Astronomy #3

Absolute Magnitude

The magnitude (brightness) of a celestial object as it would be seen at a standard distance of 10 parsecs.

Apparent Magnitude

The magnitude of a celestial object as it is actually measured from the earth.

Absolute Magnitude

The magnitude (brightness) of a celestial object as it would be seen at a standard distance of 10 parsecs.

Apparent Magnitude

The magnitude of a celestial object as it is actually measured from the earth.

Binary Star System

A system of two stars that are gravitationally bound to and in orbit around each other.

Black Hole

A region of space having a gravitational field so intense that no matter or radiation can escape.

Brown Dwarf

Celestial objects that are intermediate between a planet and a star.

Close Binary

A pair of stars that are bound together by gravity and orbit a common center of mass.

Event Horizon

A boundary that separates one region of the universe from another.

Exoplanet

A planet that orbits a star outside the solar system

HR Diagram

A scatter plot that illustrates the relationship between the luminosity, or absolute brightness, and the surface temperature or spectral type of stars.

Light Year

A unit of astronomical distance equivalent to the distance that light travels in one year

Luminosity

The intrinsic brightness of a celestial object

Magnetar

A neutron star with an extremely strong magnetic field.

Main Sequence

A star that fuses hydrogen atoms to form helium atoms in their cores.

Microlensing

An astronomical phenomenon where the gravitational field of a massive object, such as a star or planet, acts like a lens, temporarily magnifying and distorting the light from a background star.

Multiple Star System

A system that consists of 3 or more stars

Nebula

A cloud of gas and dust in outer space, visible in the night sky either as an indistinct bright patch or as a dark silhouette against other luminous matter.

Neutron Star

A very dense and compact star composed primarily of neutrons.

Nova

A star showing a sudden large increase in brightness and then slowly returning to its original state over a few months

Nuclear fusion

A process in which two light atomic nuclei combine to form a single heavier nucleus, releasing massive amounts of energy.

Optical Binary

Objects that appear to be a binary system but are not.

Parallax

The effect whereby the position or direction of an object appears to differ when viewed from different positions, e.g. through the viewfinder and the lens of a camera

Parsec

A unit of distance used in astronomy, equal to about 3.26 light years (3.086 × 10 kilometers). One parsec corresponds to the distance at which the mean radius of the earth's orbit subtends an angle of one second of arc.

Protoplanet

A large body of matter in orbit around the sun or a star and thought to be developing into a planet

Pulsar

A celestial object, thought to be a rapidly rotating neutron star, that emits regular pulses of radio waves and other electromagnetic radiation at rates of up to one thousand pulses per second.

Radial Velocity Method

An indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in the spectrum of the planet's parent star.

Red Giant

A very large star of high luminosity and low surface temperature. These are thought to be in a late stage of evolution when no hydrogen remains in the core to fuel nuclear fusion.

Roche-Lobe

The region around a star in a binary system within which orbiting material is gravitationally bound to that star.

Spectral Type

The group in which a star is classified according to its spectrum, especially using the Harvard classification.

Star

An astronomical object luminous spheroid of plasma held together by self-gravity. A luminous ball of gas, mostly hydrogen and helium, held together by its own gravity.

Supernova

A star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass.

Supernova Type I

Lack hydrogen in their spectra and have a common origin in binary star systems.

Supernova Type II

Show spectral lines of hydrogen and have a different origin.

Transit Method

A technique used to detect and study exoplanets, or planets orbiting stars other than our Sun

Visual Binary

A binary star of which the components are sufficiently far apart to be resolved by an optical telescope.

White Dwarf

A small very dense star that is typically the size of a planet. It is formed when a low-mass star has exhausted all its central nuclear fuel and lost its outer layers as a planetary nebula.

Wide Binary

Pairs of stars that orbit each other