What’s Up this Week: July 10 – July 16, 2006

Greetings, fellow SkyWatchers! The Moon starts off the week, but be sure to watch for aurora activity despite its bright influence. There will be plenty of objects to study, and take the time to check Heaven’s Above for visible passes of Discovery and the ISS. Now, grab your binoculars or scopes, because…

Here’s what’s up!

Monday, July 10 – Yes. It is big. Yes. It is bright. And yes…it’s officially the Universal date of the Full Moon. Are you ready to risk a little night blindness to see something new? Then let’s head towards the great Grimaldi and turn south. Close to the terminator west of Mare Humorum you will see the very bright Class III crater Byrgius. On its northeast wall is another impact named Byrgius A and it is the center of a prominent ray system splashed over the older crater. The ejecta brightens the whole area and makes it difficult to resolve Byrgius. Look just to the west along the terminator for Darwin – an ancient multi-crater complex.

Now, let’s go really look again at Antares. Like many red giants, 520 light-year distant Antares A is variable with around a 5.8 year-long cycle. Such a cycle occurs as Antares’ photosphere alternately swells and cools, then shrinks and warms. Driving this cycle are events deep within the star itself. As Antares’ nuclear fuel waxes and wanes – delivering more, then less food to feed its enlarged form – a tug-of-war occurs between radiation and gravity within it. Think of red giants as a “star within a star.” Antares’ massive core and mantle is actually a fiercely radiant blue-white star surrounded by an expansive shroud of diffuse hydrogen and helium gas. This shroud is so large that it would engulf all our solar system’s inner planets plus the asteroid belt.

Tuesday, July 11 – During July, something strange is happening in the woods…deer sprout antlers. Due to this natural phenomenon, tonight’s Full Moon is sometimes referred to as the “Buck Moon.” For some of us, however, the month of July also brings fearsome storms and Luna is also referred to as the “Thunder Moon.” In more agricultural regions it’s the “Hay Moon.” Among coast dwellers, this is the “Sturgeon Moon” – a name given by ancient fishermen whose best catches occurred during this month. Elsewhere it has been called the “Red Moon” because hazy-heat rising from the Earth’s surface at low angles gives the Moon color as it rises. This month’s moon is also the “Grain Moon,” or for scholars, the “Green Corn Moon.”

No matter what it’s called, we can watch it rise and enjoy the “Moon Illusion.” Everyone knows the Moon looks larger on the horizon, but did you know this is a psychological phenomenon and not a physical one? Prove it to yourself by looking at the rising Moon upright…it looks larger, doesn’t it? Now stand on your head, or find a comfortable way to view it upside down…now how big is it?

Take a look at the stars overhead. For northern observers, you can’t miss the “Summer Triangle” now entering the middle third of the sky at dark. Look to Vega, Deneb, and Altair – three stars of the first magnitude and make note of the constellations within their bounds – within a few days the Moon will rise later and the subtle beauty of the shimmering summer Milky Way will reveal itself!

Wednesday, July 12 – Haven’t found Neptune yet? Try looking north of the Moon tonight…

Tonight as Selene forecasts its brilliant rise to the south-southeast, let’s have a look at 400 light-year distant Rasalgethi – Alpha Herculis. Known as the “Head of the Kneeling One,” it’s an easily resolved (4.8 arc second spaced) double noted for its fine color contrast. At magnitude 3.5, the variable bright primary is one of the largest known stars – with a diameter four times the Earth-Sun distance. Its photospheric temperature is so low at 3000 degrees Kelvin that it barely glows a warm “red-orange.” Meanwhile, its 5.4 magnitude companion is a yellow giant with a temperature twice the primary. The two together make Rasalgethi A seem a deeper red while Rasalgethi B takes on a lovely yellow/green hue.

Tonight let’s use a bright feature to help us locate something very cool on the lunar surface. Start by identifying unmistakable Tycho to the south. Northeast of Tycho you will see a bright ray running towards Mare Serenitatis and the equally bright spot of Cassini. If you trace the great double ray northwest, you will see the fainter branch extend all the way to Bullialdus and its central peak.

