19 Nov 2007
There is a comet in the sky tonight which is normally just an occasional no-big-deal visitor to our parts of the solar system, but which for some reason has made quite the spectacle of itself this time around. And it's time for you and friends or family to go out and take a look at the little show-off before it fades away.
Comet 17P/Holmes is a "periodic comet" (hence the letter P in its name). "Periodic" is just astrospeak for "it takes less than 200 years for this guy to go around the sun." Comet Holmes only takes about 7 years to make a complete circuit.
The "Holmes" part obviously is for the man who discovered it. Edwin Holmes, a British astronomer, discovered the comet in 1892 while sightseeing around the constellation Andromeda.
The comet had just had an "outburst," a phenomenon in which a comet suddenly throws out a pile of dust and gas which gets lit up by the sun. This causes the comet to brighten many magnitudes. What may have been visible only through a telescope just hours ago is now so bright it can be seen naked eye. And Holmes was the first to see it.
And that is what appears to have happened in the last several weeks to this normally inconspicuous comet. At the end of October, this tiny little critter suddenly brightened from magnitude 17 to about 2.5 in just a couple hours. Translation: what could only be seen through the best backyard telescopes could now be seen merely by looking up into the night sky.
Now how to find it. Go out tonight and first allow a few minutes for your eyes to adapt to the darkness. Then face northeast. Look up a little more than two-thirds into the sky from the horizon. There you will find a faint circular glowing cloud in the constellation Perseus. That glowball, my comet-seeking friends, is Comet Holmes.
You will not see the expected long tail of the comet. Why? Currently we are passing by Holmes in our orbit. The sun is on one side, Holmes is about 150 million miles on the opposite side. So far, no problem.
Now the tail of a comet is caused by the sun's solar winds blowing the expanding dust and gas away from the comet, out to the farther reaches of the solar system. Since we are in the line of sight, the tail is being blown away from us, not to either side. We're looking at the comet "head on."
Use a telescope or binoculars to bring out more of the details. Binoculars are enough. And keep an eye on it in the next weeks. Will it just fade back into anonymity? Will it have another outburst? Will its tail become more visible? Will its hue continue to change in subtle ways as has been observed lately?
These are all questions you can tease your young astronomer son or daughter with. Comet Holmes might be the one minor cosmic event that sends a youngster into a future in astronomy, perhaps some day to discover a comet of her own.
Until next time, clear skies!
14 Nov 2007
In the next few days we will celebrate the 435th anniversary of The Event, an seemingly innocent incident which took no more effort than for one man to look up into the sky and see something new - and then act on it. That deed was one which helped change the face of astronomy forever and helped us all see the cosmos in a brand new light.
In November 1572, Tycho Brahe was just a 26-year-old Danish nobleman who had recently become interested in astronomy. He became fascinated in the discipline after seeing an eclipse (as do many people), and continued to delve into it - but especially after what he saw on that fateful day.
In Tycho's day there was a profound paradigm shift in western thought being birthed. Whether this new arrival would survive or not was yet to be seen. Tycho unwittingly made sure it would live by happening to be in the right place at the right time.
The prevailing worldview concerning the universe then was that the entire cosmos went around us, around the earth. It was the geocentric theory. There are several reasons why nearly everyone accepted it. For one, it actually does appear that way, it does seem that the entire heavens go around us like a giant starry-speckled sphere around our static planet. But, just as importantly, the philosopher Aristotle had said it was so. That Aristotelian philosophy of nature had been the great fortress in western thought for centuries.
That great imposing wall of geocentrism had begun to weaken - just decades before Tycho arrived on the scene - when a Polish monk named Copernicus had the gall to propose that the earth actually went around the sun!
There were a couple reasons why Copernicus's heliocentric ideas were not accepted right away. One was that this was before the invention of the telescope and there really was no convincing evidence proving we went around the sun. (It's tougher to prove than you think!) Another was that it was just plain asking too much. People love their worldviews, and feel safe there, unchallenged.
So how did Tycho affect it all?
Aristotle's views of the heavens included the belief that they were immutable, unchanging. For there to be a change up there implied Aristotle may have been - horror of horrors! - wrong! When Tycho looked up in that sky on the 11th of November 1572, he saw a bright and shiny new star, a "stella nova." Located in the constellation Cassiopeia it was quite literally a star not seen before.
Most dismissed the nova as some atmospheric phenomenon, not some event amongst the starry hosts. But as Tycho observed it, and took data on it, and analyzed that data, he realized that is was indeed in the distant starry heavens. There was something new over the sun.
It turns out what Tycho saw was what we now call a supernova, the intensely energetic death of a giant star. The remnants of that blast can still be seen today.
This was actual evidence needed to start the destruction ball swinging on Aristotle's universe. A few decades afterwards, Galileo, using his first primitive telescopes, got more evidence that the geocentric way of thinking was on its last legs by observing the craters on the Moon, moons around Jupiter, the phases of Venus, and even blemishes on the Sun - all evidence against Aristotle's view of flawless heavens.
Surprisingly, Tycho did not adopt a heliocentric world view. He had his own system which he felt much better explained all the observations. His universe had the earth as center, with the Sun orbiting around it, but with all the planets orbiting the sun. It wasn't true, of course, but it fit the limited facts of the time.
After Tycho's untimely death Johannes Kepler, Galileo, and Isaac Newton all helped bury the geocentric - and tychonic - systems forever.
But one might arguably say that the whole revolution really heard its first evidentiary shots when a young, ambitious astronomer saw something new in the skies - and acted on it.