I can’t believe it’s March already. It’s easy for the cold months to run into one another, but little hints, like later sunsets, and Robins chirping at dawn have been reminding me of the coming spring.
These are roughly the same positions as they held at 6AM back in October during AstroWeek, which makes perfect sense: we’ve progressed 5 out of 12 months since then, and the sky has similarly progressed 10 out of 24 hours over the same period of time.
While the rotation/advance of the Northern sky has been fun to watch, the progression of the Southern sky has been much more exciting. Rather than a slowly-turning wheel, the Southern sky has been a procession of new constellations climbing out of the East, one after the other. When we first started watching back in October, Orion would be center-stage in the Southern sky at ~6AM. Now it’s there at ~8PM, and by dawn it’s long since set.
Tangent: This has been one of the coolest things about this winter for me. I did AstroWeek back in October kind of on a lark, but it got me interested in the night-sky, and this has been the first year ever that I’ve really paid attention to the changing stars. Oh, I always knew a constellation or two and some odd astro-factoids, but I never really put it all together before, the way it’s coming together for me this year.
Lots of people I think get curious about the stars and get a book or chart or whatever and try to check stuff out all at once, then get distracted or what-not and never get a feel for the “map” up above us. My advice to any novice star-watcher is this: Start slowly. Pick one-just one- constellation and really get to know it. It doesn’t matter if you know anything about the stars (though obviously, that’s what I get off on) but just get a feel for the positions, brightness and color hues of the members of that constellation. When you know it well enough that it starts to seem familiar, like an old friend, pick another one next to it, and start to do the same, paying attention to how the 2 fit together. A natural way to progress is to take the next constellation East, as it rises in the sky above you over a few weeks.
After a while, “chunks” of sky will start to fit together, and large stretches of night-sky will become as familiar as your neighborhood, yard or office park. But unlike those places, even when you’re far from home, you can look up at night and quickly get a reassuring twinge of familiarity, of something you know and can count on, when you’re thousands of miles from friends and family.
2 weeks ago I landed in San Jose at night. It was one of those small Canadair jets where you all mill around on the tarmac for a bit, waiting for your roller-bags to be brought around. I’d been traveling a lot and working long hours, and I was feeling a bit down and beat up. I looked up and recognized the Southern sky- Orion, Auriga, Pleiades, Aldebaran, Gemini- the same familiar view from my own back yard- and suddenly I felt grounded, reassured, and well, not alone somehow all at the same time.
I’ve mentioned Gemini in passing a couple of times; it lies North and East of Orion, or as you’re looking South at the “upright” Orion, it’s above it and to the left. It’s not quite as obvious as Orion or the Big Dipper, but easy enough to spot that once you find it, you’ll almost always pick it out right away (sort of like Auriga.) “Gemini” refers to the mythological twins, Castor and Pollux, for whom the brightest, and Northern/topmost stars of the constellation are named.
Tangent: As most longtime readers know, 2 of my children- Twin A and Twin B*- are- yes, that’s right- twins. When people learn you have twins, they often ask questions about them. Some of these questions (“Are they identical?”, right after I’ve told the questioner they’re boy-girl) are just plain dopey, but most are just curious. One of the most common is: “What’s it like to have twins?”, to which my honest answer is: “It’s like having 2 kids the same age.” Really, that’s what it’s like. They don’t look particularly much alike, they don’t have a secret language, and one doesn’t say “ouch” when you poke the other with a pin (though in fairness, I haven’t actually tried that**.)
*They were named Twin A and Twin B by the OB during the first ultrasound, in the order in which he located them. As it turned out, they were born in the same order.
Nested Tangent: When I answer the “secret language” question (always in the negative, of course) the questioner always seems a bit deflated. People so want twins to have a secret language or special connection or telepathic powers. But it just isn’t the case. Sometimes I try to console the disappointed questioner by offering some other mental-prowess factoid in our family, such as Bird Whisperer’s ability to recall endless animal-related facts, or my own ability to recite the entire prologue from Bitchin’ Camaro, but these feats never seem to deliver what the questioner was looking for.
