Skywatch Line for Friday, March 8 through Sunday, March 10, 2019

This is Dudley Observatory’s Skywatch Line for Friday, March 8 through Sunday, March 10, written by Sam Salem.

On Friday, the Sun rises at 6:20am and sets at 5:54pm; the waxing crescent Moon rises at 7:35am and sets at 7:54pm. Daylight-saving time begins on Sunday. Set your clocks ahead one hour before going to bed Saturday night.

Starting Sunday night, and for the next three evenings, the waxing crescent Moon sweeps to the south of the red planet Mars. On Sunday evening, the Moon will be shining beneath Mars in the western sky. Mars looks like a modestly bright ruddy star above the Moon, and easy to see in a dark sky.

Mercury is now difficult to observe without a telescope. It rapidly loses both altitude and brightness, fading from magnitude 0.8 to 4.2. It’s. Mars, shining at magnitude 1.2, has ceased to be a rewarding telescopic sight. Jupiter gleams at magnitude –2.1 and rises around 1:45am. By far, Jupiter is the best telescopic planet at the moment. Wait as late as you can for best observing results. Jupiter reaches the meridian, when it’s highest and positioned due south, just as the Sun rises. Trailing behind Jupiter is another telescopic favorite, 0.6-magnitude Saturn. The ringed planet rises around 3:30am (4:30am on Sunday) and reaches an altitude of nearly 15 degrees, 45 minutes before sunrise. Venus is last to rise, at 4:40am (5:40am on Sunday). Gleaming at magnitude –4.1, Venus is the reigning “morning star”, though its current apparition is nearly half done and the planet is very slowly losing ground to twilight.

Nights over this weekend are almost entirely free of moonlight, which makes them ideal for deep-sky observing. Spiral galaxies M95 and M96 are located in the constellation Leo, about mid-way between the stars Upsilon and Iota Leonis. M95 is located about 38 million light years away. M96 is slightly further away, located about 41 million light years. Both galaxies are members of the Leo I Group of galaxies. They can be viewed together in a small telescope at low magnifications.

Saturday marks the 455th. Birthday of the German astronomer David Fabricius. Fabricius discovered the first known periodic variable star, Mira, in 1596. At first he believed it to be a nova. When Mira was seen bright again in 1609, it became clear that a new kind of object had been observed in the sky. This discovery helped verify that the stars were not eternal and invariable, as ancient philosophers such as Aristotle had believed. With his son, Johannes, David observed the Sun and noted sunspots. For further observations they invented the use of a camera obscura and recorded sunspot motion indicating the rotation of the Sun.

On March 10 1977, the rings of Uranus were discovered from earth by stellar occultation experiments made when Uranus passed in front of a star. It was noticed that there were dips in the brightness of the star before and after it passed behind the body of Uranus. This data suggested that Uranus was surrounded by at least five rings. Four more rings were suggested by subsequent occultation measurements from the Earth and two additional ones were found by space probe Voyager 2, bringing the total to 11. Direct observations of the rings from earth had not been possible because the rings are lost in the planet’s glare as seen through terrestrial optical telescopes. Most of the rings are not quite circular, and most are not exactly in the plane of the equator.

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