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  • Rapt in Awe

    My Journey through the Astronomical Year

    Think of this as a "companion text" to this, the main web site. Not required reading, butI hope you'll find it interesting and helpful.

Look East: March 2012 – with Mars – Roars in like a sickle and triangle! (Huh?)

Sure, I’d like to tell you March roars in like a lion – but honestly it’s easier to point to the sickle and the triangle and the “Little King” we call Regulus, this last being the new guidepost star for March. But there is a lion there, too. Let’s look at the sickle and triangle first, though, because they’re two very easy asterisms you’ll see in the east about an hour or so after sunset. The Big Dipper off to the northeast gives you an idea of size for comparison.

This is the eastern sky as it will appear about an hour after sunset from mid-northern latitudes. The circle represents a typical field of view for low power binoculars. While you should see the brightest stars easily, in twilight - or in typical light pollution - you'll find that binoculars will show some of the fainter stars nearby and help you be sure you have identified the correct bright star. The Mars position is for the 15th, but it will change a little each night. Click image for larger view. Prepared from Starry Nights Pro screen shot.

Click here to download a black-on-white (printer-friendly) version of this chart.

OK – so can you make this into a lion? I find it fairly easy if I consider the sickle his head and mane – and I consider the triangle his rear haunches. I leave the rest to my imagination and don’t really attempt to connect the dots.

Leo does look much like the Lion depicted inthe 1603 Bayer catalog.  Click image for larger version.
The stars of Leo do indeed trace out some key parts of the Lion depicted in this plate from the 1603 Bayer atlas. (Click image for larger view.) Note that the bright star that marks the tail is named “Denobola,” which in Arabic really does mean “tail.” We encounter this also in the tail of Cygnus the Swan where the bright star is named “Deneb.” The Arabic star names are frequently descriptive. (Image courtesy of Linda Hall library of Science, Engineering and Technology.)

 

Regulus, our new bright guidepost star for this month, means “little king,” or “prince,” in Latin. That fits right in with the lion‘s reputation as King of the Beasts. And what a lovely image to have a prince leading a lion onto the night-time stage this month!

Is Regulus memorable in its own right? Well yes. It’s a star that is spinning so fast that if we could see its disc, it would look like a beach ball that someone sat on. It takes Regulus about 16 hours to make one rotation – in comparison, our Sun, a smaller star, takes about a month to rotate. In fact, if Regulus were spinning just a bit faster, it would spin itself apart!

The rapid spinning gives Regulus an equatorial diameter that is about one-third bigger than its polar diameter. This also results in the polar regions of Regulus being much hotter than its equator.

Regulus is also a multiple star system, but as such rather dull visually. The second star in the system is much fainter, so it can barely be detected by a skilled observer using binoculars – and in a telescope it’s so far away from the primary star that the two stars don’t seem like a pair at all. Both these stars are spectroscopic doubles – meaning the companions are so close we can’t see them with a telescope.

Though a relatively young star – about 250 million years as compared to the five-billion-year age of our Sun – Regulus is apparently nearing the end of its normal life as a “main sequence” star. That is, it’s about to finish burning hydrogen, which means it will soon go into the last stages of its life. But according to Jim Kaler, Regulus is also a curious case. It appears to have a very close white dwarf companion which scientists believe once was much larger and brighter than Regulus. But the gases were drawn from the white dwarf into Regulus, making Regulus both huge and bright and causing it to spin the way it does.

In total, Regulus is another example of how what looks like a common star to us, is quite fascinating when seen in the light of modern science.

Vital stats for Regulus:

• Brilliance: Magnitude 1.35, 22nd among the brightest stars in our sky; shines with the luminosity of about 150 Suns.
• Distance: 77 light years
• Spectral Type: B7V
• Position: 10h:08m:22s, +11°:58′:02

The buzz about the Beehive (M44) and Leo’s whiskers – a binocular treat!

In ancient times the constellation Leo extended much farther east and west, and M44 was considered to be its whiskers.

from “The Next Step – Finding and Viewing Messier Object” by Ken Graun

Whiskers indeed! I like that. It’s a great way to remember where to look for M44, for if you can find the Sickle – the huge head and mane of Leo – then all you have to think is “now where would his whiskers be?” Scan 2-3 binocular fields in that direction – westward – and you should soon stumble upon M44, the Beehive. Here is a chart you can use to find it. Do wait  until about two hours after sunset when it is really dark and M44 is well up in the sky.

Click image for larger view. Prepared from Starry Nights Pro screen shot.

Click here to download a black-on-white (printer-friendly) version of this chart.

M44 also is known as “the Beehive,” and Praesepe, which is Latin for manger. And if you have dark skies, away from light pollution, you will see this as a small, wispy cloud, perhaps suggestive of Leo’s whiskers. It is, in fact, a beautiful star cluster as binoculars or a small telescope will reveal. Galileo first discovered its true nature, and in this hazy patch counted more than 40 stars. You should see about that many with your binoculars. This is one of the nearest star clusters to us, and although there is still debate over its exact distance, it is around 580 light years. That compares with about 400 light years for the Pleiades. The two clusters are pretty close to the same size, but M44 is considered much older. M45 – the Pleiades – is estimated to be 78 million years old, while M44 is thought to be about 660 million years old. As star ages go, they’re both quite young. But open clusters, such as these, do not last too long – the members stars tend to get drawn off by close encounters with other stars as the whole clusters moves about our Milky Way galaxy.

The Latin name, Praesepe, is worth examining because it explains the names of two relatively bright stars which flank it – Asellus Borealis and Asellus Australis. Borealis means “northern” and Australis means “southern.” Asellus means “ass” – as in donkey – and Praesepe means “crib” or “manger.” In other words, the Beehive apparently looked to some like a pile of hay in a manger, and these two flanking stars were donkeys eating that hay, one to the north and one to the south. In binoculars the scene should look something like this.

M44 and surroundings as it would appear in binoculars with a 5-degree field of view. Click image for larger view. (Chart derived from Starry Nights software screen shot.)

Click here to download a printer-friendly version of this chart.

The two donkeys are about as bright as the stars in the handle of the Little Dipper, so under dark skies should be faintly visible to the naked eye with the northern one the dimmest. The third star, Eta Cancri, is dimmer still. Its name, however, indicates that it, the Beehive, and other stars shown here are all part of the rather obscure constellation known as Cancer, the crab.

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