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

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

On Friday, Sun rises at 7:09am and sets at 5:10pm; the Waning Gibbous Moon sets at 8:34am and rises at 7:56pm.

Look toward the southeast around 6:30 am to see planets Jupiter, Mars, and Saturn. Jupiter, at magnitude –2.0, is by far the brightest and easiest to identify, sitting due south. Mars, at 1.2-magnitude, sits roughly 12 degrees east of Jupiter. Mars spends the week moving past the 2.6-magnitude star Beta Scorpii. Saturn shines at magnitude 0.6 and is positioned less than 10 degrees above the southeast horizon at dawn.

Under dark-sky conditions, the zodiacal light is visible in the western evening sky this weekend and for the next two weeks. Moonless evenings in February, March and April present the best time of year to see zodiacal light in the Northern Hemisphere evening sky. The light is most visible after dusk at this time of year because the “ecliptic” stands nearly straight up with respect to the horizon after the Sun sets in February and March. The zodiacal light looks like a hazy pyramid of light in the west after true darkness falls. When you see the zodiacal light, you are looking edgewise into the plane of our solar system. The zodiacal light is sunlight reflecting off dust particles that move in the same plane as Earth and the other planets orbiting our Sun.

The dwarf planet Ceres reaches opposition this week. At opposition it is closest to Earth, well placed for viewing most of the night, and at peak brightness. Ceres appears as a 6.9-magnitude point of light in northern Cancer, which is near the meridian at 1:00am. Use binoculars or a telescope at low power to scan roughly 1½ degrees east of 5.4-magnitude Tau (τ) Cancri. Use the same method Giuseppe Piazzi used to be sure you have located the dwarf planet and not just a field star. Note your suspect’s position over a period of two or three nights. If it moves, then you’ve found Ceres. When Giuseppe Piazzi discovered Ceres in 1801, he believed he had found a comet. Later, Ceres was thought to be the long-searched-for planet expected to circle the Sun between the orbits of Mars and Jupiter. When similar “planets” started turning up in the same zone, astronomers realized they had stumbled across a whole new class of solar system object. These bodies were called “minor planets” or “asteroids”. In 2006, Ceres was reclassified as a “dwarf planet”.

Sunday marks the birthday of Clyde W. Tombaugh. Born on February 4 1906, Clyde was the American astronomer who discovered Pluto, then known as a planet. He was 24 years old working at Lowell Observatory when he located it on March 13 1930. He was comparing a photographic plate taken on January 23 1930, with another made a few days later. He saw a star-like speck that changed position between the two photographs. Tombaugh also discovered several clusters of stars and galaxies, studied the apparent distribution of extragalactic nebulae, and made observations of the planet surfaces. Pluto was the only planet discovered in the 20th century, and the only one found by an American.

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