It’s an interesting question though, because you know who does often have a secret language? Married couples, that’s who. Think about it- if you have a long-term spouse or partner, I’m betting the 2 of you have code-words for things you want to communicate but don’t want others to understand*. Awesome Wife and I have number of code-words we use. One example is “boob job”, for which we use the word trabajo (Spanish word for “job”.)
*My own birth family used the Greek words for things like “money”, “tip”, “shut up”, or “woman of questionable moral character.”
Of course lots of people around here speak Spanish, and for a time we wondered whether trabajo was really a great code-word choice. Then one day about 4 years ago, coincidentally I found myself in a Mexican resort hot tub with 4 other guests, none of whom I knew. 2 were an American couple, who through their interactions with the waiter, had made clear that they spoke zero Spanish, and the woman sported a rather impressive (but frankly improbable) trabajo. The other 2 guests were Mexican men, both doctors, on vacation from Mexico City. So I chatted a bit with the doctors, in Spanish, and then asked them- carefully- what a boob job was called in Spanish. I had to ask it in a roundabout way, so as to avoid any obvious English cognates which the Americans might pick up on. So I said something like, “When a woman has had medical construction to the front part of the chest to make larger those specific parts, what is it called in Mexico? A trabajo?” It took a few tries, but finally one understood. “No,” he explained helpfully, “it’s not called a trabajo, we call it SILICONE…” thereby clearly and loudly articulating the one cognate I’d been hoping to avoid…
And generally they interact with one another much like other similar-aged siblings- sometimes best of friends, sometimes arch-enemies. What is different about having twins is 2 things. First, you tend to notice differences in development- walking, talking, reading, times-tables, bike-riding, skiing- much more so than you do between ordinary siblings. And second, you have absolutely zero patience for anyone else’s singleton-oh-having-a-baby-and-getting-up-in-the-night-is-so-hard story. Until you have newborn twins (or other multiples), you have absolutely no idea what “hard” is.
Castor and Pollux are the brightest stars in Gemini, and the easiest to pick out. Right off the bat, if you stare at them for just a bit, you’ll notice something pretty cool- they’re different colors. Pollux, on the left/Southeast and just a titch brighter, is orange, while Castor is appears white.
Pollux is orange, because, like Betelgeuse and Aldebaran, it’s another late-in-life, helium-fusing red giant. At 34 light years it’s closer than either of those stars, practically right in the neighborhood. But that’s not the cool thing about it. No, the cool thing about Pollux is that it is the easiest star in the sky to find that we know has a planet. That’s right- if you want to know you’re looking at a star with planets, just look up at Pollux.
To be sure, the planet we know of orbiting Pollux isn’t anything like Earth, but rather a giant almost 3 times the size of Jupiter. Bigger planets are easier to find* than little planets, so it doesn’t mean that Pollux doesn’t have smaller, Earth-sized planets, just that we haven’t found them.
*Specifically, Astrometry- or the detection of position changes of a star due to gravitational influences- and Transit Method- slight dimming of a star due to a partial “eclipse” by an orbiting body- both work better the larger the exoplanet in question.
Pollux’s planet lies roughly the same distance from Pollux as Mars does from our own Sun, but due to Pollux’s size it appears far larger- nearly 6 times as large- in the sky as our sun does in ours. Planets around red giants have so far appeared to be pretty rare, possibly because such planets don’t fare so well when a star becomes a giant.
Side Note: As it turns out, there are 2 other planet-bearing stars within Gemini. The first, HR 2877 Geminorum, lies slightly outside the main constellation. It’s known planet is 6.5 times the size of Jupiter and orbits at a distance similar to that between Venus and our sun.
The second, HD 54554 Geminorum, is a yellow-white dwarf star lying inside the constellation. Its planet, nearly 5 times the mass of Jupiter, has highly elliptical orbit, ranging about 130 million miles to more than 300 million miles from the star, with a “year” of ~3.5 Earth-years. Imagine if our sun increased in size and shrank every year by more than 2 times!
