Skywatch Line for Friday, April 27 through Sunday, April 29, 2018

This is Dudley Observatory’s Skywatch Line for Friday, April 27 through Sunday, April 29, written by Sam Salem.

On Friday, the Sun rises at 5:56am and sets at 7:52pm; the waxing gibbous Moon sets at 5:04am and rises at 5:23pm. Full Moon occurs on Sunday at 8:58pm. The Full Moon in April is the Pink Moon, from the pink flowers “phlox” that bloom in the early spring. Other names for this full Moon include Sprouting Grass Moon, Fish Moon, Hare Moon, and the Old English/Anglo-Saxon name is Egg Moon. On Friday and Saturday, the Moon is in front of the constellation Virgo and close to Spica, Virgo’s brightest star. However, the glare of the waxing gibbous Moon may make it difficult to see Spica these next few nights.

Venus, at magnitude -3.9, is visible shortly after sundown, and doesn’t set until around 10:00pm. Jupiter, shining at magnitude –2.5, appears in the east-southeast around 9:00pm. Jupiter is highest at around 2:00am. Saturn, at magnitude 0.4, rises a little before 1:00am, while Mars, at magnitude –0.3, is up an hour later. Saturn’s rings are an easy target even in a small telescope. Mercury is at its greatest western elongation of 27 degrees west of the Sun on Sunday. Due to the shallow angle the ecliptic makes with the horizon at dawn at this time of year, Mercury is a challenging find even with binoculars.

Double stars are telescopic sight relatively immune to lunar light pollution this full-Moon weekend. You can split Regulus, the leading light in Leo, in a small scope even at low magnification. Regulus’ companion, at 8.2 magnitude, lies 176 arc seconds northwest of the 1.4 magnitude main star. Next aim your telescope north right at the pole star, Polaris. Alpha Ursae Minoris is also a striking double star that spans a range of brightness. However, the Polaris pair isn’t nearly as widely separated as Regulus’. The 2.1-magnitude pole star is accompanied by a 9.1 magnitude companion, 18.6 arc seconds away. That close separation, together with the brightness difference, makes spotting the secondary star such a delight.

Saturday marks the birthday of astronomers Francis Baily and Jan Oort.
Born on April 28 1774, the English astronomer Francis Baily contributed in describing the striking optical effect of what is now called “Baily’s Beads”. The optical effect is an arc of bright spots briefly seen during solar eclipse, immediately before and after totality. It is due to the light shining through the Moon’s irregular surface features. Baily also contributed to revising the British Nautical Almanac and several star catalogs.
Born on April 28 1900, the Dutch astronomer Jan Hendrik Oort was one of the most important figures in 20th-century efforts to understand the nature of the Milky Way Galaxy. Oort measured the rotation of the earth’s galaxy and hypothesized an “Oort Cloud” of predominantly icy planetesimals proposed to surround the Sun to as far as somewhere between 50,000 and 200,000 Astronomical Units (0.8 and 3.2 light years). In 1927, Oort analyzed motion of distant stars, found evidence for differential rotation and founded the mathematical theory of galactic structure. After World War II, he led the Dutch group that used the 21-cm line to map hydrogen gas in the Galaxy. In 1950, Oort proposed the now generally accepted model for the origin of comets.

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