The distance light would travel in a vacuum in one year. Approximately 5,880,000,000,000 miles ( 9,460,000,000,000 km ) That's six trillion miles or nine point five trillion kilometers.
A unit of distance approximately equal to 3.26 light-years. It originates from using parallax to calculate distance of a star, where 1 parsec = 1/Pi is the parallax angle in seconds of arc. See Parallax and Stellar Parallax for more information.
A scale used to rate stars by their brightness. Smaller numbers are brighter. In the first star catalogues, issued by Hipparchus and Ptolemy, the stars were first assigned a numerical value to indicate their relative brightness. The 20 brightest stars were designated 1st magnitude and the stars at the edge of visibility 6th magnitude. The current system of relating the brightness of a star is still based on this ancient system. In the 19th century, Sir John Herschel found the apparent magnitude of a 1st magnitude star to be about 100 times brighter than a 6th magnitude star.
The brightness of a star as seen from earth on the stellar magnitude scale.
The brightness of a star if it were seen from 10 parsecs ( 32.6 light-years ). The apparent brightness of a stellar object depends both on the intrinsic brightness of the object and the distance the object is from the observer. The absolute magnitude of a star is the apparent brightness, expressed on the stellar magnitude scale, as it would appear at a distance of 10 parsecs from the viewer.
For example, Rigel, with a apparent magnitude of 0.3 and a parallax of 0.005, has an absolute magnitude of -6.2.
The brightness of a star with the sun being unity. If our sun were to be replaced by a star of luminosity 100, we would receive 100 times as much light from that star.
For example, Vega, which has a absolute magnitude of 0.5, has a luminosity of 48. Rigel, with a absolute magnitude of -6.2, has a luminosity of 23,000.
A system that grades stars by their temperature and color. A casual examination of the stars will reveal that they are not all the same color. Spectral class is a system which grades stars by their color and surface temperature. The designations are W, O, B, A, F, G, K, M, R, N, and S. The classes from B through M are further broken down into 10 units; thus, there is B0, B1, B2, etc., to B9 and G0, G1... Stars at the O end of the spectrum are blue. F stars tend to be light blue to white. G stars ( like the sun ) are white to yellow. K stars are orange, while M class stars are red.
The H-R diagram illustrates the relationship
between the spectral class and
absolute magnitude of a star. It
is named for the Danish astronomer Ejnar Hertzprung and the
American astronomer Norris Russell who came up with the idea for
the diagram independently at about the same time in the early
1900's. The diagram is a graph of a star's absolute magnitude
plotted on the vertical axis and it's spectral class plotted on
the horizontal axis. It was discovered that the points
representing most stars fall in a horizontal line that astronomers
refer to as the main sequence. The
diagram also identifies other kinds of stars such as
giants, supergiants, and
white dwarfs.
Main sequence stars are ordinary stars like the sun. They make up about 90% of the stars visible from the earth. It is thought that stars start their lives toward the left of the main sequence band ( bright and blue ) and move toward the right as they age ( towards dim and red ). Our sun is in the middle of the main sequence band ( 4.7 G2 ). See H-R Diagram above.
These stars are much larger than main sequence stars. Hence their luminosity is greater than a main sequence star of the same spectral class. Blue giants are more dense than main sequence stars. This increased density makes them hotter, which corresponds with their blue color. Red giants tend to be larger than blue giants, and are usually less dense than main sequence stars. See H-R Diagram above.
White dwarfs are smaller than main sequence stars and shine with a hot white light. It is believed that intense gravity is responsible for their small size. This makes them extremely dense, which explains their high temperature. They are so dense that a spoonful of their gases would weigh tons if you could weigh them on earth.
A pair of stars revolving around each other. Binary star systems are quite common, with about 25% of all systems being binary systems and possibly as many as 10% being multiple star systems, i.e., containing more than two stars. A spectroscopic binary is defined as being two stars with the same stellar parallax, right ascension, and declination ( at least as far as we can tell from the earth ). 3D Starchart groups spectroscopic binaries into the same star system, while visual binaries are represented as separate, but close star systems.
A binary star system in which one star periodically blocks the other's light. This makes them a type of variable star. Not because the luminosity of the star is changing, but because they are periodically eclipsing each other.
The luminosity of these stars appears to increase and decrease in cycles. There are three types of variable stars: (1) pulsating variables, (2) exploding variables, (3) eclipsing binaries.
An extremely small star that may be made almost completely out of neutrons. Such a star may only be 20 km in diameter, which makes it incredibly dense ( billions of tons per cubic centimeter ). It is thought that supernovae with a remaining mass between 1.44 and 3 solar masses collapse into neutron stars. Most known neutron stars are pulsars; that is they give off an intense radio energy pulses at regular intervals.
A collapsed star with gravity so intense, not even light can escape. It is thought to be the final state of a star with more mass than the upper limit of a neutron star.
The apparent change in the position of an object resulting from the change in the position from which it is viewed. The parallax angle can be used to determine the distance to an object. Our brain uses parallax for depth perception. In this case, the viewpoints are our eyes, and the parallax angle is one half the angle formed by the right eye, the object being viewed, and the left eye. The distance between our eyes is too small to perceive the distance to a star.
A term used by astronomers as a means of expressing the distance of a star. The parallax angle is determined by viewing a stellar object from opposite sides of the sun. Technically defined, stellar parallax is the angle that would be subtended at the distance of one AU at the distance of the star from the sun. The symbol Pi is used and it is always given in seconds of arc.
For example, Vega, with a parallax of 0.123, is 8.12 parsecs or 26.5 light-years from the sun.
The mean distance of the earth from the sun.
Approximately 93,000,000 miles ( 155,000,000 km )
A coordinate system which represents stars as points on a sphere. From the earliest historical records, through the seventeenth century, the concept of the heavens being a sphere onto which the "fixed stars" are projected has persisted. The celestial sphere may be thought of as a sphere of infinite radius with the center being the sun. The coordinate system of this sphere is similar to that of the earth. right ascension being the equivalent of longitude and declination the equivalent of latitude. The locations of stars are usually defined by their coordinates within the celestial sphere. For example, the coordinates of Vega follow.
Right ascension is one of the two spherical coordinates of the celestial sphere. It is the celestial sphere's equivalent of longitude. It is measured in hours and minutes eastward from the vernal equinox. 24 hours = 360 degrees.
Declination is one of the two spherical coordinates of the celestial sphere. It is the celestial sphere's equivalent of latitude. It is measured in degrees and minutes above or below the celestial equator. Northern coordinates are positive and southern coordinates are negative.
The three dimensional location of a star is defined by its stellar coordinates. Most often the location of a star will be described by its right ascension, declination, and parallax. That is to say, a point on the celestial sphere and the radius from the center of that sphere. 3D Starchart uses rectangular coordinates (x,y,z), rather than the spherical coordinates typically used. The sun is defined as the origin, or (0,0,0) The units are in parsecs. To convert from conventional spherical coordinates to rectangular coordinates, use the following:
3D Starchart comes with a command line program for converting parallax, right ascension, and declination into x,y,z coordinates.
The individual motion of a star relative to other stars. It is measured in seconds of arc per year on the celestial sphere.