24 08 08
School is back! It's time for the pencils and books and iPods to make a reappearance in the hallowed halls of learning. But wait! That means it's also time for the instructor to utter the words, "And did anyone learn anything new this summer?" Well, rather than answer with nothing but a blank stare or a goofy look that never seems to meet the teacher's eyes, let me do this: I'll throw you - or your son or daughter - some interesting facts about the universe that will be sure to make them think twice before challenging you again in class. Ready?
1. I learned that most stars up there have companion stars orbiting them, but thankfully we do not.
Stars are born in huge nurseries and as a result have dozens to hundreds of nearby siblings. Most of them end up gravitationally bound to another, some so close they nearly touch. Some star systems up there are triplets, some quadruplets, some quintets. There are even sextets.
Our star is the equivalent of an only child. Its brothers and sisters have long since left home. But that's a good thing. This way we have no other nearby stars knocking us off our very delicate orbit around our life-giving sun. But we are a minority. Most stars above have sibs.
2. I learned that the nearest star beyond the sun is not alpha Centauri!
Most people incorrectly say that alpha Centauri is our nearest neighbor at a distance of 4.37 light years. But alpha Centauri has what we believe to be a little brother, proxima Centauri, that is slightly closer to us at 4.2 light years. But proxima is a red dwarf star, meaning it is small and dim, with an apparent magnitude of near 11. Translation: Don't even bother looking unless you have a telescope; you will not see it. But however dim it may be, it is closer.
3. I learned that the biggest volcano in the solar system is not on earth, it's on Mars!
We have some mighty big volcanoes on this planet. We all awe at Vesuvius and St. Helens and Pinatubo and Soufriere and their explosive destructiveness. Our biggest volcano, though, is the relatively docile Mauna Loa on the big island of Hawaii. It rises nearly 14,000 feet above sea level, and from its submarine base to its high-altitude peak it is more than 3000 feet taller than Everest. And it is made of more than 15,000 cubic miles of rock. It is capital-B big.
But there is one still bigger - much bigger. On Mars there is a volcano called Olympus Mons. This guy is a heavyweight, one that makes our volcanoes look like dust bunnies. It rises to a mind-numbing 88,500 feet above the Martian surface and stretches more than 340 miles across.
But why does Mars get the big guy and we do not?
Mars has no plate tectonics so volcanoes there in days gone by would grow and grow without plates shifting and reshaping and pulling them under. And Mars' gravity is less so, believe it or not, its volcanoes can grow much higher.
4. There is gravity in space!
Surprise! A very common misconception is that in space there is no gravity. Things just float about. Well, not exactly. Everything that has mass has gravity. That means you and I and your dog and that TV remote over there all have gravity. And a body doesn't run out of gravity after a certain distance; gravity merely diminishes with distance. So, in a very literal sense, all things in the visible universe are attracted to one another. Gravity fills space.
But far away from a planet or star the gravity is so slight that it almost appears to vanish. But it's there! You will fall towards something. This all-pervasive force is how planets orbit around stars, and how stars orbit around galaxies.
Learn anything new? Hope so. To all students out there, young and old, have a great school year! Teachers, too!
10 08 08
We're having a tough month here in southern California. August has three big sky events this year - a total solar eclipse, a partial lunar eclipse, and a meteor shower - and we might get to see one of them.
The solar eclipse happened in a narrow strip across Siberia and China. The lunar eclipse on Saturday will put on a show for everyone on the whole other side of the planet. Neither have offered any hope for us here.
Our best chance of one of the August events happening here is the meteor shower Monday night, during the late night/early morning hours. It is then that we experience the peak of the annual Perseid meteor shower. But will the movements of the Moon, responsible for our other August phenomena, interfere with this one?
For those of you new to astronomy, a meteor shower is a wonderful thing to behold, with the sky putting on a fireworks show, free of charge.
It happens when earth's orbit happens to cross the orbit of a comet. Now I know what some of you may be thinking: Crossing
paths with a comet means death and destruction. That is true, but only if we are at the crossroads at the same time.
Think of it like an intersection of two circular streets; streets that have but one car on each, streets that are thousands of miles around. The chance that the two cars actually collide at the intersection is slim to none.
No, a meteor shower happens when we pass through the intersection and slam into the dust particles left by the comet which has already passed by and is long gone. The Perseid meteor shower is a result of our slamming into debris left behind from Comet Swift-Tuttle.
Because the orbit of Swift-Tuttle is slightly askew to our orbit, our Northern Hemisphere gets the brunt of it, and people there get a much better view of it than our southern friends. And we see the shower best when our planet swings around full-face into the crud stream. That means that after midnight is the time to see the best and brightest the shower has to offer.
And when the Perseids are good, they are amazing. Averaging about one per minute at the peak, the meteors are usually bright and beautiful.
I say "peak" because it actually takes several days to get through the debris. It is just that Tuesday, early morning, is when we go through the area most concentrated with the schmutz. That also means that if you have already seen some bright meteors in the sky in the last week, and/or if you see some in the next days, the prime suspects are Perseids.
Why are they called Perseids? The tradition in astronomy is to name a shower after the constellation from which the meteors appear to streak. You will notice, if you are able to see several of them that they appear to be shot out of the northern skies. If you had the time, you could draw lines back from the streaks to a point in the northern constellation of Perseus, their seeming point of origin.
Now, the not-so-good news. Our Moon, which put on the fabulous solar and lunar eclipse shows for the rest of the world, will partially ruin this year's Perseids. That is because that same orbit which blesses us with the eclipses will be taking the Moon close to Full by the time the Perseids peak. And a bright Moon can mean ruination for a meteor shower which practically demands the darkest skies. Good news? The Moon sets at about 2 AM.
Bottom line: If you want to see them at their best, be brave and adventurous and head outside after the moon has set. Wipe the sleep from your eyes, lie down, and look up. If they are good this year, you'll swear you are still dreaming.
Until next time, clear skies!