Thursday, May 20, 2021

Fixing Hubble

In the course of your life, all of you will have happened to admire at least one of the numerous and beautiful photographs taken by the Hubble Telescope.

However, the quality of the images obtained by the telescope has not always been as sharp as what we are used to today.

A few weeks after it was launched in 1990, astronomers found with great disappointment that the quality of Hubble's images was much lower than expected. As you can also see in the image on the left of the post, the images were clearly out of focus.

Analysis of the images thus showed that there was a serious problem in the telescope's optical system, particularly with respect to its 2.4 meter primary mirror. It was realized that the latter had been incorrectly sanded. The error was only one-fiftieth of the thickness of a human hair. As small and insignificant as this value may seem, it was enough to create the problem in the Hubble images.

The astronomers then immediately set about looking for a solution to correct the imperfection in the telescope optics. Replacing the entire primary mirror was unthinkable, so it was thought to build instruments that, acting like glasses, would correct Hubble's vision.

These new instruments after being built were then taken into space and installed inside the telescope by the astronauts of the Shuttle STS-61 mission in 1993.

The image of the post shows how the quality of the images taken by Hubble has improved significantly thanks to the corrective optics.

Both photos show the spiral galaxy M100: on the left seen in November 1993, on the right in December of the same year, just a few days after the Shuttle service mission.

Credit: NASA, ESA, Hubble.

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