How Many Stars Are There In The Universe?

How Many Stars Are There In The Universe?

There are more stars in the universe than grains of sand on all the beaches of the world.


Observable Universe with Measurements 01.png


This is a well known space fact that was first attributed to Carl Sagan the famous astronomer and astrophysicist. How true is it?

The answer is that there are probably more than 10 stars for every grain of sand on planet Earth's beaches. The number of stars in the observable universe being estimated at between 10,000 trillion to one quadrillion (in UK long scale) or 10 sextillion to one septillion in US short scale numbers.

This large number was estimated after the amazing discovery of the Hubble Telescope's Deep Field. In this long exposure image of a tiny one 24-millionth of the area of the night sky Hubble resolved 3,000 galaxies. This was 2.5 arc minutes of sky, which is about a 12th of the diameter of the full moon.

XDF-scale.jpg


As the universe is assumed to be uniform in every direction this same finding should be true for any point in the night sky of the same area. To further complicate things Hubble then spent some time observing this area for longer. After 23 days worth of exposure amounting to 10 years worth of data collection the Hubble eXtreme Deep Field was released that added a further 5,500 galaxies to the area.

Hubble Extreme Deep Field (full resolution).png


The Hubble eXtreme Deep Field.

Credit: NASA; ESA; G. Illingworth, D. Magee, and P. Oesch, University of California, Santa Cruz; R. Bouwens, Leiden University; and the HUDF09 Team

Image of observable universe credit: Azcolvin429 


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