19 Aug 2007
This is the last of our trilogy on the starry points of the Summer Triangle. Our first two visits took us to bright blue Vega and her companion across the Milky Way, Altair. Now we will sail upstream, along the Milky Way to Deneb, the main star in the constellation Cygnus the Swan, and the northernmost of our triad.
Cygnus is also known as the Northern Cross. (You'll never guess why.) But not only does our constellation look like a cross, it also, surprisingly, looks like a swan! Remember, not many constellations actually look like their namesake; Cygnus is an exception.
If you go out tonight you can see the cross overhead, with the top of the cross in the north, the foot of the cross more southerly and almost overhead. One can imagine the pole of the cross as the swan's body, with is tail on the north end, and head at the south. The two perpendicular stars are its outspread wings.
There are several stories that accompany the Swan. But one is a story that remains fresh especially in today's culture with our fair share of wild youth.
Helios, the sun god, had an ungodly son named Phaethon. As is the nature of many young sons, he decided to take his dad's Sun Chariot for a spin one day. Big mistake. Phaethon was not the best driver and apparently had little respect for the houses of the gods and their peaceful existence above. His hellish driving put the heavenly hosts in immortal danger.
Jupiter was not amused. He finally decided he had had just about enough of this young whippersnapper, and chucked him from the chariot. Thrown to earth in a flash, Phaeton fell fatally into the river Eridanus. Enter Cycnus.
Cycnus was a friend of Phaeton. Devastated by the turn of events that resulted in his friend's death, he felt it his duty to collect every body part of his charred, dismembered friend for a proper burial. He made several arduous dives into the Eridanus to gather all his remains.
Seeing all this devotion, Jupiter and his minions were moved. So Jupiter decided to reward Cycnus for his act of selflessness, although the reward by today's standards may not be a welcome one.
Jupiter thought it would be nice to turn Cycnus into a waterfowl! And since he ruled the heavens there was no discussion about it. Behold! Cycnus metamorphosed into a swan. And his name was now Cygnus. And, as an added bonus, he was placed into the starry dome above where we see him still today.
Let's focus now on our star of the week, Deneb, the brightest star in Cygnus. Deneb is the top of the cross, the tail of the swan. Its name, like so many other stars, is from the Arabic. Al Dhanab al Dajajah is its full name, which means "the hen's tail."
Deneb is one of the brightest stars in the summer sky, but it is also very, very far away. Vega and Altair are just tens of light years away, Deneb is over 3000 light years beyond that!
What does this tell us? For Deneb to shine that brightly at that great distance makes him a monster big star. How big? Our best estimates put him at over 250 times the size of our sun!
Deneb may have a claim as Cygnus' brightest, and it may be one member of our very elite Summer Triangle club, but for a beautiful sight through the telescope, and a favorite at star parties, go to the foot of the cross. There, like two brilliant starry diamonds are Albireo, a double-star system containing a striking blue star and its reddish companion.
In fact, take a telescope and, using the Summer Triangle as a reference, scan the skies in the region and farther south down the Milky Way. You will find nebulae and double stars and what seems like sparkling dust, which is the star-studded Milky Way itself. It is an awesome trip. But don't scan too quickly, Jupiter might object and we know what happens to those who race through the Milky Way!
Until next time, clears skies.
05 Aug 2007
To most humans throughout history the stars have been more than mere points of light. We connect the dots and see the obvious shapes and figures, and if we look deeper, with our mind's eye, we see stories all over. It's the way we were designed, to see beyond the obvious - if we choose to look.
In our last time together we looked at some stories surrounding Vega, the great blue star directly above our heads in the evening, and one point in our Summer Triangle. Today we look closer at our second featured star in this trilogy, the star Altair in the constellation Aquila.
The bright star located to the south and east of Vega, just across the Milky Way, Altair together with Vega played a primary role in an ancient Chinese myth.
There are variations of this story, to be sure, but basically it goes like this. The Sun Emperor has a daughter, Tchi-niu, an expert weaver. Reliable sources say she could weave some amazingly colorful sunrises and sunsets.
But she is lonely, which in the old stories means romance is soon to follow. Sure enough, Tchi-nui looks out the window one day toward the river that we call the Milky Way and her eyes meet those of the herdsman, Kien-nou. Fireworks go off and they are in love.
The herdsman is very good at his job and so the Emperor has no problem with his daughter marrying this fine, young Kien-nou.
Things go well for a while, but soon the two begin neglecting their duties. Tchi-niu is not weaving her sunsets with the usual rich colors and Kien-nou's cows are wandering all over the place. What to do!
The Emperor is not pleased. After repeatedly telling them to get their proverbial act together, he finally banishes his heedless herdsman son-in-law to the other side of the Milky Way.
The star-crossed lovers cannot convince dad to change his mind. The now crestfallen Tchi-niu, try as she may, just cannot overcome her grief enough to weave out a nice sunset. The Emperor has to do something!
So he summons all the magpies in China to spread their wings into a bridge once a year, on the seventh day of the seventh month, across the Milky Way, so the couple can spend one day together.
We still see the two in the skies during the summer months, with Vega in the role of the weaver princess, and Altair as the herdsman. Sadly, our modern civilization with all its light pollution has all but dried up the Milky Way. Weaving any myth today about the two would require no magpie bridge; there is barely a river to cross.
To cold science, Altair is a type A star. That means it is about twice the size of our sun, with a surface temperature about 2000 kelvins hotter than our sun. It pours out more than ten times the amount of energy than our own star does. Again, not to beat the dead star, but Altair is another big, nasty star best kept at a distance.
Which is actually its standout characteristic. Altair is a mere 17 light years away, almost 100 trillion miles away. That, believe it or not, is very, very close as star distances go, just at the end of the block.
Altair is part of the great constellation Aquila, the Eagle. In our next time together we fly over to another great bird in the sky, Cygnus the Swan. Nested there is our third and last of the Summer Triangle, its northernmost star, Deneb.
Until then, clear skies!