SKYLIGHTS

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

Photo of the Week. Evening clouds and shadows.

Astronomy news for the two-week period starting Friday, November 21, 2008.

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.

NEW! Heavens Above: Stars, Constellations, and the Sky from Recorded Books.

View Jim Kaler's "From Pluto to Planets: What Other Stars are Telling us" at the World AstroCast 2008 archive, brought to you by the Astronomy Section of the Northampton Natural History Society, England.

NEW! Read Tea With the Scorpion in Stellar Stories.

Skylights was featured on the Earth Science Picture of the Day for October 2, 2008.

The Constellations celebrates its millionth visitor.

Skylights is presented early. Last week's is still available. The next Skylights will appear December 5, 2008.

To all those in the US, and for those abroad, a Happy Thanksgiving.

The Moon slowly disappears during most of the first week of our fortnight within its waning crescent phase, as it heads toward new Moon on Thanksgiving, Thursday, November 27th. The remainder of our period finds it as a waxing crescent, which ends with the first quarter on Friday, December 5. Your last view of the waning crescent will be in dawn's light on the morning of Wednesday the 26th; then look for the first glimpse of the waxing version in bright twilight the evening of Friday the 28th. The Moon passes apogee, where it is farthest from the Earth, on Saturday the 29th.

The middle of our two-week interval will witness a superb gathering of Venus, Jupiter, and the Moon. The two planets have been approaching each other since Venus first became visible in evening's dusk, with Jupiter moving only slowly to the east in northeastern Sagittarius, Venus rapidly gaining on it. Watch as they converge on each other, and then pass conjunction on Sunday, November 30, when they are but two degrees apart, brighter Venus to the south of the giant planet within a beautiful setting to the northeast of the Little Milk Dipper. Venus will then rapidly whip to the east of Jupiter, the two providing a wonderful example of planetary motion. The conjunction of course is just along the line of sight, as Jupiter will be nearly 6 times farther away!

Then the Moon gets into the act by passing the two, unfortunately during the day in North America. (The crescent actually occults Venus as seen from Europe.) The evening of Sunday the 30th thus finds the Moon down and to the right of the pair, while the following evening, that of Monday, December 1, will provide us with a beautiful triangle, the growing crescent up and to the left of the planetary duo. You won't see another display like this one for some time. After all this activity, you can relax until you see Saturn rising in southern Leo to the east of Regulus within about an hour after midnight.

As an anticlimax, the Moon then goes north of Neptune on Wednesday, the 3rd. In the rest of the invisible- event category, Uranus also celebrates Thanksgiving by ceasing retrograde motion on Thursday the 27th, while Mercury passes superior conjunction with the Sun (far on the other side of the Sun) on Tuesday the 25th.

As one great celestial hero, Hercules, descends into northwestern twilight, another, great Orion (the Hunter), makes himself prominently visible by rising shortly after the end of evening twilight. Climbing ever higher as the evening progresses, he crosses the meridian to the south about 1 AM with Taurus up and to the right, brilliant Sirius in Canis Major down and to the left, Gemini and Auriga over his head, all announcing the closeness of winter.

STAR OF THE WEEK: MASYM (Lambda Herculis). Rather oddly, few of the brighter stars of Hercules carry classical proper names. After the luminary, third magnitude Kornephoros (Beta Herculis) and Rasalgethi (Alpha Her), we must drop to fifth magnitude Marsic (Kappa) and then just along the Greek letter progression to somewhat brighter fourth magnitude (4.41) Masym (Lambda), a name (from Allen) saddled with six different spellings (Maasym, Maasim, etc.) And even that assignment is a mistake. Out of Arabic meaning "the wrist," the name was originally applied to Omicron Herculis, but later given by Bayer in error to his Lambda star. As seen below, it's an ironic "twist of the wrist." But first, this class K (K5) giant star is in an interesting part of its evolution, though we are not sure just which interesting part it is. With a temperature of 4215 Kelvin, it shines from a distance of 367 light years with the power (including infrared radiation) of 345 Suns, from which we calculate a radius of 35 times solar. A projected equatorial rotation speed of 6.2 kilometers per second then gives a rotation period less than 281 days. The numbers make us uneasy, however, since direct measure of angular diameter yields a much larger radius of 56 times that of the Sun, sixty percent larger. Something is either radically wrong or the star just looks bigger in the far red part of the spectrum where the measure was made (which seems unlikely). Leaving the problem aside (no choice), Masym's mass comes in at about three times that of the Sun. Theory shows it brightening as a giant, either with a dead helium core (350 or so million years old, prior to helium ignition into carbon and oxygen), or with a post-helium-fusion dead carbon and oxygen core 430 million years old, in which case it is soon going to get a LOT brighter, reaching more than 3000 thousand times as luminous as the Sun, over a dozen times its current luminosity, before it begins to pulse as a Mira-type variable prior to losing its outer envelope. Starting life as a rather ordinary class B8 dwarf, the star has a chemical composition quite similar to that of the Sun. All stars orbit the center of the Galaxy, though on slightly different paths, which causes them to move through the local Galaxy relative to the Sun. We see them moving both along and across the line of sight, motions that over the very long term -- millions of years -- will ultimately destroy the constellation patterns (new ones of course taking their place). Our own Sun must have its own motion among the stars of the local swarm. The first to calculate the "solar motion" was William Herschel, the discoverer of Uranus, who measured the direction toward none other than our Masym, Lambda Herculis. Much more modern calculations, however, have it moving at about 20 kilometers per second not toward Lambda, but more to the southeast toward, you guessed it, Omicron Her, from which Lambda stole the proper name, perhaps something of a fair trade. (Thanks to Joseph Jarrell, who recommended this star.)

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.