FirstLight Astronomy Club

33°29.6'N / 117°06.8'W / 1190 ft.

The Summer Triangle - Vega

The skies above are filled with stars whose patterns try - successfully - to force our minds to see common geometric shapes in them. There is the quadrangle outlining Orion, the trapezoid trapped in Hercules, the Great Square of Pegasus, the semicircle of the Corona Borealis, and that dipper-looking thing in... well, the Big Dipper.

During the summer, above our heads throughout the night, is a triplet of stars that plots out a very nice triangle. It is called, to no one's surprise, the Summer Triangle.

It is made of the stars Vega, the brightest of the three, Deneb, the northernmost, and Altair.

In this week's column and for the next two consecutive, we will spend our time getting to know these three a little better - by looking at the constellations they call their home, their mythical pasts, and what they mean to us in the sciences.

Let's start with Vega, the brightest star overhead in the evening and the fifth brightest star in all the sky. It is part of the constellation Lyra, a tiny but story-filled collection of stars.

Lyra's story comes to us westerners from a story involving the likes of the mythological Mercury, Orpheus, and Eurydice. In short, it goes like this.

Once upon a time, Mercury fashioned a really nice harp out of some strings and a nice shell he found on the banks of the Nile.
Apparently it made one sweet sound, so sweet that Apollo traded Mercury his wing-tipped, snake-entangled, power-filled staff for it.

Sweet deal!

Eventually Apollo passed on this lyre to his son Orpheus, who used it to get his dead wife, Eurydice, back from Pluto, King of the Dead, after Eurydice had a fatal accident.

Orpheus played the lyre so well that Pluto told him to go ahead and take Eurydice back home to the living, but with this restriction: He may not look back to the Death Realm on his way out.

Surprise! Orpheus glanced back at the last moment and - alas! - Eurydice slipped back into Hades. No amount of strumming on his fancy instrument changed Pluto's mind.

Orpheus, still a prize to women who were enchanted by the sweet sounds of the lyre, was in such despair that he shunned his many wooers. Eventually the rejected women murdered Orpheus, and tossed said lyre in the river.

Jupiter, witnessing the whole thing but apparently more concerned about the lyre than Orpheus, commanded that the lyre be taken from the river and placed into the sky. It can be seen tonight in the exact spot where Jupiter had it placed.

Vega, the brightest of stars of our tiny celestial lyre, is a blue star a mere 25 light years away. It is only about 3 times bigger than our sun, but because of the laws of stellar burning, pours out 60 times more energy than our star. It, like so many other stars, is best seen at a great distance. Trust me.

But because of its great size, it is burning its fuel quickly and will live just a fraction of the time our sun will, maybe a mere billion years total. It's probably at midlife now.

One interesting fact about that bright starry beauty is that it used to be our Pole Star, and will be again. Right now, Polaris, the North Star, sits in that coveted spot. It is directly over our planet's spin axis, specifically the North Pole - so all the stars appear to spin around Polaris.

But our planet, like a spinning top, slowly wobbles over time - very slowly. Because it wobbles, or precesses, the star directly above our planet's axis changes over time. About 14,000 years ago, Vega was overhead, a fact alluded to in ancient Akkadian and Sumerian texts. But if you missed it the first time, don't worry! Vega will again be our pole star, when we spin back around to it in about 12,000 years.

In our next installment we'll hop over the Milky Way to another point of the Summer Triagle - Altair.

Until next time, clear skies!

AM/PM Mini-explanation

Some of the most common words and phrases we use are based on phenomena in the skies above. All the days of the week, some months and seasons, even the names of some geographic features of our globe, can find their origins in the heavens.

And our common terms of telling time, specifically the ubiquitous AM and PM, are also based on the movements of the sun above our heads.

For most of us, AM and PM are quick and simple ways of indicating morning and afternoon or evening. But it goes a little deeper than that. Ready?

AM stands for ante meridiem, Latin for "before the middle of the day." PM is for post meridiem, "after the middle of the day."
So far, so good. Before noon, after noon - no big deal. But what exactly is the middle of the day? And is my middle of the day the same as yours? If not, how does that change things?

It takes no great strain of the imagination to see the middle of the day as the time when the sun is highest in the sky, essentially dead between sunrise and sunset. But let's be more precise.

Imagine splitting the sky with a line from true north all the way over your head down to true south. We could call it the meridian, the midday line, and that's what astronomers call it. It is the border between AM and PM. Before the sun gets there, before the meridian, we have AM. When the sun gets there, we have midday or "local noon." Afterwards, it is PM. But, as we'll see, this noon is not the noon we are accustomed to.

This whole midday line and how the sun moves through it is one of the foundations for the old sundial way of timekeeping. But the old observational ways of telling time pose a great problem in the modern world, because - cue dramatic music - not everyone's meridian is the same!

It is easy to see that when the sun reaches midway in an Arizona sky, it still has a ways to go before it reaches midway in a California sky. More dramatically, the sun at the meridian in San Diego still has 5 minutes of sky-crossing before it reaches meridian in Los Angeles. Bottom line: Go east or west and your time changes.

Imagine living back 150 years when timekeeping was indeed important, but pretty much only at the local level. You live in a village or city, and most of your life was spent doing business there. You set your watch or clock by the local noon, a time determined by the sun in your own local sky. All is well.

But then the train is introduced to modern civilization and suddenly great distances are covered in short order. Now you go a hundred miles to the east or to the west in a day and the sun isn't exactly moving with your watch. Because of this, you must constantly reset your timepiece to match the local time.

Some clever people at the end of the 19th century saw a big mess coming as more people traveled, and came up with the idea of time zones, huge areas locked into a certain time regardless of when the sun was crossing the local meridian.

Of course this move saved a lot of time adjusting timepieces, and meant people in different cities could synchronize when to meet or call or plot. But it also meant that noon was no longer true noon, AM and PM had lost their original meanings, and sundials went the way of the dodo. Scheduling a duel at "high noon" was a thing of the past.

Again we see that the great lights in the heavens, especially that bright one that rules the day, has far-reaching effects in nearly every facet of our lives together down here, even if the effect is slightly modified by man. Timekeeping, temperature, climate, weather, ocean currents, seasons, a host of astronomical influences, and of course life itself can find a common starry thread in the sun.

Until next time, clear skies!
Temecula Valley High School / Temecula, CA · Some images © Gemini Observatory/AURA Contact Me