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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 2010 roars in like a Lion – with Saturn tagging behind!

March roars into our eastern night sky like a lion – Leo, the Lion that is, led by the Little King “Regulus” and in 2010 brings Saturn with it. Just ahead of it is a special binocular treat, M44, a veritable beehive of stars barely visible to the unaided eye. Think of it as the lion’s whiskers. And don’t forget to look for the zodiacal light!

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.)


I don’t usually put an emphasis on constellations, but in March it is fitting, for it makes it easy to remember what it is you see in the East just after sunset and besides, this is one of those constellations where when you connect the dots it looks something like it is supposed to look.

In fact, in my mind’s eye I can see the classic lion of the old Bayer star charts, but I more often see two very easy to remember asterisms – the Sickle that forms Leo’s head and mane, and the Triangle that forms Leo’s rump. And 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! Here’s our eastern sky chart. (As usual, click the image for a larger version, or download a printable version.)

Click image for larger view. Use link below to download a printer-friendly version. (Chart developed from Starry Nights screen shot.)

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

If you look in the same spot an hour or so later – or wait until mid-month, you will get the special treat of seeing Saturn, a favorite target for small telescopes, though this month it will be a tad disappointing to telescope users. Right now Saturn’s rings appear tilted as seen from Earth so that they make a thin line extending out from either side of the planet. In most years, they are at such an angle that they make a much better display. But Saturn is a special feature for this year, 2010. It won’t be back with the stars of Leo for another decade. So lets get on to the prime star in the east that’s there every year at this time, Regulus.

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 they don’t seem like a pair at all. Both the primary and secondary 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 it 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), Mars, and Leo’s whiskers

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 main 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. In 2010 this is especially easy. Start at Regulus and scan towards Mars, one of the brightest objects in the sky. M44 will be along this path, much nearer to Mars than to Regulus. Here is a chart you can use to find it – and to map the changing position of Mars, which will be especially interesting in March.

Following Mars and finding M44, the Beehive - or if you like, Leo's whiskers! Click chart to see larger image. (Chart developed from Starry Nights screen shot.)

Click here to download a black-on-white (printer-friendly) version of this chart that you can also use to chart the movements of Mars.

Over the next couple of months Mars will serve as a bright beacon making it easier to locate M44 whose other names are “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 discovered 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.

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 screen shot from Starry Nights software to which I’ve added labels.

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.

There’s a revealing naked eye exercise buried here as well. This is a good month to chart the course of Mars across the background of stars. Mars starts out the month appearing to run away from the Beehive – that is, it’s moving westward against the background of stars. Then, just before mid-month it appears to stand still for a couple of days as it reverses direction and starts to come back towards the Beehive (eastward) as if tugged by an invisible cord. In April it will skip right by, missing the Beehive by less than a degree and passing between the Northern Ass and the Southern Ass.

Keep in mind that all this happens over a period of days and weeks, and to see it you need to carefully chart the position of Mars against the background of stars on several nights. This sort of exercise helps you appreciate great observers who charted the heavens before the invention of the telescope. It also helps you understand how puzzled early observers were by the apparent behavior of Mars and why this had them scratching their heads for centuries trying to make sense of these movements in a universe where Earth was at the center of everything. During any given night, of course, everything appears to move westward because of the rotation of the Earth. The movement we’re interested in here is the revolution of Earth and Mars around the Sun.

It’s much easier today – with a sun-centered solar system – to understand why Mars first appears to move in one direction, then the other. This is caused simply by Earth overtaking Mars as the two planets orbit the Sun at different distances and speeds. Here’s where the planets are in mid-March, courtesy of John Walker’s “Solar System Live” online orrery.

Click image for larger view.

See the Zodiacal Light

Finally, don’t forget to look for the zodiacal light this month – especially if you missed it last month.

You don’t need a totally clear horizon to see the zodiacal light, or binoculars, but you do need total darkness and that means little-to-no light pollution. I feel I have a good shot at it from my favorite ocean-front observing point where I have a clear horizon to the west with no cities to create light domes there. Moonless evenings in February, March, and April – and mornings in September and October – are the best time for folks at mid-northern latitudes to look for this subtle phenomena. In March 2010 that means to look about 80 minutes after sunset on a clear night between March 1 and March 15.

For more detailed information on this, see the February posting here.

One Response

  1. […] at least two nights during this time frame and use the chart below to mark its position. (For other charts to help you locate Mars and the Beehive, see this posting. ) Click image for larger version. Prepared from Starry Nights Pro screen […]

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