As the Earth orbits the Sun during this period, the observer (taking measurements at the opposite sides of the Earth's orbit) notices an apparent movement of the star compared to more distant stars. To determine the distance to a star, astronomers measure the apparent change in its position over one year. Next article: Stellar Parallax > Stellar Parallax Andromeda is the nearest major galaxy to the Milky Way.The Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are small satellite galaxies of own galaxy visible from the southern hemisphere.The Pleiades Cluster is a nearby open cluster of stars also known as the Seven Sisters.Proxima Centauri is the closest star to the Sun.Light Time is the distance as measured if travelling at the speed of light:.It is clear from this table why different units are used for defining distances to different objects. Table 3.1: Distances to various astronomical objects in different units. "The distance at which an object has a parallax of one arc second."Īn arcsecond is equivalent to 1/3600 of a degree, that is an angle of one second of arc (") is equal to one sixtieth of one minute of arc ('), and one minute of arc equals one sixtieth of a degree.ġ parsec = 3.26 light years = 3.09 x 10 13 km = 206 265 AU Since stars are distant, the parallax angle is very small and is usually measured in arc seconds (fractions of a degree) rather than degrees.
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