SKYLIGHTS

Skylights featured on Astronomy Picture of the Day

Scout Report Selection Webivore Selection SpaceCareers Selection

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

Waxing Moon

Photo of the Week.A waxing crescent Moon is surrounded by a colorful diffraction corona produced by interference among light waves as they pass through thin clouds.


Astronomy news for the two weeks starting Friday, November 7, 2014.

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

Clear skies and thanks to Skylights' blogger visitor reader.


Go to STARS for previous stars of the week. Access Skylights' Archive and photo gallery. From the Sun to the Stars: the OLLI Lectures provides a linked, illustrated introduction to astronomy.
The Constellations has a linked list with locations and brightest stars. Constellation Maps show the locations of the constellations. The 170 Brightest Stars lists them through magnitude 3.00. For more on stars and constellations, visit Stellar Stories.
Tour the Milky Way. Watch a total eclipse of the Moon and an annular eclipse of the Sun. Moon Light presents scenic photos of the Moon. Go to MoonScapes for labelled telescopic images of the Moon and other lunar information.
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. Read the illustrated Day Into Night on the phenomena of the sky See the The Aurora and the Midnight Sun. See and understand the ocean tides.
Enjoy Our Complex Universe: A Human Understanding through Art, with 12 illustrations. Advances in Astronomy, 1989-2011. Take a ride aboard Asteroid 17851 Kaler (1998 JK). Look for Books about the sky and stars.

SG
Logo

ASPSupport 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.

Enjoy Our Complex Universe:A Human Understanding through Art, with 12 illustrations.

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

SSTo learn about stellar spectra, read STARS AND THEIR SPECTRA: An Introduction to the Spectral Sequence, Second Ed., with two new chapters and 140 new illustrations, Cambridge University Press (UK or North America), 2011.


Read From the Sun to the Stars: the OLLI Lectures, which provides a linked, illustrated introduction to astronomy.

SSNEWEST! FIRST MAGNITUDE: A Book of the Bright Sky, World Scientific, 2013. Read the interview with Jim Kaler.


NEW! Read Under the Handle in Stellar Stories.



The next Skylights will appear Friday, November 21.

Having passed full the evening of Thursday, November 6 the Moon wanes through its gibbous phase during the first week of our fortnight, which ends at third quarter on Friday the 14th with the Moon descending the daytime western sky. The second week features the waning crescent, whose last view will be the morning of Thursday the 21st as slim as can be seen, new Moon passed the following morning. The morning of Friday the 14th, the near-quarter will glide under Jupiter, while the following morning it will appear beneath Regulus in Leo, the trio making a fine sight. Friday the 14th, a busy day, sees the Moon going through its apogee, where it is farthest from the Earth.

The planetary sky remains dominated by Jupiter (in Leo to the east of Regulus), which rises half an hour before midnight at the start of our term, an hour and a half before by the end of it. At the opposite ends of the nighttime sky we find Mars and Mercury. In the evening, the red planet persists in setting at 8 PM as it runs through northern Sagittarius, north of the Little Milk Dipper. At the start of our period Mercury shines in morning twilight. The little one then quickly disappears. With us during much of the year, Saturn finally goes through conjunction with the Sun on Tuesday the 18th to become a morning object, rising at the start of dawn in mid-December. In a minor note, Neptune ceases retrograde motion on Sunday the 16th.

The Taurid meteor shower, which is the debris of short-period (3.3 years) Comet Encke, is still active, to which we add the Leonids the mornings of Monday the 17th and Tuesday the 18th. While capable of huge numbers of meteors, the Leonids (from 33-year Comet Tempel-Tuttle ) are well off their peak, and will produce a mere dozen or so meteors per hour.

In the evening, the Zodiac climbs from a southwestern low in Sagittarius, which holds the Winter Solstice, to the east through Capricornus, on to Aquarius with its distinctive Y-shaped Water Jar, then to dim Pisces, which wraps itself south and east of Pegasus and contains the Vernal Equinox. To the southeast of Pisces, we find Cetus, the Sea Monster, one of the numerous constellations of the Andromeda myth. Then look up to see another, W-shaped Cassiopeia, who represents the myth's ancient Queen.

STAR OF THE WEEK: PI CAP (Pi Capricorni). Enter here with brave caution unless you like uncertainty and confusion. Fifth magnitude (5.25) Pi Capricorni, in western Capricornus (the unlikely Water Goat), a few degrees south-southeast of (and pointed to by) brighter Alpha and Beta Cap, might better be known as the "if" star, as so much has to be assumed: "if this, than that," etc. Hardly anybody has observed it, the star getting a miserable 42 citations over the past century and most of these useless. We do know at least that it's a triple star. The luminary, Pi Cap A is a blue-white class B star, the Bright Star Catalog giving it as a B8 giant or even bright giant, whereas later classification makes it to be a much hotter B4 dwarf, quite a divergence. The color favors the former. Right next to it, a tenth of a second of arc away, is an eighth magnitude (7.9) companion labelled Ab, while fainter Pi Capricorni B at magnitude 8.5 lurks farther away, currently 3.2 seconds. It's kept pretty good track with Pi A, and is almost certainly gravitationally bound to it. (Fourteenth magnitude Pi C at 38 seconds of arc distance, is speeding along far too fast, and just lies in the line of sight.) The companions could well have obscured the class of "A," making it appear too cool. Who knows? Given some uncertainty in the magnitude of Pi A, we adopt a simple 5.2. Rather amazingly, there are no temperature measures. If Pi-A is indeed a B8 giant, then its surface should radiate at a temperature of 12,000 Kelvin. From their classes (A4 and A8 dwarfs) Ab and B should be at 8500 and 7700 K. From a rather uncertain (that word again) of distance of 545 light years (give or take 53) and allowing for some ultraviolet radiation from Pi-A, the three should have luminosities of 315, 15, and 8.6 times that of the Sun, radii of 4.1, 1.8, and 1.7 solar radii, and from theory masses of 3.8, 1.9, and 1.7 Suns. At a minimum distance of 17 Astronomical Units from Pi-Aa, Pi Ab takes at least 29 years to orbit, whereas at least 535 AU away, Pi-B must take more than 4600 years to make its rounds. But then there is the matter of Pi-A. If it's a B4 dwarf, it's much hotter, 17,000 or so Kelvin. The increased ultraviolet contribution gives it a luminosity of 640 Suns, almost double that figured before. Theory in turn suggests a mass of 5.3 Suns. The increased mass shortens the minimum orbital periods of the two class A companions to 24 and 4200 years, not that much of a difference. After stellar evolution has taken its turn, and the stars slough off their outer envelopes, Pi Aa, Ab and B will turn into white dwarfs with masses of 0.8 (or if the hotter choice is made above, 0.9), 0.62, and 0.60 solar masses, providing the inner two do not interact during their giant stages.


Valid HTML 4.0! 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.