Constellation of the month: Cetus and its Variable Star

A variable star is, quite simply, a star that changes brightness.

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)


David Baumgartner

I am a local fella. Local schools from Fremont, Sacred Heart, Santa Anita, Hollister High, to San Benito Jr. College (Now Gavilan). Then joined the US Air Force where I specialized in Airborne Radar. Married my high school sweetheart JoAnne., shortly after three children arrived; Cindi, Michael, and Lisa. Somehow we ended up with nine Grandchildren.  Went on to San Luis Obispo, Questa, Colleges, and on to Univ. of New Mexico. Came back to Hollister. Opened up Three Pet Stores; Dave's Aquarium Pets & Supplies in SLO, Watsonville, and Hollister. The family spent two and a half years running a ranch up in Oregon. Made our way back to Hollister.  Got my Real Estate License in 1982, opened my own office in 93'. In the mean time raised Swans and revitalized my old hobby of Astronomy.  In 2001 I was named Chamber of Commence Man of the Year. I think I was the only one nominated. I don't care, I'm taking it. In December of 2018 I retired. Not sure if I was forced out or not. None the less, I am retired and I think it was time. Now the last thing I have to do is buy a coffin. I hear COSCO sells them now. But the only drawback is; you have to buy them in lots of six.  I guess I could buy them for the whole family. Not that funny, but thrifty.