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. Glory at sunset.

Astronomy news for the two-week period starting Friday, November 20, 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.

Skylights, presented a day early, will resume its normal weekly schedule on Friday, December 4. Best wishes for a fine US Thanksgiving.

We begin with the Moon in its waxing crescent phase as it closes in on first quarter on Tuesday, November 24. Continuing to wax in the gibbous phase, the Moon then hits full a week later, around or just after midnight the night of Tuesday, December 1. The remainder of the week then sees it gibbously wane. The Moon passes apogee, where it is farthest from Earth, on Sunday the 22nd of November and then makes its perigee passage the morning of Friday, December 4th.

Even given the two weeks available, there is but one obvious planetary passage. Look for the fat crescent Moon a few degrees to the north of Jupiter the evening of Monday the 23rd. Later in our period the Moon will make a nice triangular configuration with Castor and Pollux (to the southwest of the two stars) the night of Thursday, December 3. In lesser passages, the Moon zips north of Neptune the night of Monday the 23rd, then north of Uranus on Thursday the 26th. Speaking of the seventh planet from the Sun, Uranus, just below the Circlet of Pisces, ceases retrograde motion on Tuesday the 1st as it resumes its slow easterly motion against the stars.

The early evening is still home to Jupiter. Now transiting the meridian to the south in twilight, the giant planet sets around 10 PM, but around half an hour after Mars rises, so the sky does not become completely planetless (excluding dim Uranus and Neptune). The red planet then rides the eastern sky for most of the remainder of the night, not transiting the meridian until close to 5 AM. During our period, Mars moves from eastern Cancer into Western Leo to the west-northwest of Regulus. In between, look for the rising of Saturn around 1:30 AM, the ringed planet closely holding its position just to the northeast of the Autumnal equinox in Virgo. At the end of the story is Venus, which is now slipping into invisibility as it slowly becomes lost to bright twilight.

As Cygnus (the Swan, with Deneb) and Lyra (the Harp, with Vega) move steadily, night after night, into the evening northwestern skies, Perseus (the Hero who rescued Andromeda from dim Cetus) and Auriga (the Charioteer, with bright Capella) climb oppositely into the northeastern heavens. In a ragged triangle to the south of the two snorts Taurus (the Bull, with orange Aldebaran). Toward the east find Gemini with Castor and Pollux, all of them focused on bright Orion (the Hunter, with Betelgeuse and Rigel).

STAR OF THE WEEK: 59 CYG (59 Cygni). Brightness is hardly the only criterion in making an outstanding star. Many are the others. How about complexity, a bit of mystery, high heat, and fantastic spin. You have them all in Flamsteed's 29 of Cygnus, the Swan. Shining but at fifth magnitude (4.71) amidst the stars of the Milky Way, this hot (taking an estimate of 25,500 Kelvin), blue, class B (B1, some say O9) hydrogen-fusing dwarf is relatively faint only because of its substantial distance of 1420 light years (with a 200 light-year uncertainty) and 0.7 magnitudes of dimming by interstellar dust. When we take these into account, along with a huge amount of ultraviolet light emitted as a result of the high temperature, we find a luminosity of 35,000 times that of the Sun, which leads to a radius 9.5 times solar. The very high rotation speed of around 320 kilometers per second (with a spread in measures from 260 to as high as 374) is enough to create a radiating, rotating disk around the star, making it into a "B-emission," or "Be," star (like Zeta Tauri). The disk appears to be in the line of sight, so is especially thick to us, rendering 59 Cyg a special kind called a "shell star." The average rotation speed above gives a rotation period of just 1.5 days and perhaps as short as 1.3 days (as opposed to the Sun's 25 days). Such stars behave erratically, 59 Cyg's disk more or less shutting down for a couple years in the mid-1970s. Luminosity and temperature lead to a mass of 15 times that of the Sun and an age of 9.5 million years. The core hydrogen will run out in another two million years and 59 Cygni will be on its way to becoming a red supergiant and then blowing up as a supernova.

Or not. The spectrum reveals a close-in evolved hot "subdwarf" companion with a 28-day period that might be adding to the light. Orbital analysis suggests that the stars weigh in at no more than 11 Suns and (for the subdwarf) 2.3 solar, which, however, is inconsistent with the spectral class. Given these masses, the stars are no more than a few tenths of an Astronomical Unit apart. So with conflicting evidence, we do not quite know what the star is up to.

Two more companions watch the action. At a separation of only a couple tenths of a second of arc (around 85 AU) lies a 7.6-magnitude neighbor that, from its brightness, should be a class B4 dwarf with a mass of four Suns, giving an orbital period of at least 200 years. Then in the far distance, 20 seconds of arc (at least 9000 AU) away, is a 9.4- magnitude probable A0 dwarf that takes at least 200,000 years to circuit the inner triple. (Two other so-called "companions" lie just in the line of sight.) The mystery of course relates to the purported innermost companion, which is giving us contradictory information. As usual, these hot distant stars give up their secrets only slowly. The best guess, though, seems that the star will in some not-so-distant (at least astronmically) future grace the sky with explosive brilliance.

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.