Comet C/2011 L4 (PANSTARRS) Brightens Nicely for Saint Patrick's Day


A new comet, called C/2011 L4 (PANSTARRS), is expected to become visible for a few weeks from approximately 10th March in the western sky after sunset. The comet has come from the Oort cloud, which comprises a vast swarm of comets surrounding the solar system and extending more than halfway to the nearest star, that is more than two light years from the Sun. With an orbital period of many millions of years, it is thought that this is probably the comet’s first passage through the inner solar system since it was formed along with the Sun and planets some 4.5 billion years ago.

According to current predictions the comet may reach naked-eye visibility for northern-hemisphere observers during the second half of March. It will first appear low in the West after sunset, lying not far from the thin crescent Moon in the evening twilight on the 12th and 13th March. Later, as it moves northwards and farther from the Sun with each passing day, it will become more easily seen in the dark evening sky. After sunset on the night of St. Patrick’s Day it will lie close to the setting diamond-shaped asterism known as the Square of Pegasus, part of which will be visible (assuming clear skies) low in the West-North-West. At this time the comet will be approximately 175 million kilometres from Earth.

The comet 2011 L4 (PANSTARRS) was discovered using the 1.8-metre Pan-STARRS I (Panoramic Survey Telescope and Rapid Response System) Ritchey-Chretien telescope on Haleakala, Hawaii, USA on 6th June 2011. Several pre-discovery images were soon found, which enabled its orbit to be quickly confirmed. These data showed that it would reach perihelion, the closest point of its orbit to the Sun, on 10th March 2013 at a heliocentric distance of around 45 million kilometres, which is similar to the orbital distance of the closest planet to the Sun, Mercury.

Comets are usually very difficult objects to spot, unless they happen to be exceptionally bright. In order to see Comet 2011 L4 (PANSTARRS), you are advised to choose an evening when the sky is clear nearly all the way down to the horizon, and to travel to a dark-sky location far from city or town lights.

Bring binoculars if you have them, and scan the sky in the expected direction of the comet until you find the small misty patch of light that is the comet. Comet PANSTARRS should be easily visible with binoculars, displaying a bright cometary “head” or coma, and a fan-shaped tail or tails pointing away from the general direction of the Sun, below the horizon. Comets usually show two kinds of tail: a straight, highly structured gas tail, produced by the sublimation of ices from the comet’s “dirty snowball” nucleus, and blown away from the Sun by the solar wind; and a curved, more diffuse dust tail, produced by small dust particles ejected from the nucleus and blown outwards by the Sun’s radiation pressure.

A bright comet, with its head and two tails, is an impressive, but rare celestial sight. It is worth the effort to get a good view of such a visitor to the Earth’s near-space environment. If you miss PANSTARRS, then the next bright comet expected to become visible with the naked eye in our evening sky will be Comet 2012 S1 (ISON), a sun-grazing “Christmas” comet expected to be visible from around the end of November to the end of December later this year.

FOR FURTHER INFORMATION PLEASE CONTACT: John McFarland at the Armagh Observatory, College Hill, Armagh, BT61 9DG. Tel.: 028-3752-2928; FAX: 028-3752-7174; jmfat

See also:

Image of Comet C/2011 L4 PANSTARRS taken in August 2012

Viewing Comet C/2011 L4 PANSTARRS on St. Patrick's Day

Royal Astronomical Society Press Release

Where to look for Comet C/2011 L4 PANSTARRS on 17th March at 7.00 pm
Image created by Stellarium software
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Where to look for Comet C/2011 L4 PANSTARRS on 17th March at 7.00 pm
Image created by Skychart software
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Last Revised: 2013 March 11th