Astronomy & telescopes glossary - S

Astronomy & Telescopes Glossary - S

Satellite - Any object that orbits a planet or a moon.

Schmidt camera - A type of telescope used for astrophotography that has an extremely fast focal ratio and provides very high-quality images.

Schmidt-Cassegrain telescope - A type of compound telescope, abbreviated SCT, that uses both lenses and mirrors to focus light.

Scintillation - The twinkling of stars seen through a planet's atmosphere.

Secondary mirror - In reflecting telescopes, the smaller mirror that reflects light to the eyepiece.

Setting circles - Circular scales attached to the telescope marked off in degrees of Declination and hours of Right Ascension (RA). Together, the circles allow the position of a known celestial object to be found.

Shepard moon - A moon that orbits alongside a ring of a planet, confining the ring and giving it a sharp edge.

Shooting star - A meteor that is burning up in the Earth's atmosphere.

sidereal drive - A motorized drive used to make a telescope track stars across the sky as the Earth rotates.

Solar system - Any group of planets, moons, asteroids, and comets that orbit around a sun.

Spherical aberration - A blurring of an image caused by the inability of a mirror to focus properly.

Spider - The arms or struts used to support a secondary mirror in Newtonian reflecting telescopes.

Star cluster - A group of stars that are bound together gravitationally.

Star diagonal - A mirror on some refracting telescopes that bends light 90 degrees, allowing an observer to look down through the eyepiece instead of squatting to look directly through the telescope.

Sun dog - Bright spots of light sometimes seen around a solar halo, which is a luminous ring surrounding the Sun. Two such sun dogs are located on opposite sides of the Sun.

Sungrazer - A comet that either crashes into the Sun or gets so close that it burns up.

Sunspots - Cooler, dark patches on the Sun's surface caused by disturbances in the Sun's magnetic field.

Superior planets Planets that are farther away from the Sun than the Earth is, including Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.