SKYLIGHTS

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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. Sunrise.

Astronomy news for the week starting Friday, October 30, 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.	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.

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.

The week begins with our viewing the Moon rather late in its waxing gibbous phase as it heads toward full during mid-daylight on Monday, November 2. The Moon will then be just shy of full the evening of Sunday the 1st (rising just before sunset), and just past the phase the following night (rising just after sunset). It then wanes in the gibbous over the remainder of the week.

As the Moon makes its rounds it also glides through some nice passages. Though its brightness will hamper the event, on the night of Tuesday the 3rd, just after full phase, the Moon will pass through the Pleiades of Taurus, while by the following night it will have moved into central Taurus to the northeast of the Hyades cluster. Then the night of Thursday the 5th, look for it between Taurus and classical Gemini.

With Daylight Savings Time ending on Sunday, November 1, all times below are Standard. During the early evening hours you can admire bright Jupiter, which now transits the meridian to the south right at the end of twilight, around 6:30 PM. Now setting just before midnight, the giant planet has become fully an evening object as it makes its way to the east against the stars of northeastern Capricornus. Then around 10:30 PM, up comes Mars. In a fine setting in Cancer, the red planet (2 magnitudes fainter than Jupiter, a factor of 6 in brightness) crashes through (really, against) the Beehive cluster around Sunday the 1st, the sight quite lovely in binoculars or a small telescope.

In the morning sky, we are slowly losing Venus, which rises at 5 AM, just as formal twilight begins to light the sky. Look for it to the southwest in dawn's brightening light. On Sunday the 1st, with Mars visiting the Beehive, Venus passes 4 degrees north of Virgo's Spica. The dark morning hours thus belong to Saturn. Rising to the east at 3 AM, the ringed planet is now in Virgo just a couple degrees north of the Autumnal Equinox, between Spica and Leo's luminary, Regulus. In invisible news, Neptune ends retrograde motion (westerly against the stars) on Wednesday the 4th, and Mercury passes superior conjunction with the Sun (on the other side of it) the following day.

The Zodiac, through which all the planets move (only Pluto, if you wish still to call it a planet, significantly deviating), is quite a mix of figures, some bright and beautiful, others dim and hard to see. Cancer, noted above and flagged by Mars, is one of the latter. So are the three constellations of the "wet quarter" now visible, Capricornus (the Water Goat), Aquarius (the Water Bearer), and Pisces (the Fishes), although in a dark sky they will still stand out for you.

STAR OF THE WEEK: SKAT (Delta Aquarii). Some stars are just not what they at first appear to be, and are a bit of a surprise when you dig into them. Rather well to the south (15 degrees or so) of Aquarius's Water Jar, the proper name "Skat" comes to us from an Arabic word that means "The Shin," a clear reference to the star's position within its constellation. Third brightest in this relatively dim figure (following third magnitude Sadalmelik and Sadalsuud, the Alpha and Beta stars), Skat (better known by its Greek letter name of Delta Aquarii), shines from a distance of 161 light years still at third magnitude, though at 3.27 just a bit fainter than those two. It's usually called a class A (A3) dwarf, though an alternative is an A2-4 giant. As we will see below, both seem to be wrong, though an average of sorts may be right on the mark. Other than that, and its relative brightness and prominence in its constellation, it has, as they say, few distinguishing characteristics. There seem to be no companions. The data from Hipparcos (the parallax satellite) suggest a binary, but the orbit makes no physical sense. Nor does sophisticated interferometry reveal any gravitional neighbors. There is also no evidence of any surrounding disk as there are for so many class A stars (for example Vega and Fomalhaut), which suggests that there is no planetary system either. That lack may go along with a modestly low heavy element content (70 percent solar iron, 40 percent solar oxygen), as stars with planets tend to have more heavy stuff relative to that found in the Sun. What we do have is a star on the verge of seriously aging. A distance and a temperature of 8525 Kelvin lead to a luminosity of 95 solar and a radius 4.5 times that of the Sun. A fairly fast projected equatorial spin speed of 76 kilometers per second puts the rotation period at under 3.0 days. Theory then shows the star to be right on the verge of shutting down its core hydrogen fusion, if it has not done so already, the mass falling between 2.5 and 2.7 Suns, depending on the exact state, the age between 500 and 600 million years. From theory, Delta Aqr is quite clearly physically a "subgiant," a star just starting on its trek to becoming a true giant. Too bad we can't actually watch it happen. By the time the star's collapsing core hits the temperature at which it begins to fuse core helium into carbon and oxygen, it will have tripled its total luminosity (most of which will be in the infrared).

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.