Asteroid Vesta moves into Virgo in April

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Moon names and legends

The full moon of April is called the Grass Moon, Egg Moon or Pink Moon. The last name comes from the herb moss pink or wild ground phlox that, in colonial times, was one of the widespread flowers blooming in the spring. Some coastal American Indian tribes called it the Fish Moon because salmon swam upstream to spawn. One source says the Anishinabe call it the Maple Sugar Moon without further comment.

Our celestial neighborhood

During the coming weeks, the constellation of Virgo (see star chart) will play host to the naked-eye asteroid Vesta. This may not seem like a big deal but of the tens of thousands of asteroids in the solar system, the main asteroid belt of which lies in the region between Mars and Jupiter, Vesta is the only one that consistently can be seen readily with the naked eye.

Vesta was discovered in 1807 by Wilhelm Olbers and is among the largest of the asteroids, with a diameter of nearly 350 miles. It is neither the largest nor closest of the asteroids but it does have one advantage that makes it so bright – its albedo, or ability to reflect sunlight from its surface. Most asteroids reflect around 10 percent of the sunlight reaching their surface, a few up to 22 percent, but Vesta’s surface geology reflects 42 percent, giving it the appearance of a large pink grapefruit. Certainly Vesta will be clearly visible with small binoculars, but you might need a finder’s chart such as the one in the April issue of Astronomy, which lists its position through April 30.

Focus on the planets

Mercury opens the month very low on the western horizon about an hour after sunset. By midmonth, Mercury will have climbed well up on the horizon at twilight, affording sky watchers the best view of the innermost planet during 2003.

Venus is low in the east at twilight’s dawning as April opens. Later in the month, it rises only an hour before the sun and is becoming increasingly difficult to see as it hovers just above the horizon.

Mars rises around 2 a.m. and is a prominent red-orange presence on the southeast horizon just before dawn. Mars continues to grow in both size and magnitude during April as it heads for its most striking appearance in thousands of years.

Jupiter is situated high in the south among the stars of Cancer the Crab at sunset, where it outshines all other planets and stars in the night skies. April brings a variety of interactions between Jupiter’s major moons. On the 19th, for example, viewers will see Ganymede eclipse its sister moon Io, with the action taking place in front of the giant planet.

Saturn lies well up on the western horizon about an hour after sunset and sets after midnight. Saturn is at a tilt, offering the most optimal viewing of its ring system since 1973. On the night of April 10, Saturn will pass directly north of the Crab Nebula, with the pair being close enough to fit into a single field of view at medium magnification.

Uranus and Neptune rise after midnight and are low in the south at dawn, with Uranus in Aquarius and Neptune in Capricornus respectively. The best chance of seeing these distant planets will come in May, when Mars passes just to their north.

Pluto rises after midnight and serious viewers armed with a finder’s chart and at least an 8-inch telescope will have their best chance to view it just before dawn.

April events

1 Sunrise, 5:17 a.m.; sunset, 6:02 p.m. New moon, 2:19 p.m.

2 Look very low to the west about an hour after sunset for a very thin crescent moon, with Mercury to its right.

4 The moon is at apogee, or most distant point from Earth, today.

5 Orange Aldebaran is to the upper left of the moon tonight. Saturn is above Aldebaran, with Orion to the left of all three.

6 This is the first Sunday in April. Put your clocks ahead by one hour. Mercury is the only bright point of light to be seen very low in the northwest for the next two weeks.

9 Moon in first quarter, 7:40 p.m.

10 Look for the moon and Jupiter together tonight.

16 Full moon, 3:36 p.m.

17 The moon is at perigee, or closest approach to Earth, today. This fact, along with the recent full moon, could lead to abnormally high tides.

19 The sun enters Aries on the ecliptic.

20 Easter. Although there is now a complicated formula for determining the date of Easter, the old “rule of thumb” that it is the first Sunday after the first full moon after the spring equinox still holds true.

23 Moon in last quarter, 8:19 a.m. Look for Mars directly above the moon about an hour before dawn.

28 Look for Venus and the thin crescent moon just above the eastern horizon about an hour before sunrise.

30 Sunrise, 5:27 a.m.; sunset, 7:39 p.m. This is also May Eve, that some sources list as a cross-quarter day, although May 1 more commonly is given.