"Let your soul stand cool and composed before a million universes" Walt Whitman

The Moon's current phase, courtesy of USNO.
Sierra NightSky for the period starting Friday, July 3, 2009 by Jim Kaler

Happy Birthday USA. The Moon celebrates by starting off in its waxing gibbous phase, then passing full the night of Tuesday, July 7, when it will undergo a penumbral eclipse that peaks at 4:38 AM CDT. Don't expect any grand sight, or for that matter of even think of getting up to look. The Moon will just clip the outskirts of the partial shadow of the Earth. If you were standing on the Moon, you would see the Earth take a just small bite off the edge of the Sun. The amount of light lost is minimal, and the effect on the Moon as seen from here is about zero. Following full, the Moon then enters its waning gibbous as it heads towards third quarter, that phase not reached until next week.

It'll be a far better sight to watch the waxing gibbous plow through Scorpius. Look the night of Friday the 3rd to see the Moon just to the right of bright reddish Antares. By the following night, the Moon will have shifted to the other side, appearing above the curve of the Scorpion's tail. In between the Moon will occult the star as viewed from Japan to Hawaii.

The night of Thursday the 9th, the Moon will then lie to the northwest of Jupiter, which now rises around 10:30 PM Daylight Time just as formal twilight comes to an end. Before that, you can admire Saturn, which will grace the western sky in Leo until it sets about an hour after Jupiter rises.

The morning sky is now the domain of Mars and Venus, much fainter Mars rising around 2:30 AM, brilliant Venus about half an hour later. Both planets are now making their way through Taurus, beautifully placed to the west of the Hyades Cluster and south of the beloved Pleiades.

Most likely, however, the biggest news involves us, the Earth, as our planet passes aphelion the evening of Friday, July 3, when we will be farthest from the Sun for the year, at a distance of 147.1 million kilometers (91.4 million miles), 1.7 percent farther than average. Given the heat of the day, it's clear that the solar distance has nothing to do with the seasons, but everything to do with the 23.4 degree tilt of the rotation axis against the orbital axis.

Follow the curve of the Big Dipper's handle south first to Arcturus in Bootes and then to Spica, the centerpiece of the otherwise dim constellation of Virgo, the Maiden. This blue first magnitude star ranks 16th in the list of brightness and anchors the rest of the constellation, which sprawls broadly to the northeast and northwest.

STAR OF THE WEEK: SYRMA (Iota Virginis)

Most of the brighter stars of Virgo spread to the northwest of the luminary Spica. The dimmer ones go to the northeast, including our current star Syrma, which from Greek refers to the train of a dress, appropriate to the celestial Maiden of the Zodiac. It's far better known not by its Greek proper name, but by its Bayer Greek letter name, Iota Virginis.

Like the others in the neighborhood, Syrma is relatively dim, just fourth magnitude (4.09), but of interest in that it is not all that much different from the Sun, a class F (F6) giant, but just barely, really a subgiant that has just ceased its core hydrogen fusion and is just beginning to pass on to becoming a true giant. (Indeed, it has also been classed as an F7 subgiant, even an F7 dwarf.) Rather nearby, only 72 light years away (just a bit closer than the stars of the Big Dipper), Iota Vir shines at us with the light of 9.4 Suns from its 6185 Kelvin surface, just a bit greater than the solar temperature (the metal content similar to that of the Sun as well).

With a mass of between 1.5 and 1.55 solar, the dying star has swollen to a radius of 2.7 times that of the Sun, having begun life at roughly half that size as a white class F2 star some 2.7 billion years ago. A modest (and uncertain) rotation speed of at least 24 kilometers per second (and a rotation period under 5.5 days) helps produce magnetic activity and a hot outer corona estimated at two to eight million degrees Kelvin, not dissimilar to the one that surrounds our own Sun. Iota Vir is also surrounded by some mystery. First, it's slightly variable, shifting between magnitude 4.06 and 4.11.

Though the period is unknown, it's probably in the neighborhood of a day or so in the mode of Gamma Doradus. Even the closest look shows the star to be decidedly single. Very subtle motions, however, allow the suspicion of a companion with a period of around 200 years, but about which nothing is known and probably never will be. If it exists at all. (Thanks to Paolo Colona, who suggested this star.)

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. 

Sierra NightSky thanks to Jim Kaler.
Check out his site for more