SKYLIGHTS

PLEASE NOTE: SKYLIGHTS has moved to http://stars.astro.illinois.edu/skylights.html.

Skylights featured on Astronomy Picture of the Day

Skylights featured nine times on Earth Science Picture of the Day: 1 2 3 4 5 6 7 8 9 -- Full List Restored!

Photo of the Week. Sunray spectacular, cloud shadows thrown across the sky.

Astronomy news for the week starting Friday, February 5, 2010.

Phone: (217) 333-8789
Prepared by Jim Kaler.

Clear skies and thanks to Skylights'

reader.

Go to STARS for previous stars of the week.	Last week's Skylights is still available.	Access Skylights' Archive and photo gallery.	Find out what happened in astronomy at Astronomy Updates.
The Constellations has a linked list with locations and brightest stars.	Constellation Maps show the locations of the constellations.	The 151 Brightest Stars lists through magnitude 2.90.	For more on stars and constellations, visit Stellar Stories.
Tour the Milky Way as seen from the northern hemisphere.	Watch a total eclipse of the Moon and an annular eclipse of the Sun.	Moon Light presents photos of the Moon.	See the Moon move and pass just below Nu Virginis.
Watch planets move against the background stars.	See a classic proof of the curvature of the Earth with a "hull down" series.	Visit Measuring the Sky to learn about the celestial sphere.	Admire sunsets, rainbows, and other sky phenomena in Sunlight.
Go from Day Into Night, with 83 linked illustrations.	See the The Aurora and the Midnight Sun.	Take a ride aboard Asteroid 17851 Kaler (1998 JK).	Look for Books about the sky and stars.

Support science literacy by joining the Astronomical Society of the Pacific, an international organization that is among the world's premier providers of astro education. Get Mercury and a variety of other benefits.

Presenting three audio courses with 70 to 100-page study guides, narrated and written by Jim Kaler.
Heavens Above: Stars, Constellations, and the Sky from Recorded Books.	Astronomy: Earth, Sky, and Planets, is available from Recorded Books.	Astronomy: Stars, Galaxies, and the Universe, is also now available from Recorded Books.
Astronomy: Earth, Sky, and Planets is published as Vault of the Heavens: Exploring the Solar System's Place in the Universe by Barnes and Noble.

The Earth Science Pictures of the Day (see above) have been restored.

Read Riding the Chariot in Stellar Stories.

NEW. "Heaven's Touch: From Killer Stars to Seeds of Life, How We Are Connected to the Universe," Princeton University Press.

Skylights now resumes its normal weekly schedule. Thanks for your patience.

Happy Birthday! The Star of the Week, born January 30, 1998 (with Aldebaran as the first star), is twelve years old. The archive has grown as of this writing to 635 stars. With one more (below) to add and many more to follow.

We begin our more normal single week with the last (third) quarter Moon, which takes place the night of Friday, February 5, 2010, well before Moonrise in North America. Seems odd to write "2010," almost futuristic. The Moon then wanes in the crescent phase toward new, that phase not taking place until Saturday the 13th. Your last view of the slim crescent may be had in twilight the morning of Friday the 12th. Mercury, slipping away, will be to the southwest of the Moon at that time, but will be a tough find. The night of Saturday the 6th (rather the morning of Sunday the 7th, as we must wait 'till after Moonrise) finds the Moon to the west of Antares of Scorpius, while the following morning we will see the Moon flipped to the other side of the star.

In the evening, Jupiter is a more than a tough find, as it now sets in mid-twilight, and after and nice long run is effectively gone except to the truly dedicated. But not so Mars and Saturn. While they are about all we have left in the planetary sky, their prominence more than makes up for the general lack. Already up in the east at sunset, but still close to opposition to the Sun, Mars crosses the meridian to the south around 11:30 PM as it dominates the faint stars of Cancer (the celestial Crab) to the north of the charming Beehive star cluster, providing a fine chance to find and look at the thing, the cluster a lovely sight in binoculars. Well before Mars transits, Saturn rises in Virgo, still to the east of the Autumnal Equinox between Regulus (in Leo) and Spica. Locating all four -- Mars, Regulus, Saturn, Spica -- gives a sort of natural dotted line that traces out the ecliptic, the apparent path of the Sun, near which the planets roam.

Two scary figures hold their heads above the celestial equator, the pair neatly split by the head and shoulders of Orion (who, apparently not aware of them, does not hunt them in any known mythology). To the west is the roundish head of Cetus, the Whale or Sea Monster, while to the east, below Cancer (and now Mars), is the more distorted oval that makes the head of Hydra, the Water Serpent. To the west of Cetus, find Aquarius's Y-shaped Water Jar, while to the east of Hydra's head the modern figure of Sextans, the Sextant, water of prime importance to both ancient and modern makers of the constellations.

STAR OF THE WEEK: LAMBDA CET (Lambda Ceti, the former "Menkar"). Except for those that belong to the brighter or otherwise prominent stars, proper names, while charming, can be problematic if not downright confusing. Many are the duplications. Think first of Deneb, Deneb Algedi, Denebola, Deneb Kaitos, and the multitudinous rest of them. Then there are the real duplications. There is a Gienah in Corvus, another in Cygnus. At least they are in different constellations. Worse are the numerous stars WITHIN a constellation that share a name. Zeta and Epsilon Aquilae are both "Deneb al Okab," a situation moderated by respectively calling them "Australis" and "Borealis." Then there are Lambda and Alpha Ceti, both within the head of Cetus, the Whale or Sea Monster. Rather faint fifth magnitude (4.70) Lambda was the original "Menkar," which from Arabic refers to the Beast's nostrils. Someone in medieval times, however, took it upon himself to transfer the name to brighter, nearly-second-magnitude Alpha, which is in Cetus's jaw. The wrongful title stuck, and Lambda lost out. Alpha, whether properly of not, is "Menkar." The long story rather makes up for the relative lack of knowledge about the star itself, which falls in league in the neglected category with Beta Equulei and Beta Piscis Austrini. And rather too bad. As a relatively hot (13,400 Kelvin) class B (B6) giant (but see below) 576 light years away (give or take 18), it's rather out of place, as it is well off the path of the Milky Way, the natural home of youthful class B stars. And it's really quite an impressive star (surely deserving of keeping its more ancient mythological title) with a total luminosity (including a lot of ultraviolet radiation and a small ten-percent correction for interstellar dust) 920 times that of the Sun. From temperature and brightness, we find a radius of just 5.4 solar, not much for a "giant,' an ill- determined projected rotation speed of 128 kilometers per second (appropriate for the class) yielding a rotation period of under two days. Theory gives an impressive mass between 4.5 and 4.8 Suns (depending on exact details of internal structure) and shows the star to be more a subgiant (one that has given up, or soon will give up, core hydrogen fusion). Youthful indeed, the star is only 100 to 125 million years old. Its fate is to become a fairly white dwarf of about 0.85 solar masses (white dwarfs the cores of the once far more massive stars), massive for such a leftover remnant, but not quite up to the classic example, Sirius B.

For more on the sky, visit the Earth and Sky Skywatching and General Science pages.

Copyright © James B. Kaler, all rights reserved. The written contents and (unless otherwise specified) the photograph are the property of the author and may not be reproduced in whole or in part without the author's consent except in fair use for educational purposes.