(also called a “minor planet”) A small solar system object in orbit around the sun composed mostly of rock. Many of these objects orbit the sun between Mars and Jupiter. Their size can range anywhere from 100 meters in diameter to almost 1000 kilometers.
- Principal asteroids – Ceres, Pallas, Juno and Vesta
- C-type asteroids are carbon-rich, very dark, reflect only 3%-9% of sunlight.
- S-type asteroids are comprised of metallic nickel-iron mixed with iron- and magnesium-silicates.
- V-type asteroids contain more pyroxene than S-type asteroids.
This law describes a mathematical method for calculating planetary distances which states that the distance to the nth planet is 0.4 + (0.3)n Astronomical Units. Bodes law works surprisingly well out to Uranus.
The apparent brightness of a star is called the apparent magnitude and that is what is measured by a telescope: how much energy the star puts into the telescope's collecting area per second.
The outer part of a planet, moon, or asteroid composed essentially of crystalline rocks—generally the crustal composition is different from the bulk composition of the planet (adapted from Merriam-Webster.com).
Electron Volt (eV)
A unit of energy used to indicate the energy of a charged particle. 1 eV is the energy gained when an electron is accelerated by a potential of one volt. 1 electron volt = 1.6 x 10-12 ergs
Circular orbit of a body round a point that is itself in a circular orbit round a parent body—such a system was formulated to explain some planetary orbits in the Solar System before they were known to be elliptical
Fusion crust is the outer covering that a meteorite has acquired as a result of the melting of its surface layer as it passes through the atmosphere. The compression of the Earth's atmosphere heats the surface of the meteoroid to its melting point. Most of the melted material is ablated (removed): what remains resolidifies as the fusion crust. The thickness of these crusts can range from less than one millimeter up to several millimeters. Typically, the leading side of the meteoroid will have a thinner crust than the trailing side. Fusion crusts can be light or dark in color depending on the amount of iron in the meteorite minerals.
Very energetic EMR photons with energies between 1 MeV–¬10 GeV
Inelastic collision; a collision between two particles in which part of their kinetic energy is transformed into another form of energy (gamma rays)—the total amount of energy remains the same
Hubble Space Telescope (HST)
NASA launched the Hubble Space Telescope in 1990. It orbits around the Earth every 97 minutes about 600 kilometers above the Earth, above the distorting effects of the atmosphere. Hubble’s instruments include cameras and spectrographs, using mirrors to focus and magnify light.
In the case of meteorites the term “igneous” refers to a rock formed by solidification of a molten rock or metal. Examples of igneous meteorites include the iron meteorites, and basaltic meteorites (Howardites and Eucrites) thought to come from the asteroid Vesta.
Impact basin (also impact crater)
A circular depression on the surface of a planet, moon, asteroid, or other celestial body. Craters are typically caused by meteorite impacts. In complex craters formed by large impacts, a central peak or peak ring is caused by rebounding crustal rock after the impact. In the center of some impact craters on Earth, a crater lake accumulates; but some crater lakes occur in volcanic craters, as well.
In astronomy, the angle between one plane and another. The (equatorial) inclination of a planet is the angle between the plane of its equator and that of its orbit. The inclination of the orbit of a planet in the Solar System other than Earth is the angle between the plane of that orbit and the ecliptic.
Loss or gain by an atom of one or more electrons, by which process the atom becomes an ion and instead of being neutral, has a charge: positive if it has lost an electron, negative if it has gained one.
A system in which the atoms of the propellant are given an electrical charge by removing electrons. The charged atoms—ions—are then accelerated with electric or magnetic fields and emitted at very high velocity, imparting a thrust to the spacecraft. The high velocity of the propellant makes this technology very efficient. On Dawn, xenon atoms are ionized and accelerated with an electric field which is produced with a voltage between two grids. This design is inherited directly from Deep Space 1 (DS1), which was the first interplanetary mission to use ion propulsion.
The radiant energy that enables organs of vision to perform the function of sight—more accurately called luminous energy. (see also Electromagnetic Radiation).
- Emitted - An emanation of light from a light-giving body, such as the Sun
- Infrared light - Electromagnetic radiation with wavelengths too long to be detectable by the human eye, yet able to be seen by an infrared camera.
