I was up before dawn today hoping to find the returning comet 205P/Giacobini and a faint new supernova in the galaxy IC 1776 in Pisces. I was fortunate to see them both. But the morning held a pleasant surprise I hadn’t anticipated. Venus rose brilliantly in the east followed by the much dimmer planet Mars some 10° to its lower left. And there, not more than a couple degrees below Mars, shone Leo’s brightest star, Regulus. At first glance both appeared about equally bright, but looking closer, it was clear that Regulus, at magnitude +1.3, bested Mars by nearly half a magnitude. What was especially appealing was the color contrast between the two with Mars’ dusty, rusty surface so different from the pure white radiance of Regulus.
While star and planet are both close enough to catch the eye, they’re headed for an excellent conjunction Thursday and Friday mornings, September 24 and 25. The actual time of closest approach, when star and planet will be separated by just 0.8°, occurs around 11 p.m. CDT — before Mars rises for skywatchers in the Americas and Canada, but about perfect for European and African observers.
Just the same, everyone around the planet will see them less than a degree apart low in the eastern sky about 90 minutes to an hour before sunrise on those dates. Joining the scene will be Venus, now spectacularly bright against the deep blue, early dawn, and Jupiter, bringing up the rear further lower down in Leo’s tail.
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Regulus is a main sequence star like the Sun but hotter. It spins so fast that it’s stretched into an oblate spheroid 4.3 times the diameter of the Sun.
Regulus, Latin for “little king”, may have received that name because it’s the brightest star in the Leo the Lion, king of the beasts. The ancient Greeks knew it by the same name, Basiliscos, as did the Babylonians before them who called it Lugal (king). Regulus is the only 1st magnitude star to sit almost directly on the ecliptic, the path followed by the Moon, Sun and planets through the sky. That means it gets regular visitors. Mars this week; Venus and the crescent Moon both on October 8. Few bright stars are as welcoming of unannounced guests.
I encourage beginning and advanced astrophotographers alike to capture the Regulus-Mars conjunction using a tripod-mounted camera. Just find an attractive setting and make a series of exposures at ISO 800 with a standard 35mm lens. Click here to find out when the Sun rises, so you’ll know what time to back up from to see the event. Now that fall brings much later sunrises, it’s not so hard anymore to catch dawn sky offerings.
It’s also a delight to see the Red Planet again, which will come to a close opposition in the constellation Scorpius next May. Let the fun begin!
5 Replies to “Mars Meets the King of the Beasts”
Two quick questions from Rob to Bob:
1) Is the oblate spheroid shape of Regulus directly observed, or is it surmised from measurement of its rotational period?
2) Do we know that it has ‘sunspots’, as shown in the animation?
Rob Stuart, Utrecht, NL.
Great question. Rotation speed is measured using spectroscopy. From that we can model shape, but in the case of Regulus, we’ve done better, using the CHARA array to actually measure its shape. (See http://www.astronomynow.com/news/050121_regulus.shtml). As for the starspots, they’re more likely theoretical – fast rotation speeds can produce sizable starspots.
When you gaze at Regulus in the Heavens it is an almost white colour because of its high temperature but who would have imagined that its equatorial spin was at a massive speed of 700,000 mph compared to our own Sun at 4,500 mph, If the spin of Regulus was just 12% faster it would fly apart and because Regulus is 3.5 x the mass of our Sun the break up of Regulus could have made a few more Earth size Suns to gaze at in the night sky.. thanks Bob for yet another great topic.
Hey, thanks! And thanks for the particulars on Regulus. I love naked eye stuff.
Mars, Jupiter and Venus will continue to dance together in the eastern sky throughout October, Regulus will stay in touch for the first week or two.
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