August 13, 1998
3. After a long summer with no bright evening planets, the late evening skies are welcoming the return of Jupiter and Saturn. Jupiter is poised on the boundary between zodiac constellations Pisces and Aquarius, while Saturn hugs the southern boundary of Aries. While the exact boundaries of these constellations have been arbitrarily (and recently) fixed, their status as zodiac constellations is not; a zodiac constellation is any constellation through which the paths of the sun and the planets pass.
5. The semi-annual eclipse season continues and tomorrow morning's full moon (at 6:21 a.m.) will coincide with a penumbral eclipse. Unfortunately for Midwestern astronomers, this eclipse will culminate and end after the moon sets. Viewers in the western United States will have better timing, but it is still only a penumbral eclipse, with the moon passing through Earth's partial shadow.
6. Here's your chance to make up for this morning's disappointing eclipse. A beautiful conjunction of the full moon and Jupiter is scheduled for prime time this evening. Jupiter is nearly at opposition, when it will be 180 degrees away from the sun's direction. The moon accomplishes this trick every month, as it did earlier today.
8. Coastal dwellers know that full and new moons always mean extreme tides because the forces of the sun and moon are acting in parallel directions. These tides, known as spring tides, are accentuated even further when the moon is closer than average, such as today when the moon is at minimum distance from the Earth soon after full moon.
9. Saturn is making its way slowly into the evening sky. The moon, just a few days past full, slides two degrees south of Saturn tonight. Saturn is on the Aries-Pisces constellation border, while the moon is actually in the constellation Cetus to the south.
11. Aldebaran, one of the stars of the zodiac constellation Taurus, is close to the moon this evening. The moon is at last quarter phase at 8:58 p.m., so you'll need to wait until after midnight to see this close encounter above the eastern horizon. Aldebaran is a yellow giant, larger and more luminous than our sun.
13. Astronomical terminology refers to a number of great circles in the sky. One, the celestial equator, is an imagined extension of Earth's equator. Another important great circle is the ecliptic; it shows the projection of the plane of the solar system on our sky. This is the path followed by the sun, moon, and major and minor planets. In the late evenings this month, the ecliptic is anchored by Saturn in the east, rising to about 40 degrees above the southeastern horizon near Jupiter and on past Neptune, Uranus and Pluto to the western horizon.
15. Jovian opposition should occur at 10:00 this evening, which means that Jupiter is above the horizon for as long as the sun is not, because their positions are opposite in the sky. This also puts Jupiter at its minimum distance from Earth, about 480 million miles away.
16. The moon continually works its way eastward, covering its own diameter each hour. From one night to the next, the moon will appear 13 degrees further to the east, about the width of your fist at arm's length. Mars has been inching eastward at its much slower pace, covering about ten degrees in the past three weeks. Look for these two neighbors in the east after 5:00 a.m. tomorrow morning.
17. Normally, the bright star Regulus dots the question-mark shape of the constellation Leo. Tomorrow morning, the waning moon will be near enough to take over the job. How close do they seem to you? The moon provides a handy estimate for small angles, with its diameter equalling about half a degree of arc.
20. At one minute past noon, the moon will be at new moon phase. We can't see the moon because its sunlit side is facing away from us, but its position is a little above and left of the noonday sun.
21. Many traditional calendars mark months by the arrival of new moon phase; some calendars, including the one in use in Europe until 1582, start the new year with one of these new moons, usually the one closest to the spring or autumnal equinox. This marks the first full day of the new year as reckoned by the Jewish calendar, the feast of Rosh Hashanah.
23. There's no connection between the times of our moon's phases and the moments critical to our seasons; the moment of the autumnal equinox happens to be 12:37 this afternoon, a little more than 48 hours after the new moon phase. At this moment, the sun crosses the celestial equator for the second time this year, this time heading south.
25. The summer triangle is still easy to spot in the evening sky, with the bright star Vega near the point directly overhead - the zenith. Between Vega and the North Star lies Draco, a large, snakelike constellation, whose name means "dragon." None of Draco's stars is exceptionally bright, but one of them, Thuban, has an interesting history. This star could be seen, by night or even by day, from the bottom of a central passage in the Great Pyramid of Cheops. Astronomers since John Herschel have wondered if Thuban used to be brighter than it is now.
28. The moon is at first quarter phase at 4:11 this afternoon, setting the stage for a beautiful moonlit evening. If you have a small telescope or binoculars, this is a wonderful time to look at the moon because the deep shadows near the twilight regions of the moon make its crater and mountains easier to see than they would be at full moon.