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Astronomy Picture of the Day

Planetary alignment

Photo of the Week.. The planets align in early May. Jupiter shines at upper left. Between the trees, from top to bottom, are Saturn, Mars, and Venus. Auriga, the Charioteer, rules the upper left.

Astronomy news for the week starting Friday, June 7, 2002.

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

Clear skies and thanks to Skylights' * reader

If you like stars, go to STARS: Portraits of Stars and their Constellations, compiled from previous stars of the week. Want to know what happened? Last week's Skylights is still available. Enjoy photographs of the January 20, 2000 total eclipse of the Moon. Watch planets move against the background stars. See sunsets, rainbows, the Moon and planets, and other sky phenomena in Sunlight.
Skylights now resumes its normal weekly schedule.

The beginning of the week finds the Moon in a thin waning crescent phase just visible in early morning twilight. The morning of Sunday, the 9th, the Moon will pass three degrees north of Mercury, which has now switched places from the evening to the morning sky. Our companion will then pass through its new phase on Monday June 10th, and by the next night, Tuesday the 11th, will just barely be visible as a thin crescent in bright evening western twilight. Climbing the nighttime sky, the Moon will make close and quite beautiful passes to Jupiter the evening of Wednesday, the 12th and then brilliant Venus the evening of Thursday, the 13th.

Having passed conjunction on June 3, these two brightest planets are now separating, Jupiter being overtaken by the Sun, Venus still moving away from it. Mars is lost to twilight, and Saturn even more so as it passes conjunction with the Sun on Sunday, the 9th.

This new Moon will produce an "annular" solar eclipse. The Moon is a bit too far away from Earth to cover the Sun completely, and at eclipse will leave a ring of surrounding sunlight. The path of "annularity," where the eclipse is at its maximum, stretches almost exactly across the Pacific Ocean from Borneo to Mexico. While the main event will not be seen in the Americas, the Moon will produce a fine partial eclipse that includes all the US, Canada, and Mexico except for the extreme east coasts. Just inland from the east coast, the eclipse begins at sunset the evening of Monday the 10th. Mid-eclipse will be seen at sunset across the midwest, while the whole thing will be seen west of a line that stretches from Baja California through Ontario. The west coast sees the event shortly before sunset. So bright as to harm the eye, the Sun is dangerous to look at directly even in partial eclipse. View the event only with professionally-made solar filters or by pinhole projection. Punch a very small hole in a piece of cardboard and let the sunlight fall through it onto a piece of paper. (Do NOT look through the hole or attempt to make any kind of filter!)

The new Moon also produces a dark nighttime sky. Around 10 PM find Arcturus crossing the meridian to the south. Below and to the right is Spica in Virgo, and farther down, cut in half by the southern horizon for those in mid-northern latitudes, is Centaurus, the Centaur. From the tropics, its two luminaries, Rigil Kentaurus (the closest star to Earth) and Hadar shine brightly. To the east of Centaurus are the bright stars of Lupus, the Wolf, and farther west yet is one of the grand markers of the coming northern-hemisphere summer, Scorpius, the Scorpion, with the bright star Antares beating at its heart.

STAR OF THE WEEK. MUHLIFAIN (Gamma Centauri). Lying in east- central Centaurus, the name Muhlifain refers to "two things" and to the "swearing of an oath," hardly appropriate for a Centaur. No wonder, as the name is not at all representative of the star, but was given by mistake, taken from a star all the way around the sky, Muliphein, the Gamma star in Canis Major. No one seems to know why, though such name-transference is rather common. Seen below 40 degrees north latitude, this star follows the order of the Greek alphabet, and is in fact the third brightest in the constellation. At mid-second magnitude (2.17) it is commonly ignored in favor of the constellation's pair of first magnitude stars, Rigil Kentaurus (Alpha Centauri) and Hadar (Beta). Muhlifain deserves more respect than it gets. Classed singly as a warm A (A1) subgiant, the telescope shows it to be a pair of identical white A stars (that are sometimes classed as A1 giants). At a distance of 130 light years, the twins are separated by under a second of arc, each shining with the light of 95 Suns from surfaces heated to about 9300 Kelvin. Luminosity and temperature indicate masses 2.8 times solar. Though close together, their mutual orbit has been well- mapped. They circuit each other every 83 years (coincidentally about the same as the period of Rigil Kent's pair) at an average distance of 34 Astronomical Units (just short of the distance between Neptune and the Sun), but in elliptical paths that take them as close as 7 Astronomical Units and as far apart as 62 AU. Under such conditions, no planetary systems seem likely. The orbit tells of stars with masses of 2.9 solar, almost exactly that derived from luminosity and temperature, telling that we have everything just right. The stars are so close in character that they are evolving at the same time, producing rather a rather rare combination of two subgiants (stars that have either just given up their hydrogen fusion or are preparing to do so) that will produce a pair of giants -- and maybe even (as they lose mass together) a unique double planetary nebula as their outer envelopes flee into space before the twins turn into identical white dwarfs.

Do you have a favorite star or one you would like to see highlighted on the Star of the Week? Send a suggestion to Jim Kaler.
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