Hunt Nebulas and Stars in Orion
Check out astronomical objects in and around the Orion constellation before it’s gone for the season in the Northern Hemisphere.
April 12th’s NASA Astronomy Picture of the Day (above) is of the Flame Nebula and Alnitak, the star in the bottom left of the image. Both of these are located in the constellation Orion, the hunter, with Alnitak being the easternmost star in the belt. Orion is a wonderful constellation to view especially for beginner stargazers as it has a number of fascinating astronomical items inside of it to teach us about the universe. So first, let’s familiarize ourselves with Orion, using the subject of this image as our starting point and then delve into even more objects you can find in Orion, the science behind them, and finally the myths behind them.
Orion is currently low in the Western sky in the northern hemisphere as it is a winter constellation so make sure to check it out early in the night and soon before it goes back under the horizon until later in the year. Below is a screenshot of Orion from Stellarium, a tool that lets you explore the night sky similar to how a planetarium works, all on your device!
Orion is easily spotted thanks to the belt of three stars which is fairly noticeable in our sky. Alnitak is the first star on the left side of the belt, with Alnilam in the middle and Mintaka on the right. The Flame Nebula is not visible in the picture as it is set at naked-eye viewing (just our eyes with no binoculars or telescope). From our view here on Earth, the Flame Nebula is actually directly above Alnilam. To get the stunning image of the Flame Nebula featured for the NASA Astronomy Picture of the Day, they rotated the view to center on the Nebula and feature the distinctive flame shape. Below, you can see the zoomed in picture of the belt to spot the Flame Nebula or V1197 which would be visible as a cloudy area with a good set of binoculars or telescope.
You can also see that the Flame Nebula is part of a larger cloud structure, the Orion Molecular Cloud Complex, that continues down below Alnitak. This cloud structure also contains the famous Horsehead Nebula which you can see above as the dark shape in about the middle of the cloud trail heading in a left diagonal from Alnitak. And this isn’t the only Nebula inside of Orion. You can actually see the Orion Nebula with your naked eye if you travel down from the left side of the belt to a fuzzy area with a few bright stars.
But what is a Nebula? Very briefly, a nebula is a cloud of gas and dust and is a part of the life cycle of a star. Certain nebulas (or nebulae) are stellar nurseries which are essentially growing stars. The gas and dust will slowly clump together until it is big and dense enough for atoms to collide at high enough speeds that they fuse together in a process known as nuclear fusion. When this happens, a star is born. The atoms inside a star will continue to collide and fuse, creating heavier and heavier elements over its lifetime of billions of years until it becomes too heavy to stay in balance. At this point, it will die in one of a couple ways depending on the type of star. A small or medium star like our Sun will make several adjustments to its size and density over the last stage of its life until it just slowly dies and dissipates away. A large star will explode in a spectacular event called a supernova, leaving behind a cloud of gas and dust… another nebula. Over billions of years, new stars will eventually form from this nebula. You can see lots of other nebulas (and more!) on Astropix, a database of astronomical images from telescopes around the globe!
So now that we have found some nebulas and learned about them, let’s dive into the stars in Orion more. Above and below the right side of the belt you can see two larger bright stars with the top exhibiting a more red color and the bottom exhibiting more blue. The top one is Betelgeuse, a supergiant red star near the end of its life, while the bottom is Rigel, a supergiant blue star. There are different colors of stars in the night sky and these colors can tell us about the star. Betelgeuse and Rigel are wonderful examples of this and within the same constellation, making them easy to spot.
Contrary to what we see here on Earth, red stars are actually the coolest stars compared to the hotter blue stars. Red stars are still quite hot compared to anything we see here, but much cooler than blue and blue-white stars. Our yellow Sun is in the middle of this range.
You can see the distribution in star temperature, size and color in the H-R Diagram from the European Southern Observatory above with smaller red stars being cooler on the right at 3,000 degrees Kelvin and larger blue stars being hotter on the left at 30,000 degrees Kelvin. There are exceptions to this trend including our supergiant and dwarf stars.
Now that we’ve gone into the science of nebulas and stars, let’s delve into the storytelling tradition of constellations. Constellations are groups of stars that we have chosen to group together to form a shape (like playing connect the dots!) based on how we see the stars from here on Earth. We have used these shapes for thousands of years to tell our histories, myths, and legends*. Orion is the hunter in Greek mythology. We can connect the stars to create him as seen to the left, both with just the lines connecting the stars and the artwork to bring it all together.
