The Great Basin Observatory is located in Great Basin National Park and is the first research-grade observatory in a U.S National Park. The high altitude, clear skies, and minimal light pollution over the basin and range in eastern Nevada make Great Basin National Park an ideal place to perform world-class astronomical research and to raise awareness of the need to preserve awe inspiring and quickly disappearing dark-night skyscapes.
The Great Basin Observatory is remotely operated. Aside from occasional maintenance or installation of new components, no one need be present to operate the telescope. This is one of the interesting things about the Great Basin Observatory- it's isolation is what allows it to function so well. The observatory’s position in one of the most remote and dark areas in the contiguous United States, is what makes it so exceptional.
The dome itself automatically opens in the evening and closes in the morning. In the case of inclement weather, it will automatically shut down the telescope and close the dome. Students and researchers can operate the telescope via web based controls from anywhere in the world with an internet connection. After the telescope takes the images, the files are emailed to the researcher for analysis.
The centerpiece of the Great Basin Observatory is a 0.7 meter (27.5”) reflecting telescope built by PlaneWave Instruments. 0.7 meters refers to the diameter of the main light-gathering mirror, the number one gauge of a telescope’s capabilities. With a diameter of 0.7 meters, the telescope can gather nearly 40 times as much light as a backyard 4.5” telescope, allowing it to study faint objects throughout the universe.
The telescope is a Schmidt-Cassegrain design which bounces the light twice inside the scope, allowing the focal length (length of the telescope) to be cut in half, and uses a Corrected Dall-Kirkham (CDK) optical design to minimize distortions that are inherent in other types of reflecting telescopes. The result is that a photograph taken at the Great Basin Observatory will show stars as pinpoints of light from the center of the image all the way out to the edge of the field of view.
Here is the outside of the Great Basin Observatory. You can view the stairs leading up towards the dome. The telescope on the inside is mounted to concrete for extra stability and an air conditioning unit keeps the inside of the dome a stable temperature. The dome itself separates into segments to allow the telescope a 360° view.
The telescope rests on a study alt/az (altitude/azimuth) mount that can quickly slew the telescope to nearly any object in the night sky. Once an object is located, the mount is able to track the object very precisely as it moves slowly across the sky due to Earth’s rotation. This keeps the object stationary in the field of view, allowing the camera to take a long-exposure photograph. Accurate tracking is crucial to taking such images. If the object moves even slightly during the time that the shutter is open, the image will be blurry.
The Great Basin telescope can track celestial objects with an incredibly high precision: <1 arcsecond over a 10 minute period. An arc second is the angle of a dime seen at a distance of 2.5 miles. The mount also uses direct drive motors that eliminate the need for the gears used in most telescope mounts, which can cause undesirable movements when taking long exposure images of the sky.
The scope needs to be the same temperature as the atmosphere outside to obtain the clearest images. Therefore the fans are mounted on the back of the scope, positioned to keep the mirror’s temperature equal to the outside temperature and eliminate turbulence in the air.
This photo gives a full view of the altazimuth mount and the fans. Fans are also needed to cool the camera. You want the mirror to have the same temperature as the outside, but the camera needs to be colder to reduce the noise in the images.
The diameter of the primary mirror determines how much light the telescope is able to collect, and its quality determines in large part how sharp the resulting images will be. The primary mirror of the Great Basin telescope is 0.7 meters (27.5”) in diameter. It is slightly curved (in order to redirect light to the secondary mirror) and is made from fused silica glass, which has a very low coefficient of thermal expansion, meaning that it maintains its shape when heated or cooled. Regular glass expands and contracts when exposed to changing temperatures, which can cause the image in the telescope to blur. You are familiar with this concept if you’ve ever used borosilicate (Pyrex) glass bakeware. Borosilicate glass has a low coefficient of thermal expansion, allowing it to withstand the large temperature changes that occur when you put it in an oven or freezer. While borosilicate glass is often used to make telescope mirrors, fused silica glass has a coefficient of thermal expansion six times lower! This makes it an ideal material for building telescope mirrors because of its ability to maintain its shape over a wide range of temperatures.
The secondary mirror lies near the top of the telescope tube. It receives light from the curved primary mirror, and redirects it down to the tertiary mirror, which then redirects the light to the focal point. In the Great Basin telescope, the tertiary mirror sits on a rotating platform that can quickly redirect the light to either the CCD camera or the spectrograph, depending on research needs.
Here you can clearly see the tube trusses that hold the secondary mirror of the telescope. These trusses significantly decrease the weight of the telescope, making it easier to move.
The camera is a black and white digital camera.
To the right of the camera is a filter wheel. Within this wheel are a number of glass filters that preferentially let certain wavelengths of light into the camera, while blocking others. Use of these filters allows astronomers to compose a color image (the CCD chip itself is monochromatic) of a celestial object.
Digital sensors are much more sensitive to faint light than the human eye, so virtually all modern astronomical research is performed by taking digital images rather than looking through a telescope eyepiece. A high-quality CCD camera is an essential component that allows the observatory to fulfill its mission.
The CCD camera uses a digital sensor not that unlike the one in your digital camera or smartphone, but with some key differences. First of all, the CCD sensor on the Great Basin telescope measures about 1.4” on each side, whereas the camera sensor in your smartphone likely measures less than 0.25” on a side. Secondly, the sensor is electronically cooled to -58° F. Operating the camera at a low temperature reduces the noise in the image, helping to increase the sensitivity of the chip and allowing it to see fainter objects more clearly.
The CCD camera can take exposures ranging from 0.1 seconds (for very bright objects) to an hour (for fainter objects). In most cases the telescope will take multiple images of the same object and then researchers will “stack” the images together to reduce noise and get a more detailed image of the object.
The instability of Earth’s atmosphere has plagued astronomers for centuries. Starlight is always distorted as it passes through Earth’s atmosphere to the ground, making celestial objects look inherently blurry. Atmospheric conditions, known as “seeing” by astronomers, can make this phenomenon better or worse depending on the night.
An adaptive optics system helps counteract this effect (and distortions caused by other factors, such as vibration of the mount) and is crucial for taking pin-point sharp image of stars and other celestial objects.
The adaptive optics system on the Great Basin telescope is attached to the camera itself and utilizes a computer and a movable glass window that corrects for these distortions, sort of like a pair of eyeglasses or contact lenses for the telescope. This results in sharper star images and better resolution. You can also think about adaptive optics as sort of like the image stabilization feature on your DSLR camera or binoculars.
The electronic focusing accessory allows the telescope to adjust for different sky conditions.