Astronomy Topics

Absolute Altitude
Altitude above the actual surface, either land or water, of a planet or natural satellite.
Absolute Brightness
The total luminosity radiated by an object.
Absorption Edges
Sudden rises superposed on the smooth decrease of the curve of the attenuation coefficient, which cause the curve to have a typical sawtooth aspect.
Absorption Lines
Dark lines in a spectrum that are produced when light or other electromagnetic radiation passes through a gas cloud or similar object closer to the observer.
Absorption Trough
Range of wavelengths at which atomic hydrogen absorbs or emits radiation.
Accretion
The process by which the terrestrial planets grew.
Accumulation Theory
The theory by which planetesimals are assumed to collide with one another and coalesce, eventually sweeping up enough material to form the planets.
Active Sun
The Sun during its 11-year cycle of activity when spots, flares, prominences, and variations in radio frequency radiation are at a maximum.
Adaptive Optics
A technique that uses deformable mirrors on a telescope to correct the blurring caused by turbulence in the atmosphere.
Aeon
In astronomical terms, 1,000 million years.
Angle of Elevation
The angle between the horizon and a point above the local horizon in the celestial sphere, measured along the great circle that passes through both the zenith and the point in question.
Annular Eclipse
An eclipse in which a thin ring of the source of light appears around the obscuring body.
Anomalistic Month
The average period of revolution of the moon from perigee to perigee, a period of 27 days 13 hours 18 minutes 33.2 seconds.
Anomalistic Year
The period of one revolution of the earth about the sun from perihelion to perihelion.
Antisolar Point
The point on the celestial sphere 180° from the sun.
Apoapsis
That point in an orbit farthest from the centre of attraction.
Apocentre
The point on a spacecraft′s orbit at which it is furthest away from the body it is orbiting.
Apocynthion
That point in the orbit of a moon satellite which is farthest from the moon.
Apofocus
The point on an elliptic orbit at the greatest distance from the principal focus.
Apparent Position
The position on the celestial sphere at which a heavenly body would be seen from the centre of the earth at a particular time.
Astrometric Position
The position of a heavenly body on the celestial sphere corrected for aberration but not for planetary aberration.
Astrometry
The branch of astronomy concerned with measuring the positions of celestial bodies, such as stars and galaxies, and their real and apparent motions.
Astronaut
A person who rides in a space vehicle.
Astronomical Constants
The elements of the orbits of the bodies of the solar system, their masses relative to the sun, their size, shape, orientation, rotation, and inner constitution, and the velocity of light.
Auger Shower
A very large cosmic ray shower.
Aurora Australis
The aurora of the Southern Hemisphere.
Auroral Oval
The region in which aurora appears at the same time, corresponding to the ring of fire around the magnetic pole.
Auroral Zone
The region on Earth where auroras are common.
Binary Star
Pair of stars bound together by mutual gravitation and orbiting their common centre of mass.
Black Hole
A massive star that has collapsed to such a small size that its gravitational force is so strong that not even light can escape from its 'surface'.
Blue Supergiant
A supergiant star with spectral type O or B.
Bow Shock
The shock wave caused by the edge our Solar System travelling through deep space.
Brahe, Tycho
Danish astronomer who made precise observations of the sky.
Carbonado
Carbon that has metamorphosed into its diamond phase but remains black.
Cascade Shower
A group occurrence of cosmic rays.
Cassegrain Telescope
Two-mirror reflecting telescope.
Cataclysmic Variable
A binary star system containing a white dwarf that exhibits sudden outbursts of energy.
Celestial Sphere
An imaginary sphere of infinite radius centered on the Earth and poles aligned with the poles of the Earth.
Chemical Enrichment
The process in which a star manufactures chemical elements, such as carbon and oxygen, in the nuclear reactions in its interior and then ejects these elements into space.
Cosmological Constant
The constant introduced to the Einstein field equation, intended to admit static cosmological solutions.
Decaying Orbit
An unstable orbit from which the orbiting object will gradually spiral into the body it is orbiting.
Double Star
Two stars in nearly the same line of sight and at approximately the same distance from the observer.
Drake Equation
A way of estimating the number of intelligent, technological species in existence in our Galaxy.
Earth
The basic Earth data.
Emission Nebula
A type of nebula that shines by emitting light when electrons recombine with protons to form hydrogen atoms.
Eon
In astronomical terms, 1,000 million years.
Evening Star
Name given to Venus when observed in the evening, also known as Phosphorus.
Faculae
Bright granular structures on the surface of the Sun that are slightly hotter than the surrounding photosphere.
Faint Young Sun Paradox
Calculations suggest that at about the time of the formation of Earth, the Sun was roughly two-thirds the brightness that it is now. However, there is no geological evidence.
Galactic Year
The unit of time in which the Solar System makes one revolution around the Milky Way galaxy.
Galaxy Clusters
Groups of galaxies that may contain up to a few thousand galaxies.
Gas Cap
The gas immediately in front of a body as it travels through the atmosphere.
Great Year
Or Platonic Year, the period of one complete cycle of the equinoxes around the ecliptic, about 25800 years.
Heliopause
The boundary between the solar wind and the interstellar wind, where the pressure of both are in balance.
Heliosheath
A vast, turbulent expanse where the solar wind piles up as it presses outward against interstellar matter.
Hemmungspunkt
The end of the highly luminous path of a visual meteor.
Jupiter
The largest planet in our solar system.
Keplers Laws
Kepler found three laws defining the orbit of planets.
Kerr Black Hole
A rotating black hole.
Lagrangian Points
