SKYLIGHTS

PLEASE NOTE: SKYLIGHTS has moved to http://stars.astro.illinois.edu/skylights.html.

Skylights featured on Astronomy Picture of the Day

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

Photo of the Week. The Milky Way in Sagittarius, holds the center of the Galaxy, obscured by the dense dust clouds near lower center. (The streak at upper left is a satellite trail; the cluster called Messier 7 sits distinctively at lower left.)

Astronomy news for the week starting Friday, July 30, 2010.

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

Clear skies and thanks to Skylights'

reader.

Go to STARS for previous stars of the week.	Last week's Skylights is still available.	Access Skylights' Archive and photo gallery.	Find out what happened in astronomy at Astronomy Updates.
The Constellations has a linked list with locations and brightest stars.	Constellation Maps show the locations of the constellations.	The 151 Brightest Stars lists through magnitude 2.90.	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 photos of the Moon.	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.
Go from Day Into Night, with 83 linked illustrations.	See the The Aurora and the Midnight Sun.	Take a ride aboard Asteroid 17851 Kaler (1998 JK).	Look for Books about the sky and stars.

Support 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.

The Earth Science Pictures of the Day (see above) have been restored.

Read Riding the Chariot in Stellar Stories.

NEW. "Heaven's Touch: From Killer Stars to Seeds of Life, How We Are Connected to the Universe," Princeton University Press.

The Moon fades away this week, starting in the waning gibbous phase, then passing third quarter the night of Monday, August 2, about the time of Moonrise in North America, making for a fine sight. The remainder of the week sees it in the waning crescent phase, new Moon not reached until next week. Oddly, sitting rather high along the ecliptic path, it visits no planets at all.

The lack of lunar activity is more than made up for by the parade of evening planets, the least of which is nearly invisible Mercury, which passes greatest eastern elongation with the Sun on the night of Friday the 6th, rather well out of visibility. The real sight belongs to Venus, Saturn, and Mars. Not too long ago they were stretched out on a line. Now the night of Sunday the 1st (give or take a day or two) look to see them in a fine flat triangle. Venus will be at the lower right apex, while Saturn and Mars make the left-hand end, brighter Saturn on top, the color contrast with Mars rather obvious. They will continue to dance with one another the remainder of the week.

Mars and Saturn come into formal conjunction during the day on Sunday, August 1, just two degrees apart. As July comes to a close, faster moving Mars will be to the west of Saturn, while as August begins the two will have slightly switched places. Mars and Saturn will then point up and to the right to Denebola in Leo, while up and to the left will be Porrima in Virgo. But look early, as the planetary clump sets early at the end of twilight, about 10 PM. Needless to say, a good flat western horizon is essential.

But not all is lost in the after-dark hours, as with the setting of the gang of three, giant and very bright Jupiter rises almost due east within the confines of western Pisces. Now slowly moving westerly against the stars, Jupiter takes just under 12 years to go around the Sun, thus on the average visiting a different Zodiacal constellation each annum. This year it is Pisces' turn to host the King (barring, of course, the Sun) of the Solar System.

With the Moon getting out of the way, the southern sky grabs the week's attention. The great curve of Scorpius south of bright Antares hits the meridian to the south around 9 PM, with the Little Milk Dipper of Sagittarius right behind it to the east. Below them is a curve of lesser-known constellations visible from southern climes that starts in the west with ancient Lupus the Wolf, then goes to the east with Norma (the Square), Ara (the Altar), Telescopium (the obvious Telescope), and finally, under Sagittarius, the graceful curve of Corona Australis (the Southern Crown).

STAR OF THE WEEK: MU NOR (Mu Normae). The stellar world was electrified last week (July 21, 2010) by the likely discovery of supermassive stars in distant dense southern star clusters NGC 3603 and R136, the latter in the Large Magellanic Cloud, a nearby companion galaxy to ours). One, with an immense luminosity of close to nine million Suns, seems to have been born with a mass of some 300 solar masses, far beyond the long-thought maximum of 120-150 Suns. We will see, as astronomers rush to confirm or discount the claim, which is the essence of science. That discovery only serves to highlight our star, fifth magnitude (4.94) Mu Normae, which lies within the obscure modern constellation of Norma, the Square (originally Norma et Regula, the Level and Square), which lies to the southwest of Scorpius. As a blue class B (B0, some say O9.7) supergiant, it is still among the most luminous stars of the Galaxy. And measures agree. Obscured by nearly a magnitude of dust absorption, the result of a grand distance within the Milky Way of 4240 light years (give or take a whopping 1540), if in clear space it would shine at magnitude 4 (4.01). From that and a temperature of some 30,500 Kelvin (to account for a LOT of ultraviolet light), we get a luminosity of half a million times that of the Sun. The uncertainty in distance could halve it, but also allows for a luminosity twice as great, a million Suns. Luminosity and temperature, plus theory, then give a mass somewhere between 25 and 60 times that of the Sun, centering on 40 solar. The latter scenario suggests that the star is not yet a true supergiant but is closing in on the end of its four-plus million year hydrogen-fusing dwarf lifetime. With a radius of 25 or so times that of the Sun, plus a projected equatorial rotation speed of 72 kilometers per second, the rotation period must be under 17 days. Like most such stars, it possesses a powerful wind, one that blows with a surface velocity of 1750 km/s. With a current mass-loss rate that could be as high as a few millionths of a solar mass a year (nearly 100 million times the solar mass loss rate), it has already lost perhaps ten percent of itself back into space. While seemingly single, with no orbiting partner, Mu Normae still has plenty of local companions, as it appears to be by far the brightest of a poorish cluster called NGC 6169, about which almost nothing is known. Looking farther afield, Mu Nor is also touted as belonging to the Ara (the Altar) OB1 association of hot class O and B stars, such OB associations holding so many of Mu Nor's kind.

For more on the sky, visit the Earth and Sky Skywatching and General Science pages.

pyright © 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.