This is Dudley Observatory’s Skywatch Line for Friday, February 17, through Sunday, February 19, written by Sam Salem.
On Friday, Sun rises at 6:50am and sets at 5:30pm; the 61% illuminated waning Gibbous Moon rose at 11:26pm on preceding day and sets on 10:21am. Last Quarter Moon occurs on Saturday at 2:33pm. On Sunday, before sunrise, look in the south to southeast sky for the Moon, Antares, and Saturn in the predawn and dawn sky. Every year, the Sun and Antares, the brightest star in the constellation Scorpius the Scorpion, are in conjunction on or near December 1, where Antares is behind the Sun each year, as seen from our earthly vantage point. At that time Antares is lost in the light of the Sun. By mid to late January, Earth is moved far enough along in its orbit that Antares begins to appear from behind the Sun. Antares rises at 2:14am, reaching transit altitude of 21 degrees south at 6:28am on Sunday. Seeing Antares and the constellation of Scorpius before dawn is a sure sign that spring is approaching.
Venus and Mars are well up in the west-southwest during twilight, separated by roughly seven degrees. Gleaming Venus is at its greatest illuminated extent at magnitude -4.8, while Mars is roughly 250 times fainter at magnitude 1.2. Jupiter shines at magnitude –2.2 and rises around 10:30pm. Jupiter lies less than four degrees northeast of first-magnitude Spica, the brightest star in constellation Virgo. Jupiter transits the meridian around 4:00am, which is about the time Saturn rises in the southeast. Saturn, at magnitude 0.6, climbs to an altitude of 15 degrees by the start of morning twilight.
M35 in Gemini is one of the finest open clusters for the season. M35 stands out best in binoculars or a small telescope. In a telescope you will be able to resolve many more stars. The 5.1 magnitude cluster is located just above the westernmost foot of the Twins, marked by Mu (μ) and Eta (n) Geminorum.
Saturday marks the 87th anniversary of the discovery of Pluto. The dwarf planet was discovered in 1930 by Clyde Tombaugh when comparing two photographic plates taken six days apart the previous month. The search for Planet X started three decades earlier. Deviations in the positions of Uranus and Neptune were suspected to be due to the gravity of an undiscovered ninth planet. Locating it meant sifting through the millions of star images for one dim dot that moved. Pluto was the only planet, now a dwarf planet, found by an American.
Sunday marks the birthdate of Nicolaus Copernicus. Born on February 19 1473, the Polish astronomer triggered the Copernican Revolution, shifting the Earth from the center of the cosmos to a secondary place, orbiting around the Sun. In his book “De revolutionibus orbium coelestium” (On the Revolutions of the Celestial Spheres) he proposed the heliocentric model of the Solar System in which all the planets orbit around the Sun at the center. Although his book was completed in 1530, he requested it be published after his death in 1543. The book was banned until 1758.