Cetus is another one of the “Watery” constellations, along with Capricornus, Aquarius, and Pisces. All of which are dim and hard to recognize, let alone fine in their part of the sky.
Cetus means “whale” in Latin. This is the same creature that attacked Andromeda. It could have been a whale, or a mystical sea-monster, no one is quite sure. It isn’t easy to make Cetus, the sky-creature, into a whale; he has a fan-shaped head and a bell-shaped lower end. The “clapper” of the bell, or tail of the animal, is where you’ll find the constellation’s brightest star, Diphda. I’m really not sure how to pronounce that properly.
In the throat of Cetus is the star called Mira, “the wonderful” (in Latin). Mira can only be seen a few weeks of the year, not because it is below the horizon, or behind a tree, but because it is a variable star and becomes so dim most of the year that one finds it too difficult to locate until it brightens up again for those few weeks. Mira was the first variable star to be discovered back in 1638 by Johannes Holwards. So good luck finding Mira, you just have to know when to look for it.
So what is a variable star anyway? Well this one I had to look up. Thank goodness for my trusty set of encyclopedias. Where would I be without them? I must admit that my set is getting kind of old. In the front of the book it says 1936, I’m guessing that was the year it was published. Oops, pages 27 through 96, of volume T, just fell out. Maybe I should invest in a new set. Does anyone know where I could purchase a new set, or at least one a little newer than mine? Please let me know.
A variable star is, quite simply, a star that changes brightness. A star is considered variable if its apparent magnitude (brightness) is altered in any way from our view on Earth. These changes can occur over years or just in seconds, More than 100,000 variable stars are known and have been catalogued, with thousands more suspected variables out there. Our own sun is a variable star; its energy output varies by approximately 0.1 percent, or one-thousandth of its magnitude, over an 11-year solar cycle. At the end of that 11 year period is when we have the majority of Sun Spots.
Now you want to know how does a star, such as Mira, vary in magnitude unlike most stars we know of? Doesn’t anyone here have their own set of encyclopedias? Come on people you’d better keep up with the times.
There are a number of reasons for variability. These include changes in star luminosity or in star mass, and obstructions in the amount of light that reaches Earth. Pulsating variables swell and shrink. Eclipsing binaries get dimmer when a companion star or one or more of those suns planets, moves in front, then brighten as the occulting object moves away. Some of the identified variable stars are actually two very close stars that exchange mass when one takes atmosphere from the other.
I didn’t have the time to go into the different categories of variable stars here today, but if you are interested to learn more, look up in your trusty encyclopedia, “Intrinsic and Extrinsic Variables”. Quite interesting. Hope you all are having a good year so far. Clear Skies….
Coming in the skies the rest of the month:
Jan 17 Full Moon
Jan 25 Last quarter Moon
Jan 29 Moon passes 2° south of Mars
Jan 29 Moon passes 10° south of Venus
Jan 30 Moon is at perigee (225,093 miles from Earth)