Day 32: A little bit of star wonder – understanding parallax

How do scientists know that stars are so far, far away? Here’s a little bit of wonder explained and a lit of bit of cool science appreciation – thank you scientists for coming up with theories and information that knocks our socks off!

Scientists affirm that stars are billions of kilometers away – but how do they know that if we can’t travel there? One of the methods scientists use to measure the distances of stars is to calculate their parallax. Parallax is the amount an object appears to “shift” when you view it from different positions. Then, scientists use trigonometry to find out the distance that corresponds to the angle that the object shifted.

To understand this easier, hold your finger in front of your nose and “plot” its position comparing it to something more distant – like a map on the wall. My index finger is pointed towards Africa on the map for example. Keep your finger steady and close your left eye. You’ll notice that your finger “shifted” to the left. Now open the left eye and close your right – your finger will appear to have shifted again, this time to the right. Parallax is the amount that the finger appears to have shifted. By measuring this amount, and knowing the distance between your eyes and your nose, you can calculate the distance between your nose and your finger using trigonometry – yes, those formulas that you learn in high school.


Scientists apply this concept to calculate how far a star is. As a reference, they use stars that are far, far away and don’t shift when you change positions – like Africa on the map, that doesn’t shift when I close my left or my right eye. Then, they pick a star that is closer to them and observe how much it shifts by plotting its position when the Earth is at one extremity of its orbit around the sun and again at the other extremity. Since stars are so far away, they shift very slightly – but that distance is enough to give us an angle which we can use to calculate their distance.


Source: Imagine the Universe, NASA/GSFC

But what about all the other stars, that are too far to observe a parallax?

Since we have a catalog of star distances of all the stars that are closest to us, thanks to parallax, we’ve established a relationship between color, spectrum, and brightness. We can then compare the stars that are far away to those that are close and measurable, and have a good idea of how far the other stars actually are.

Fun Facts: The closest star to our solar system is Proxima Centauri, which is 4.2 light years away (the light that it emits takes 4.2 years to reach us).  The farthest stars known to us are in a galaxy called GN-Z11, which is 13.4 billion light years away (it takes light 13.4 BILLION years to reach us, which means that spotting this galaxy is like looking at the universe when it was very, very young, at about 3% of its current age).


Amazing view of galaxies as seen from Hubble. Image credit: NASA, ESA and the HST Frontier Fields team (STScI)



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