The southern autumn night sky is often referred to as the “wet quarter” because that’s where we find such constellations as Aquarius the Water-bearer; Pisces the Fish; and, most notorious of all, Cetus the Sea Monster.
Although renderings of Cetus date back to its first appearance as one of 48 star patterns in the Almagest, written by Ptolemy around A.D. 150, one particular star went unnoticed. That could have been because it’s not always visible. At times, it shines as brightly as the constellation’s brightest star, Diphda (Beta [β] Ceti), while at others, it disappears entirely.
The earliest observation of this strange star’s eccentric behavior was made by German astronomer David Fabricius in 1596, making it the first variable star ever discovered. Although it was designated Omicron (ο) Ceti in Johann Bayer’s 1603 catalog of stars, it wasn’t until 1662 that Polish astronomer Johannes Hevelius christened it Mira, meaning “wonderful.”
Mira is the archetype of a class of stars known as long-period variables, red giants that steadily pulse over periods lasting about a year. In Mira’s case, the period is 332 days. During that time, it fluctuates from 2nd to 10th magnitude, making it nearly 1,600 times brighter at maximum than at minimum.
Mira’s light curve, a plot of the star’s magnitude over time, shows that it ascends in brightness quickly but trails off toward minimum more slowly. Mira was last at maximum brightness in early December 2019. Throughout last winter and this past spring, it dwindled in brightness as it set earlier each night, eventually disappearing into the sunset. Mira returned to the predawn sky at the start of summer, growing in brightness as it progressively rose earlier each morning. It is anticipated to be back at full light early this month.
As October opens, Mira rises around 8 P.M. local standard time (9 P.M. Daylight Saving Time). But you should wait at least two hours for it to rise higher above the horizon. To find it, imagine the Hyades, the head of Taurus the Bull, as an arrowhead. Follow its aim southwestward, either by eye or through binoculars, for about 24° to the star Menkar (Alpha [α] Ceti). Menkar is joined by four fainter stars to create a pentagon that was portrayed on classical star maps as Cetus’ hideous head. In fact, the name Menkar stemmed from the Arabic word for “nostril.”
Once you locate the sea monster’s head, slip 12° to the southwest, where you’ll find a reddish star. That’s Mira. (Or maybe you’ll see nothing. It all depends on when you’re reading this.) Look for it a little south of the central point in an equilateral triangle of 5th- and 6th-magnitude stars.
