Skywatch Line for Monday and Tuesday, March 21st and 22nd, 2016

This is the Skywatch Line for Monday and Tuesday, March 21st and 22nd.

The Sun sets at 7:09 PM; night falls at 8:45. Dawn breaks at 5:19 AM and ends with the Sun rising at 6:43.

The twilight sky contains Jupiter and a nearly “Full” Moon.

The Moon rises just before sunset and remains up the rest of the night. Monday night finds the Moon only two degrees from Jupiter. Both sit by the hind leg of Leo, the Lion. Tuesday sees the Moon migrated to Virgo. Although the Moon turns officially “Full” on Wednesday morning, the Moon is for all practical purposes “Full” all Tuesday night. The Moon sets at sunrise Tuesday morning, and at 7 AM on Wednesday.

Jupiter, as mentioned, lies by Leo’s hind leg. Jupiter, the Moon and the star Sigma Leonis form a neat triangle, visible in binoculars. As mentioned last week, this is the “season” for “double shadow transits.” Monday night, at 11:43 PM, the Jovian moon Europa begins to cross Jupiter’s face with its shadow trailing. Another Jovian satellite, Io, begins its transit at 11:56 PM, followed by its shadow at 12:15 AM on Tuesday. The two moons and their shadows cross Jupiter until they exit by 3:11 AM, Tuesday. Several more double shadow transits occur this month.

Mars rises in Scorpius at 12:24 AM. The Red Planet daily becomes brighter and larger in our telescopes. Its distinctive color makes finding it in the Scorpion’s head easy. Last week, the Mars Reconnaissance Orbiter (MRO) celebrated its 10th year photographing the Martian terrain. Over the decade, the MRO changed both scientific and popular views of Mars. Once thought dead and lifeless, the MRO demonstrated that Mars has varied surface features and good evidence for at least some subsurface water. It also serves as a relay for signals to Earth from the Opportunity and Curiosity rovers.

Saturn rises about an hour after Mars and is located in the dim constellation Ophiuchus.  Saturn is slightly dimmer than Mars, which is eleven degrees away. Can you tell the difference? Saturn is best observed about 5 AM, when it is highest before Dawn begins. Its famous rings are still tilted to maximum for our enjoyment.

Since Jupiter and Saturn are visible simultaneously, comparisons are in order. Both are gas giants – planets composed mostly of gas. Jupiter is larger; Saturn is about a third of Jupiter’s mass. In telescopes, Jupiter’s colored bands signify very active weather systems; one storm, the Great Red Spot, has been continuously observed for centuries. Saturn’s weather appears more subdued, with occasional faint features. Saturn’s   ring system is easily visible from Earth; Jupiter’s rings are observable only from space-borne telescopes. Both planets’ 120 moons account for most of the Solar System total. Four of Jupiter’s moons appear in binoculars, while Saturn’s satellites can only be spotted through a telescope. Jupiter’s moon Io is the most volcanically active moon in the Solar System; while Europa, Ganymede and Callisto may conceal oceans beneath their icy surfaces. Saturn’s moons Enceladus and Titan are geologically active, spurting ice fountains. Titan is the only moon to have an atmosphere; its atmosphere contains cold methane, rather than oxygen. Titan also has vast lakes of liquid methane on its surface.