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

Tropical susnset

Photo of the Week.. Tropical susnset.

Astronomy news for the two weeks starting Friday, March 24, 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, April 7.
Primary source: The Astronomical Almanac.


7 MON (7 Monocerotis)

Near the extreme southeastern corner of the modern constellation of Monoceros (the Unicorn), making a flat triangle with Gamma and Beta Mon to the north, lies fifth magnitude (5.27) 7 Monocerotis of the Flamsteed catalogue. As are so many of the faint stars seen near and east of Orion, 7 Mon is a hot, blue class B (B2.5) luminous dwarf. The star is faint partly because of its great distance of 872 light years (give or take 68), which is farther than either the other two of the little triangle. With the star not far off the Milky Way, we might expect a good deal of dimming by interstellar dust. But the line of sight is pretty clear, the star dimmed by a mere 0.16 magnitude There seems to be but one temperature measurement of 16,338 Kelvin (low for the class, which averages closer to 20,000 Kelvin). Including a rather large correction for ultraviolet radiation, 7 Mon shines with the light of 1905 Suns, which leads to a radius of 5.46 solar radii. Application of the theory of stellar structure and evolution tells of a mass 6 times that of the Sun and that the star is nearing the end of its 6.3 Megayear hydrogen-fusing main sequence dwarf lifetime, after which it will swell to become a giant star, produce a planetary nebula from the ejection of its outer layers, and die as a white dwarf of about 0.95 solar masses. It's not massive enough to blow up as a supernova. The star is listed as a candidate for Beta-Cephei-type oscillations, though none has as yet been found, nor is there any indication of infrared radiation that might imply a surrounding dusty disk. The projected equatorial rotation speed is not well known, with values ranging from 95 to 152 kilometers per second, which give respective rotation periods under 1.8 and 2.9 days. 7 Mon has a companion separated from it by about a tenth of a second of arc, which implies a minimum actual separation of 87 Astronomical Units and, given a low mass for the companion, a minimum orbital period of 100,000 or so years, but nothing whatever is known about it.

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