Putting a telescope in space has its limitations. It can't be too big, it's difficult to repair, and it costs a lot of money. So why do we even do it?
Ground-based telescopes are also subject to weather. On the ground, we tend to put optical and near-infrared telescopes high up on mountain tops or in deserts where rainfall is minimal so that we can maximize the number of nights with clear skies. (These locations also help avoid light pollution from neighboring cities.) But there will be cloudy or rainy nights when telescopes on the ground are out of luck.
There are also some wavelengths where the atmosphere doesn’t matter at all, and observations can even be done under cloudy or rainy conditions. For example, at longer radio wavelengths, the light is not easily deterred by motions in the atmosphere or by any intercepting clouds. The more limiting factor for the crispness of images from radio telescopes, relative to optical telescopes, tends to be the size of the telescope rather than the atmosphere. So radio telescopes are built where it is convenient to put a very large dish, like in karst limestone sinkholes in the Puerto Rican jungle.
What Is Adaptive Optics?
Astronomers are developing tricks to improve observations here on Earth so that our ground-based observations might better compete with those from space-based facilities, at least in the optical and near-infrared. Adaptive optics, for example, allows astronomers to correct for the distortion or blurring of images by the atmosphere using deformable mirrors. By observing a nearby bright star while also observing the astronomical target of interest, instruments can model the motions of the atmosphere in real time. That model is then used, again in real time, to adjust the shape of the telescope’s mirror to cancel out those atmospheric distortions.
But what if the planet or galaxy you want to observe is not close to a nearby star that can be used for this modeling? Are you out of luck? In that case, astronomers just shoot a giant laser into the sky and observe that instead. So cool!
The Hubble Space Telescope helped us to measure the expansion rate and the age of the universe, to image in detail moons in our solar system, and to observe the catastrophic supernova explosions that end the lives of certain stars. The Spitzer Space Telescope has shown us galaxies from a time when the universe was still very young and told us the most we know about any star system of planets outside of our own. We can observe a lot from the ground, but our space-based telescopes are crucial for unlocking more of the universe’s mysteries.
Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at email@example.com. Image courtesy of nasa.gov