CHENNAI: This New Year, sky-watchers will witness a partial lunar eclipse.

As we step into 2010, the moon’s southern tip will move into earth’s shadow. The moon will pass into the penumbral shadow of the earth between 0021 hours IST and 0124 hours IST. The result is a slight reduction in the brightness of the moon along the area that passes through the shadow of the earth.

Lunar eclipses occur when the moon moves into the shadow of the earth and takes place only on full moon days when the moon comes diametrically opposite the position of the sun as viewed from the earth.

“The partial lunar eclipse will be visible when the moon starts passing the umbra [the darkest part of shadow of the earth cast by sunlight],” explained P. Iyamperumal, Executive Director, Tamil Nadu Science and Technology.

The shadow of the earth cast by the sun has two components. One is the dark shadow or umbra and the other lighter shadow is the penumbra.

Blue-moon eclipse

It is a blue-moon eclipse and a rare one, he said. A blue moon is the second full moon in a calendar month.

For a blue moon to occur, the first of the full moons generally appears during the beginning of the month and the second would fall within the same month.

This month has two full moons. The first one was on December 2 and the second falls on the night of December 31.

As there are roughly 29.5 days between two full moons, it is rare for the two to fit in a month. On an average, there will be one blue moon every 2.5 years.

On January 15, sky-watchers will also be able to view a partial annual solar eclipse that visits the same place once in 108 years.

It will be seen mainly from parts of Tamil Nadu and Kerala. Globally, the annular phase will run between 1044 hours and 1429 hours IST.