Monday, January 20, 2014

The Big Dipper and Orion: Naked Eye Astronomy Lesson II

IN OUR LAST POST, I gave you guys a brief introduction to naked eye astronomy by showing you a bit about how the heavens move every night.  Now, I'm going to have you guys actually apply what you've learned, and go out into the night and try and find a few basic constellations and stars!  We will start with one of the most famous: the Big Dipper!*  But first, pull up the video supplement by clicking HERE, or clicking it below.  We will be consulting it several times throughout this post, so make sure that you have this pulled up!
The Big Dipper is officially an asterism within the official constellation of Ursa Major, or the "Big Bear."  In this case, an asterism is when a portion of a constellation is more famous than the official constellation.  We will talk about another important asterism, Orion's Belt, in just a few minutes!  In the meantime, below is a picture of the constellation Ursa Major.  The Big Dipper appears to be seven very bright stars that make up the tail of the bear.  Besides being an obvious and easily recognizable constellation, the Big Dipper is important for another reason: two of its stars point the way to Polaris, or the North Star!  We talked about Polaris in the last post, so to refresh yourself on the importance of this star, make sure to check out the link I provided above.

At this point, consult Part I of the video supplement, a link to which I have provided at the top of this post.  Part I shows you not only where to look for the Big Dipper in the night sky, but also outlines the constellation, and shows how to use the stars Merak and Dubhe as "Pointer Stars," as guides to locate the North Star.  Below you can see a picture of the same thing.  The constellation of the Big Dipper is outlined in red, with the yellow line being drawn from Merak and Dubhe to Polaris, which has a blue circle around it.

At this time of year, the Big Dipper rests on the horizon at sunset, and not all of it is visible.  It isn't until around 21:00 (9:00 PM) that the entire constellation completely clears the horizon, and doesn't get high in the sky until after midnight.  As we get closer to summer, watch for the position of the Big Dipper at sunset: it will continue to rise high in the sky, and in several months will be at the same position at sunset as it is at midnight tonight.  Furthermore, for the most part, the Big Dipper does not drop below the horizon here in Boulder.  This is because for this latitude, the Big Dipper is a circumpolar constellation, meaning it never sets.  (To learn a little more about what it means to be circumpolar, make sure to check out the last post.)

Next, we will use another constellation to locate two more objects of interest in the night sky.  The constellation is the very famous constellation of Orion.  These days, Orion has already risen in the east by sunset, and is instantly recognizable.  Even in the brightness of many cities, the most prominent stars are still visible.  Below is a picture of Orion, with art of the constellation depiction overlaying the stars.

Now we refer to Part II of the video supplement.  Part II shows us where to see Orion, and also shows us how to use the asterism of Orion's Belt to locate two objects of celestial significance: the bright star Sirius, and the star cluster called the Pleiades.  Just as with the Big Dipper and Polaris, the constellation itself is outlined in red, and the yellow line points the way to Sirius and the Pleiades, which are both circled in blue.

Sirius will not have risen immediately after sunset at this time of year, and you will have to wait for 20:00 or 21:00 to get a nice view of it.  Despite the fact that, at a mere 8.6 light-years, it is only the 5th closest star to the Earth (not including the Sun), it is the brightest star in the night sky when viewed from Earth.  Sirius is a part of the constellation Canis Major, which we will discuss in a future lesson.
You can see Orion in the center of the photograph.  The bright star in the bottom of the photograph a bit to the left is Sirius.
Most constellations are composed of stars that have little to no physical relation to each other.  To see what I mean, refer to Part III of the video supplement.  In Part III, we take a virtual voyage to Alnilam, the center star in the belt of Orion.  As you can see as we get closer and the constellation becomes more and more warped, it is only on Earth and in the nearby Solar System that these stars appear to have any relation to each other.  There are notable exceptions, however, and when it comes to these exceptions, the Pleiades shine brighter than all the rest.  This is where we travel to in Part IV of the video supplement, to Alcyone, the brightest star in the Pleiades.
Another picture of Orion that I took in my backyard.  Alnilam is the center star in the Belt.
Called "Subaru" by the Japanese (yes, just like the car company), the Pleiades is actually an open star cluster, composed of many more stars than can be easily viewed here on Earth, possibly as many as 500!  Located in the classical constellation of Taurus the Bull, almost every culture that could see the Pleiades created some sort of story about them.  Although the stars that are visible within it are not very bright compared to the main stars of Orion or the Big Dipper, it is their close proximity to one another that make the Pleiades instantly recognizable.  You might even be able to see them in the city, but you will have to know where to look, which is covered in Part II of the video supplement.
The Pleiades are the cluster of stars in the center of the photograph.
Next time, we will look at some more of the major constellations in the vicinity of Orion, including the aforementioned Canis Major and Taurus, as well as Auriga and Gemini.  We will also learn a bit about the current location of Jupiter, and the possibility of viewing some of Jupiter's moons!
**I am writing from a latitude of about 40 degrees North, in Boulder, Colorado. The information in this post can apply to anyone within that belt around the world. For example, people in Beijing and Baltimore, both cities around 40 degree North latitude, will see the same thing every night as people in Bursa and Boulder.

Works Cited:

The video and some of the pictures in this post were made using the Stellarium app or the Celestia app.


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