#astronomy Meet Gamma Cassiopeiae, the Traditional Eruptive Variable – Sky & Telescope

September 1, 2021 - Comment

Gamma Cassiopeiae Vitals Widespread identifyGamma CassiopeiaeDifferent designationsHIP 4427, HR 264, HD 5394NicknamesNavi, Tsih (the Whip) in outdated ChinaObvious magnitudeVaries; at present about 2.15 (traditionally 1.6–three.zero)Distance from Earth613 light-yearsKindB0.5IVpeColourBlueMass17 M☉Radius10 R☉ConstellationCassiopeiaProper Ascension0h 56m 42sDeclination60° 43′ 00”A number of system?SureVariable star?SureExoplanet standingNone identifiedPossible destinySupernova Bodily Traits A variable star is a star that fluctuates in brightness over


Gamma Cassiopeiae Vitals

Widespread identifyGamma CassiopeiaeDifferent designationsHIP 4427, HR 264, HD 5394NicknamesNavi, Tsih (the Whip) in outdated ChinaObvious magnitudeVaries; at present about 2.15 (traditionally 1.6–three.zero)Distance from Earth613 light-yearsKindB0.5IVpeColourBlueMass17 M☉Radius10 R☉ConstellationCassiopeiaProper Ascension0h 56m 42sDeclination60° 43′ 00”A number of system?SureVariable star?SureExoplanet standingNone identifiedPossible destinySupernova

Bodily Traits

A variable star is a star that fluctuates in brightness over a time period, maybe lower than a day, or perhaps weeks, months, or years. Variable stars are a big class of objects that beginner astronomers have lengthy chased for each enjoyable and science. Even the Solar is barely variable, brightening and dimming over a roughly 11-year interval by zero.1%. Different stars are extra dramatic, together with a category of irregularly altering stars generally known as eruptive variables.

Northern Lights over a forest, with Cassiopeia constellationCassiopeia hangs above the glow of Northern Lights. Gamma Cassiopeiae is the center level of the “W”-shape constellation.
Daniel Johnson

For those who’d like to hunt out one in all these for your self, there’s a vibrant and easy-to-find eruptive variable within the northern sky — and also you’ve most likely seen it many instances with out understanding it. That star is Gamma Cassiopeiae, the center level within the W form of Cassiopeia. Typically Gamma Cassiopeiae dims to Third-magnitude, whereas throughout different durations it shines as brightly as magnitude 1.6, because it did within the 1930s. However these modifications aren’t predictable, so what’s happening?

Gamma Cassiopeiae rotates at a excessive velocity — so quick that its form is distorted, much like the consequences seen on Vega, Regulus, and Altair. However Gamma Cassiopeiae spins a lot quicker, some 400 kilometers per second (900,000 mph), and the ensuing colossal forces are sturdy sufficient to often dislodge matter from the star. This materials then kinds a disk of orbiting materials. Whereas distance prevents us from instantly observing the disk, we are able to nonetheless decide its existence via spectroscopy. The star’s brightness modifications as matter is flung from the star — therefore the identify eruptive variable.

Gamma Cassiopeiae is assessed as a Be star, totally different from atypical B-class stars. The lowercase e stands for emission strains from hydrogen, first famous by Father Angelo Secchi within the 19th century. These strains come from the ejected gases.

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Origin / Mythology

In Greek myths, Queen Cassiopeia was the relatively useless mom of Andromeda, and a few star map illustrations painting the constellation because the queen seated in a W-shape chair, taking a look at herself in a mirror. In some Chinese language mythology, the W is included in a chariot driver constellation, with Gamma Cassiopeiae representing the whip (“Tsih” in Chinese language).

Cassiopeia as rendered by Johannes eveliusin Greek mythology, Cassiopeia is a queen whose boasts about her magnificence land her and her royal household in massive hassle. The “W” form right here is upside-down.
Supply: Johannes Hevelius

Nonetheless, there may be little current mythology involving the star Gamma Cassiopeiae particularly, and the star oddly lacks a standard Greek or Arabic identify, and doesn’t have a correct identify in any respect. The Gamma Cassiopeiae label we use at present is strictly utilitarian, a part of Johann Bayer’s star-cataloging efforts of the 1600s.

Often, although, Gamma Cassiopeiae is referred to informally as “Navi.” This latest nickname got here out of the Apollo Program of the 1960/70s. Gamma Cassiopeiae was one of many many stars used as to calibrate the gyroscopes aboard Apollo spacecraft. Noticing that the star lacked a standard identify, astronaut Gus Ivan Grissom playfully labeled Gamma Cassiopeiae “Navi” on his star chart — utilizing his personal center identify spelled backwards. Later Apollo astronauts continued the custom, and Navi has since discovered its means into common use in some cases — akin to within the well-liked astronomy software program Stellarium.

See Gamma Cassiopeiae

Gamma Cassiopeiae is simple to search out from the U.S. From about 35°N latitude, the star is circumpolar and by no means drops beneath the horizon. Cassiopeia might be one of the vital recognizable constellations within the northern sky. The acquainted W form is simple to recollect, and Cassiopeia rotates round Polaris roughly reverse the Large Dipper.

Stars; Cassiopeia constellation with the Andromeda GalaxyGamma Cassiopeiae is the center level star of the Cassiopeia constellation, proven right here close to the Andromeda Galaxy.

Cassiopeia sits proper in the midst of the Milky Method band, so it’s value looking for a darkish sky away from synthetic lights for viewing, with the intention to see the complete impact of the constellation backlit by the sting of our galaxy. When you’re there, use the bigger level of Cassiopeia’s lopsided W to take a fast jump over to a unique galaxy altogether: the majestic Andromeda. (Bear in mind, the Andromeda Galaxy is after all within the constellation Andromeda, and Andromeda is Cassiopeia’s daughter, in order that they’re subsequent to one another within the sky — is smart, proper?)

Observing Gamma Cassiopeia can be a pleasant solution to examine the interstellar medium. We have a tendency to think about house as utterly empty, however there are many gasoline and dirt particles drifting about, notably in step with the sting of our galaxy. Gamma Cassiopeiae would really shine about zero.35 magnitudes brighter if it have been in one other part of the sky, however its location in step with the aircraft of the Milky Method locations it in a relatively dusty area. While you level your telescope at Gamma Cassiopeiae, you’re not solely taking a look at a distant star, you’re trying via untold numbers of house mud particles slowly rotating across the heart of our galaxy.

When you observe Gamma Cassiopeiae, attempt to visualize the immense exercise going down there and in between — and on the identical time, be pleased about the relative tranquility of our personal Solar.

Daniel Johnson is a Wisconsin-based freelance author photographer and the co-author of over a dozen books. He’s a longtime beginner astronomer and lucky sufficient to stay in a rural area with glorious seeing circumstances. You’ll be able to view a few of Dan’s images (he does quite a lot of animals!) at www.foxhillphoto.com



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