The constellations also work together to tell myths. In the zoomed out picture below, you can see that Orion is facing the bull Taurus to get to the Pleiades, the Seven Sisters. The Pleiades is the cluster of stars located in Taurus directly above the word moon.
You can find the Pleiades by tracing or “starhopping” from the belt up to Betelgeuse in the armpit, then down to the bright red star Aldebaran signifying Taurus’s evil red eye, and then continuing to trace right and down to the cluster of stars. (Observing Note: in the picture above taken this week we can see that Mars also happens to be very close so don’t confuse it for Aldebaran as it is also a red object in the nearby night sky. It is a pretty cool addition to our already full plate of astronomical objects to see in this part of the sky right now.) The Pleiades are actually not a constellation, but a cluster of stars. While you can typically see about six, there are actually over a thousand.
In Greek mythology, Orion pursues the Seven Sisters with “amorous intent” for years until Zeus finally intervenes on behalf of the Pleiades, turning them into doves to fly away into the sky. Orion ends up following them up into the sky as a constellation. There is a common addition to this story that Zeus then added Taurus between them to protect the Sisters, but that is not officially in the mythology. While many constellations come together to form a story, just because one is next to another does not mean they are part of the same myth. Another fun constellation mythology fact is that we will never see Orion in the same sky as the summer constellation Scorpio because Scorpio either killed or severely wounded Orion depending on the myth interpretation.
Names of stars also often have meaning as evidenced by several of the stars in Orion. Betelgeuse means “armpit” and Rigel means “foot”; both are apt names considering the location of the stars in the picture of Orion as discussed earlier. However, this is not always a perfect pairing as evidenced by the other main stars in Orion. The left foot is the star Saiph which comes from the Arabic phrase saif al jabbar, meaning “the sword of the giant.” I suppose it could be the tip of his sword if his sword was depicted hanging from the belt. Bellatrix in the right shoulder (across from Betelgeuse) means “female warrior” and you may know this name from the popular Harry Potter series. J.K. Rowling actually named several of her characters after stars and other astronomical objects.
Another character, Sirius, is the brightest star in Canis Major (the Big Dog), which can be seen not far away. Simply follow the belt to the left until you see a really bright star, the brightest star in the night sky. Again, as we are in Spring now, our winter constellations are moving under the horizon and so you have to be quick to catch Orion and Canis Major. An hour after sunset is typically recommended as a start time for stargazing although you might be able to catch Sirius and the brighter stars in Orion a little sooner than that depending on your sky conditions.
That wraps up our discussion on the constellation Orion, inspired by April 12th’s NASA Astronomy Photograph of the Day. Hopefully you learned a few things about the science of stars and nebulas as well as a few stargazing tips to help you spot a few fun things in the night sky the next time you are out. A future article will focus on resources for the beginner stargazer.
*A quick note about constellations and global astronomy. While the current 88 official internationally recognized constellations are based on Greek and Roman mythologies primarily, this was not always the case. Prior to the IAU officially defining the constellations so that astronomers from all over the world could have a common language to discuss the night sky, each culture had their own constellations and many other ancient civilizations studied the stars, contributing to our modern understanding of astronomy including the Mayans, Ancient Egyptians, and Ancient Mesopotamians most notably typically in today’s culture. I have included several resources below that delve into multicultural astronomy if you are interested in exploring this topic more.
Same Stars, Different Constellations: A quick data visualization on Betelgeuse in different cultures’ constellations if you are looking for a quick example.
Figures in the Sky: A more detailed article with awesome animations that focuses on constellations from different cultures and the myths behind them.
Star Art: Tells several different myths relating to the night sky from around the world. It was originally designed as a resource and activity for children, but has some good info.
The Multiverse Unheard Stories from Berkeley: Lots of resources on the study of astronomy from different cultures.
Science Across Cultures The History of Non-Western Science Volume 1 Astronomy Across Cultures: Almost 700 pages of information on ancient astronomy from all over the world. Fascinating if you want to delve deep and/or are curious about a culture that often isn’t highlighted in these discussions.