Skylights featured on Astronomy Picture of the Day

Scout Report Selection Webivore Selection SpaceCareers Selection

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


Photo of the Week.. Autumn's coming.

Astronomy news for the two weeks starting Friday, August 25, 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 172 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.

The next Skylights will be presented Friday, September 8, 2017.

The Great American Eclipse was a spectacular success. Running down the middle of the US from Oregon to South Carolina, it was an easy trip for a vast number of people to be able to witness it. The New York Times commented (paraphrasing) that travel to the band of totality caused the biggest one-day migration in US history.

With all the fun over, at least until North America gets the next Big One in 2024, we can turn our eyes once more to the darkened sky. Which because the Moon has just cleared the Sun will not be all that dark. We pass first quarter the morning of Tuesday, August 29, and head for full Moon the night of Saturday, September 5. In between of course is the ever-brightening waxing gibbous. The evening of Friday the 25th, look in western twilight for a pretty triangle made of the waxing crescent Moon, Jupiter down and to the right of it, and the star Spica down and to the left. The Moon then passes four degrees north of Saturn on Wednesday the 30th and only four hours before its apogee, where it is farthest from Earth.

Jupiter graces the western evening sky until nearly the end of twilight, passing only three degrees north of Spica on Saturday September 5. Saturn then follows, disappearing beyond the horizon shortly before local midnight. On the other side of the sky, Venus rises in a dark sky about an hour before dawn (which commences around 4 AM Daylight Time) well above much fainter Mars and Mercury, the latter having undergone inferior conjunction with the Sun on Saturday the 26th. For what it's worth, Neptune (now near the Piscis-Aquarius border) stands in opposition to the Sun the night of Saturday the 5th.

If you are in middle latitudes, in the early evening, the sky looks as it were pinned to the zenith by Vega, the second brightest star of the northern hemisphere. Roughly halfway above the northern horizon is rather lonely Polaris, the North Star, whose altitude in degrees is always equal to the observer's latitude. To the south-southwest of Vega, you will see another first magnitude star, Altair of Aquila, with its two flanking stars that make the trio look as if it were flying across the sky, as a celestial eagle should.

STAR OF THE WEEK: MU AQL (Mu Aquilae). Wander around through the Milky Way in Vulpecula with a telescope or binoculars and you may come across a charming "star_intro.html#openclus">cluster" called "the Coathanger." It's an extreme example of a "non-cluster," a chance alignment of differently-colored stars. At the other extreme of alignment is the region around Mu Aquilae, a rather non-descript common fifth magnitude (4.45) class K (K3) giant that lies some 4.5 degrees west-southwest of Altair, the luminary of Aquila, the celestial eagle. K giants are common as dirt. Most of them are stars that have used their internal hydrogen fuel, the cores now slowly heating and contracting in size as the stars grow larger and cooler on the outside, or have fired up their internal helium to fuse to carbon and oxygen. This one, Mu Aquilae, is no different. Take the K giants from the sky and many of the constellations would nearly disappear or at least be severely altered. Imagine for example Taurus without Aldebaran, Bootes without Arcturus. And what happened to that second twin, Pollux, anyway? (Though we must admit that removing Mu Aql from Aquila's outline would do little harm.) They are all going to slough off their outer hydrogen envelopes and reveal their inner, now-dead cores as nascent white dwarfs, perhaps producing expanding shells, planetary nebulae, along the way. At a distance of 108 light years (with an uncertainty of just 1), Mu Aql has a typical temperature of 4520 Kelvin, which means that a fair amount of infrared radiation must be added to the visible starlight to get a luminosity of 25 times that of the Sun, which in turn yields a radius of 8.1 times that of the Sun. That's not much for a "giant," but then neither is the mass very high, at most just one and half Suns. Even the metal content is near-solar as well. The only thing that's a little off about the star is the velocity of 48 kilometers per second relative to the Sun, some three times normal. What brings us back to the Coathanger is that Mu Aquilae is surrounded by "companions" of tenth to thirteenth magnitude (Mu Aql B through F), and one's first reaction is that we've found a "mini-cluster" with Mu Aql A at the top. Measurements of motion, however, disabuse one of such a notion. What IS odd is that in looking at this loose swarm as a cluster, we inadvertently seem to have found a REAL double, as Mu Aql B and C (each about a minute of arc from Mu-A) have almost identical motions relative to A and are probably a real pair, but of unknown distance and type. Best perhaps to go back and admire the real Coathanger before the motions of its member stars dissipate, in the case of Mu Aql leaving the real double of Mu Aql behind.

Valid HTML 4.0! Copyright © James B. Kaler, all rights reserved. The written contents and (unless otherwise specified) the photograph are the property of the author and may not be reproduced in whole or in part without the author's consent except in fair use for educational purposes.