Astronomy news for the week starting Friday, June 18, 1999.

The Moon grows toward first quarter the beginning of the week, the phase reached on Sunday the 20th just about the time of moonrise in North America, the Moon midway between Leo and Virgo. The night of Tuesday, the 22nd, the Moon will be found several degrees to the northeast of Mars.

The red planet is now moving to the east, the motion easily noted relative to the bright nearby star Spica. In the west, Venus, having passed elongation, is now slowly being overtaken by the Sun, though it is still moving easterly relative to the stars and still brightening.

The week belongs not to the Moon or planets, however, but to the Earth and Sun, as on Monday the 21st at 2:49 PM Central Daylight Time, the Sun will pass the Summer Solstice in Gemini, beginning northern summer. At that moment, the Sun will reach its maximum angle of 23 1/2 degrees (23 degrees 26 minutes 21 seconds) north of the celestial equator, and the Earth's axis will be tilted as much as possible toward the Sun. The Sun will rise for us as far north of east as possible and set as far north of west, and the duration of daylight will be at a maximum, though earliest sunrise and latest sunset do not quite coincide in part because of the slight eccentricity of the Earth's orbit. On that special day Sun will pass overhead at the Tropic of Cancer (at 23 1/2 degrees north latitude) and will be circumpolar (yielding a midnight Sun) as far south as possible, technically at the Arctic Circle, but actually a bit to the south of it because of the extended solar diameter and lofting by refraction in the Earth's atmosphere. From that point on the Sun will move to the south until it passes the Winter Solstice in Sagittarius on December 22.

With the Sun at the Summer Solstice, the Winter Solstice and Sagittarius (now opposite the Sun) will pass to the south at local midnight (1 AM daylight time). Sagittarius contains the center of the Galaxy and the brightest part of the Milky Way, which unfortunately for most northerners is so far south that the Earth's atmosphere gets in the way, dimming its grandeur, the sight best seen from the southern hemisphere. At the center of the Galaxy, coincidentally pointed to by Sagittarius's arrow, lies a brilliant point called "Sagittarius A-star." Visible with radio telescopes, but obscured in the optical by interstellar dust, Sagittarius A- star is produced by hot matter that orbits a black hole over a million times as massive as the Sun.
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