Thursday, July 13 – Tonight the Moon is not only closest to Earth, but rises just as the sky gets dark. We’ll only have time for two deep sky studies, so let’s make them galaxies! The constellation Draco is filled with them…

First revisit “the Cat’s Eye” planetary – NGC 6543, and enjoy a high-power view through improved skies. Move north at low power less than four degrees and breathe west. This is 10.1 magnitude, near edge-on, spiral NGC 6503. Through scopes, this fine, evenly-balanced spiral displays the kind of patterned mottling associated with pinwheel galaxies when viewed face on. If you have trouble locating it, try dropping about a finger-width southeast of faint Psi Draconis.

Northeast of Psi is brighter southeast Phi and northwest Chi. Mark the distance between them and continue that same distance northwest beyond Chi for small scope challenge – 11.1 magnitude NGC 6643.

Friday, July 14 – Today in 1965, Mariner 4 became the first spacecraft to perform a flyby of Mars. Tonight Mars is “flying by” Regulus in Leo. Look for it in binoculars about a hand span above the western horizon just after sunset.

Although the “Red Planet” is around 2.0 magnitude, it’s less than 4 arc seconds in size – making it barely larger than Uranus in a telescope. Meanwhile 5.8 magnitude Uranus follows magnitude 7.8 Neptune above the horizon. Look for them around midnight dancing with the gibbous Moon roughly between them. You can recognize Neptune by its telescopic blue disc, around two finger-widths northwest of Gamma Capricorni and Uranus further east between Lambda and Phi Aquarii. Be sure to check IOTA for information, because the Moon and Uranus will be having a close encounter of the occultation kind on this Universal “date!”

Tonight while waiting for Uranus and Neptune, why not take a binocular sweep of the sky due south of Epsilon Scorpii all the way to the horizon. Although we’ve already made a bit of a study of this region, get a sense of just how rich it is in terms of faint stars and open clusters – a part of the night sky leading southwest into Ara and the exotic constellations of the southern hemisphere Milky Way – Norma, Centaurus, and Crux…

Saturday, July 15 – With the Moon now well east, let’s search out “the God of the Underworld” – Pluto. Right now the solar system’s ninth planet lies near a pair of bright stars that should make it easy to track down and follow its motion over the next several days. But before you start, make sure you have access to a telescope able to reveal stars down to magnitude 14.0. Ready to discover Pluto?

Start by drawing a circle on a clean white sheet of paper. Make it large enough to represent the field stop in an eyepiece. Then go out and aim your telescope directly at 3.6 magnitude Xi Ophiuchi. Shift Xi to the north of the eyepiece field and position 10 arc minute distant 5.9 magnitude SAO 160700 in the center of the field. Now shift SAO 160700 to where Xi was located in the eyepiece. Tonight, Pluto should lie somewhere near the center of the eyepiece field and to the east. Make a sketch of all the stars in the field – including SAO 160700. Be sure to come back several nights later and compare your original sketch. The “star” that has moved is Pluto!

Sunday, July 16 – Today in 1850 at Harvard University, the first photograph of a star was made (other than the Sun). The honors went to Vega. In 1994, an impact loomed as nearly two dozen fragments of Comet Shoemaker-Levy 9 sped toward the cloudtops of Jupiter. The results were spectacular. As fragment after fragment struck Jupiter, parts of the Gas Giant shone as bright as the Sun. Meanwhile very dark footprints were left behind – holes punched through the planet’s atmosphere. Although such footprints are no longer visible, take the time to look at Jupiter again. No matter where you observe from, this dynamic planet offers a wealth of things to see – be it the appearance of the “Great Red Spot,” or just the ever changing waltz of the Galilean moons.

Just after skydark this evening, three fine globular clusters (M10, M12, and M14) are well placed in the south. Revisit all three with binoculars, then track them down through the scope. Start at Delta Ophiuchi and sweep east a hand span to catch all three. Each globular cluster will look like a round haze condensing toward their centers.

May all your journeys be at light speed… ~Tammy Plotner with Jeff Barbour.