Comet Lulin, a backward-flying comet that's "zipping by Earth this month, can be seen during the next three nights passing by our planet. As it makes its way around the Sun, 800 gallons of water will evaporate from the comet every second, making it visible also for the naked eye, in darkened places, or it "should be a fairly easy object [to see using] modest amateur telescopes or even binoculars," Don Yeomans, a comet expert at NASA's Jet Propulsion Laboratory in Pasadena, California, said.

Glowing green, it will come within 38million miles of Earth, the closest it has ever been, and about the same distance away as Mars.

As Lulin is exposed to the sun's heat for the first time, those ices are vaporizing—activity that could cause the comet to brighten rapidly or even break apart. Even now the comet is spewing cyanogen and diatomic carbon, both gases that glow green in sunlight out in the vacuum of space.

The stellar traveller is very active, shedding nearly 800 gallons of water each second on its journey around the Sun. That's enough liquid to fill an Olympic-sized swimming pool in less than 15 minutes. Jets from the nucleus throw out cyanogen, a poisonous gas found in many comets, and diatomic carbon, which glow green when lit by sunlight.

Nasa said: “Dark country skies will be required. But no one can say for sure. This appears to be Lulin's first visit to the inner solar system and its first exposure to intense sunlight. Surprises are possible.”