SKYLIGHTS

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

Sunset

Photo of the Week.. Quiet sunset.


Astronomy news for the two weeks starting Friday, December 30, 2016.

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, now in Chinese translation.

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.


SSLive in town? Read FIRST MAGNITUDE: A Book of the Bright Sky, World Scientific, 2013. See the interview with Jim Kaler.


NEW! Read Dust to Dust in Stellar Stories.

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


IT'S HERE!, From the Sun to the Stars by Jim Kaler, World Scientific, 2016, a new book based on From the Sun to the Stars: the OLLI Lectures, which provides a linked, illustrated introduction to astronomy.



Please Note

Skylights has been produced in various forms for 31 years, since 1985, and even before that as an annual bulletin. However, all the information has become easily available elsewhere via various devices and apps, and it's time to simplify and bring part of Skylights to a close. We will continue to list lunar phases, planetary passages, and other significant events for the coming two weeks on the website, but by bullet only. Because there will no longer be any script, the telephone and emailing services will be dropped. The Star of the Week will continue as before, as will the Photo of the Week. Thanks all for your support.
Jim Kaler


The next Skylights will appear Friday, January 13. Happy New Year to all.
Look for Orion on the meridian in the late evening, with pentagon-shaped Auriga above it. Faint box-like Lepus is below him, with brilliant Sirius of Canis Major down and to the right. Leo rises a couple hours past midnight, while Pegasus gallops to the west.

Primary source: The Astronomical Almanac; numerous secondary sources.


STAR OF THE WEEK

56 PEG (56 Pegasi)

Just barely fifth magnitude (4.74, almost fourth), 56 Peg (commonly designated by its Flamsteed number), lies practically on the outline of the Great Square of Pegasus about 2.5 degrees due south of Beta Peg (Scheat). At first it looks like just another class G or K helium-fusing giant that so abound (and make much of our constellations), though one a bit brighter than most. Originally classed as G8 lesser supergiant, it's also been called a K1 subgiant. We'll go here with the last one, though it is of little consequence. Common as it appears, the star harbors a secret, though one not all that rare. At a healthy distance of 592 light years (give or take 25), assuming there is no interstellar dimming (of which there is some evidence), and adopting a temperature of 4509 Kelvin (the average of several measures) from which we can assess the amount of infrared radiation), we come up with a luminosity of 570 times that of the Sun (less than we'd expect for a supergiant), a radius of 39 times solar, and a mass of 4 Suns, putting it smack into the so-called "clump" of helium-fusing giants with similar properties though of differing masses. A maximum interstellar dimming of 1.25 magnitudes raises the luminosity to 1800 Suns, the radius to 70 times solar, and the mass to 6 Suns. It's really just a good old K1 or so giant with a rotational period of a year of less. An interferometric measure of angular diameter gives 46 solar radii, not that far from the mean of the dimmed-undimmed values and about half the size of Mercury's orbit. At least we are more or less on the right track. 56 Peg is special because it's a "barium star" with an elevated abundance of barium as well high levels of other elements produced by the slow capture of neutrons. Such abundances cannot be innate to a simple giant, so it must have been contaminated by enriched gas flowing to it from a companion that was once a highly advanced giant with a dead helium core that is now lost on the glare of 56. Sure enough, 56 Peg is orbited by a white dwarf with a temperature of 32,000 Kelvin that makes the star shine brilliantly in the ultraviolet where it is easily detected. Doppler shifts in the spectrum of 56 proper reveal an orbital period of 111 days, which is next-to-shortest for barium-star white dwarfs after 80-day HD 77247. To have already evolved to a white dwarf, the smaller star must once have been the more massive of the two. Not too long ago, the current giant must have been surrounded by a planetary nebula, the older star's ejecta illuminated by what is now the white dwarf. The lost mass, rich in new chemical elements will eventually find its way into another generation of stars. (Thanks to R. F. Griffin in "The Observatory," February 2006.)


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