July 2008 Sky from the Keeble Observatory
Not only has Phoenix landed, but it seems to have found frozen water exactly where it was supposed to find it. Recall that Phoenix is in the far northern hemisphere of Mars, near but not on the north polar cap. Its latitude is similar to northern Alaska on Earth. Early images from under the probe show that the landing rockets blew away the surface material and revealed a hard, light colored layer beneath. It looks like ice. Also, the robotic digging arm found a hard layer beneath the surface. The arm is equipped with tools which will make it possible to chip off some of that material and bring it into the spacecraft’s analyzing instruments to melt and determine its exact composition. Even before those samples are taken, however, we’ve seen visual evidence that this material is really ice and not salt (we’ve found salts in the Martian soil at the southern sites being explored by the rovers Spirit and Opportunity). At the bottom of one of the early trenches excavated by Phoenix, we see a handful of dice-size light chunks of material. A few days later, they were gone. At the temperature and atmospheric pressure found at the landing site (pressure is about 1% what you’re experiencing, temperatures range from minus 115 to minus 4 degrees Fahrenheit) water ice doesn’t melt. Rather it sublimates – changing directly from solid to gas. Calculations show that the time for the chunks to disappear was what would be expected of water ice.
Lunar phases for July: New Moon on the 2nd, at 10:19 pm; First Quarter on the 10th, at 12:35 am; Full Moon on the 18th, at 3:59 am; Last Quarter on the 25th, at 2:42 pm.
Predawn skies still provide little opportunity for planet watchers. Jupiter sets just about at sunrise early in the month, and buy the end of July it will set nearly an hour and a half before sunrise. Mercury will be rising to the east about an hour and a half before the Sun on the 1st, reaching its maximum western elongation of 22 degrees. However, the tilt of the ecliptic leaves it only 15 degrees off the horizon at sunrise. By month’s end it will disappear back into the solar glare.
Evening viewers will see Mars and Saturn to the west near Regulus, in Leo. Early in the month they will make a nice binocular target, all within about 5 degrees, with Mars only about a degree from Regulus. Jupiter rises about 30 minutes before sunset, and travels low to the south as the evening advances. Later in the month you will see Mars, Saturn, Regulus, and Venus aligned like beads on a string to the west shortly after sunset, with Venus closest to the horizon. The alignment of the planets is because they all orbit in essentially the same plane around the Sun as Earth does – the so-called ecliptic plane. Regulus lies on the ecliptic, but that alignment is accidental.
About two hours after sunset, our overhead view at mid-month find the constellation Hercules at zenith. On a clear, moonless night you should be able to see even without binoculars the fuzzy patch of M13, the “great globular cluster in Hercules.” This swarm of perhaps a million stars is one of many orbiting the Milky Way Galaxy. The stars in this cluster are among the oldest stars in the Galaxy.
As Mars sets to the west, you can also see the red giant star Antares (“Mars’ rival”) to the south, in the constellation Scorpio. To the left of Mars you’ll find Jupiter in the constellation Sagittarius, which makes a familiar “teapot” asterism. Well beyond the stars we can see in Sagittarius lies the center of our own Galaxy, some 28,000 light years away. Following the plane of the Milky Way from south to north, bowed to the east we find Cygnus the Swan and its brightest star Deneb to the east-northeast. This constellation lies in the direction of the Sun’s motion about the center of the Galaxy.
Above Deneb, high to the east we find the bright blue star Vega in the constellation Lyra. Turning to the northeast we see the familiar crooked W shape of Cassiopeia. To the northwest we find the even more familiar Big Dipper of the constellation Ursa Major. If you follow the arc of the dipper’s handle towards the west, you’ll find Arcturus in Bootes.
Copyright 2008George Spagna