Skywatch Line for Friday, March 31, through Sunday, April 2, 2017

This is Dudley Observatory’s Skywatch Line for Friday, March 31, through Sunday, April 2, written by Sam Salem.

On Friday, Sun rises at 6:39am and sets at 7:21pm; the 17% illuminated Waxing Crescent Moon sets at 11:42pm. First quarter occurs on Monday at 2:39pm.

The next few nights offer a good opportunity to catch Mercury, the illusive planet that’s often lost in the glare of the sun. On Saturday, Mercury is at greatest elongation where it swings farthest east of the setting Sun by 19 degrees on the sky’s dome. Mercury’s present apparition as the “evening star,” started on March 7 and will end on April 20. Look to the west for Mercury over the sunset point on the horizon 45 to 60 minutes after sunset. Use binoculars to help searching for Mercury.

Mars is about 10 degrees higher than Mercury in the evening sky. At magnitude 1.5, Mars is fainter, however, still easy to find. Jupiter, at magnitude –2.5, is the most prominent planet in the night sky before Venus appears shortly before sunrise. Jupiter hovers low in the east before the end of twilight. For telescopic viewing, wait until Jupiter reaches the meridian, around 2pm. Saturn rises in the southeast shortly after 2am, reaching its greatest altitude at dawn. Venus, the new “morning star”, rises just 45 minutes before the Sun.

On Friday, the waxing crescent Moon shines in front of the constellation Taurus, the Bull and near its two most prominent signposts, Aldebaran and the Pleiades star cluster. See the Moon to the west of Aldebaran on Friday, and to the east of this star on Saturday night. On Sunday night, use the Moon to find the bright stars of the Winter Circle. The Winter Circle is found over the western horizon as soon as darkness falls. The Winter Circle surrounds the Moon and the Orion constellation. Pollux and Castor, the two brightest stars in the constellation Gemini mark the top of the circle. Capella, the brightest star in the constellation Auriga, and Aldebaran, the brightest star in the constellation Taurus, sit west of the Moon. Procyon, the brightest star of the constellation Canis Minor, and Sirius, the brightest star in Canis Major lie on the east side. Rigel, the lowest star of Orion Constellation marks the bottom of the circle. The Winter Circle stars, Sirius, Rigel, and Aldebaran, loom low at nightfall. They sink below the horizon by early evening.

This weekend marks the anniversary of two major achievements by the French physicist Léon Foucault. On March 31 1851, Leon Foucault demonstrated his pendulum experiment in a public exhibition at the Pantheon of Paris at the request of Napoleon the Third. The pendulum is a simple device conceived as an experiment to demonstrate the rotation of the Earth. While it had long been known that the Earth rotates, the introduction of the Foucault pendulum in 1851 was the first simple proof of the rotation in an easy-to-see experiment. The pendulum demonstration at the Pantheon used a 62-pounds sphere on a 220-ft wire. Movement of the oscillation plane of the pendulum relative to the marked circle on the ground showed that the Earth was rotating underneath the swinging pendulum. On April 2 1845, Léon Foucault and Armand Fizeau took the first successful daguerreotype photograph showing details of the Sun. The 5-inch image had an exposure of 1/60 second, and showed the umbra/penumbra structure of several sunspots, as well as limb darkening. The daguerreotype is the early photography process, named after the French artist who perfected the method of producing direct positive images on a silver-coated copper plate.

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