How far are the stars in the sky?

 

https://youtu.be/kpQE6tmscuk

Teks An Kreyol Aysyen            Text In English

How far are the stars in the sky? When we look at the night sky, we see how beautiful the stars are... they all seem to be hanging on one plan, one ceiling! But in reality, each one has its own distance, and they are very, very far away... After all, there is nothing in our daily life that can allow us to compare and understand the distance of the stars so far away. On Earth, the greatest distance we can travel is 40,000 km which is the circumference of our Earth; and yet, in reality, the closest star to us, after the Sun, is located at 40,000 billion km. The light from this star, called Proxima du Centaure, takes more than 4 years to reach us on Earth...

But how do we know how far a star is relative to us, on Earth?

In fact, there are several methods, but today we are talking about the simplest method: stellar parallax.

Do not forget that the Earth is moving in space, it is revolving around the Sun. This movement makes the person on the surface change their perspective from time to time, like when you are in a car that is moving with you and you see the trees moving. So you can also see things that are not far from the Earth moving faster and even farther than usual in the sky compared to things that are further away. This explains the apparent retrograde movement of the planet Mars in the sky, and thus the parallax movement. Likewise, for the stars, which are closest to the Earth, they have an apparent displacement in the sky, when the Earth moves in its orbit around the Sun. It is the apparent displacement that astronomers call stellar parallax.

To understand this technique better, let's look at how the human eye naturally uses parallax as well. When you look at a book in front of you, you focus your vision, therefore both your eyes, on the book, but if you were looking at a tree that is far from your vision, both your eyes would not be able to focus on the tree . It is the angle cross vision of your two eyes that will allow the brain to estimate the distance of the book or the tree.

It is on the same principle that the stellar parallax works: when the Earth moves around the Sun, from one position on its orbit to another opposite position, if you look at the sky, in 6 months you will notice the position of the nearest stars is shifted relative to other more distant stars. It is a German astronomer, named Friedrich Wilhelm Bessel, who for the first time used this technique in 1838 to calculate the distance of the star 21 Cygni.

Visual angle, so as you see it appears in the sky, when the apparent angle separates 2 objects really by 1 AU two distances from each other, astronomers call it "parsec", parallax second, in a standard way. Mathematically, you can calculate the distance of a star if you use the parallax with this formula: d=1/p where d is the distance, and p is the parallax angle of the star in arc seconds.

For the stars closest to us, yeah, only this technique is useful, because the further away the star, the more angular resolution becomes unusable. The angle of parallax becomes very small, and at more than an angle of 0.01 arcsecond. it is no longer accurate. Even in space, this method has its limits, so it's even worse at the surface of the Earth! Fortunately, astronomers have other techniques for other more distant stars. Proxima du Centaure is the closest star to us, after the Sun, and its parallax is 0.769 arcsec. After it, it is Eloile de Barnard 0.547 arcsec. Well, there are still others... let's stop there.