These refer to time relative to the celestial objects (the fixed stars). This is true with two exceptions known as sidereal days and sidereal years. Earth MassesĪstronomers use the same time units as everyone else, from the very small nanoseconds, to seconds, minutes, hours, days and years. For planets, astronomers use Earth masses and Jupiter masses for understanding the relative size of rocky planets and gas giants. This is a comparison of their mass to the mass of our sun ( one solar_mass). For example, stars are often measured in mass units of solar masses. For this reason, astronomy also employs mass units that compare other objects to ones familiar to us. ParsecĪstronomical units also apply to the mass of enormous objects such as moons, planets and stars. Proxima Centauri, is the nearest star to the Sun and is approximately 1.3 parsecs (4.2 light-years) from the Sun. A parsec was redefined in 2015 to 648000/π astronomical units. A parsec was traditionally defined as the distance where one astronomical unit subtends an angle of one arcsecond. This shift is used as the basis of a unit knows as a parsec. Since even these units are not enough when computing distances across the universe, there is also a light relative distance of kilo-light years ( 1000 light years), or the distance light travels in a thousand years! Light SecondĪngle Shift Seen from Earth: Because the Earth goes around the Sun, our observation of distant objects such as stars results in an angular shift when observed at opposite sides of the elliptical orbit. The same exercise can be used for light traveling shorter periods of times, light seconds, light minutes, light hours and light days. Since the speed of light is 299,792,458.0 meters per second, one can compute the distance equal to a light year as follows:ġ light year = 299,792,458.0 (meters / second) x 31,536,000 (seconds / year) = 9,460,528,405,000,000 meters We can say that an object is one light-year away, and that means that the object is at a distance where it took an entire year for light from the object to travel to Earth. For this reason, the distance to these objects are measured in the amount of time it would take light to travel from there to the Earth. Light Travel in Time: Light is a primary observable when studying celestial bodies. A single astronomical unit is the mean distance from the Sun's center to the center of the Earth. The following is a brief description on the distance, mass and time units employed in the field of astronomy Astronomy Distance UnitsĪstronomical Unit (au): Within our solar system, a common measure of distance is au, which stands for astronomical units. Nonetheless, these units do translate into common units at a grand scale, and vCalc provides automatic conversions between units for calculator inputs and answers via the pull-down menus. 206,264,767,389 astronomical units (ua)īecause of the enormity of space and the size of the objects studied, the field of astronomy employs units not commonly used in everyday life.One Mega-Parsec is approximately equal to:
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