SKYLIGHTS

Skylights featured on Astronomy Picture of the Day

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

Eclipse

Photo of the Week.. The fully eclipsed Moon of October 8, 2014, sets in early morning twilight. See a somewhat later view with the Moon deeper into Earth's shadow.


Astronomy news for the week starting Friday, October 10, 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.

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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.



After full Moon and the glorious total eclipse last Wednesday morning, the Moon fades this week in its waning gibbous phase, finally passing third quarter on Wednesday, October 15, about the time of Moonset in North America. Look for it in the morning sky when it is so close to the actual quarter that you cannot tell the difference. We thereafter see a little bit of the waning crescent as our companion dives toward new Moon and a partial eclipse of the Sun late next week.

In the third century B.C., 2300 years ago, Aristarchus of Samos actually made an estimate of the ratio of the distance of the Sun to that of the Moon by observing the angle between the Moon and the Sun at the time of the quarters. If the Sun is infinitely far away, the angle should be exactly 90?. The closer the Sun, the smaller the angle. Aristarchus found an angle of 87? and announced that the Sun is 20 times farther from the Earth than is the Moon. Unfortunately, his method is impossible to apply with any accuracy because the Sun is so far away (20 times more distant than he thought), and because the true angle is so close to 90? that it cannot be discriminated from a right angle. His result was produced by simple (and understandable) observational error. Nevertheless, the idea is ingenious, and even if his measurement was wrong, his conclusion of enormous distance was correct. (From Astronomy! HarperCollins 1994, copyright J. B. Kaler)

Though Saturn is effectively gone, lost to twilight, Mars drifts along to the east against the background stars to the east of Antares between Scorpius and Sagittarius almost as far south of the celestial equator as the planet can get (nearly 25 degrees) and not setting until an hour and a half after the sky is fully dark. Then around 2 AM Daylight Time, Jupiter makes its dazzling appearance popping up above the eastern horizon, the giant planet on the border between Cancer and Leo to the west of Leo's luminary, Regulus, and very obvious as the sky lightens. On Thursday the 16th, Mercury passes inferior conjunction with the Sun, the little planet more or less between us and the Sun (though not crossing it) and quite invisible.

By mid-evening, the Summer Triangle of Deneb, Vega, and Altair (the Triangle's southern anchor) is slipping to the west of the celestial meridian, while Pegasus, with its Great Square, lies to the east of that north-south line. Not quite 30 degrees to the east of Altair, find Enif, the bright western leader of the celestial Horse. Just to the west of Enif, in a dark sky you might spot the small ragged rectangle that makes Equuleus, the "Little Horse, which frisks just to the southeast of Delphinus, the Dolphin.

STAR OF THE WEEK: KAPPA DEL (Kappa Delphini). Kappa Delphini, in Delphinus (the Dolphin), a couple degrees southwest of Epsilon (the fingertip of the hand that appears to point south), at first appears to be a bit of a mess. The Bright Star Catalogue lists Kappa Del as a fifth magnitude (5.05) star with a combined spectral class, a G5 subgiant (more recently given as G1) plus a K2 subgiant, giving us some semblance of solar types to look at. Or perhaps not. The dimmer K2 star, Kappa B, was last measured 45 seconds of arc from Kappa Del A. But it's moving so fast relative to Kappa A that it's clearly an "optical" line of sight coincidence and does not belong to Kappa A at all. Much farther (212 seconds, 3.5 minutes of arc) is ninth magnitude (8.62) Kappa Del C, which for 160 years has been keeping a fine pace with Kappa A and clearly DOES belong to it. Its spectral class, however, is not known. Given an accurate distance of Kappa A (and thus C) of 98.2 light years (the uncertainty but 0.8), it should be a K2 or so dwarf, both B and C then confusingly sharing part of a spectral class. Given a recent magnitude of 5.15 for Kappa A, respective temperatures for Kappa A and C of 5675 (measured) and 5000 (estimated) Kelvin, we get respective luminosities of 6.85 and 0.34 times that of the Sun and radii of 2.7 and 0.8 times solar. The theory of stellar structure and evolution then indeed shows Kappa A to be a subgiant 50 percent more massive than the Sun, one that after a hydrogen-fusing lifetime of 2.7 billion years is ready to brighten as a true giant, following which it will slough off its outer layers to become a white dwarf. The companion, Kappa C, comes in at 0.8 solar masses, theory showing it not to be a subgiant as is Kappa "B," but a common low mass hydrogen-fusing dwarf. If that is not enough, subtle wobbles in Kappa A's motion detected by the Hipparcos parallax satellite suggest a much closer faint companion (more than 4 magnitudes dimmer than Kappa A) at a separation of half a second of arc (corresponding to 16 AU), probably a white or red dwarf with a mass of under 0.4 Suns that takes 45 years to orbit. We thus have ourselves a triple star. Given the huge separation between A and C, at least 6400 Astronomical Units, some 200 times greater than Neptune is from the Sun, it's amazing that they have stayed together and that Kappa C has not broken loose of its gravitational bonds, leaving the inner two (if indeed there ARE two) to themselves. If left undisturbed, Kappa C would have an orbital period around Kappa A of more than 300,000 years. Such "fragile" binaries are not all that uncommon. We have a more extreme example in Proxima Centauri, the nearest star, which orbits Alpha Cen (third brightest in the sky) with a period of perhaps three-quarters of a million years. From Kappa A, Kappa C would shine a magnitude or more brighter than our Venus, while from Kappa C, Kappa A would be brighter than a quarter Moon, Kappa B entirely out of the picture as it sails away. (Thanks to Bill Hartkopf for extensive discussion of this star.)


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