Hubble Deep Field: How a Photo Revolutionized Our Understanding of the Universe
these questions Hubble’s camera pointed near the handle of the Big Dipper a star pattern in the constellation Ursa Major the Great Bear Using Earth-based telescopes that little piece of space in Ursa Major appeared to be mostly black and empty of cosmic objects It contained a few stars known to be in one of the Milky Way’s outer arms Telescopes had also detected a handful of tiny blurry blobs of light in the target region which might be galaxies But if so there were not many of them Otherwise the area Williams had singled out seemed to be composed mostly of empty space Considering these facts several of Williams fellow astronomers felt that devoting 10 days of Hubble’s time to such a venture might be a serious mistake There was wide agreement that every minute of Hubble’s time was scientifically valuable even precious What if after the 10 days Williams proposed photo showed mostly empty space Further complicating matters was the fact that Hubble already had gained a reputation for not living up to expectations Not long after the telescope’s launch its
first photos had been a disappointment An unexpected flaw in its mirror had caused the pictures to be blurry Astronauts repaired Hubble’s faulty mirror in December 1993 A group of astronauts from the space shuttle Endeavour had saved the day by repairing the space telescope and fixing the problem But the effort had been costly and both politicians and the public were now sensitive about projects that might waste Hubble’s valuable time Not surprisingly some of Williams colleagues urged him not to move forward with his plan Some strongly warned him that if his 10-day experiment failed it might be a public relations nightmare for Hubble and NASA One of them Lyman Spitzer Jr a physicist and astronomer was more diplomatic Bob are you sure
you want to do this 2 he cordially asked PICKING THE PATCH Some technical problems had to be overcome in order to take the Hubble Deep Field HDF photograph One was getting around the many stars and other objects in the Milky Way in order to see galaxies lying far outside our local galaxy Bob Williams and the other scientists who helped him take the HDF solved this problem by choosing a tiny patch of sky in the constellation Ursa Major Because of the location only a handful of stars inside the Milky Way would block the view of deep space The target patch was also chosen because it is in a continuous viewing zone in relation to the Hubble Space Telescope’s orbit Such a zone is a place in the sky where the space telescope can see and take photographs without Earth’s getting in the way Williams and his colleagues realized that NASA had already eliminated the problem of taking long-exposure photos from a space platform moving at high speeds As Earth travels around the sun views from the planet of various objects in space are constantly changing Because Hubble is in Earth’s orbit whatever spot in the sky it sees also appears to be constantly and quickly changing position How then could astronomers keep Hubble’s onboard camera focused on a spot long enough to take a long exposure picture NASA scientists overcame this challenge by developing sophisticated computer software It compares the position of the target spot in the sky with certain guide stars and calculates tiny course corrections for the camera several times per second Once the camera is locked on the guide stars Hubble would barely wobble off its target According to a NASA book about the space telescope it is like holding the beam of a laser pointer all day on the face of a dime located 200 miles away 1 The Hubble Space Telescope floats gracefully above Earth But regardless of how many other scientists cautioned Williams he continued on He believed that the proposed photo would reveal at least some galaxies Now that Hubble’s optics were as good as new he reasoned they might be able to pick up the light of faint galaxies
In fact bursting with a spirit of exploratory zeal Williams was willing to go full speed ahead no matter what the consequences might be If you’re going to make advances in science he later said you must take risks I was well aware of the possible consequences if we were to obtain no results So I was prepared if necessary to turn in my resignation 3 Before and after photos of the galaxy M100 show the dramatic improvement in the Hubble Space Telescope’s view of the universe after the 1993 repair mission There was another reason that Williams felt comfortable moving forward with his bold hunt for distant galaxies As director of the STScI he was allowed to schedule a certain amount of time to use Hubble for personal projects The telescope allocation committee would never have approved such a long risky project he said later But as director I had 10 percent of the telescope time and I could do what I wanted 4 So Williams and his team began preparing in earnest to aim Hubble’s great orbiting eye at a tiny piece of dark sky in the Great Bear They knew that the galactic snapshot they sought to create would be composed of more than 340 separate images Each of those would require an exposure time of up to 40 minutes Simple math revealed that this would tie up Hubble for quite a number of its revolutions around the planet
