SKYLIGHTS

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

First quarter

Photo of the Week. Twilight first quarter Moon (20 hours past the exact phase) with delicate clouds.


Astronomy news for the two weeks starting Friday, August 14, 2015.

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

Clear skies and thanks to Skylights' blogger visitor reader.


Go to STARS for previous stars of the week. 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.

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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 Bearly North in Stellar Stories.



The next skylights will appear August 28, 2015.

The symmetry between our fortnight and the lunar phases nicely continues, with new Moon taking place on Friday, August 14, and full Moon on Saturday, August 29, during the day in North America, so the Moon will rise a bit past the phase that evening. After the new phase, the Moon will wax as a crescent, culminating in first quarter on Saturday the 22nd, with the Moon already climbing the daytime sky. You might get your first look at the ultra-thin crescent in western twilight the evening of Saturday the 15th. Following first quarter, the Moon grows in the gibbous phase until it finally passes full. The evening of Friday the 21st the Moon will lie to the west of Saturn, while by the following night it will have flipped to the other side. Our companion passes apogee, where it is farthest from Earth, on Monday the 17th.

Throughout most of the year, Jupiter and Venus dominated the nightly skies. Now the two do a disappearing act as Venus goes through inferior conjunction with the Sun (more or less between it and us) on Saturday the 15th, while Jupiter will pass solar conjunction on Wednesday the 26th. The evening now belongs to Saturn. Still northwest of Antares in Scorpius but moving easterly against the background stars, in the middle of our period the ringed planet sets around 11:30 PM Daylight time. In the morning, Mars begins to make an appearance, rising about the beginning of dawn. Far away and still faint, it's hard to spot. Mars will pass nine degrees north of Venus, which begins to make its own notable appearance, as our period closes.

As the days of August cool into those of September, the Big Dipper begins to fall into the northwest, while the "W" of Cassiopeia rises in the northeast. South of the Dipper's curved handle lie the two stars that make up the modern constellation of Canes Venatici, the Hunting Dogs, while further down is the lacy sprawl of Coma Berenices, one of the closest star clusters to Earth. On the other side of the sky, Perseus, which follows Cassiopeia in its rising, is home to the much more distant, but equally famed, Double Cluster. In early evening, Scorpius and Sagittarius (the latter to the east of the Scorpion) are nicely paired low in the south. Below Sagittarius, notable by its "Little Milk Dipper," lies the ragged semicircle that makes Corona Australis, the Southern Crown, whose counterpart, Corona Borealis, the Northern Crown, fits nicely between Hercules and Bootes to the northeast of orange Arcturus, the brightest star of the northern celestial hemisphere.

STAR OF THE WEEK: 10 CVN (10 Canum Venaticorum). Solar type stars are for obvious reasons inherently fascinating. Those with known planets are even more so. In between are stars with circumstellar dusty debris disks like the one around our own Sun (caused by colliding small bodies, disintegrating comets, etc.) in which planets might be buried but are so far hidden. Flamsteed 10, in Canes Venatici (the Hunting Dogs, south of the Big Dipper), a class G (G0) dwarf a hair up the spectral scale from our G2 Sun, is a fine example, though there is a notable departure from a true sunlike character (see below). While faint to the naked eye, just sixth magnitude (5.95), 10 Canum Venaticorum is remarkably easy to find just barely south of a line between Cor Caroli and Chara (respectively Alpha and Beta CVn), which together make most of the constellation. Oddly, Chara and 10 CVn share the same spectral class. Two dozen measures of 10 CVn's temperature give an accurate average reading of 5855 Kelvin, just 75 Kelvin warmer than the Sun and consistent with the star's spectral class. From a super-accurate distance of 567 light years, give or take only 0.3, and a small correction for radiation outside the visual band, 10 CVn is seen to shine with a luminosity just seven percent greater than that of the Sun, luminosity and temperature combining for a radius of 1.01 times solar. The most recent projected equatorial rotation velocity of 3.0 kilometers per second together with a published rotation period of 13.0 days gives an axial tilt of 50 degrees to the line of sight. All these properties point to a "solar clone." But 10 CVn does not quite make it as the star is fairly metal-poor, with an iron abundance relative to hydrogen that is only a third the solar value. Consistent with 10 CVn's chemical properties, it's also pounding along with a speed relative to the Sun of 86 kilometers per second, around five times average. The star is thus a visitor from a different part of the Galaxy, probably from the inner halo, published analysis suggesting a mass of 0.86 Suns. Most intriguing, however, is the dusty disk that surrounds the star, which is big enough to have been directly imaged in the infrared part of the spectrum. Modelling of the observations suggest a disk with a radius of 70 to 80 Astronomical Units in the form of an annulus perhaps 10 AU wide, which is rather reminiscent of our Sun's Kuiper Belt beyond the orbit of Neptune. We might wonder if there is not some kind of yet-undetected earthlike planet orbiting inside the disk closer to the star. If anybody's there they might be looking back at our 6.0 magnitude Sun, which for them would lie on the border between Sculptor and Pheonix. Perhaps too they might note several planets, maybe even the third one out. (Disk and some stellar data from J. P. Marshall et al., Astronomy and Astrophysics, 570A, 114, 2014.)


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