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The Sky This Week, 2012 March 13 - 20

Cozy planets in the west at dusk, and spring officially begins!

Mars, imaged 2012 March 11, 04:19 UT
Note north polar cap on bottom limb, blue CO2 clouds
over Syrtis Major near right limb, and white H2O clouds
over the Elysium volcano field below left of center.

The Moon wanes in the morning sky this week, coursing her way through the southern reaches of the Ecliptic as she glides through the rising summer constellations. Last Quarter occurs on the 14th at 9:25 pm Eastern Daylight Time. Look for Luna just over seven degrees northeast of the ruddy star Antares in the pre-dawn hours of the 14th.

The vernal equinox occurs on the 20th at 1:14 am EDT. At this moment the center of the Sun's disc reaches an Ecliptic longitude of zero degrees. For all practical purposes this is also the time when the Sun crosses the celestial equator from south to north. Residents of Singapore will see Old Sol nearly directly overhead.

This week starts the March campaign for the Globe At Night "Citizen Science" program. The object of this exercise is to document the effects of light pollution on our awareness of the nighttime sky. By engaging people to count the number of stars that they can see within the boundaries of familiar constellations we can determine locations that are conducive to astronomy education near cities and towns. The campaign hopes to record over 15,000 observations from around the world during its four monthly observing periods. This month you can choose between two constellations to make your observations. Orion may be found high in the southwest as evening twilight ends, while Leo crosses the meridian at around midnight. Orion is the better choice for urban locations due to the number of bright stars that form his familiar outline. Those of you living in darker areas may wish to count stars in Leo. This constellation should be easy to find since it is currently hosting the bright planet Mars.

The early evening sky is dominated by the beautiful pairing of Venus and Jupiter that will be playing out in the western sky during twilight and the first dark hours. Venus has journeyed almost halfway around the sky since she first became visible in the evening sky last fall. At that time Jupiter was just reaching opposition, but Venus has steadily closed the gap and passes the giant planet as the week opens. They are closest together, just three degrees apart, on the evening of the 13th. For the next two nights Venus lingers near Jupiter, but by the end of the week there’s nearly seven degrees of open sky between them. It is an interesting time to compare the two worlds through the small telescope. Venus resembles a dazzling white, nearly featureless gibbous Moon, while Jupiter has a distinct creamy color crossed by darker horizontal bands. The telescope should also easily reveal Jupiter’s four bright Galilean moons. On the 13th all four will be to the east of the planet itself.

Mars ascends in the eastern sky during the waning hours of evening twilight. The red planet is the brightest object you’ll see in the eastern sky, and his distinct hue sets him apart from the nearby star Regulus, lead star of Leo, the Lion. Mars is just past opposition, in the middle of the prime period to observe him through the telescope. Even though he will remain visible in the evening sky through the end of the year, the time when he is close enough to us to reveal details on his distant disc will only last until early May. A telescope of modest aperture and a night of steady air should still show you a number of his interesting features, however. His north polar ice cap is visible as a small white dot on the planet’s limb, tipped advantageously in our direction as martian boreal summer approaches. White water-vapor clouds may be seen forming around the summits of the planet’s huge volcanoes, often resembling the appearance of the polar cap. Thinner blue-tinted clouds grace the east and west limbs where carbon dioxide freezes close to the surface. Very careful observation can pick out these delicate features, but it takes time and a patient eye to fully appreciate them.

Saturn’s entry into the evening sky has been pushed back an hour by the change to daylight time, so you now have to wait until around 10:00 pm to see him break through the haze of the southeastern horizon. The ringed planet comes up in the company of the bright blue star Spica, which offers a distinct contrast to the planet’s decidedly yellow cast. By midnight Saturn will be high enough for a glimpse through the telescope.