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


Photo of the Week.. Soaring in fresh air.

Astronomy news for the two weeks starting Friday, April 7, 2017.

Prepared by Jim Kaler.

Clear skies and thanks to Skylights' blogger visitor reader.

Last week's Skylights is still available. 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.


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. It's now time to simplify Skylights and bring parts of it to a close. We will continue to list lunar phases, planetary passages, and other significant events for the current fortnight on this website, but by bullet, not by prose text. Because there will no longer be any script, the telephone and emailing services have been 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, April 21.
Primary source: The Astronomical Almanac.


Zeta CMI (Zeta Canis Minoris)

Even small constellations hold their charm, curiosities, and treasures. Canis Minor, Orion's smaller Hunting Dog) glows with zeroth magnitude (0.34) Procyon, the eighth brightest star of the sky, taking its place at the northeastern apex of the Winter Triangle (completed by Sirius at the southern apex, and Betelgeuse to the west). Here we find an odd and instructive coincidence. Third magnitude (2.90) Gomeisa (Beta CMi) is a class B8 dwarf that lies some 4.5 degrees to the northwest of Beta. Directly opposite Procyon, 4.5 degrees to the southeast of the bright star, we find much fainter Zeta CMi (mag 5.14), an almost identical class B8 "bright giant" (but see below). The difference in apparent brightess is almost all due to difference in distance, Zeta CMi falling 624 (give or take 43) light years away, with Gomeisa at just 162 light years (plus or minus 2) in the second Hipparcos reduction), almost four times as far. The thin dust in the Milky Way toward the Anticenter of the Galaxy dims Zeta by a mere 0.06 of a magnitude. A temperature of 11,680 Kelvin gives us the amount of ultraviolet light to add to the visual, which results in a total luminosity of 478 Suns and thus a radius 5.4 solar radii. There seems to be no excess infrared radiation, nor are there companions to be seen. The application of theory gives a mass of 4.0 times that of the Sun and shows the star to be at or near the end of its hydrogen fusing lifetime. Not a giant at all, Zeta CMi is barely a subgiant (such classification anomalies quite common among the B stars). What makes the two so interesting is not their coincidental classification and placement relative to Procyon, but their differences, seemingly produced mostly by rotation. Zeta has a projected equatorial rotation speed of just 35 kilometers per second, giving it a rotation period of under 7.7 days. Gomeisa on the other hand is really whirling around with a projected velocity of 250 km/s that is much more appropriate to the class. Probably as a result of its great rotation speed, Gomeisa has produced a surrounding, radiating disk that turns it into a "B-emission") ("Be") star similar to Zeta Tauri or Gamma Cas. Zeta, however, spins too slowly to have created one. On the other hand Zeta CMi's slow rotation produces a quiet atmosphere that allows gravitational settling of some chemical elements and the lofting of others, making it into a "mercury-manganese star" with huge surface overabundances of these and other elements such as europium and strontium and underabundances of others such as calcium. Gomeisa's faster spin keeps the outer atmosphere stirred up, which helps the star maintain more or less normal chemical abundances. We still do not know the exact mechanism for producing the "Be" disk. Magnetic fields might be involved. Consistently, Zeta CMi seems to have none of significance. If nothing else, the two seem to provide clues to the astrophysical phenomena involved. Not massive enough to blow up as a supernova, Zeta CMi should slough its outer layers to produce a white dwarf with about 78 percent the mass of the Sun.

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