New Delhi (PTI): A penumbral lunar eclipse will occur on Tuesday, the second of four such phenomena this year, but sky watchers in India will be a disappointed lot as it will not be visible in the country.

The July 7 penumbral lunar eclipse will occur as the moon rises over Australia and sets in western North and South America in the early predawn hours, Science Popularisation Association of Communicators and Educators (SPACE) Director C.B. Devgun told PTI.

The last penumbral lunar eclipse this year took place on February 9 and two more will occur after the July 7 event on August 6 and December 31.

During Tuesday's eclipse, the moon will only enter the southernmost tip of the penumbral shadow of the earth and thus will be very difficult to observe visually, Mr. Devgun said.

The moon will be located in the constellation of Sagittarius when the eclipse occurs. Thus, the eclipse will be visible in North America west of the Great Lakes, including Hawaii, and many parts of Alaska (Harrington, 1997). The moon will also be high in the sky over New Zealand and eastern Australia during the eclipse, he said.

The eclipse is an event of Saros series 110. The previous such phenomenon occurred on June 27, 1991. The next is on July 18, 2027, which will end the series.

According to NASA, the phenomenon is only of academic interest since the magnitude of the eclipse is just 0.156 at its maximum. Therefore, there is only a little chance for seeing any of the eclipse's dimming effect. It will, however, last for two hours.

The first penumbral contact is predicted to occur at 8.37.51 am Universal Time (2.07.51 pm IST). The ecliptic conjunction will occur at 9.21.25 am UT and the point of greatest eclipse occurs at about 9.38.37 am UT. It is predicted to end at about 10.39.23 am UT.

A lunar eclipse occurs when the earth is in a direct line between the sun and the moon and the shadow of the earth falls on the moon, Mr. Devgun said, adding that a penumbral lunar eclipse occurs when the moon passes through penumbra, the lighter part of the earth's shadow.

The lighter part of the earth's shadow is called the penumbra and the totally dark part is called the umbra.