How many stars are visible to the naked eye?

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

13 December 2020

Astronomers estimate that there are about 200 billion stars in our galaxy – the Milky Way; but when you look up in the night sky, you do not see all of them – obviously! There are several reasons for this:

First, you cannot see the entire sky – more than half of it is blocked from view by the earth. Secondly, the majority of the stars are either too far away or too faint to be seen without a telescope. Due to these factors, it turns out that, on a cloudless, moonless night and from a place that has no artificial lights, we are only able to see about 3,000 to 4,000 stars.

At 4.25 light years away, Proxima Centauri is the nearest start to our sun but it can only be seen with the aid of a telescope. The nearest star visible to the naked eye is the two-star system called in the neighbourhood of Proxima. They are Alpha-A and Alpha-B Centauri located some 4.36 light years from us.

Now, a light-year is the distance that light travels in one year. This is equal to about 9.5 trillion kilometres! Thus, our nearest neighbours in the universe are about 40 trillion kilometres away.

The fastest man-made object is the Parker Solar Probe which reaches about 690,000km/h or 200km/second as it sweeps near the sun’s surface at just 4 million kilometres above it. If we sent a spacecraft to Alpha Centauri at that speed, it would take about 6,500 years to get there!

Still, the farthest star that is visible to the unaided eye is 4,000 light years away. But it is not the most distant object that we can see. There are 9 galaxies that can be seen without a telescope.

Our nearest major galaxy, the Andromeda, is one of those visible to unaided eyes; it is 2.5 million light years away. Even though it looks like a single object when viewed from Earth, it is actually a collection of about one trillion stars!

For that reason, it might then be argued that when you look up at night, we might be able to see trillions of stars. The 3,000 to 4,000 in our Milky Way plus the trillion others “crammed up” in the Andromeda Galaxy.