This is the Skywatch Line for Monday and Tuesday, April 24th and 25th.
The Sun sets at 7:48 PM; night falls at 9:35. Dawn breaks at 4:10 AM and ends with the Sun rising at 5:58.
Only two planets are visible in the twilight sky. Mars is moderately low in the western sky; at civil dusk, it is 18 degrees high and appears as a tiny first magnitude red dot in Taurus. Do not confuse Taurus’ red star Aldebaran for Mars. Mars sets at 10:11 PM.
Jupiter, in Virgo, is up moderately high in the eastern sky. It flashes at minus 2.4 magnitude and appears about 44 arc-seconds wide in our instruments. It rises at 6 PM and is best observed at 11:43 PM and sets at 5:27 AM. Jupiter’s moon Io presents an interesting set of appearances and occultations:
Tuesday, at 1:59 AM it is hidden by the planet and reappears at 4:36 AM; then at 11:17 PM it begins marching across Jupiter’s face, followed by its shadow at 11:42; Io exits the planet at 1:27 AM Wednesday, followed by its shadow at 1:53 AM.
Saturn rises shortly before Midnight in Sagittarius. It appears as a cream-colored orb just above the eastern horizon. In binoculars or telescope, it glows at zero magnitude and is 17 arc-seconds in size. Saturn is best seen at 4:30 AM, when it lies due South.
Venus rises in Pisces, in the East, at 4:23 AM. It blazes at minus 4.5 magnitude, is 11 degrees high at civil dawn and appears about 22 percent illuminated. The Moon is not visible because it is too close to the Sun and turns “New” Wednesday morning.
Last week, we discussed Saturn’s moon Iapetus; today, let us consider another Saturnian moon – Enceladus. Jupiter owns 67 moons; Saturn commands a fleet of 62 satellites, 8 of which are visible in amateur telescopes. Sir William Herschel discovered Enceladus in 1789 and named it for one of the mythical Giants that fought the Greek gods. Enceladus is medium sized, about 504 KM (313 mi) in diameter and orbits Saturn in 1.37 days. NASA’s Cassini space probe revealed an ice-covered world, with strange blue “tiger stripes.” Planetary scientists soon realized that there was an ocean beneath the ice. They also witnessed water spouting from those “stripes.” Like Jupiter’s moon Europa, Enceladus is being squeezed by Saturn’s huge gravity and heating up the interior, causing the venting. As the Cassini 12-year mission wraps up, NASA dared to have Cassini make close passes on several moons. A pass through Enceladus’ vapor revealed salt and silica nanoparticles, which were picked up by the water’s contact with hot interior rocks. Hot rocks should leach oxygen from seawater leaving molecular hydrogen. A recent flyby of Enceladus verified its existence. Molecular hydrogen creates a chemical imbalance that may be conducive to life. However, astrobiologists are not claiming life, but only the conditions that may make it possible.