Who devised the astronomical units?

Answer 1

Astronomers use AU to measure distances around the solar system, when miles are too small and light years are too long.

Many astronomers already are using "light-seconds" as a more standard measure; this is especially useful when working with deep space probes, because the distance directly gives you the travel time of a radio signal one way. I expect that as mankind expands into space for the long run, that light seconds will become the preferred measurement.

One Astronomical Unit = 500 light-seconds, almost exactly.

Answer 2

The astronomical unit (AU) was devised by the ancient Greeks to measure distances within our solar system. However, the modern definition of the AU as the average distance between Earth and the Sun was established in the 20th century by the International Astronomical Union.

Answer 3

An Astronomical Unit (AU) is ideal for determining the distance(s) between celestial or astronomical bodies within or relatively near our solar system. A single AU is 149,600,000 kilometres in length. Objects within the known solar system (Generally within 100 AU) are commonly ranged by the use of Astronomical Units. Light travels a single AU in roughly 8.3 minutes. For extremely distant objects and/or entities, the term lightyear may be more appropriate.

Answer 4

You could, of course, but the distance from the sun to the former last planet, Pluto, is only about 40 AU's... and only about 340 light minutes.

Since a light year has 525,600 light minutes in it... that would mean that any calculation of distance within the solar system would involve decimals with lots and lots of zeros!

1 AU (the distance from the Earth to the Sun) is only 0.0000158128588 light years!

So it is MUCH easier to use AU's within the Solar System!

Answer 5

It is a convenient unit of measurement for measuring distances between planets and other objects within the solar system. Using kilometres means dealing with large numbers; and light years are too large to be useful on this scale.

Answer 6

Just another way to describe large distances that are familiar. Take a light year for example. One LY is around 6,000,000,000,000 miles. We can envision a mile but not 6 trillion of them. Same with AU. It is the same as the distance from Earth to the Sun. The Solar System is about 40 AU describe the size better than 4 billion plus miles.

Answer 7

Because the astronomical unit - the distance from the Earth to the Sun - is a useful unit of distance in the solar system that does not need a lot of zeros.

It is also used as the baseline in measuring stellar parallax. If a nearby star moves by one arc-second relative to the background of distant stars in 6 months, its distance is one parsec. In fact all stars are further away than that and the distance in parsecs is 1 / the parallax in seconds.

Answer 8

This is because the distances dealt with in astronomy are enormous. As a result any distance expressed in kilometers would yield an extraordinarily large number. Just the distance to the nearest star to the sun (4.2 light years) is nearly 40 trillion (40,000,000,000,000) kilometers. Also, using a smaller unit implies a greater degree of accuracy that we are capable of.

Answer 9

It is convenient to use units that result in reasonable numbers. It would probably be more appropriate to use, for example, gigameters (109 meters) or terameters (1012 meters); 1 AU = 150 Gm or 0.15 Tm, but astronomers just got accustomed to use astronomical units. In part, this is for historical reasons: initially, the ratios of the distances from the Sun to different planets was known, but the absolute distances were not.

Answer 10

Space is massive so to chart and keep track of its massive distances we use massive scales like astronomical units (or AU) and light years