Skywatch Line for Friday, April 7, through Sunday, April 9, 2017

This is Dudley Observatory’s Skywatch Line for Friday, April 7, through Sunday, April 9, written by Sam Salem.

On Friday, Sun rises at 6:27am and sets at 7:29pm; the 87% illuminated Waxing Gibbous Moon sets at 4:49am and rises at 3:49pm. On Friday evening, the waxing gibbous Moon passes just one degree south of Regulus, the brightest star in Leo. The Moon will be closest to Regulus around 12:40am. On Sunday night, the almost full Moon is coming closer to planet Jupiter. Watch the Moon moving closer to Jupiter in the next nights as the full Moon and Jupiter move in front of the constellation Virgo. Full Moon occurs on Tuesday at 2:08am.

Spot Mars, at magnitude 1.5. The red planet hangs 20 degrees above the horizon at dusk. Mercury, at magnitude 1, sits just eight degrees high 45 minutes after sunset. Saturn rises around 2:00am and reaches the meridian at 6:00am as twilight increases. Venus, our newly “morning star” clears the east horizon almost an hour ahead of the Sun. At magnitude –4.4, Venus is easily seen even in twilight. Venus’ morning apparition will last through to the end of the year.

Jupiter rises towards the east at sunset, at magnitude –2.5, dominating the entire sky. Earth passes between the Sun and Jupiter, placing Jupiter opposite the Sun in our sky on Friday at 6:00pm. This means that Jupiter will be up all night at its brightest for this year. Jupiter now rises in the east around sunset, climbs highest in the sky at midnight and sets in the west around sunrise. Jupiter moves in front of the constellation Virgo, the Maiden. The closest first magnitude star to Jupiter is Spica, the brightest star in Virgo. Jupiter comes to opposition about every thirteen months.

This year, the Sun enters the constellation Virgo on September 16 and leaves Virgo on October 31. Constellation Virgo is lost in the sun’s glare at this time of year. April is a much better time of year for viewing the constellation Virgo than in September and October. The bright Moon passing in front of Virgo for the next several days will make it difficult to see the starlit figurine of Virgo, the Maiden right now. The Moon will drop out of the evening sky in a week, giving a chance to better observe the stars of constellation Virgo and planet Jupiter.

On April 9 1895, American astronomer James Keeler proved that the rings of Saturn were composed of meteoric particles, as predicted by James Maxwell. Keeler’s spectrogram of light reflected from Saturn’s rings showed a Doppler shift indicating a variation in radial velocity. Thus, particles in the inner part of a ring, closer to Saturn, move at a different rotational speed from those in more distance parts of a ring.

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