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

Earth shadow

Photo of the Week. The Earth's shadow rises over the sea after sunset.

Astronomy news for the two weeks starting Friday, November 20, 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. 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.

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 Dangerous Waters in Stellar Stories.

The next skylights will appear December 4, 2015.

With first quarter passed the night of Wednesday, November 18, the Moon starts our session in the waxing gibbous phase, which fattens until it hits full phase on Wednesday the 25th just about the time of Moonrise in North America. It then switches to the waning gibbous, which fades until third quarter is passed the morning of Thursday, December 3, again about the time of Moonrise. We close out the fortnight with a bit of the waning crescent.

The evening of Tuesday the 24th, the rising Moon will appear to the right of the Pleiades, the following night to the west of Aldebaran. With the Moon moving its own angular diameter in an hour, by the morning of Thursday the 26th, it will cross over, or occult, the bright star, the event visible from Canada and the northern US (starting 4:44 AM CST for Chicago). Those to the south will see the Moon go north of Aldebaran. "Visible," however, is problematic as the Moon will be just past full and far brighter than the star. It will be far easier to watch the Moon slip below Leo and Jupiter. The morning of Tuesday the 1st the Moon will be directly west of Regulus, while the following night it will fall below the star. The quarter Moon then appears to the southwest of Jupiter the morning of Thursday the 3rd and then passes a couple degrees south of the giant planet shortly before Moonrise, by which time the Moon will be also slightly east of Jupiter, the pair making a fine sight. The Moon passes perigee, where it is closest to Earth, on Monday the 23rd.

With Saturn going through conjunction with the Sun on Sunday the 29th and Mercury lost in western twilight, the evening sky is devoid of the ancient planets, those known since we first looked upward. The morning sky, however, makes up for that lack. Jupiter rises first, about 1 AM as our period opens, near midnight as it ends, Mars (brightening into first magnitude) about an hour and a half later. The pair is followed by unmistakably-bright Venus shortly before 3 AM, the trio parading across the sky until sunup. If you have the time, try to follow Venus into daylight. Even Jupiter has been seen with the naked eye in a clear blue sky. Venus will appear a few degrees north of Spica in Virgo the morning of Thursday the 26th.

Orion is coming strongly onto the nightly scene, the seven-starred Hunter well up by late evening with the reddish supergiant Betelgeuse at the upper left corner, the three-star Belt to the southwest of it, the closely-spaced trio as unmistakable in its way as Venus. With the Belt closely marking the celestial equator, Orion serves to divide the northern celestial hemisphere from the southern. While from northern lands we get to see the whole northern celestial hemisphere, much of the good stuff is in the south. From mid-US latitudes, anything south of 50 degrees below the equator is cut off by the horizon, rendering the southern Milky Way, the Southern Cross, and our biggest galactic satellites, the two Magellanic Clouds, quite invisible.

STARS OF THE WEEK: MU-1 and MU-2 PAV (Mu-1 and Mu-2 Pavonis), a two-for-one special. Odd coincidences abound amongst the stars and here's "one for the books" as they say. At sixth and fifth magnitude (5.76 and 5.31), Mu-1 and Mu-2 Pavonis (in Pavo, the Peacock) appear as a faint naked-eye double just a degree southwest of much brighter Delta Pav. Deep in the southern celestial hemisphere, the two are only 23 degrees from the South Celestial Pole and are circumpolar for points south of the Tropic of Capricorn. You'd likely not notice them. But they are so close together, just 9.1 minutes of arc apart, that they begin to intrigue as a possible, though wide, physical pair. Not only are they close together on the sky, but both are also class K giants! Mu-1, the western of the two, is a K0 giant, while Mu-2, the eastern (the numbers usually based on west-east position, though not always, as seen in Orion's "Pi stars") is formally classed a K2 subgiant . Theory, however (see below), reveals it to be a real red giant (such dichotomies not unusual as the criteria are for the two modes of classification are different). More oddly, they are nearly at the same distance, Mu-1 at 240 light years (give or take 28), Mu-2 at 236 light years (with a formal uncertainty of 6). They must then be partners in loose orbit, an unusual giant pair. But no. Their motions are quite different. Mu-2 is moving roughly southeast at 50 kilometers per second relative to the Sun, while Mu-1 is clipping along to the southwest at a high rate of 74 km/s, six times normal. The two are just "strangers passing in the night," perhaps making them even more intriguing. With distances and respective temperatures of 4660 and 4434 Kelvin (from which we evaluate the amounts of infrared radiation) we find luminosities of 33 and 57 times that of the Sun and radii of 9 and 12 times solar. It's hard to tell exactly what is going on. With masses of say one and a quarter Suns, the stars could be brightening with dead helium cores or fading some to become ordinary K-giant helium burners (the cores turning into carbon and oxygen in the process). But let's be creative and use these two stars, along with nearby Delta Pav, to illustrate what will happen to the Sun. Delta is a hydrogen-fusing dwarf with about a solar mass. It will someday (ignoring mass differences) appear as Mu-1 Pav and then as Mu-2, all three examples of stellar evolution within about a degree of one another. Being so close, the two Mu's must be very bright in the others' skies. At the given distances, they are but 2.6 light years apart, and each would glow for the other at the bright end of magnitude -4, roughly about that of our Venus. If they are at the same distance, allowed by the uncertainties, they would be but half a light year apart and would shine more at -8, corresponding to some 30 Venus's. Unfortunately there is no evidence for any companions, let alone planets, so there is nobody there to see them shining with their orange light as they pass, never to see each other again.

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