Stars over Sisters 8/02/2022
Last updated 8/2/2022 at Noon
With the arrival of August, the constellations of mid-summer are on full display. The group of stars we are highlighting this month has a feature that makes it truly unique among the modern constellations. Serpens, the Serpent, consists of two non-contiguous parts, known as Serpens Caput (the serpent’s head) and Serpens Cauda (its tail).
To understand why the serpent is separated into two parts in the sky, it is necessary to introduce another celestial figure, namely Ophiuchus, the Serpent Bearer. On star chart illustrations, Ophiuchus is depicted as a man holding a large snake, the snake’s head in his left hand, its tail in his right. But most of these drawings show that a portion of the serpent’s body lies behind Ophiuchus, or passing between his legs, thus hiding it from view.
Serpens takes the spot of the 23rd largest constellation, occupying an area of 637 square degrees in the sky. It is also one of the fifteen equatorial constellations, those that are visible from most places on Earth at various times of the year.
The only star in Serpens that shines brighter than third magnitude is Unukalhai (meaning “neck of the serpent” in Arabic, “heart of the serpent” in Latin.) It is an orange-giant star located in Serpens Caput that has a radius about 12 times greater and is 38 times more luminous than our sun and lies at a distance of 74 light-years.
Serpens can be best seen during late July and early August. To locate this constellation in the night sky, look to south-southwest at nightfall and you will notice a bright reddish star in the constellation of Scorpius called Antares. From here extend a line northward about 30 degrees and you will be in the star field of western Ophiuchus and Serpens Caput.
With part of the Milky Way’s galactic plane passing through Serpens Cauda, the area possesses a plethora of unique deep-sky objects. The most notable among these include M16, or the Eagle Nebula, synonymous with the iconic “Pillars of Creation” photograph taken by the Hubble Space Telescope in 1994. This area of the sky contains several other massive star-forming regions, such as Westerhout 40.
Not to be outdone, Serpens Caput brings forward its own selection of fine deep-sky objects. Most noteworthy of these is Hoag’s Object, the most famous example of the rare class of galaxies known as ring galaxies. Discovered by Art Hoag in 1950, this galaxy has an outer ring of hot, young blue stars surrounding an older yellow nucleus. Located approximately 600 million light-years away, astronomers still don’t know how this object was formed. Other notable treasures that reside in the forward region of Serpens include the dazzling globular cluster M5 and a group of six galaxies in the process of merging to become a single giant elliptical galaxy.
In Greek mythology, Serpens represents a giant snake held by Ophiuchus, symbolic of the healer Asclepius. Son of the god Apollo, Asclepius was said to be able to bring people back to life with his healing powers. In one story, he killed a snake and witnessed another snake reviving it with an herb, a technique he later used in his healings.
The Perseid Meteor Shower puts on one of the most prolific displays of shooting stars of the year. This year’s peak is expected to occur on August 11-12, when 50-75 meteors per hour are anticipated. Unfortunately, the Full Sturgeon Moon will significantly reduce the number of meteors that can be seen.
The two giants of the solar system are getting set to transition from the morning to the evening sky. Saturn does so first when it reaches opposition on August 14. Jupiter follows suit in late September.
The dark sky preservation tip of the month: Check to make sure your lamps are properly shielded in a way that directs light downward illuminating only a targeted area. Doing so increases energy efficiency and reduces light pollution that helps preserve our dark skies.