Meet Gamma Cassiopeiae, the Classic Eruptive Variable

Gamma Cassiopeiae Vitals

Common title Gamma Cassiopeiae
Other designations HIP 4427, HR 264, HD 5394
Nicknames Navi, Tsih (the Whip) in previous China
Apparent magnitude Varies; at the moment about 2.15 (traditionally 1.6–3.0)
Distance from Earth 613 light-years
Type B0.5IVpe
Color Blue
Mass 17 M
Radius 10 R
Constellation Cassiopeia
Right Ascension 0h 56m 42s
Declination 60° 43′ 00”
Multiple system? Yes
Variable star? Yes
Exoplanet standing None recognized
Probable destiny Supernova

Physical Characteristics

A variable star is a star that fluctuates in brightness over a time frame, maybe lower than a day, or perhaps weeks, months, or years. Variable stars are a big class of objects that novice {and professional} astronomers have lengthy chased for each enjoyable and science. Even the Sun is barely variable, brightening and dimming over a roughly 11-year interval by 0.1%. Other stars are extra dramatic, together with a category of irregularly altering stars often called eruptive variables.

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

If you’d like to hunt out one in all these for your self, there’s a shiny and easy-to-find eruptive variable in the northern sky — and also you’ve in all probability seen it many instances with out understanding it. That star is Gamma Cassiopeiae, the center level in the W form of Cassiopeia. Sometimes Gamma Cassiopeiae dims to Third-magnitude, whereas throughout different durations it shines as brightly as magnitude 1.6, because it did in the Nineteen Thirties. But these adjustments aren’t predictable, so what’s occurring?

Gamma Cassiopeiae rotates at a excessive speed — so quick that its form is distorted, much like the results seen on Vega, Regulus, and Altair. But Gamma Cassiopeiae spins a lot sooner, some 400 kilometers per second (900,000 mph), and the ensuing colossal forces are sturdy sufficient to sometimes dislodge matter from the star. This materials then types a disk of orbiting materials. While distance prevents us from immediately observing the disk, we will nonetheless decide its existence via spectroscopy. The star’s brightness adjustments as matter is flung from the star — therefore the title eruptive variable.

Gamma Cassiopeiae is classed as a Be star, totally different from extraordinary B-class stars. The lowercase e stands for emission traces from hydrogen, first noted by Father Angelo Secchi in the 19th century. These traces come from the ejected gases.


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Origin / Mythology

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

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

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

Occasionally, 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 in all the many stars used as to calibrate the gyroscopes aboard Apollo spacecraft. Noticing that the star lacked a standard title, astronaut Gus Ivan Grissom playfully labeled Gamma Cassiopeiae “Navi” on his star chart — utilizing his personal center title spelled backwards. Later Apollo astronauts continued the custom, and Navi has since discovered its way into basic use in some situations — similar to in the well-liked astronomy software program Stellarium.

How to See Gamma Cassiopeiae

Gamma Cassiopeiae is straightforward to seek 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 in all the most recognizable constellations in the northern sky. The acquainted W form is straightforward to recollect, and Cassiopeia rotates round Polaris roughly reverse the Big Dipper.

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

Cassiopeia sits proper in the center of the Milky Way band, so it’s price looking for a darkish sky away from synthetic lights for viewing, so to see the full impact of the constellation backlit by the fringe of our galaxy. While you’re there, use the bigger level of Cassiopeia’s lopsided W to take a fast jump over to a special galaxy altogether: the majestic Andromeda. (Remember, the Andromeda Galaxy is in fact in the constellation Andromeda, and Andromeda is Cassiopeia’s daughter, so that they’re subsequent to one another in the sky — is smart, proper?)

Observing Gamma Cassiopeia can also be a pleasant way to research the interstellar medium. We have a tendency to consider space as utterly empty, however there are many gas and dirt particles drifting about, significantly in keeping with the fringe of our galaxy. Gamma Cassiopeiae would truly shine about 0.35 magnitudes brighter if it had been in one other part of the sky, however its location in keeping with the plane of the Milky Way locations it in a somewhat dusty area. When you level your telescope at Gamma Cassiopeiae, you’re not solely taking a look at a distant star, you’re wanting via untold numbers of space mud particles slowly rotating round the heart of our galaxy.

While you observe Gamma Cassiopeiae, attempt to visualize the immense exercise happening there and in between — and at the identical time, be glad about the relative tranquility of our personal Sun.


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

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