How far is Betelgeuse?

In the article, How far is Betelgeuse?, on, author Larry Sessions explains how astronomers measure the distance between stars that are far away. It is very difficult to directly measure the distances between faraway astronomical objects in the night sky. By using the concept of parallax, one would be able to measure the distance to nearby stars. As an example to understand what a parallax is, hold your arm directly out in front of you with your thumb pointed up. Pay attention to where it seems to be against the background. Close one eye while holding your arm in the same position. Now close the other eye while opening the first. Your thumb should have appeared to shift slightly to the side. That is because you have two eyes at two separate positions looking at one object independently from one another. The reason the object doesn’t appear to shift while looking at it with both eyes is because our brains automatically calculate the distances from which the view differs. Ancient astronomers thought that using this concept to measure the distance to stars would work in the same way. They were correct. So instead of using two eyes, they used two different locations of the Earth, two positions, each at opposite sides of the sun. Using the diameter of Earth’s orbit, one can observe an object and measure the distance easily.

Stellar parallax

Using this method, astronomers were able to correct their inaccurate original estimated distance to Betelgeuse from a parallax angle of 7.63 milliarcseconds and at a distance of 430 light-years to 5.07 milliarcseconds and at a distance of approximately 643 light-years away.

This article relates to our eleventh conceptual objective, “I can explain how astronomers study the properties of stars including: distance, size and mass.” In our Lecture Tutorials workbook, we looked at The Parsec section to help us understand how to use parallax. This is the apparent motion of nearby objects relative to distant objects. We were able to determine that the closer a star is, the larger the parallax angle. Likewise, the farther away a star is from Earth, the smaller the parallax angle. Another connection to class would be another Lecture Tutorials section, Parallax and Distance. Parallax angles are so small that they are measured in units of arcseconds. 1 arcsecond is 1/3600 of 1 degree. In this tutorial we were to able to follow a set of drawings of a starfield showing one star moving back and forth across the starfield with respect to the more distant stars. These drawings are taken at different times in the year to show the star gradually moving across the starfield. This star exhibits parallax.

I was interested in reading this article. I liked that the article gave a personal example of how to understand parallax and parallax angles. This concept is helpful in understanding how astronomers are able to measure distances between stars. Overall, I enjoyed reading this article.


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