In a system of two large bodies (Sun-Earth or Earth-Moon), these are the points where a small third body will keep a fixed position relative to the other two.
Lunar Eclipse
When the Moon enters the Earth′s shadow as the Earth moves between the Sun and the Moon.
Lunar Gravity
The force imparted by the moon to a mass which is at rest relative to the moon. It is approximately 1/6 of the earth′s gravity.
ly
Abbreviation of Light Year.
Major Planets
The four largest planets: Jupiter, Saturn, Uranus, and Neptune.
Mars
The fourth planet from the sun in our solar system.
Mercury
The planet nearest to the sun in our solar system.
Meteor
A meteoroid that has entered Earth′s atmosphere.
Meteor Shower
A number of meteors with approximately parallel trajectories.
Meteor Stream
A group of meteoric bodies with nearly identical orbits.
Meteorite
The remnants of a meteor after it has actually impacted the Earth.
Meteoroid
An object in space similar to but smaller than an asteroid.
Micrometeorite
A very small meteorite or meteoritic particle with a diameter in general less than a millimeter.
Moon
Basic Moon data.
Morning Star
Name given to Venus when observed in the morning, also known as Hosperus.
Nadir
The point on the celestial sphere directly below an observer, diametrically opposite the zenith.
Neptune
The outermost gas giant in our solar system.
Neutron Star
A star composed only of neutrons.
Newtonian Telescope
A reflecting telescope in which a small plane mirror reflects the convergent beam from the objective to an eyepiece at one side of the telescope.
North Pole
That end of the axis of rotation of a celestial body at which, when viewed from above, the body appears to rotate in a counter-clockwise direction.
Nova
A star which suddenly becomes many times brighter than previously, and then gradually fades.
Olbers Paradox
If the Universe is infinite, uniform, and unchanging then the entire sky at night would be bright, about as bright as the Sun.
Opposition
The point at which a planet that is further away from the Sun than the Earth.
Optical Double Star
Two stars in nearly the same line of sight but differing greatly in distance from the observer.
Orbit Acquisition
Reception of the telemetry containing the information about the orbital parameters of the spacecraft.
Palermo Scale
Used by astronomers to assess the risk of an impact on the earth by a comet or asteroid.
Planet
A spherical ball of rock and/or gas that orbits a star.
Platonic Year
The period of one complete cycle of the equinoxes around the ecliptic, about 25800 years.
Pluto
The outermost planet in our solar system and it′s double Charon.
Poynting-Robertson Effect
Gradual decrease in orbital velocity of a small particle in orbit about the sun due to the absorption and reemission of radiant energy by the particle.
Protoplanet
Any of the sun′s planets as it emerged or existed in the formative period of the solar system.
Protoplanetary Disc
The disc of dust surrounding a star out of which planets might form.
Protosun
The sun as it emerged in the formation of the solar system.
Pulsar
A stellar source, such as a rotating single star or pair of stars, emitting electromagnetic radiation which is characterised by rapid frequency and regularity.
Red Supergiant
A supergiant with spectral type M. These are the largest stars in the universe.
Reflecting Telescope
A type of telescope using a mirror as the objective.
Refracting Telescope
A type of telescope using a lens as the objective.
Satellite
An object in an orbit around a planet.
Saturn
The sixth planet from the sun in our solar system.
Schwarzschild Black Hole
A nonrotating, spherical black hole that has no electric charge.
Shooting Star
Another name for a meteor.
Solar Eclipse
When the Earth enters the Moon′s shadow as the Moon moves wholly or partially in front of the Sun as seen from Earth.
Solar Energy
Electromagnetic energy transmitted from the sun.
Spectrum
A spectrum is a definition of the magnitude of the frequency components that constitute a quantity.
Standing Wave
The interference pattern produced by two waves of equal amplitude and frequency traveling in opposite directions.
Star
A ball of mostly hydrogen and helium gas that shines extremely brightly. Our Sun is a star.
Starburst Galaxy
Galaxy in which a large burst of star formation is observed.
Stellar
Of the stars.
Stellar Wind
A steady or unsteady outflow of material from the surface of a star.
Stopping Point
Hemmugspunkt: the end of the highly luminous path of a visual meteor.
Submillimeter Wave
The portion of the electromagnetic spectrum between 300 GHz and 1 THz, also known as microwave.
Sun
The star at the centre of our solar system.
Sunspot
An area on the surface of the sun marked by a lower temperature than its surroundings and that has magnetic activity.
Telescope
Instrument used to focus electromagnetic radiation into an image.
Termination Shock
Particles from the Sun begin to slow and clash with matter from the sparse gas found between the stars.
Trojan Points
The two dynamically stable Lagrange points.
Trojan Satellites
Satellites which orbit a body at one or the other Trojan points relative to a secondary body.
True Sun
The actual sun as it appears in the sky.
Uranus
The seventh planet from the sun in our solar system.
Vertical Circle
A great circle of the celestial sphere, through the zenith and nadir, perpendicular to the horizon.
Voyager Probes
Space probes launched by NASA in 1977. Their official missions were to study Jupiter and Saturn, but the probes were able to continue on.
Yellow Supergiant
A supergiant star with a spectral type of G.
Zenith Distance
This is for bodies above the horizon and is the arc of a vertical circle between the zenith and a point on the celestial sphere, measured from the zenith through 90 degrees.
Zenith Telescope
Instrument for observing stars near the zenith.
Zero-age Main Sequence
The position on the main sequence of a Hertzsprung-Russell diagram.
Zone of Avoidance
An irregular zone near the plane of the Milky Way where the absorption due to interstellar dust is so great that no external galaxies can be seen through it.

See also: Astrophysics.

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Subjects: Physics