This famous double star shows off gorgeous contrasting colors. You can find it in the W-shaped constellation of the Queen tonight.
Cassiopeia the Queen swings in a wide circle around the North Celestial Pole, visible much of (if not all of) the night for most northern observers. This evening around 11:30 P.M. local daylight time, you’ll find the famous W asterism of Cassiopeia right-side up in the north, just below the house-shaped constellation Cepheus.
Cassiopeia is home to several deep-sky delights, including Achird (Eta [η] Cassiopeiae), a fine double star that is lovely in any telescope and a great object for beginners. It’s easy to find — locate the W and find the star at the peak in the center of the celestial letter. About 4.5° to its lower right tonight (south-southwest) is the second valley (reading the letter left to right). The star at the peak is magnitude 2.2 Navi (Gamma [γ] Cas); the star at the valley to its lower right is similarly bright magnitude 2.2 Shedar (Alpha [α] Cas). Just east (to the lower left) of a line drawn between Gamma and Alpha and about two-thirds of the way from the former to the latter is mid-3rd-magnitude Eta Cas.
The two stars of this system are separated by 11”, shining at magnitudes 3.4 and 7.5. Their color contrast is quite noticeable to most observers, and is why the pair is particularly famous. The brighter primary is a yellow G-type star much like the Sun in mass and brightness, while the fainter secondary is a cooler orangey-red K-type dwarf with less than half our Sun’s mass.
Sunrise: 5:32 A.M.
Sunset: 8:32 P.M.
Moonrise: 2:06 A.M.
Moonset: 4:39 P.M.
Moon Phase: Waning crescent (19%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 12 P.M. local time from the same location.
For a look ahead at more upcoming sky events, check out our full Sky This Week column.