- Reflected Light - Light that is purely returned back from or bounced off an object.
- Visible Light - Electromagnetic radiation with wavelengths of or close to those detectable by the human eye.
A plot of the amount of light detected from an object (i.e., the apparent magnitude) as a function of time. Light curves provide evidence of eclipsing binaries, variable stars, and track the progress of nova and supernova explosions. Asteroid light curves can give evidence of the asteroid's shape, or how its surface properties vary.
An astronomical unit of brightness—originally corresponding to the eye's response to starlight—the magnitude system is logarithmic, with 5 magnitudes corresponding to a factor of 100 in brightness. To further confuse things larger magnitudes correspond to fainter objects.
A metamorphic rock contains minerals that have recrystallized after melting. In meteorites, the melting may occur due to internal heat on the parent body—heat from radiogenic decay—or heat from impacts.
(see Asteroid) Technically, anything that is not classified as a planet is a minor planet, so any small body in the solar system that primarily orbits the Sun that is not characterized as a satellite of another planet. Pluto is a minor planet, for example.
A configuration of the Sun, Earth and a planet or asteroid in which the apparent geocentric longitude of the planet or asteroid differs by 180 degrees from the apparent geocentric longitude of the Sun. During opposition, the planet is closest to full for that particular orbit.
The measurement of light. Specifically refers to the procedure of highly accurate measuring of the apparent magnitudes of astronomical objects. In general, astronomers measure only a portion of the wavelength spectrum when they do photometry. Different types of photometry are defined by the portion of the wavelength that they examine. Differential photometry, or "UBV Photometry", measures the light within three standard regions defined by filters. These are Ultraviolet, Blue and Visual (hence UBV). There are many different photometry systems and standards.
A vacuum encapsulated photocathode from which electrons are ejected by the photoelectric effect followed by multiple cathodes from which many additional electrons are emitted in a cascade—when finally collected, the original single electron may have generated a pulse of over one million electrons; first used in astronomy in the early 1950s in a process known as differential photometry
A large object formed from the solar nebula; the disk-shaped cloud of gas and dust surrounding a protostar. The classification of a planet by type (such as giant, dwarf, terrestrial, jovian, super Earth, etc.), depends on the body's intrinsic and orbital properties.
Ptolemaic system or Ptolemaic Model of the Universe
A geocentric model in which the Earth remained stationary as the other planets the Sun, the Moon and the stars orbited it on their spheres— was eventually replaced by the Copernican model
Right ascension (RA)
Right ascension is measured in hours of time. It is similar to longitude on the Earth. Astronomers have chosen the Vernal Equinox to define the starting point for the measurement of right ascension. The Vernal Equinox is the point where the Sun appears to cross the Celestial Equator at the beginning of spring. It is therefore one of the two points where the Ecliptic intersects the Celestial Equator.
A substance or material, typically crystalline, that conducts electricity better than an insulator, but not as well as a conductor, because it only allows current to flow under certain condictions. Common semiconductors are silicon, germanium, and gallium arsenide.
A process that uses ground-based telescopes and computer technology to make highly detailed or high-resolution images of asteroids by clustering together loads of tiny “specks” to form a clearer picture
The energies of the photons emitted or absorbed by an atom or compound are distinct. Photon energies are directly related to their frequencies and thus wavelengths, which dictate the colors in the spectrum. By observing the wavelength or frequency of a reflected or emitted photon, it is possible to determine which atoms or compounds comprise the body being observed. Spectra can be detected from the light reaching us from stars and planets, near or very distant, enabling us to identify the composition of the observed object.
Spectroscopy is the study of the detailed features of a body's spectrum, accomplished by measuring the intensity of light emitted or reflected at as many different wavelengths as possible. The resulting spectrum of light allows us to locate emission or absorption lines which determine the object's composition, temperature, and properties—and for a distant, fast-moving object, even its velocity relative to Earth.
The process by which a substance transitions directly from the solid to the gas phase. By comparison, evaporation is the process by which a substance transitions from a liquid to a gas phase.
The Titius-Bode Rule was first devised in 1772 and comprised the series 0 + 4/10, 3 + 4/10, 6 + 4/10, 12 + 4/10, 24 + 4/10 and so on. It was found to describe fairly accurately the distance in astronomical units of the then known planets from the Sun.