THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
43.6667° N, 70.2667° W
Founded January 1970
"Made from the best stuff off Earth"
THE DAILY ASTRONOMER
Wednesday, April 20, 2016
Orion's Death and Other Catastrophes
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A SACRED SOUND JOURNEY INTO SPACE
Gong Concert at the Southworth Planetarium
Sunday, April 24, 2016 at 6:00 p.m.
$10 adults; $5.00 children
http://usm.maine.edu/planet/gong-concert-sunday-april-24-2016-600-pm
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Our week delving into Pandora's depths continues. For the benefit of those hapless few who just linked their fates with this star-crossed odyssey, Pandora is our question vessel: the storage container for the queries that we promptly neglected on receipt, but promised to address presently. And, as presently is presently the time, it is high time to put pen to parchment.
"When will Orion die? Or, when will the motions of the stars within Orion make it unrecognizable?" -Anonymous, Pittsfield, ME
While Orion and the other constellations seem immortal to us humans, they are similar to cloud forms in that their structures will change by virtue of the independent motion of their component parts. For constellations, these parts are the stars. While some stars travel in clusters and therefore have physical associations, most of the stars within a given constellation are quite far from each other. They only appear close because the night sky does not reveal depth. All stars also move, often at speeds exceeding 100 miles per second. As the stars are so remote, these speeds won't shift their apparent positions relative to each other very much even over many centuries. However, after tends of thousands of years, these position shifts will become far more noticeable.
Orion the Hunter, the winter constellation that begins the night over in the western sky, and the Big Dipper, an asterism within Ursa Major, provide us with examples of how stellar motions can alter star patterns over time. In the graphic below, we see both the Big Dipper (above) and Orion (below) at approximately 50,000 year intervals. We see that 52,000 years ago, both the Big Dipper and Orion were starting to look similar to the patterns we observe today. Back then, the Big Dipper's bowl was smaller and its handle straighter. Orion's shield was bent and its head -marked by the rapidly moving star Meissa- was raised high above the shoulder. In 48,000 years from now, Orion's head will vanish and his curved shield will become a jumble of stars. The Big Dipper's bowl will have become wider and thinner, while its handle will be shaped like an inverted "v." Note that five stars within the Big Dipper (the two handle stars closest to the bowl and the the bowl stars except for the upper star farther from the handle) are part of the Ursa Major moving cluster. These stars share a similar motion through space and therefore their positions relative to each other won't change significantly during this time.
This image shows the Big Dipper (above) and Orion the Hunter (below) as they appeared in the remote past, as they appear now, and as they will appear in the distant future (Image by Martin Vargic)
Around the year 100,000 CE (or, if you prefer AD), the Big Dipper's bowl will be unrecognizable. So, too, will most of Orion. The stars comprising his bronze club and shield will have scattered. The belt, consisting of the stars Mintaka, Alnilam, and Alnitak, will still look very much the same. The hunter's knee stars, Saiph and Rigel, will also be in about the same positions relative to this belt.
So, to answer your question, about 100,000 years from now, one would be hard pressed to see Orion the Hunter amongst the stars that now comprise his pattern. Then again, even at this point, one would still see the belt.
An important caveat: Betelgeuse, the star representing Orion's eastern shoulder, will eventually go supernova, or explode. Astronomers know this catastrophic event will occur within the next one million years. It might occur within the next 100,000 years or it might not. If it does, Orion's eastern shoulder will then be gone, as well.
"In a previous article, you mentioned that the last total solar eclipse will occur in about 600 million years. Do you know where on Earth one would have to be to observe this eclipse?" -Jean S, Biddeford, ME
Mathematical astronomy has enabled us to predict that total solar eclipses will end in about 600 million years. They'll end at this time because the moon, which is slowly moving away from Earth at about 4 cm/year, will then be smaller in angular diameter than the Sun. Therefore, whenever the moon blocks the Sun, the result will be an annular eclipse: an eclipse in which the outermost part of the Sun remains visible.
Unfortunately, we have no way of knowing where on Earth this final eclipse will be observable. Although mathematical astronomy is very powerful, it remains limited. Uncertainties within the Sun-Earth system, which are slight over short time periods, accumulate over long durations. In fact, we cannot predict eclipse times or even planet positions even up to a million years in the future, let alone 600 million. My apologies for the inconvenience.