site, Galileo to Gamma Cephei.
For more skywatching tips, astronomy news, and much more, read StarDate magazine.