This is the Skywatch Line for Monday and Tuesday, April 22nd and 23rd.
The Sun sets at 7:45 PM; night falls at 9:31. Dawn begins at 4:16 AM and ends with the Sun rising at 6:01.
Mars is the sole planet in our evening sky. In Taurus, it appears about 95% illuminated, about 4 arc-seconds in size and glows with first magnitude. It sets at 11:25 PM.
The annual Lyrid meteor shower occurs on Monday’s pre-dawn hours. However, it peaks at about 8 PM on Monday. The shower is the debris that Comet Thatcher generates. One can expect between 10 and 20 meteors per hour. The radiant, the area of the sky from which the comets appear to originate, is near the brilliant star Vega in Lyra. Sky watchers are advised to observe before Monday’s Midnight. The 19-day-old Moon rises then and will overwhelm the meteor shower by its bright light. The shower ends before dark on Tuesday.
Midnight sees not only the Moon but Jupiter rising and sharing Ophiuchus. As mentioned, the Moon rises at 11:30 PM on Monday. It appears about 84% lit, blazes with minus 11th magnitude and 31 arc-minutes in size. A slimmer Moon rises in Sagittarius at 12:28 AM on Wednesday, slightly dimmer, smaller and 74% crescent. Jupiter rises about 24 minutes behind the Moon and is one of the few sky objects to resist the Moon’s glare. Jupiter shines with minus 2nd magnitude and appears a large 43 arc-seconds in size. Observers can telescopically witness the Jovian moon Ganymede completing its travel across Jupiter’s face at 2:02 AM, Tuesday. They can also see the Great Red Spot, a giant storm on Jupiter, at 2:57 AM, also Tuesday.
Dawn skies are far more active. Besides the Moon and Jupiter, Saturn occupies Sagittarius, having risen at 1:41 AM. It shines with zero magnitude, appearing a third Jupiter’s size. By Dawn, it is about 20º high in the South.
Neptune rises in Aquarius at 4:26 AM, but is a dim 8th magnitude and a tiny 2 arc-seconds in size in the rapidly brightening sky. Venus, to Neptune’s lower left, rises in Pisces at 5:03 AM, appears about 87% lit and shimmers with minus 4th magnitude. Finally, Mercury brings up the rear in Cetus, appearing about 65% lit and shining at zero magnitude. However, it is only 2º high and requires an unobstructed view of the eastern horizon.
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 Cassini’s 12-year mission wrapped 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 subsequent flyby of Enceladus verified its existence. Molecular hydrogen creates a chemical imbalance that may be conducive to life. Astrobiologists are not claiming life, but only the conditions that may make it possible.