But cool as Pollux is, Castor is even cooler, the most complex multiple star system we’ve looked at yet. Through a half-decent telescope, it appears as a double star. The 2 stars, Castor A and Castor B, are both hydrogen-fusing white stars*, orbiting each other once every 445 years, in a highly elliptical path, which brings them as close together as about 70 times the distance from Earth to the Sun, and as far apart as almost 138 times the Earth-Sun distance. But it turns out that each of these 2 stars has another, closer companion. Castor A’s close-companion (Castor Aa), is small orange star about half the mass of the sun, and orbits the main star every 9 days at a distance of 11 million miles. Castor B’s close companion (CastorBb) is a small red star, also of about ½ a solar mass, orbiting the main star every 3 days at a distance of less than 3 million miles.
*This makes them Class A stars. Our sun, which shines yellow-white, is Class F.
Extra Detail: Both of these small companions BTW, are spectroscopic doubles, meaning that they’re too close to be distinguished by telescope, but instead are detected by analyzing variations in the spectrum of the (apparent single) star which are cause by the close companions orbiting one another.
So Castor’s not a double star, it’s a quadruple. But wait- we’re not done yet! Orbiting this elliptical foursome at roughly 10 times the (average) distance between Castor A & B, and completing its circuit around them every 14,000 years, is another star, Castor C, which turns out to be yet another spectroscopic double! This double is 2 small red stars, each with about 60% the mass of the sun, which lie just over 3 million miles apart and orbit each other every 19 hours. So Castor is actually a sextuple system, consisting of 2 double stars orbiting one another, which together are orbited by another double star! Wow, that’s one complicated star.
Another interesting thing about Castor is that, like Mizar, Merak, Alioth, Phecda and Megrez in the Big Dipper, Castor appears to be part of a moving group, that is a bunch of stars of similar age, composition and presumably origin, which are headed in the same direction. But the Castor Moving Group doesn’t include any other stars in Gemini, which is one of those constellations in which practically none of the stars have much of anything to do with one another*. From our perspective it’s a broadly scattered group of a couple dozen stars, including Fomalhaut in Pisces and Vega** in the Summer Triangle.
*For example, Pollux is 34 light years away, Castor 51, and Mekbuda 1200 light years distant! Mekbuda is the true monster of Gemini; if it were in the position of our sun it would occupy a full 30 degrees of sky.
**A bright, fascinating star whose eventual fate might impact life here on Earth. I plan to blog about it come Summer.
In between Pollux and Castor, on a clear night, you may spot a dim star between the two, closer to Pollux. This is Sigma Geminorum, which may not look like much, but if your vision extended into the X-Ray end of the spectrum this would be far and away the brightest star in Gemini, and one of the brightest in the entire sky. Sigma Gemini is a double star, consisting of a giant and a dwarf that have become tidally locked*, with the same sides always facing each other (like the Moon and Earth.) This locking has effectively sped up the rotation of the giant, amping up its magnetic field, which in turn is heating the corona of the star and making it shine brightly in the X-Ray spectrum.
*I explained tidal locking in this post.
Mebsuta, a supergiant 900 light years away, is interesting in that it’s a late-in-life star of about 9 solar masses, right on the cusp of ending it’s life in a supernova, like Betelgeuse. But stars less than about 10 solar masses, end up as white dwarfs (as our sun will.) Mebsuta’s close enough to the limit that it could go either way- maybe blow up, but probably just burn out…
Practically every star in Gemini has a cool story, but we’ll wrap it up with just one more- Wasat. This star is classified as a “subgiant”, which means that its hydrogen core is just giving out, and it’s morphing into a giant. But that’s not the cool thing. Wasat lies within 0.2 degrees of the ecliptic, the path that the sun travels across the sky. Since the planets orbit the sun on a rough plane, this means that pretty much every visible planet* passes by Wasat at some point.
*Visible, as in naked-eye visible, is the important qualifier here. All the naked-eye visible planets (Mercury, Venus, Mars, Jupiter, Saturn, and maybe, sorta, possibly if you have phenomenal eyesight and the sky is super-clear Uranus) orbit pass within 7 degrees of the ecliptic. Pluto is off by as much as 17 degrees, and distant Eris is off by 44 degrees.
If fact, if you’ve been watching Gemini of late, you’ve no doubt noticed the huge orange star- brighter than any star in Gemini proper- just to the East of Wasat. That’s no star of course, but rather the “star” of this winter’s sky- the Red Planet.
Next Up: All About Mars