S3 EP8: Messier 40, an Optical Double Star

Hello and welcome back. Today Season 3 ends here and with that my journey with this podcast. In this final episode, we will travel to Messier 40 which is also known as Optical Double Star in astronomy. Is it because its a binary star or something else? I will answer that as well. It is also known as "Messier’s Mistake" and there is a very interesting story behind it.Before we dive into why this object is a mistake, let’s first understand what the Messier Catalog actually is. Back in the 18th century, a famous French astronomer named Charles Messier was a passionate about comet hunting. But he kept getting frustrated as whenever he would point his telescope at the sky, he would see a fuzzy object, and think he found a new comet, only to realize it was a nebula, a star cluster, or a galaxy. To prevent other astronomers from making the same mistake, he compiled a list of 110 deep-sky objects to avoid.But entry number 40 is completely different. It isn't a deep-sky object at all. It is just a pair of stars sitting right next to each other.
Now, you might be wondering, how did a simple pair of stars end up in this catalog? Fear not, let me break down the history for you in simple words. In the 17th century, a Polish astronomer named Johannes Hevelius reported seeing a fuzzy cloud in the sky. Fast forward to October 1764, Charles decided to look for Hevelius's nebula. He pointed his telescope at the coordinates, but he couldn't find any fuzziness. Now astronomers think  that what Hevelius was looking at was actually a faint, distant galaxy called NGC 4290, which Messier's telescope simply wasn't powerful enough to see. Instead, all Messier saw at those exact coordinates was a tight pair of stars. He noted it wasn't a nebula but he still logged it into his catalog as M40. So, what exactly is Messier 40? And this is where i will tell you what is an optical double star. Try to imagine that you are standing outside at night. You look down a long street and see two streetlights that look like as if they are touching each other. But as you walk closer, you realize one streetlight is actually right next to you, and the other is on the other side of the road. They only looked close because they lined up perfectly from your view.That is exactly what Messier 40 is. For a very long time, astronomers questioned whether these two stars were a true binary system, meaning they are gravitationally locked and orbit each other or just an optical illusion.The mystery was finally solved recently thanks to high-precision data from the Gaia satellite. The data revealed that the two stars are completely unrelated objects who appear as one from our perspective. 

Now let me tell you more about this interesting object. Messier 40 is located in the constellation Ursa Major. The first star, HD 238107, is an red giant star and the second star, HD 238108, is a main-sequence star like our Sun. They aren't bound by gravity, and they are actively drifting away from each other in different directions. Thank you for being on this journey with me. This was the final episode of Season 3. 

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