Skywatch Line for Friday, March 2 through Sunday, March 4, 2018

This is Dudley Observatory’s Skywatch Line for Friday, March 2 through Sunday, March 4, written by Sam Salem.

On Friday, the Sun rises at 6:30am and sets at 5:46pm; the Moon sets at 7:02am and rises at 6:41pm. The full Moon occurred on Thursday at 7:51pm.

All five naked-eye planets are on display for the first time since November. The inferior planets Mercury and Venus, which orbit inside Earth’s orbit around the Sun, are located in the western sky after sunset. Both planets hug the west horizon due to the shallow angle of the ecliptic at dusk at this time of year. Venus, at magnitude –3.9, sets roughly one hour after the Sun. Mercury, shining nearby at magnitude –1.3, starts climbing higher than Venus this weekend. On Saturday, Look low in the west during evening twilight to see Mercury and Venus just 1 degree apart. You might be able to spot both planets with the eye alone. If you spot Venus, but not Mercury, aim binoculars at Venus to see both planets in a single binocular field. For the coming weeks, use Venus to find Mercury. Venus and Mercury will remain close enough together on the sky’s dome to fit inside a typical binocular field of 5 degrees for the first three weeks of March.

The superior planets Mars, Jupiter and Saturn, which orbit outside Earth’s orbit around the Sun, are best viewed after midnight, or in the predawn hours. Jupiter gleams at magnitude –2.2 and rises just a little after midnight. Mars, at magnitude 0.8, gains luminosity and size. Saturn, at magnitude 0.6, clears the southeast horizon shortly before 4am.

This weekend try to spot two of the winter sky double stars. Look for Castor in constellation Gemini. Castor appears essentially white, while Pollux has a slightly golden hue. While Castor appears as a single point of light to the naked eye or in binoculars, a telescope working at 100× or greater will split Castor into two stars. The component stars shine at magnitudes 1.9 and 3.0, and are separated by 4.2 arc seconds. The second double star is Rigel in constellation Orion. Seeing Rigel’s faint companion isn’t easy. Rigel shines at magnitude 0.3, but its partner, 9.4 arc seconds away, is a 6.8-magnitude glint almost lost in the brighter star’s glare. A 6-inch scope would help spotting the faint companion.

This weekend and for the next several weeks look for the zodiacal light. The next two weeks provide a good window for watching the zodiacal light in the west each night as full darkness falls, because the moon is rising later at night. The weeks around the March equinox present the best time of the year to catch this pyramid of light illuminating the western sky as soon as true darkness falls. Look westward about 80 to 120 minutes after sunset. If you find yourself beneath a dark country sky or driving along a country road after dusk look for this eerie light. Look for the zodiacal light extending upward from the western horizon and toward the constellation Taurus. The zodiacal light is caused by sunlight reflecting off interplanetary dust particles that orbit the Sun within the inner solar system. People at mid-northern latitudes can see the zodiacal light after dusk at present because the ecliptic is nearly perpendicular to the horizon on March/April evenings.

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