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Skylights featured nine times on Earth Science Picture of the Day: 1 2 3 4 5 href="http://epod.usra.edu/blog/2006/04/sundog-and-parhelic-circle .html">6 7 8 9

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Photo of the Week.Before the chill of winter comes the beauty of Fall and its clear skies.


Astronomy news for the week starting Friday, August 8, 2014.

Phone: (217) 333-8789
Prepared by Jim Kaler.

Clear skies and thanks to Skylights' blogger visitor reader.


Access Skylights' Archive and photo gallery.
Go to STARS for previous stars of the week. 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.

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.


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

SSNEWEST! FIRST MAGNITUDE: A Book of the Bright Sky, World Scientific, 2013. Read the interview with Jim Kaler.


NEW! Read The Harp in Stellar Stories.



The Moon starts our week late in its waxing gibbous phase, which ends at full Moon on Sunday, August 10, during the day around noon in North America when it is quite out of sight. The Moon will thus rise the night of Saturday the 9th just short of full and the night of Sunday the 10th just past that phase as it begins to gibbously wane. Last quarter is not passed until Sunday the 17th. Sadly the Moon makes no passages by any planets except for Neptune and Uranus (on Monday the 11th and Thursday the 14th) as it works its way up to and past the celestial equator into the northern celestial hemisphere. On Sunday the 10th the Moon passes perigee, when it is closest to the Earth, to the hour the same time as it achieves full phase, the coincidence bringing especially high and low tides to the ocean coasts.

In the planetary realm, Mars continues its rapid trek to the east against the background stars as it continues to pull away from Spica in Virgo and head toward Saturn in Libra, the two bright planets quite obvious. But you have to look early, as Mars is gone by 11 PM Daylight Time, and if you have any horizon obstructions, well before that. Saturn follows a little over half an hour later. On the other side of the sky, Venus begins to rise shortly after the break of dawn, followed by Jupiter. Mercury is impossible, as it passes superior conjunction with the Sun (the planet to the rear) on Friday the 8th.

All year we wait for the king of annual meteor showers, the Perseids, which will peak the night of Tuesday the 12th and the morning of Wednesday the 13th. They are the debris of comet Swift-Tuttle, which returns to us every 133 years and last came by in 1995. Unfortunately, the shower, which usually feeds us 60-100 meteors per hour that seem to emanate from the constellation Perseus, will be mostly ruined by the brightness of the waning gibbous Moon.

The summer stars are much upon us. In mid-evening, the Summer Triangle of Deneb, Vega (marginally the second brightest star of the northern hemisphere), and Altair, is rising high in the east, while Hercules rides high near the celestial meridian and Bootes (with Arcturus, which barely beats out Vega) descends into the northwest. To the south, the deadly Scorpion (with Antares at its heart) lurks to the west of Sagittarius.

STAR OF THE WEEK: OMI AQL (Omicron Aquilae). Within the Milky Way, fifth magnitude (5.11) Omicron Aquilae sits in Aquila 1.5 degrees almost due north of first magnitude Altair, making it quite easy to find. A class F (F8) dwarf, Omi Aql is almost sunlike, though with some notable exceptions, one of major importance. The distance of 62.6 light years is known to remarkable accuracy, within just 0.4 light years. Though in the Galactic disk, the star's closeness precludes significant dimming by interstellar dust, and a well-determined temperature of 6125 Kelvin places almost all the radiation in the visible band of the electromagnetic spectrum. From these considerations, we get a total luminosity of 2.73 times that of the Sun and a radius of 1.47 times solar. Oddly, there is no measure of rotation speed. Theory then gives a mass of 1.2 to 1.25 Suns. With an age of 3 billion years, the star has less than a billion to go before it gives up core hydrogen fusion and turns into a subgiant on its way to gianthood.

There's nothing much unusual here, so why bother with it? First, Omi Aql is not metal-poor (a common condition), but metal-rich, with an iron-to-hydrogen ratio 25 percent greater than the Sun's, suggesting that it came from somewhere in the Galactic interior where more metals are available to birth clouds thanks to a denser stellar population and more supernovae. Yet the star's velocity of 25 kilometers per second is not all that high, just double normal. Metal-rich stars are breeding grounds for planets, but Omicron Aquilae does not even seem to have a debris disk around it that would at least be evidence for a planetary system (none at this time obviously detected or inferred). It's also quintuple. OK, not quite. Omi Aquilae C, D, and E, respectively of 14th, 13th, and 12th magnitudes, are separated from bright "A" by 22, 50, and 82 seconds of arc. Alas, their motions relative to Omi Aql A over only short timelines reveal all to be just in the line of sight and not actual companions. But then there is Omi Aql B. Now 19.5 seconds away from "A," the separation has changed by only a second of arc over the past century even though the AB pair has shifted relative to its surroundings by nearly a full half minute of arc, some 30 times the stars' separation. Moreover, Omi B's absolute brightness is consistent with it being classified as an M3 red dwarf, so the two stars are almost certainly partners. If so, the companion is at least 375 AU away from its much brighter mate, and would take 6000 years or more to make a full circuit. Assuming the above distance, from Omicron A, Omi B would appear five times brighter than our Venus, while from Omi B, Omi A would be would shine as a point of light glowing with 10 full Moons. By far the most absorbing feature of Omicron Aquilae is that in 1979-80 it burst forth with two superflares in which it brightened by 0.09 magnitudes, nearly nine percent! The first flare could have lasted up to five days, while the second stayed up for nearly two weeks. Red dwarfs are supposed to behave this way, not those more or less like the Sun. Omi Aql thus joins an exclusive club that includes 5 Serpentis and Groombridge 1830 (HR 4550). Reasoning from ordinary solar and red dwarf flares, imagine what the X-ray intensity must have been. Imagine too what it would be like if the Sun were to join the group. Why such stars go off this way is a mystery, as is how frequently such flares go off. Without a planet, or so it appears anyway, there is nobody there to report back, which is probably a good thing, as it sure would be a dangerous place to be.


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