Observing Uranus, the ice giant

The planet Uranus reaches opposition Sept. 29, when it lies opposite the sun in its orbit and remains visible from sunset to sunrise on Earth.

This configuration also brings the planet closest to us, so it is brighter in the sky and appears larger through a telescope than at any other time in 2012.

One day after opposition, the full moon passes 5 degrees above the planet. One degree as applied here is the width of your little finger at arm's length held up to the sky. (Your first three fingers held together at arm's length with the back of your hand facing you span 5 degrees of sky, and your fist in the same position covers 10 degrees.)

Uranus peaks this month at magnitude 5.7, making it just bright enough to see with naked eyes under a sky with little to no light pollution, but binoculars or a telescope easily reveal the planet regardless of the presence of the moderate light pollution found throughout much of New London County. A view through a telescope reveals Uranus' planetary disk, which displays a distinct turquoise hue.

You can find the planet on the border between the constellations Pisces and Cetus, low in the east-southeastern sky, just below the Great Square of Pegasus. High in the eastern sky about an hour after sunset, you can find four stars about equal distance from one another comprising the four corners of a large rectangle. This is the Great Square. The bottom left corner/star is directly between the planet Uranus and the Great Square's top left corner/star. If in doubt about where to look, consult a star map online.

The planet is named after the ancient Greek god of the sky, Uranus, and was the first planet discovered with a telescope. Although it is visible to the naked eye, it wasn't originally recognized as a planet by observers centuries ago because of its dimness and slow orbit. British astronomer Sir William Herschel announced its discovery on March 13, 1781.

Uranus's atmosphere contains more "ices" such as water, ammonia and methane, along with traces of hydrocarbons. It has a complex, layered cloud structure with water likely forming the lowest clouds, and methane the uppermost layer of clouds.

Like the other giant planets, Uranus has a ring system and several moons, but has its own thing going on, because its axis of rotation is tilted sideways. Its poles are where most other planets have their equators.


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Sept. 16 - New moon. Best time of the month to stargaze.

Sept. 22 - September equinox. The sun shines directly on the equator and day and night last the same amount of time throughout the world. This marks the first day of fall in the northern hemisphere and the first day of spring in the southern.

Sept. 29 - Uranus at opposition.

Sept. 30 - Full moon. Worst time of the month to stargaze.


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