Astro Glossary

Taurus, the Bull

A constellation of the zodiac marked by a V-shaped pattern of stars that outlines the bull’s face.

Telescopes and Modern Observatories

A telescope is an optical instrument that gathers and focuses light into a camera, CCD, spectrograph, or an astronomer’s eye. Two major types of telescopes dominate astronomy: reflectors and refractors. Many of the world’s largest telescopes are housed at observatories: The entire complex of buildings, telescopes, equipment, and staff involving scientific astronomical observations. Small observatories might consist of just one telescope situated in a dome, one instrument and computer, and one observer. McDonald Observatory is an example of a major observatory, and consists of five major telescope in five different domes, numerous instruments, computers, living quarters, outbuildings, astronomers, and engineers.

Teotihuacan

Thuban

A former “North Star” 300 light-years away in the constellation Draco, the dragon.

Tides

A stretching force that is caused by the difference between gravitational forces on opposite sides of an object, such as a planet or moon. For example, because the Moon pulls on opposite sides of the Earth with different strengths, water on the Earth is pulled either toward or away from the Moon, resulting in the ocean tides. Elsewhere in the Solar System, the magnitude of gravitational force on Jupiter’s moon Io is greatest on the side of Io that faces Jupiter and least on the back side. The difference between the two forces compresses and stretches Io, which in turn heats up Io’s interior. As a result, Io is the most geologically active body in the solar system.

Timekeeping and Calendars

Titan

The largest moon of Saturn and the second-largest moon in the solar system. Titan has a thick, cold, nitrogen-rich atmosphere that supports winds, clouds, and rain. The rain, which consists of droplets of liquid methane and ethane, fills hundreds of lakes and seas in Titan’s polar regions, and appears to carve river channels. Tiny grains of methane ice form long, tall dunes across parts of Titan, and “volcanoes” may spurt frozen water onto the surface. A vast ocean of liquid water may lie far beneath Titan’s crust. The Huygens probe landed on Titan in 2006, with its images showing rounded pebbles on the surface, perhaps smoothed by water. Titan is difficult to study from afar because the atmosphere is topped by “smog” — a layer of hydrocarbons that turn orange when exposed to sunlight. The Cassini spacecraft, which ferried Huygens to Titan, has made by dozens of passes by the big moon, using radar and instruments sensitive to infrared and ultraviolet light to peer through the haze and map much of Titan’s surface.

Tombaugh, Clyde

An American astronomer who discovered Pluto in 1930. He was the first American to discover a planet in our solar system.

Transiting Exoplanet Survey Satellite (TESS)

TESS is a space telescope, launched April 18, 2018, designed to follow up on the discoveries of planets orbiting stars other than the Sun. In particular, it is studying planets around particularly bright stars, which generally are among the closest to Earth. Its observations will allow astronomers to determine the sizes and masses of the planets it studies, which reveals their density. That can tell us whether the planets are dense and rocky, like Earth; big and fluffy, like Jupiter and Saturn; or somwhere in between, like Neptune. Additional observations can reveal whether a planet has an atmosphere, and perhaps tell us something about the atmosphere's composition. The TESS observations also will reveal supernova explosions, variable stars, and other astronomical phenomena.

Triangulum, the Triangle