SkyWatch

April 2003

By Steve Stefanik

Good morning! Did you remember to set you clocks ahead 1 hour? We’re now on daylight-savings time.

As April opens the planet Mercury can be seen low in the west about half an hour after the sun sets. Ordinarily this speedy little planet is difficult to see because it doesn’t get very bright or wander very far from the sun. This will be Mercury’s month to "shine". Mercury reached greatest illumination on April 4^th, shining at –1.1 magnitude. By April 16^th , it will dim to +0.2 magnitude but it will reach greatest elongation (20 degrees in angular separation) from the sun and highest in altitude (19 degrees above the horizon). A few days before and after it will remain in view for more than an hour and a half after the sun sets. After this it will fade fast dimming to +2.3 magnitude.

While Mercury is "doing its thing" the planet Saturn is high in the western sky in the constellation Taurus the bull where it has been throughout the winter. This month its rings will be the most "open" (27 degrees) since 1987 when the planet was near aphelion (farthest from the sun in its orbit). This year it will be at perihelion (closest to the sun) for the first time in the past 29 years. As a result, Mars will appear as big and as bright as it ever gets this summer.

The giant planet Jupiter reigns supreme high in the southern sky at sunset although it has lost some of its luster having dimmed from –2.3 to –2.1 magnitude since opposition this past February and its angular size has "shrunk" from 41 to 37 arc seconds in apparent diameter. However, it still "rules" this region of sky and nothing but the moon is as big or bright.

Pluto, the smallest and most distant planet rises around mid-night with the constellation Ophiuchus but at +13.8 magnitude you’ll need a telescope with at least an 8 inch aperture.

The planet Mars rises between 2 and 3 a.m. EDT in the east among the stars of the constellation Sagittarius. During this month this ruddy red little world will double in brightness to +0.5 magnitude and increase in size to 9.5 arc seconds in angular diameter when it reaches the 1 a.u. (150 million kilometer) mark. It will come within 0.373 a.u. in August when it reaches opposition the closest it ever has in the history of mankind.

The planets Neptune and Uranus rise just before dawn in the constellations Capricornus and Aquarius respectively. Unfortunately they are too dim because they are too distant to be seen without a telescope.

The planet Venus is the brilliant -3.9 magnitude "morning star" you can see rising low on the eastern horizon before the sun rises.