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Archive for Sunday, May 2, 1999

MAY STAR LOG

May 2, 1999

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Special to the Journal-World

Here's a look at significant stellar events this month.

Today: Uncontested dominance of the evening sky -- that's what all the planets must cede to Venus this month.

Mars was at opposition just a few weeks ago, so it is visible through the night. Due to Mars' noncircular orbit, Saturday marked the point when Mars was closest to Earth. If you have a telescope with which to view Mars, it is 16.2 seconds of arc across, 100 times smaller than the full moon but as large as the Martian disk has been since 1990. Mars will be even closer and (larger in apparent size) at its next oppositions in 2001 and 2003.

Wednesday: This day marks the 38th anniversary of a short but historic flight for the United States' first astronaut, Alan Shepard, aboard the spacecraft Freedom. Shepard's flight never achieved a true Earth orbit and lasted only 16 minutes, but it provided enough encouragement to President John Kennedy that later that month he set the national goal of reaching the moon with manned flight by the end of the 1960s.

Friday: In some parts of the world, successive occultations of Neptune and Uranus are scheduled for Friday and Saturday. These planets are rather faint, but lucky observers in other time zones will see the rare sight of the moon crossing in front of these distant worlds. Neptune, of course, was not discovered until 1846, yet historians have found evidence in the observing records of French scientist Joseph Lalande that he observed Neptune twice, on May 8 and May 10 of 1795. Lalande's methods were more precise than his star charts, and it was not possible for him to distinguish Neptune from countless background stars.

Saturday: The moon is at last quarter phase at 12:28 p.m., not long after moonset for mid-American longitudes. When the moon rises again after midnight May 9, it will be pulling away from Neptune and Uranus, crossing the border between the zodiac constellations Capricorn and Aquarius.

May 13: The eastern horizon is pretty busy this morning, with Jupiter and the moon separated by a few degrees, and Mercury and Saturn completing a nice conjunction, but sadly too close to the nearly rising sun. Jupiter is probably a safer object for your telescope, but be sure to wrap it up by a few minutes after 5 a.m. to avoid any chance scan near the rising sun.

May 15: The moon reaches new phase at 7:05 a.m., beginning a new lunar month. Astronomers keep track of lunations or lunar months, as they catalog and count many other things. The moon is also near its point of closest approach to Earth, so the typically strong spring tides associated with new or full phase should be exceptionally strong today.

May 17: Although we are justified in thinking of the solar system as flat, the orbits of the planets are not perfectly confined to the solar system's plane. It is extremely rare, for example, for Venus to pass so precisely in front of Mercury that the smaller, more distant Mercury is eclipsed or occulted. On this date in 1787, John Bevis of the Greenwich Observatory in England, observed the only such recorded occultation.

May 21: First quarter lunar phase clocks in just 34 minutes after midnight this night, near the time of its setting for mid-American longitudes. Here's another reason to check on the moon well before midnight this evening: an occultation by the moon of the brightest star of Leo, lovely Regulus, is slated for 10 p.m. Look for the moon in this question-mark-shaped constellation above the southwest horizon.

May 26: The moon and Mars are livening up the field of the constellation Virgo on this evening. Without the competition from the moon and Mars, Virgo's brightest star, Spica, would look impressive enough. Many young astronomers learn to find this lovely star by starting (as we all do!) at the Big Dipper -- follow the arc of the dipper handle to Arcturus, then continue arching towards Spica.

May 29: The moon will be full overnight, at 1:40 a.m. tomorrow. The moon played a large role in a historic event 80 years ago today, when a solar eclipse observed from the island Principe provided the first experimental confirmation that gravity (in this case, the sun's) bends light from more distant stars. The moon conveniently blocked the light of the sun so that this amazing measurement could be made.

May 30: Over the next few evenings, Venus forms one apex of a charming triangle, along with the bright twins of Gemini, the stars Castor and Pollux. Pollux is the brighter of the two stars and is the middle light of this trio. Venus is the one on the left as you look west in the evening, and definitely the brightest of the bunch. By the way, swearing by the twin stars used to be a serious matter; the expression "by jiminy" reminds us that the name for the twin constellation, Gemini, has been around for a long time.

May 31: It's much easier to tell you where Pluto is than to see it. Pluto is opposite the sun's position this day, stalled in the constellation Ophiuchus. In fact, Pluto is less than 1/2 degree to the north of a bright star, zeta Ophiuchi. Pluto is so faint that it's beyond the reach of any telescope smaller than 8 or 10 inches in diameter, but it's sort of nice to know that it's there, above the southern horizon.

-- This list of astronomical events is made possible by the Astronomy Associates of Lawrence. Readers may send questions about astronomical phenomena to AAlice, in care of the department of physics and astronomy at Kansas University. For a free star chart, enclose a stamped, self-addressed envelope.

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