Astronomy news for the week starting Friday, June 4, 2000.

The next Skylights will appear as usual, on Friday, June 9. The Moon grows through its waxing crescent phase this week, beginning far in the northwest near the setting Sun and moving both to the east and south against the background stars. It passes first quarter on Thursday, June 8. Be sure to note "earthlight," the illumination of the nighttime side of the Moon by the brilliant Earth. Just as the Moon goes through phases as seen from Earth, so does the Earth as seen from the Moon, but in reverse. When we see the Moon as a waxing crescent, an imaginary "lunarian" would see the Earth in a bright waning gibbous phase. So much light is reflected from the bigger, blue-white Earth that the lunar night -- that outside of the visible crescent -- is brilliantly lit.

Mercury dominates the evening news, while the giant twin planets dominate the morning. At the end of the week, little Mercury is just one day shy of its greatest eastern elongation, when it is 24 degrees to the east of the Sun and nicely visible not far above the northwestern horizon in twilight shortly after sundown. This is one of Mercury's best appearances of the year, and a great time to see it. IN contrast, giant Jupiter and Saturn are seen to the east in morning twilight. Having passed their Grand Conjunction last week, closer and speedier Jupiter now begins to pull away to the east of Saturn. The juxtaposition of the two planets makes the viewing of planetary motion very obvious. Both, however, move slowly enough that they will remain in good company with each other all year as they move gradually toward the evening sky late next summer.

Unlike the Big Dipper (the main figure of Ursa Major, the Greater Bear), the Little Dipper gets little respect. Now climbing ever- higher in the northern sky, only three of its stars are visible from town, Polaris (at the end of the handle) plus Kochab and Pherkad, which make the front of the bowl. The others are so faint that they can be seen only from a dark site. Polaris, the "star of the sailor," is only 3/4 a degree from the sky's northern rotation pole, and its elevation above the horizon in degrees is very nearly equal to the observer's latitude. From polar regions, Polaris is high in the sky, while from the northern tropics it is low. Below the equator, it cannot be seen at all. If you keep the star at a constant elevation while travelling, you track close to a parallel of latitude, allowing simple navigation across the ocean. Even in an age of satellite navigation, the stars are always there to advise. Indeed, satellite navigational systems must still depend on observations of the sky in order to know the position of the Earth in its rotation.
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