The Pan-STARRS sky survey telescope — known as PS1 — utilizes four separate optical systems, including four mirrors and four 1400-megapixel cameras that comprise the world’s largest imaging system. With about 150 times as many pixels as the average camera, each PS1 camera is able to gather detailed images of almost three-quarters of the night sky from its base in Hawaii. The astronomical project based around the PS1 will enable scientists to assess wide areas of sky at a level of detail that was previously impossible, and will enable a better understand the mysteries of dark matter and dark energy. Astronomers from the University of Durham, the University of Edinburgh and Queen’s University Belfast, together with researchers from around the world, are using the telescope to scan the skies from dusk to dawn each night. The dome of the PS1 telescope at the 10,000-ft summit of Haleakala in Hawaii. (Photo: Brett Simison) Scientists believe that the device, which was built by the University of Hawaii, will provide vital clues into the nature of dark energy and dark matter. They hope to use images of galaxies to validate Einstein’s theory of general relativity, which predicts that light can bend around an object in space — such as dark matter — because it is pulled towards the object by gravity. “PS1 will generate the largest ever multicolor survey of the cosmos. Alongside supercomputer simulations of the universe, these data will help us understand the life cycles of galaxies and, if we are very lucky, the nature of the mysterious dark matter and dark energy that control the evolution of our cosmos,” said professor Carlos Frenk of Durham University, the UK’s member on the Pan-STARRS board. Each of the four Pan-STARRS cameras will be the largest digital camera ever built, and will have approximately 1.4 billion pixels spread over an area about 40 cm square. For comparison, a typical domestic digital camera contains about 5 million pixels on a chip a few millimeters across. The focal plane of each camera contains an almost complete 64 × 64 array of CCD devices, each containing approximately 600 × 600 pixels, for a total of about 1.4 gigapixels. The CCDs themselves employ the innovative technology called “orthogonal transfer. The individual CCD cells are grouped in 8 × 8 arrays on a single silicon chip called an orthogonal transfer array (OTA), which measures about 5 cm square. There are a total of 60 OTAs in the focal plane of each telescope (The four corner OTAs are omitted because they are too far from the optic axis of the telescope to collect useful data) Four CCDs are used in the telescope for several reasons. One is that manufacturing defects usually cripple a single CCD. By dividing the focal plane into a large number of CCD devices, the damage caused by a chip faults is limited. The ability to make good use of slightly imperfect chips results in a very large saving of both cost and manufacturing time. Another reason is that bright stars can saturate CCDs very quickly. CCDs that include a bright star image can be set to read out very fast, with no ill-effects on the neighboring CCDs. “The huge camera lets us map about one-sixth of the sky every month, in five different colors. We compare every image with one taken previously and try to track everything that either moves or flashes. Already we have discovered hundreds of supernovae, some of them the most luminous explosions known,” added professor Stephen Smartt of Queen’s University Belfast and Chair of the Pan-STARRS Science Council. Schematic of one of the four Pan-STARRS 1.4-gigapixel cameras. About half of the 60 OTA devices can be seen through the 56-cm diameter window, which also comprises the final corrector lens in the optical path of the telescope. The four grey boxes on each side of the camera contain the readout electronics for the OTA devices. The overall length of the camera is about 1.5 m. (Image: Pan-STARRS/University of Hawaii) Pan-STARRS is primarily sensitive to visible light, though observations can be extended slightly into the infrared passbands. Each camera will include an identical set of 5 to 6 optical filters that can be remotely positioned in front of the focal plane. Searches for asteroids and potentially hazardous objects may use a wide filter (“g+r+i”) that covers most of the visible waveband from 0.50 to 0.80 nm. This filter provides maximum sensitivity for detecting solar system objects. Surveys for stars and galaxies are much more valuable when they include color information, so Pan-STARRS will include standard photometric g-, r-, i- and z-band filters, as used in the Sloan Digital Sky Survey. The excellent near-infrared response of the Pan-STARRS detectors means that a y-band filter (1 μm) also can be used. The project teams anticipates that the read noise in the orthogonal transfer CCDs will be about 5 e– and the sky background will be about 7 e– per pixel with the broadband filter. Thus, sky noise will dominate read noise in exposures of 15 s or more. The telescope, which took more than a decade to develop, will also pinpoint new supernovae — stellar explosions — as well as near-earth asteroids. It is also able to track fast-moving objects and exploding stars across nearly the whole sky. “Pan-STARRS has immense potential for mapping the distribution of matter in the universe, even the unseen dark matter. Our goal is to do this over the majority of the sky for the first time — but there are still big challenges ahead for us,” said professor Alan Heavens of the University of Edinburgh. Development of Pan-STARRS — Panoramic Survey Telescope and Rapid Response System — has been funded by the US Air Force. Also involved in the project are the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society, John Hopkins University, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network, the National Central University of Taiwan and the Ogden Trust. For more information, visit: www.ed.ac.uk