[Bluearrowll]

What's in the sky tonight?
April 20, 2013

-The Moon now shines under Regulus after dark.

-Be on the lookout for the Lyrid Meteor Shower, slated to peak tomorrow.

-Saturn (magnitude +0.1, in Libra) is nearing opposition. It glows low in the east-southeast as twilight fades, well to the lower left of Spica and farther lower right of brighter Arcturus. Saturn rises higher all evening and shines highest in the south around 1 a.m. daylight saving time. It's at opposition on the night of April 27th.

-Carefully note the brightness of Saturn's rings with respect to the globe. Keep watch. The rings brighten for a few days around opposition due to the Seeliger effect: the solid particles of the rings preferentially reflect sunlight back in the direction it came from, more than Saturn's cloudtops do.

-Below is Saturn on April 15th, imaged by Christopher Go in the Philippines using a Celestron 14 scope and a Point Grey Research monochrome Flea3 (ICX618) camera with Chroma Technology LRGB color filters. South is up. "The polar hexagon is prominent on this image," he writes. "Note the white spots on the North North Temperate Zone."

News Posted Today:
April 19, 2013
A Tumbling Apophis: Good News for Earth


Astro Picture of the Day:
April 20, 2013

Source
As far as the eye could see, it was a dark night at Las Campanas Observatory in the southern Atacama desert of Chile. But near local midnight on April 11, this mosaic of 3 minute long exposures revealed a green, unusually intense, atmospheric airglow stretching over thin clouds. Unlike aurorae powered by collisions with energetic charged particles and seen at high latitudes, the airglow is due to chemiluminescence, the production of light in a chemical reaction, and found around the globe. The chemical energy is provided by the Sun's extreme ultraviolet radiation. Like aurorae, the greenish hue of this airglow does originate at altitudes of 100 kilometers or so dominated by emission from excited oxygen atoms. The gegenschein, sunlight reflected by dust along the solar system's ecliptic plane was still visible on that night, a faint bluish cloud just right of picture center. At the far right, the Milky Way seems to rise from the mountain top perch of the Magellan telescopes. Left are the OGLE project and du Pont telescope domes.