The vast surrounding space is known as universe which contains the most distant stars, satellites, planets, galaxies and the earth where we live. There is no one knows how big the universe is or whether it has any limits. The universe contains millions of planets, stars and huge clouds of gas which is separated by a gigantic empty space. The sun sustains all the life on the earth which is also in the Universe. There are billions and billions of stars are exist in the universe are not distributed uniformly in space.. The earth is one f the planets in which it revolve around a central star known as sun. These stars occurs which is in the form of groups or clusters of billions of stars are known as galaxies.

By using telescopes, astronomers can look at the galaxies, stars, satellites, moon and many more objects are in the universe.  The Universe is very huge and infinite in volume and the matter can be seen is spread in space around 93 billion light years. In the universe, the diameter of a typical galaxy is about 30,000 light years. There is distance between two neighboring galaxies is around 3 million light years. For example Milky Way is one of the galaxies in the universe which is approximately 100,000 light years in diameter. Andromeda is the nearest galaxy which is located approximately 2.5 million light years away. As per observation, the universe has more than 2 trillion (10¹²) galaxies and an estimated 1 x 10²⁴  stars.

Now the overall density of the universe is very low that approximately 9.9 x 10^-30 grams per cubic centimeter. This mass energy appears that consists of 23 percent dark matter, 73 percent dark energy and remaining 4 percent of ordinary matter in which dark energy makes it expansion faster and dark matter slows the expansion of the universe.

The approximate age of the universe is 13.798±0.037 billion years old which is based on the measurements such as radioactive dating. In precise the estimate age of the universe is ranging from 11-20 billion years to 13-15 billion years.

Measuring units of Universe – The extremely large distances between the various heavenly bodies such as the planets and the stars which can be expressed in terms of two units

1. Light years
2. Parsec

Let us discuss in detail

1. Light years – it is the distance travelled by light which is travelled by light in one year is known as light year

1 Light year = 9.46 x 10¹² Kilometers

The nearest star to the earth (apart from the sun) is alpha century which is around 4.3 light years away from the earth.  The actual distance of the alpha century star from the earth in kilometers

1 Light year = 9.46 x 10¹² Km

So 4.3 Light years = 9.46 x 10¹² x4.3

= 40.67 x 10¹² Km

2. Parsec – It is also an astronomical unit of distance which is equal to 3.26 light years. Thai is

1 parsec = 3.26 light years

Astronomers also use another unit for measuring large distances which is known as parsec.