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. The blue sky, mirrored in deep pool.

Astronomy news for the week starting Friday, November 6, 2009.

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 Hot Crab Sandwich in Stellar Stories.

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

Having passed full, the Moon spends the earliest part of the week waning through the gibbous phase. It then crosses third quarter on Monday, November 9, about the time of Moonset in North America. The remainder of the week then sees our companion waning through the crescent as it heads toward new early next week. The night of Friday the 6th, it passes perigee , where it is closest to the Earth.

As it rounds the Earth, the Moon finds itself in some lovely settings. The night of Friday the 6th, the waning gibbous will fall smack in the center of Gemini to the southwest of Castor and Pollux, while the following night the two stars will point southeasterly toward it. Then the night of Sunday the 8th, the Moon will rise just three degrees to the south of reddish Mars. Saturn gets into the act as well, as on the morning of Thursday the 12th, the crescent will be seen several degrees to the right of it.

Though Mars encroaches on it by rising now at 10:30 PM, the evening still belongs the king of the planetary system (with three times the mass of all the other planets rolled together), Jupiter. Look for it to the south as twilight draws to a close around 6:30 PM. Slowly drifting to the east against the stars, Jupiter still holds court in northeastern Capricornus near the Aquarius border. Then its back to Mars, the red planet now appearing just a bit to the east of the Beehive cluster, which it crossed in front of last week.

An hour after Mars rises, Jupiter sets, and we are into the morning hours to wait for Saturn's 3 AM (or so) arrival, the ringed planet creeping east in Virgo just to the northeast of the autumnal equinox. Finally, Venus enters the scene. Now rising around 5:30 AM, just after the beginning of morning twilight, the planet is becoming more elusive in a brightening sky in spite of its great brilliance.

Though the autumn constellations are upon us, the stars of summer linger on, perhaps making us feel a bit warmer. Indeed, Cygnus the Swan, with first magnitude Deneb (the faintest star of the Summer Triangle), is so far north it will be with us until winter and the end of the year. But then it's back to autumn, told to us by lonely but bright Fomalhaut, visible low in the south down and to the left of Jupiter. Then the chill of winter is in the air, as by late evening not only is Orion up but so is Sirius of Canis Major, the sky's brightest star.

STAR OF THE WEEK: 29 CYG (29 Cygni). Good things in small packages have nothing on interesting things in faint stars seemingly lost in the Milky Way. In this case it is near- dead-on fifth magnitude (4.97) 29 Cygni, which lies in an especially rich portion of Cygnus's Milky Way not quite four degrees southwest of Sadr (Gamma Cyg) and just over a degree south of the luminous blue variable P Cygni.

This wonderfully-rich segment of the Milky Way in Cygnus (roughly 3.5 degrees wide) holds a number of treasures that start with Sadr (Gamma Cygni), then down and to the left the luminous blue variable P Cygni, and at bottom center, the Lambda Bootis/Delta Scuti star 29 Cygni. Reddish interstellar clouds flood the image. The compact open cluster Messier 29 lies near the left edge.

Though seemingly an ordinary class A2 dwarf, Flamsteed's 29 Cyg has a pair of features to offer, a weird chemical composition and subtle variability. Odd chemistry can make for mis-classification. The temperature of the star, 7920 Kelvin, is way too low for its purported class, and is more appropriate to A7 (A2 more like 9200 Kelvin). At a distance of 139 light years, the star radiates at a rate only 14.5 times that of the Sun, analysis of subtle jigglings in the brightness (through the science of "asteroseismology") suggesting a very satisfying 13.2 solar. Luminosity and temperature then combine to give a radius of almost exactly double that of the Sun. The measures of rotation velocity are in rough shape, values given ranging from 37 kilometers per second to over 150. The best estimate is probably 65 km/s, which gives a rotation period under 1.5 days. Theory then tells of a mass of 1.8 times that of the Sun and that 29 Cyg is about a third to a half way through its 1.5 billion year dwarf (hydrogen-fusing) lifetime. Now to the heart of it: 29 Cygni is a rare "Lambda Bootis" star, one that has very low metals (an iron content just 6 percent solar, magnesium down to four percent) but with more normal carbon and oxygen. There is no firm theory for such stars. The usually accepted concept is that their surfaces have been affected and contaminated by accretion of gas from metal-poor surrounding interstellar clouds. These metals had previously been absorbed into the clouds' dust grains, but the dust could not fall onto the star compliments of its outgoing radiation, just the metal-depleted gas. Or not. Nobody really knows. Making 29 Cyg even rarer, it's a "Delta Scuti" star. Such stars fall in an unstable temperature region in which they subtly but rapidly vary with multiple periods (the region among dwarfs analogous to that which produces the supergiant Cepheid variables). Our star here has a major period in which it varies by 0.016 magnitudes (about 1.6 percent) over a 38.5 minute period. At least a dozen other periods are known. Off in the distance lie three so-called companions, which are probably just in the line of sight. The major one, seventh magnitude 29 Cyg B over three minutes of arc away, would have to be a mid-class F star, and if really part of a double star would be at least 9000 Astronomical Units away and orbit with a period of at least half a million years, making it a "fragile binary" indeed.

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.