Astronomy Picture of the Day
APOD: 2002 November 24 - Hubble Floats Free
Explanation: Why put observatories in space? Most telescopes are on the ground. On the ground, you can deploy a heavier telescope and fix it more easily. The trouble is that Earth-bound telescopes must look through the Earth's atmosphere. First, the Earth's atmosphere blocks out a broad range of the electromagnetic spectrum, allowing a narrow band of visible light to reach the surface. Telescopes which explore the Universe using light beyond the visible spectrum, such as those onboard the Chandra X-ray Observatory need to be carried above the absorbing atmosphere. Second, the Earth's atmosphere blurs the light it lets through. The blurring is caused by varying density and continual motion of air. By orbiting above the Earth's atmosphere, the Hubble Space Telescope, pictured above, can get clearer images. In fact, even though HST has a mirror 15 times smaller than large Earth-bound telescopes, it can still resolve finer details. A future large optical telescope in space is planned.
APOD: 2000 January 16 - The Compton Gamma Ray Observatory
Explanation: The Compton Gamma Ray Observatory (CGRO) was the most massive instrument ever launched by a NASA Space Shuttle in 1991 and continues to revolutionize gamma-ray astronomy. Before Compton loses more stabilizing gyroscopes, NASA is considering firing onboard rockets to bring it on a controlled reentry into the ocean. This orbiting observatory sees the sky in gamma-ray photons - light so blue humans can't see it. These photons are blocked by the Earth's atmosphere from reaching the Earth's surface. Results from CGRO, pictured above, have shown the entire universe to be a violent and rapidly changing place - when viewed in gamma-rays. Astronomers using CGRO data continue to make monumental discoveries, including identifying mysterious gamma-ray bursts that uniquely illuminate the early universe, discovery of a whole new class of QSOs, and discovery of objects so strange that astronomers can't yet figure out what they are.
APOD: 199 July 27 - Chandra X Ray Telescope
Explanation: Wrapped in protective blankets and mounted atop an Inertial Upper Stage (IUS) rocket, the Chandra X-ray Telescope is seen in this wide-angle view before launch snuggled into the space shuttle Columbia's payload bay. Columbia's crew released the telescope, named in honor of the late Nobel Laureate Subrahmanyan Chandrasekhar, into orbit on Friday, July 23rd, where it is now undergoing check out and activation of its scientific instruments. To help realize its enormous potential for exploration of the distant Universe at X-ray energies, controllers will perform a series of firings in the coming days which will eventually boost the 10,000 pound telescope into a highly ecentric orbit. In fact, the final working orbit for Chandra will range from a close point of about 6,200 miles out to 87,000 miles or one third of the distance to the Moon. The elongated orbit will carry Chandra's sensitive X-ray detectors beyond interference caused by the Earth's radiation belts allowing Chandra to make about 55 hours of continuous observations per orbit. The shuttle Colombia, commanded by Eileen Collins is scheduled to land this evening at 11:20 pm EDT at Kennedy Space Center.
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