Distance in Space



Dear Friend:

The distance in space is measured in Astronomical Units and Light -years.

In Solar system we describe distances in terms of Astronomical Units (AU).

The AU is defined as the average distance between the Earth and the Sun.

The Earth is about 148,800,000km or 93 million miles from the Sun.

So 1 AU = about 93 million miles.

The distances of the stars and other objects beyond the planets of our Solar System are measured in light-years.

One light-year is the distance light travels in one year.

Light travels at a speed of 299,792,458 meters per second.

It is normally rounded to 300,000 km per second or 186,000 miles per second.

One light-year is about 9.44 trillion km (9,460,000,000,000kilometers).

Astronomers sometimes use the parsec as units of distance.

One parsec is equal to 3.3 light-years.


Earth is 1 AU from the Sun.


Mercury is about 1/3 of an AU from the Sun.


Pluto is about an average 40 AU from the Sun.


The Milky Way Galaxy is about 150,000 light-years across.

Compare the size of our galaxy with the size of an atom.

The size of an atom is 10-11 meter.

The diameter of it's nucleus is about 10-15 meter.

What a big difference.


The Andromeda Galaxy is 2.3 million light-years away.


Constellation Hydra is about 800 million light-years from Earth.


Our Solar System
Name Average Distance from the Sun Equatorial radius Volume Mass Length of Day

(Rotation Period)

Length of Year

(Orbit Period)

Sun - - 6.955 x 105 km 1.1422 x 1018 km3 1.989 x 1030 kg 25.38 Earth days  -
Mercury 5.7909175 x 107 km 0.38709893 A. U. 2.4397 103 km 6.08272 x 1010 km3 3.3022 x 1023 kg 58.646 Earth days 87.97 Earth days
Venus 1.0820893 x 108 km 0.723332 A. U. 6.0518 x 103 km 9.284 x 1011 km3 4.8685 x 1024 kg -243 (retrograde) Earth days 224.7 Earth days
Earth 1.4959789 x 108 km 1.000 A. U. 6.38714 x 103 km 1.0832 x 1012 km3 5.9737 x 1024 kg 23.934 hrs 365.24 Earth days
Earth's Moon 3.84400 x 105 km from Earth 0.00257 A. U. 1.734 x 103 km 2.197 x 1010 km3 7.3483 x 1022 kg 27.321661 Earth days 27.321661 Earth days

Orbit Period = Rotation Period

Mars 2.2793664 x 108 km 1.523662 A. U. 3.397 x 103 km 1.6314 x 1011 km3 6.4185 x 1023 kg 1.026 Earth days 686.93 Earth days
Jupiter 7.7841202 x 108 km 5.20336 A. U. 7.1492 104 km 1.4255 x 1015 km3 1.8987 x 1027 kg 0.41354 Earth days 4330.6 Earth days
Saturn 1.4267254 x 109 km 9.53707 A. U. 6.0268 x 104 km 8.2713 x 1014 km3 5.6851 x 1026 kg 0.44401 Earth days 10755.7 Earth days
Uranus 2.8709722 x 109 km 19.191 A. U. 2.5559 x 104 km 5.9142 x 1013 km3 8.6849 x 1025 kg -0.7196 Earth days (retrograde) 30,687.2 Earth days
Neptune 4.4982529 x 109 km 30.069 A. U. 2.4764 x 105 km 6.2526 x 1013 km3 1.0244 x 1026 kg 0.67125 Earth days 60,190 Earth days
Pluto 5.90638 x 109 km 39.482 A. U. 1.151 x 103 km 6.39 x 109 km3 1.3 x 1022 kg 6.387 Earth days 90,553 Earth days


Our solar system is situated within the outer regions of our galaxy-The Milky Way Galaxy well within the disk and about 20 light-years above the equatorial symmetry plane but about 28,000 light-years from the Galactic Center.

The solar system is situated within a smaller spiral arm, called the Local or Orion Arm.

Our Sun, together with the whole Solar System, is orbiting the Galactic Center at 28,000 light-years, on a nearly circular orbit. We are moving at about 250 km/sec. It requires about 220 million years to complete one orbit. If our Galaxy is formed about 4.6 billion years ago, then our Solar System has orbited the Galactic Center about 20 to 21 times so far.




Distances of some of the stars from the Earth
Star Distance from Earth
GSC-02652-01324 500 light-years
HD-59686 299 light-years
HD-190228 215 light-years
HD-219449 146 light-years
Gamma-Cephei 38.50 light-years
Gliese-876 15 light-years
Epsilon-Eridani 10.40 light-years


The Milky Way is the galaxy which is the home of our Solar System contains about 200 to 400 billion stars.

The Milky Way Galaxy is about 100,000-150,000 light-years across.

Mass of The Milky Way Galaxy is probably between 750 billion and one trillion solar masses.

The Milky Way Galaxy belongs to the Local Group.

The Local Group cluster of galaxies is a group of 3 large and over 30 small galaxies.

The Local Group is about 10 million light-years in diameter,

the center of which is somewhere between the Milky Way and M31.

The Andromeda Galaxy M31 is the largest galaxy of the Local Group.

The Milky Way is the second largest galaxy of the Local Group.

The Triangulum spiral M33 is the third largest galaxy.

M31 is about 2.9 million light-years

Canis Major Dwarf is about 25,000 light-years away from us and about 45,000 light-years the Galactic Center.

SagDEG is about 88,000 light-years from us and about 50,000 light-years from the Galactic Center.

The Large Magellanic Cloud (LMC) is about 179,000 light-years away.

The Small Magellanic Cloud (SMC) is about 210,000 light-years away.

The Virgo Cluster is our nearest big cluster of galaxies.


Some of the Local Group Member Galaxies
Galaxy Diameter

(in 1000 light-years, kly)


(in million solar masses)


(in 1000 light-years, kly)

M31 195 400,000 2,900
Milky Way 100 750,000 28
M33 60 25,000 3,000
LMC 30 20,000 179
SMC 25 6000 210
M110 17 10,000 2,900
M32 8 3000 2,900


In the Universe there are clusters of clusters of galaxies called super galaxies

which are hundreds of thousands of light-years apart.

This is only about visible universe only.

How about multiple universes!