The comet dubbed C/2011 L4 Pan-STARRS was discovered in June 2011 by the Pan-STARRS telescope in Hawaii when it was hundreds of millions of miles from Earth.
As the comet brightens with the passage of day, next Tuesday and Wednesday could be the best viewing opportunity, astronomers said, and sky watchers should look in a western direction after sunset as the comet will share the sky with a thin crescent moon.
"There is a catch to viewing Comet Pan-STARRS," Amy Mainzer, of NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a statement Thursday. "This one is not that bright and is going to be low on the western horizon, so you'll need a relatively unobstructed view to the southwest at twilight and, of course, some good comet-watching weather."
Scientists said they believe the comet is non-periodic, meaning this could be the first time it has passed through the inner solar system.
The head of the comet is estimated to be 12-18 miles in diameter but the gas and dust streaming from the comet as it gets close to the sun could stretch for more 600,000 miles.