SKYLIGHTS
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Photo of the Week. White on blue.
Astronomy news for the week starting Friday, May 25, 2012.
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.
Advances in Astronomy, 1989-2011.
The Constellations has a linked list with locations and brightest stars.
Constellation Maps show the locations of the constellations. The
169 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 Enjoy
Our Complex Universe:
A Human Understanding through Art, with 12 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.
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ASP
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.
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.
NEW! Advances in Astronomy for 2011.
Our
Moon begins our week in a fat
crescent phase as it approaches its
first quarter on Monday, May 28. North Americans will see it rising in the afternoon daytime sky. In the following days, it will then grow into the
waxing gibbous phase,
full Moon not achieved until rather well into next week, when it will undergo an
eclipse seen throughout most of the Pacific basin and western and central US and Canada. On the morning of Tuesday the 29th, the Moon will pass seven degrees to the south of
Mars (the wide angle due largely to lunar orbital tilt). On the previous evening (Monday the 28th), the lunar disk will be a bit to the southwest of the planet. Then on the night of Thursday the 31st, we will find the Moon gliding about the same angle to the south of
Saturn. Since Saturn is north (and a bit east) of
Spica, the three (going north, the Moon, Spica, Saturn) will lie in a nice row, the Moon rather close to the star, making it a bit difficult to see.
Venus, which has been gloriously with us during the whole of 2012 (and for some time before), is now effectively gone, at the beginning of our week already setting in late twilight. It is preparing to sweep across the face of the Sun in a rare
transit that for North Americans will start late in the afternoon on Tuesday, June 5, at 5:05 PM CDT, and for the contiguous US and most of Canada will run until sunset. Optical aid is needed, and since the
Sun is so bright, so is a professionally-made filter. Projection of the image works well too.
This week, it is
Mercury's turn, as the planet goes through superior conjunction with the Sun on Sunday the 27th, the planet in back of the Sun, the event, such as it is, quit invisible. It will thereafter pop up in the early evening sky. The night then belongs to Mars and Saturn, the two nicely visible at the same time. The western one of the two, Mars is now moving easterly to the south of the eastern hindquarters of classical
Leo well to the southeast of
Regulus heading for
Virgo (and in mid-August for Saturn). Well into the western sky at dusk, the red planet now sets around 2 AM. Transiting the
meridian in late twilight, Saturn follows Mars to the horizon by about an hour and a half. Regulus, Mars, Spica and Saturn make for a fine evening's viewing.
If you are far enough south (meaning here mostly Hawaii), this is the season for
Crux, the Southern Cross. However, northerners can still admire some of the bright stars of
Centaurus (the Centaur) that more or less wrap around the Cross to the north. Just get a clear horizon and look well to the south of Spica past the dim tail of
Hydra, the Water Serpent.
STAR OF THE WEEK: LAMBDA CEN (Lambda Centauri).
Crux, the Southern Cross, was in the seventeenth century carved from the feet of
Centaurus, the Centaur, the two
constellations thus bearing an intimate relation with each other. Starting to the southeast (with
Alpha and
Beta Centauri), Centaurus wraps around the Cross to the north and then a bit to west, where we find the luminous mid-third magnitude (3.13) star
Lambda Cen, a class B (B9)
giant (some say bright giant) 420 light years (give or take 18) away. It's a part of the "Lower Centaurus Crux"
association of O and B (and lesser) stars that are something of a family with members born more or less at the same time, the system now expanding and dissipating into space. "LCC" lies at an average distance of 385 light years, Lambda Cen thus being a bit on the back side of it. The star is dimmed by about six percent by interstellar dust, a surprisingly small amount given its position in the
Milky Way. Separated from Lambda proper ("Aa") by under a second of arc lies Ab, which in
infrared light shines at seventh magnitude. The assumption that it is the same in visual light (perhaps a bit rash) drops Aa to magnitude 3.17. Several temperature measures are all over the place, averaging 10,170 Kelvin. Lambda itself (Aa) shines with the light of 955
Suns, which leads to a radius of 10 times solar. Measures of projected equatorial rotation speed are odd, an early citation giving zero, two later ones averaging 185 kilometers per second, which is probably the more correct. If so, the star completes a rotation in under 2.7 days. It's fast enough (supporting the rapid rotation) that the chemical abundances are not weird, as they are in so many stars of its class. That said, the star does appear to be metal-rich with an iron abundance as much as two to three times normal, with silicon and carbon a bit down. As are so many stars within its association, Lambda is on the massive side, carrying about 4.5 times the mass of the Sun. Not yet a true giant, the star is now in the process of becoming one with a dead helium core, its age about 125 million years. The companion may be a mid-class A star that carries around double the solar mass. With a mean orbital size of at least 90 Astronomical Units, from
Kepler's Laws Ab must take more than 335 years to make a full orbit. Around 16 seconds of arc distant we find 11.5 magnitude Lambda B, which if real is a solar-type star separated from the inner pair by at least 2000 AU in an orbit that must take at least 34,000 years to complete. From the outer star, the stars of the inner double would appear two or three degrees apart, their orbit making quite a sight, were there anyone there to see it. X-ray radiation may be associated with the lesser companion. Lambda Cen is associated with a small
nebula, but it's probably just a line-of-sight coincidence.
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