This is the Skywatch Line for Monday and Tuesday, June sixth and seventh.
The Sun sets at 8:31 PM; night falls at 10:45. Dawn breaks at 3:03 AM and ends with the Sun rising at 5:17 AM.
The two-day-old Moon is already up in Gemini, in the southwestern sky. Monday night sees it as a minus 3.4 magnitude thin crescent, about five percent illuminated. Tuesday’s Moon is brighter and eleven percent lit. Monday, the Moon sets at 9:58 PM; Tuesday, it sets at 10:48 PM.
Jupiter still remains a minus 2 magnitude beacon in Leo. It is currently between the Lion’s hind legs. Jupiter is slowly moving eastward – what astronomers call “direct” motion. Jupiter is still worth watching for its four Galilean moons. Jupiter sets about 1:26 AM.
Mars, too, is already up in Libra. Mars is still moving in retrograde (westward) and continues to do so until June 29th. This means that Mars is pulling away from Saturn; it is now sixteen degrees distant from the Ringed Planet. The Mars-Saturn-Antares triangle is expanding, because of Mars’ motions. Even though Mars is past opposition and perigee, it is still well worth observing its surface features. Astronomical media provide observing charts of the Martian surface. Mars dims a bit all month, ending up at minus 1.5; it also shrinks slightly. The Red Planet stands about thirteen degrees above Antares, the third point of the triangle; compare the red color of Mars and Antares. Mars is best observed at 10:46 PM and sets at 4:04 AM.
Saturn rises an hour after Mars and also is just past its own opposition on June 2nd. It is still located in the dim constellation of Ophiuchus, shines at zero magnitude, and is slightly smaller than Mars in our instruments. Saturn never disappoints, especially for first-time sky watchers. Saturn is best seen at about 12:37 AM, and sets at 5:19 AM.
Neptune rises in Aquarius at 1:12 AM, shining at 7.9 magnitude and appearing as a tiny blue dot. Late night observers can catch Neptune before the sky begins to brighten. Uranus stays up the rest of the night.
Mercury was at greatest elongation from the Sun on Sunday.
It shines at 0.4 magnitude, appears about seven arc-seconds in size, rises at 4:15 AM and is about seven degrees high a half-hour before sunrise. This is a poor opportunity to see this elusive planet; southern astronomers have a better view. Mercury is tonight’s challenge object.
All the planets of the Solar System own a total of 171 moons, or satellites, of which Saturn has 62. Saturn’s largest moon, Titan, is also the brightest at eighth magnitude – within the ability of even small telescopes. Titan is second only to Jupiter’s moon, Ganymede; our Moon is third. Titan is unique is that it is the only satellite with a substantial atmosphere. It is about 1.5 times the pressure of Earth’s atmosphere. Nitrogen is the predominant gas, with a mix of hydrogen compounds. As a result, Titan’s atmosphere can be called “smog.” This smog hindered earthbound astronomers from observing its surface. When the space probe Huygens landed on Titan, it revealed river systems and lakes, just like Earth. However, methane, not water, flowed on these rivers. Titan’s clouds also rain methane, just like earthly storms.