By rotating the carousel on which the gratings are mounted, any one of them can be brought into the optical path of the instrument, making it possible to obtain a spectrographic reading at any wavelength between 110 and 320 nanometers. The wide field/planetary camera is mounted on the side of the telescope that will generally be kept away from the sun. Incoming light passing along the optical axis of the telescope is directed outward at a right angle by means of a flat “pick-off” mirror held by a rigid arm at a 45-degree angle to the optical axis. The diagonal mirror diverts only the central part of the incoming beam; the rest of the light passes around the mirror to the other instruments.
For example, the high-resolution spectrograph will make possible the study of interstellar gas at places in our galaxy and other galaxies where it cannot now be observed. With the high-resolution spectrograph much more accurate data will be obtainable, perhaps revealing the relation between this gas and the even hotter material detected by Copernicus. Measurements of the way in which the properties of our galaxy vary from place to place will provide much-needed clues to the evolution of the system as a whole. The high-resolution spectrograph has six interchangeable diffraction gratings, each of which disperses light of different wavelengths in different directions. A camera mirror or grating then forms an image of the spectrum on the photoelectron-emitting surface of a Digicon sensor.
The reflecting telescope which uses an arrangement of mirrors to form an image. Special software designed by radio astronomers and software engineers then assembles the data to create maps of radio objects in the sky. If the size of the radio wavelength being observed is very long, such as the centimeter waves picked up by the VLA and the VLBA, then the perfection of the dish’s shape is not as critical to keep excellent observations of the radio sky.
Since the Big Bang, which is estimated to have taken place 13.8 billion years ago, it has cooled all the way to just three degrees above absolute zero. Describe two observations that Galileo was the first to make with his telescope. A light-year is equal to the distance light travels in one year, 9.5 trillion kilometers.
Infrared and ultraviolet light are affected more dramatically by the Earth’s atmosphere. Their telescopes must therefore always be positioned high above the ground or in space. Infrared telescopes are placed on mountaintops, far above the low-lying water vapor that interferes with infrared light. It is capable of very high resolution imaging and spectroscopy at optical and near infrared wavelengths. This spectrograph with its normal resolution should be able to observe stars as faint as the 13th magnitude, or about six stellar magnitudes fainter than those observed by the Copernicus telescope. Of course, there is a price to be paid for the higher resolution of this second spectrograph.
Galileo’s observations challenged people to think in new ways about the universe and Earth’s place in it. About 100 years before Galileo, Nicolaus Copernicus had proposed a controversial new model of the universe in which Earth and the other planets revolve around the Sun. In Galileo’s time, most people still believed that the Sun and planets revolved around Earth. Galileo’s observations provided direct evidence to support Copernicus’ model. Constellations help astronomers today identify different regions of the night sky. Many archaeologists think that Stonehenge was used to observe the movement of the moon and the sun.
More often, to get the most out of the giant dish’s collecting power, we use a secondary mirror called a subreflector at the prime focus to reflect focused waves down into a more convenient location — the center of the dish. Many of the subreflectors can be tilted to aim at the different feed horns in the center of the dish or to catch a glancing view of the sky to gather data about air quality conditions. Light from the telescope comes in through the window at the top and passes down through the filter stack in the centre of the camera until it reaches the mirrors at the bottom which direct it onto the detector array. The gold-plated cooling stages, cryogenic refrigerators and mechanical support legs can be seen at the top of the image. However, there are still some wavelengths that have been invisible to astronomers until recently. These wavelengths cannot be detected using standard equipment, requiring researchers to design and make their own devices if they want to capture the information that they contain.
In the wide field mode the camera has a square field of view 2.67 arc-minutes on a side, the largest field of any of the instruments. In a sense the wide field camera compromises the angular resolution of the telescope in order to provide a field of view large enough for the study of extended sources such as planetary nebulas, galaxies and clusters of galaxies. Even so, the field of view is much smaller than the field that can be recorded on a photographic plate by a ground-based telescope. In the Space Telescope the field is limited by the size of the microelectronic detectors available for remotely acquiring, storing and digitizing pictures. The CCD’s for the wide field/planetary camera, which are being supplied by Texas Instruments, Inc., have more pixels than any other CCD’s used for astronomical purposes. By John N. Bahcall and Lyman Spitzer, Jr.The earth’s atmosphere is an imperfect window on the universe.
Astronomers do not have to imagine what it is like to see beyond the visible spectrum. They have long been finding new perspectives on stars and galaxies by tuning planet fitness gunhill road into different wavelengths of electromagnetic radiation. Observing the sky at a new wavelength can reveal completely new information about the Universe.