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., taken July 8, 2016. Mars (halfway to the right), Saturn (up and to the left of center), and Antares (below Saturn), dominate this extraordinary configuration in Scorpius. Dschubba (Delta Sco), an erupting hot star, lies at dead center. It's the center of the vertical trio that makes the Scorpion's head. The "Stinger" is at the lower left corner. Compare with the configuration seen a month earlier on August 26.

Astronomy news for the two weeks starting Friday, October 21, 2016.

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. 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.

This is jk w/ skl, ui astr news for the two weeks starting Friday, October 21, 2016.

The next skylights will appear November 4, 2016.

The Moon fades away during the first week of our fortnight, beginning at third quarter on Saturday the 22nd, then slimming away as a waning crescent until it disappears in morning twilight on Saturday, October 29, new Moon passed the next day. Two days later, the Moon passes apogee, where it is farthest from Earth on its more-or-less elliptical orbit.

Flipping to the other side of the sky, the now-
waxing crescent will appear above the star Antares the early evening of Tuesday, November 1, bright twilight making the sight a difficult catch. The early evening of Wednesday the 2nd it will be much easier to see the growing crescent above Saturn, withVenus to the left. The following evening finds the Moon up and to the left of the bright planet. First quarter finally puts an end to the crescent on November 7, just after our current period ends.

Be sure to look for the "stack" of objects vertical to the horizon in twilight evening of Thursday the 27th, which features Saturn on top, Venus (the brightest of them) in the middle, and fainter Antares below. The configuration will stick around for a couple days. By the time the Moon gets into the act, Venus will have shifted well to the left, as noted above.

Mars, moving eastward against the stars to the east of the Little Milk Dipper of Sagittarius, heads for Capricornus, reliably setting just after 10:30 PM Daylight time. At least Jupiter is back, the bright planet now rising just before dawn. Mercury, now gone from the sky, passes superior conjunction with the Sun (on the other side of the Sun) on Thursday the 27th.

Orionid meteor shower, which comes from the debris of Halley's comet and emanates from the constellation Orion, peaks around the mornings of October 20-21, but is active for a few days on either side of these dates. Unfortunately, moonlight gets in the way. We get hit again by the stuff in early May.

Look to the far northwest to see the falling stars of the Big Dipper. For most of us it's near-circumpolar. The famed configuration is replaced by the prominent "W" of Cassiopeia, the Queen of the Andromeda myth. To the west is the dim pentagon that makes Cassiopeia's husband, Cepheus, the King.

STAR OF THE WEEK: PI-1 UMA (Pi-1 Ursae Majoris, with a nod to 2 UMa.) In far western
Ursa Major, about as far as you can get from the Big Dipper, seven degrees north of Omicron UMa and near the border with Camelopardalis, lies a small curve of three stars, from north to south fifth magnitude (5.47) 2 UMa (a Flamsteed designation), sixth magnitude (5.64) Pi-1 UMa, and fifth magnitude (4.60) Pi-2 UMa (which are NOT Flamsteed numbers). Pi-1 and Pi-2 have been tagged with the name "Muscida" (the "muzzle"), which more usually is attached to Omicron. They have nothing physical to do with one another. 2 UMa is 152 (give or take 3) light years away, Pi-1 a neighborly 46.8 light years (with an uncertainty just 0.3 ly), and Pi-2 the most distant at 256 (plus or minus 6) light years. At first, the prize would seem to go to Pi-2, an otherwise ordinary class K (K1) helium-fusing giant, but one with a massive orbiting planet about which little else is known and that might even qualify as a brown dwarf, a "star" with insufficient mass to fuse its core hydrogen to helium. Surprisingly, the real winner is the star in the middle, Pi-2 Ursae Majoris, which appears to be a much sought-after solar clone, a star like 18 Scorpii or 9 Ceti that is very much like our own Sun even though its dwarf classification is slightly different (G1.5 as opposed to the G2 Sun), its temperature of 5850 Kelvin about 70 K warmer, its mass three percent higher, and its radius five percent less. The object of studying solar mass stars is to see how the Sun develops from youth to old age and to test theory, that is, we would like to know both in the short and long terms what is going to happen to us. Pi-1 UMa is on the youthful side, the star roughly 500 million years old, and belongs to the Ursa Major cluster or, "moving group," of about the same age (whose most prominent members are the middle five stars of the Big Dipper). Of the star's parameters, the rotation is among the more interesting. The projected equatorial rotation speed of 10 kilometers per second gives a rotation period of under 5 days, But such a star should be magnetically active with star spots and related spectral characteristics. Periodic variations of a few hundredths of a magnitude give a true rotation period of 4.79 days, which then shows the star to be rotating with its axis perpendicular to us. A decade of data also suggests a long-term activity variation of a dozen years, perhaps one similar to the solar cycle. The rapid rotation also produces X-ray radiation 40 times that from the Sun and violent X-ray flaring. On the other hand, the global magnetic field seems to be about the same as that of the Sun. In addition, though we might expect a strong stellar wind, it appears to flow at only about half the rate of the solar wind, showing we have a long way to go in understanding early solar evolution.

What about 2 UMa, which seems to have been left behind? As a metallic- line Am star it's interesting on its own. Such stars alter their surface chemical compositions as a result of gravitational settling of some elements and radiative lofting of others. This phenomenon can give rise to confusion of the subclass depending on the ions used for classification. While usually given as A2m, 2 UMa might be classed anywhere from A3 to A7. From its distance of 152 light years and temperature of 8050 Kelvin, it radiates at a rate of 11.1 Suns. Theory then shows 2 UMa to be a young dwarf with a mass 1.8 Suns. While the rotation velocity is not well constrained, it's low enough to be consistent with the odd composition, as otherwise the atmospheric gases would be stirred back to normal. (Data on Pi-1 UMa from J.J.Bochanski et al., Information Bulletin on Variable Stars No, 5043, Konkoly Observatory, 2001: B.E. Wood et al., Astrophys. J. Letters 781:L33, 2014; I.G.Ribas et al., Astrophys. J., 622, 680, 2005.)

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.