Better optics will aid in the search for other earths
The constellations we see tonight are the same as those our ancestors saw thousands of years ago. Are the starry patterns truly fixed, or do the stars move about?
A map of the stars was left to us by the Greek naturalist Hipparchus. His map was good – so good that more than 2,000 years later, it still shows the proper relationships among the stars … with a few exceptions.
Using the Big Dipper as a sky mark, one can “follow the arc” of the handle to find the star Arcturus. On Hipparchus’ map, Arcturus is out of place.
The stars do indeed move.
When 19th century astronomers added photography to their instrumentation, they discovered that the motions of some stars are not smooth across the sky. Rather, these stars wobble across the sky.
More recently, astronomers have detected slight changes in the colors of certain stars – the Doppler shift, analogous to the “stretching” or “squeezing” of the sound of a train whistle as it moves past us. Moving toward and away from us, these stars too are wobbling.
Start the music, grasp hands, and swing your partner round and round. If you’re an adult and your partner is a child, you’ll do most of the swinging. But your child partner will still have some effect on your path across the dance floor. Your trajectory will wobble.
Like our dancers, stars wobble because they are bound (gravitationally) to smaller companions. Such companions may be small stars; the brightest star in the sky – Sirius, the Dog Star – wobbles through space accompanied by a white dwarf, the Pup.
In 1995, astronomers discovered in Cygnus the Swan a companion object even smaller than a dwarf star: a planet. From details of the wobble, they could calculate the planet’s mass, its distance from its star and the length of its year (how long it took to go around).
Just as marbles come in bags, stars come in galaxies. Our galaxy, the Milky Way, contains somewhere between 100 and 200 billion stars.
Picture the bowl of the Big Dipper as a picture frame; within that frame, astronomers have found over 1,500 individual galaxies. A rough “guesstimate” puts the number of galaxies in the universe at something like 100 billion.
Given such astronomical numbers, it’s not hard to imagine other planets where conditions would allow us to live … perhaps planets on which beings are living already. So far, though, all we can do is imagine.
By analyzing the colors absorbed as starlight filtered though its atmosphere, astronomers have recently detected the element sodium in the air of an extra-solar planet. Using the same principle, we should be able to detect oxygen. Oxygen reacts with rocks and metals; to remain in an atmosphere, it must be continually replenished … presumably by living beings such as green plants. Finding oxygen in a planetary atmosphere is tantamount to finding life.
The larger a planet, the larger – and easier to detect – the wobble it causes in a star’s trajectory. So far, all of the extra-solar planets discovered have been “Jupiters” – gas giants not amenable to life.
Advances in astronomy, like those in biology, follow almost inevitably from advances in optics. As our optics get better and better, we’re entering a new age of exploration. Sooner or later, we should expect to discover smaller terrestrial planets amenable to earthly life.
Our sun – and Earth – will not remain hospitable forever. Terrestrial planets we discover today may become home for our descendants some billions of years in the future.
Trained as a biologist, Alan Stahler is also an amateur astronomer. He teaches biology at Bitney Springs Charter High School. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).
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