The Sky This Week From Aug. 15 To 22: The Moon Hangs With Morning Planets

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Friday, August 15
Dwarf planet 1 Ceres reaches its stationary point in Cetus the Whale at 9 P.M. EDT. Previously it was moving eastward relative to the background stars. Now it will begin to move westward, or retrograde.

Ceres is only visible in the morning sky, but 4 Vesta is sliding eastward through the evening sky in Libra, still some 25° high in the southwest an hour after sunset. It's located between that constellation's two brightest stars: magnitude 2.8 Zubenelgenubi (Alpha [α] Librae) and slightly brighter magnitude 2.6 Zubeneschamali (Beta [β] Lib). This evening, Vesta is just east of the midpoint of a line drawn between these two stars, some 4.3° northeast of Alpha Lib.

Shining at magnitude 7.4, Vesta is well within the reach of binoculars or any telescope, even from the suburbs.

It's currently some 2.0 astronomical units from Earth, or nearly 186 million miles (299 million kilometers) away. (One astronomical unit, or AU, is the average Earth-Sun distance.) Vesta is moving relatively slowly — the easiest way to make sure you've spotted it is to sketch or photograph the area in your eyepiece tonight, and then return over the next few nights to repeat the exercise.

The dot you notice moving from night to night is Vesta.

The fourth asteroid ever discovered, Vesta is the second-most massive world in the main belt, after Ceres, and the third-largest, after Ceres and 2 Pallas.

Sunrise: 6:12 A.M.
Sunset: 7:56 P.M.
Moonrise: 11:15 P.M.
Moonset: 1:32 P.M.
Moon Phase: Waning gibbous (56%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon's illumination is given at 12 P.M. local time from the same location.

Saturday, August 16
Last Quarter Moon occurs at 1:12 A.M. EDT as sunset sweeps across the lunar nearside following the Full phase last week. Visible in the early-morning sky, the Moon lies just under 4° west of the Pleiades in Taurus some two hours before sunrise, rising in the east. (The Moon will continue to creep closer to the cluster over the course of the day, occulting several stars in the Pleiades in an event visible from Japan, Korea, and northeast Asia.)