Tonight’s Sky Features Cassiopeia, the Big Dipper, Cepheus and More for December 2019

Step outside on a cold December night when the stars shine bright to find the Big Dipper, Cassiopeia, and Cepheus. They will help you locate a binary star system, a fan-shaped open star cluster, and a variable star. Stay tuned for space-based views of a ragged spiral galaxy, an open star cluster, and an edge-on galaxy.

Cassiopeia is a constellation high in the northern sky, named after the vain queen Cassiopeia in Greek mythology, who boasted about her unrivaled beauty. Cassiopeia is visible year-round in Chicagoland and any latitude above 34°N. The constellation is a distinct ‘M’ or upside-down ‘W’ depending on your perspective. The five brightest stars of Cassiopeia – Alpha, Beta, Gamma, Delta, and Epsilon Cassiopeiae – form the characteristic W-shaped asterism.

In winter in Chicagoland Cassiopeia is visible “above” Polaris (the North Star) and asterism appears as the letter ‘M’ but the asterism is oriented as a ‘W’ when Cassiopeia is below Polaris during spring and summer nights in Chicagoland.

Cassiopeia was one of the 48 constellations listed by the 2nd-century Greek astronomer Ptolemy, and it remains one of the 88 modern constellations today.

The Big Dipper is a large asterism that consists of seven bright stars of the constellation Ursa Major. Four stars define a “bowl” of “pan” or and three define a “handle.”

The North Star, which is the current northern pole star, is located by extending an imaginary line through the two stars that form the pouring side of the pan in the Big Dipper. The line of Merak (β) and Dubhe (α) for a line that points to Polaris — one of the most useful aids in celestial navigation.

Polaris in the northern hemisphere is visible above the northern horizon by the same number of degrees of the latitude where the observer is standing. In other words, in Arlington Heights where the latitude is about 42°N, the star Polaris is observed at about a 42° angle above the northern horizon.

Orion is a constellation located on the celestial equator and is therefore visible throughout the world. Orion is one of the most prominent constellations with three of its stars (Alnitak, Alnilam and Mintaka) forming the belt of Orion, named after the great hunter in Greek mythology.

The brightest stars of Orion are two supergiants — the blue-white Rigel (Beta Orionis) and red Betelgeuse (Alpha Orionis).

Orion is most noticeable in late November and December because it rises above the east horizon about 9:00 p.m. In much of the summer, Orion is in the sky during daylight, but it starts to become noticeable when it rises about 3:00 a.m. in August. The brightest star in the sky is Sirius, which rises just behind Orion.

Learn more about additional constellations and galaxies from the video above.



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