Astronomers use many type of of the same devices of measurement as other scientists. They often usage meters for size, kilograms for mass, and also seconds for time. However before, the distances and also sizes in the cosmos have the right to be so big, that astronomers have actually invented more devices to explain distance.

You are watching: One of the most common units used to express stellar distance is the ________.

Astronomical Units:

Distances in the solar mechanism are frequently measured in expensive units (abbreviated AU). An expensive unit is the average distance between the Earth and the Sun:

1 AU = 1.496 x 108 kilometres = 93 million miles

Jupiter is about 5.2 AU from the Sun and also Pluto is about 39.5 AU from the Sun. The distance from the Sun to the facility of the Milky Way is about 1.7 x 109 AU.


To meacertain the ranges in between stars, astronomers often use light-years (abbreviated ly). A light-year is the distance that light travels in a vacuum in one year:

1 ly = 9.5 x 1012 km = 63,240 AU

Proxima Centauri is the nearest star to Earth (other than the Sun) and is 4.2 light-years amethod. This means light from Proxima Centauri takes 4.2 years to travel to Earth.


Many kind of astronomers prefer to use parsecs (abbreviated pc) to measure distance to stars. This is bereason its interpretation is very closely pertained to an approach of measuring the ranges between stars. A parsec is the distance at which 1 AU subtends an angle of 1 arcsec.

1 pc = 3.09 x 1013 kilometres = 3.26 ly

For even better ranges, astronomers use kiloparsecs and also megaparsecs (abbreviated kpc and also Mpc).

1 kiloparsec = 1 kpc = 1000 pc = 103 pc1 megaparsec = 1 Mpc = 1,000,000 pc = 106 pc

Powers of Ten:

The distances and sizes of of the objects astronomers research vary from very small, including atoms and atomic nuclei, to exceptionally large including galaxies, clusters of galaxies and the size of the cosmos. To define such a huge variety, astronomers need a way to protect against confmaking use of terms favor "a billion trillion" and also "a millionth". Astronomers usage a device called powers-of-ten notation, which consolidays every one of the zeros that you would usually find attached to exceptionally big or little numbers such as 1,000,000,000,000 or 0.0000000001. All of the zeros are put in an exponent, which is created as a supermanuscript, and also shows just how many zeros you would certainly have to create out the lengthy create of the number. So for example:

100 = 1101 = 10102 = 100103 = 1000104 = 10,000and also so on.

In powers-of-ten notation, numbers are composed as a number between one and also ten multiplied by a power of ten. So for example, the distance to the Moon of 384,000 km have the right to be re-composed as 3.84 x 105 kilometres. Notice that 3.84 is between one and ten. The very same number can accurately be recreated as 38.4 x 104 or 0.384 x 106, yet the wanted develop is to have actually the first number be between one and ten.

Very little numbers can likewise be written making use of powers-of-ten notation. The exponent is negative for numbers much less than one and indicates separating by that number of 10s. So for example:

100= 1
10-1=1/10= 0.1
10-2=1/10×1/10 = 0.01
10-3=1/10×1/10×1/10 = 0.001
10-4=1/10×1/10×1/10×1/10= 0.0001
and so on.

Once aobtain, numbers are created as a number in between one and also ten multiplied by a power of ten. So for example, a number like 0.00000375 would be expressed as 3.75 x 10-6.

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Some familiar numbers composed as powers-of-ten:
One hundred (100)102
One thousand also (1000)103
One million (1,000,000)106
One billion (1,000,000,000)109
One trillion (1,000,000,000,000)1012
One one-hundredth (0.01)10-2
One one-thousandth (0.001)10-3
One one-millionth (0.000001)10-6
One one-billionth (0.000000001)10-9
One one-trillionth (0.000000000001)10-12

A few websites offer demonstrations ofpowers-of-tenand also therange of the world.

Some examples to try

1.Jupiter is around 5.2 AU ameans from the Sun. How far is this in km?

2.A star is 4.94 x 1013 km away from the Earth. How lengthy will it take the light from this star to reach the Earth?

3.Anvarious other star is 3.5 kpc away from us. How far amethod is it in kilometres and also in ly?

4.Star A is 33 pc amethod, and Star B is 109 pc ameans. What is the distinction in distance in between the 2 stars in ly?