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.. It's Spring!

Astronomy news for the two weeks starting Friday, April 21, 2017.

Prepared by Jim Kaler.

Clear skies and thanks to Skylights' blogger visitor reader.

Go to STARS for previous stars of the week. 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, May 5.
Primary source: The Astronomical Almanac.


BC CMI (BC Canis Minoris)

At the tail end of fifth magnitude (averaging about 6.31), BC CMi, in Canis Minor (Orion's lesser hunting dog), caries neither Greek Letter name nor Flamsteed number, and is best known by its variable-star name. A red class M (M4, though it's been listed as cool as M5-M6) giant, it's also a little different from most that we encounter. BC CMi is listed as an "SRb", or "semi-regular type b" variable star. The SRb's don't vary by all that much and such stars might switch from regular pulsation to irregular. They seem to be at the beginning of the process that will make them true Mira (long-period variables that are in the process of ejecting their outer layers eventually to expose their inner now-dead nuclear-burning cores made of carbon and oxygen. BC, which varies roughly between magnitudes 6.14 and 6.42, is faint largely because of its considerable distance of 506 light years from us (give or take 37). Dimming by interstellar dust seems to be of little consequence. Combined with a temperature estimate of 3817 Kelvin, which is needed to assess the amount of infrared radiation, the star radiates with a luminosity of 457 Suns, which leads to a radius of 58 times that of our Sun, or 0.27 Astronomical Units, about 70 percent the size of Mercury's orbit, not all that much for a giant star. Most interesting, BC CMi seems to be multi-periodic. With a variation period originally given as 35 days, one study suggests 123, 143, and 208 days all going on at the same time. The star does not quite belong here, but is more a member of the ancient inner halo of the Galaxy, as shown by its high velocity of 96 kilometers per second relative to the Sun, the motion dominantly toward us. And ancient the star may be, as its mass seems to be only 80 percent of so that of the Sun, which is near the lower limit required to maintain full nuclear fusion in its core. Since stellar aging goes inversely as the mass, the star might have been around for a long time as well. BC CMi radiates a bit of excess infrared light, suggesting a shell or ring of dusty gas that is being ejected as the star evolves. The star is not far enough along its evolutionary path to dredge up freshly-made elements, as the search for unstable technetium, which is the marker of such a phenomenn, must all be made in stars.

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