By Dr David Whitehouse
BBC News Online science editor
There is a "peak of eternal light" on the Moon - a region from which the Sun never sets, according to astronomers.
There are places on the Moon where the Sun always shines
A team led by Dr Ben Bussey of Johns Hopkins University in the US looked at images of the Moon's poles taken by the 1994 Clementine lunar spacecraft.
The researchers produced a movie to show how illumination over the regions changed during a whole month.
They found four areas on the rim of Peary, a 73k-wide crater, that appear to stay light for the entire Moon day.
'Peak of eternal light'
The Moon's rotational axis is tilted about 1.5 degrees relative to the plane of the Earth's orbit around the Sun.
As a consequence, the Moon has small but detectable seasons, and dramatic lighting conditions at its poles.
The low axial tilt means there are crater floors and the poleward-facing sides of crater walls that never see the Sun at all. But are there mountains or the tops of crater rims, astronomers have long wondered, that always protrude into the sunlight?
It had been thought that nowhere on the Moon was there a so-called peak of eternal light - although some research had identified a few north polar regions that stayed lit for 95% of the time.
When one of these regions was dark another was illuminated, but it seemed there was no one spot that was lit permanently.
The Johns Hopkins-led analysis suggests this conclusion may be premature.
Unlike the lunar south pole, which has no mountains of eternal light, the north pole has peaks that are constantly illuminated - at least during the lunar summer.
Speaking at the Lunar and Planetary Science Conference in Houston, Texas, Ben Bussey warned the continuous illumination could be a seasonal effect that disappears in winter (for which there is no data).
Finding a permanently illuminated peak makes the lunar north pole an enticing region for exploration and for the site of the first Moonbase.
A location near the north pole that was constantly lit would have a relatively benign environment. Daily temperature changes would be only about 20 degrees Celsius, making lunar base operations easier than at the lunar equator where the temperature can change by 250 degrees daily.
Bussey's team has also identified extensive regions of permanent shadow. These regions may harbour ground ice.
A location that was constantly lit could be the best place for a moonbase
Trapped water-ice in permanently shadowed areas at the lunar poles is consistent with data from the Clementine and Lunar Prospector missions and radar measurements made with the Arecibo radio telescope in Puerto Rico.
Astronomers know that concentrations of hydrogen are associated with permanently shadowed craters. However, they do not know the total concentration of hydrogen or whether or not the hydrogen is in water-ice or some other form.