There's a comet on the horizon that has been approaching our solar system for millions of years. Named C2011 L4 (PANSTARRS), it was discovered by a team at the Panoramic Survey Telescope and Rapid Response System in Hawaii. This facility is dedicated to searching the cosmos for asteroids and comets that are moving in the direction of Earth.

Asteroids are rocky celestial objects that are smaller than planets and orbit the sun in profusion, mostly composing the asteroid belt which is located between the orbits of Mars and Jupiter. Comets are icy bodies that revolve around the sun far beyond the planets of the inner solar system in the Kuiper belt or, more distant, in a band named the Oort cloud.

A disturbance sets the comet on an elliptical orbit headed for our sun.

PANSTARRS was 759 million miles from the sun when discovered. (Earth is 94 million miles from the sun.) When a comet nears the sun, frozen gases volatilize, creating a head of gas and dust from which a blue gas tail and a yellow dust tail stream. PANSTARRS and the predicted November comet, C2012 S1(ISON), originate from the Oort cloud.

PANSTARRS has thrilled viewers in the Southern Hemisphere and is predicted to come into view here in the Northern Hemisphere perhaps as early as twilight tonight. At first, binoculars may be necessary in order to spot C2011 L4. Look close above the western horizon half an hour after sunset every evening.

Best naked-eye sightings are expected from Sunday to Wednesday during the hour after sunset. On Tuesday, the comet will appear to the left of the crescent moon.

Daylight Savings Time (DST) begins Sunday at 2 a.m. in the United States. Many other countries adopt DST on the March 31.

To contact Judy Isacoff go to www.naturesturn.org