Date: February 25, 2010
Title: Where’s the Best Place for the Biggest Telescopes?
Podcaster: Rob Berthiaume
Links: www.yorkobservatory.com
www.youdontfreezeinspace.com
Description: Scientists and engineers spend millions of dollars and many years deciding what kind of telescope to build and how to build it. With such an investment, they also put a lot of thought into where they put it. In today’s podcast, Robert goes over the few key things they consider when deciding where to put their telescope in order to ensure they get the best performance out of it once it’s built.
Bio: Robert Berthiaume is a graduate student at York University in Toronto, Canada. When not working in the atomic research lab towards his MSc in Physics, you can probably find him at the university’s observatory, where he is allowed to use a telescope that the bank says he is definitely not allowed to buy.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by David Gwyn in honor of his wife Andrea’s brithday, who has given him the universe and shares and supports his love for the night sky. Learn more at btobservatory.com. Happy birthday, Andrea!
This episode of “365 Days of Astronomy” has also been sponsored by Tom Foster.
Transcript:
Hi there. I’m Robert Berthiaume bringing you the February 25th edition of the 365 Days of Astronomy Podcast. I’m coming to you from the York University Observatory in located in Toronto, Canada. Here at the dome, we get lots of visitors in the form of cub scouts, girl guides, school groups, university students, and the general public. While showing off our telescopes and the sights we can see through them, a few questions come up every time, no matter the age or background of the audience. We inevitably get asked about black holes, the moon landings, 2012, and how big the biggest telescope is and where it is? The answers: No, we won’t be able to look at a black hole this evening, no, the moon landings weren’t faked, no, the 2012 doomsday scare has no scientific or astronomical evidence supporting it, and lastly, well, that answer is a bit longer. It’s the subject of today’s podcast: where on Earth are the biggest telescopes?
The world’s largest telescopes have mirrors that are 8 to 10 meters across. They require precise optical configuration, the latest in cameras, spectrographs, and other instruments, complex dome enclosures, and more. They cost hundreds of millions of dollars and years to build, so when we build one, we think very carefully about where to put it. There are 4 big things to consider when deciding where to put our biggest telescopes.
It goes without saying that the best time to observe the stars is during the night, and obviously that’s because during the night it’s dark. So that’s our first big concern in deciding where to put our telescope. We need to make sure it’ll be dark where we’re observing. Now with the exception of being around the North or South Poles during their local summers, there’s always a night time anywhere else on the globe, so we’re guaranteed some natural darkness anywhere we put our telescopes on Earth. But in the last little while us humans have figured out how to build cities and light bulbs, and when you put the two together, you get light pollution. This is all the light that bounces up into the atmosphere from buildings, streetlights, signs, and makes the sky look brighter in the city than in the country. This makes it harder to see stars, and to collect good observations, so we’ll want to keep our telescope far away from city lights. The astronomers might have to commute a bit further to get to work, but it pays off in better observations.
The next thing that’s important to consider is the altitude of the observatory, or how high it is. We want to avoid putting the telescope at lower altitudes, like at sea level, and instead place it high up, like on the top of a mountain. You might initially think that this is so the telescope is closer to the stars so we can get a better look at them, but a change of a few thousand meters here on Earth doesn’t make a difference when we’re looking at things that are trillions of kilometers away. It actually has to do with something astronomers call ‘seeing’. You all know that there is a blanket of air surrounding Earth, called the atmosphere. And whenever you’re looking up at stars, you have to look through all that air to see them. Now if you’ve ever looked into a pool or lake, you’ll know the things at the bottom look more distorted and less clear than if there was no water there at all. The less water you look through, the clearer the view gets. The atmosphere does the same thing when looking at the stars; the less we look through, the clearer our view gets. Generally speaking, the higher the elevation, the better the seeing. By putting our telescopes high up on mountains, we look through less atmosphere, and get clearer observations.
Alright… So far we’ve narrowed our choices down to locations that are far away from big cities, and that are at high elevations for clearer observations. But dark skies and high altitude won’t make for good observations if it’s raining outside. So we need to further narrow our list down to places with good weather. More specifically, places with good weather on average. No matter where we are on Earth, there will be some cloudy nights; we want to be somewhere where there will be as few cloudy nights as possible. Luckily, we’ve got decades of weather records for just about every place on Earth, so we have a very good idea of what the average weather is, and how many clear nights per year there should be for a location.
The last really important thing to consider is…the stars. The telescopes we’re building are going to be used by astronomers all around the world for years and years, researching everything from quasars and active galactic nuclei to exoplanets and variable stars. These different things are scattered all around in different parts of the sky, and when we build our big telescope, we don’t really know who is going to be observing with it, what they’ll observe, and when they’ll be observing it. So our best bet is to make sure our telescope has a chance of seeing every part of the sky, at some point over the course of a year. Wouldn’t it be horrible if, ten years after our biggest, best telescope was built, a really interesting and rare event like a supernova occurs in the southern sky, but our telescope is near the North Pole, and so it can’t ever look at it? Well, it would be horrible! And that’s why we typically have one last constraint on telescope location: we want it to be near the equator. A telescope placed at the equator is able to see over three quarters of the objects in the sky on any given night. On the north or south poles on the other hand, the same telescope would only ever see half of the objects in the entire sky, ever.
So we have four things that limit our choices for telescope location. We have to be far from cities, at a location that has a high altitude and good weather most of the time, and that’s close to or on the equator. What’s the final answer? Even with these restrictions, there are still a few places that are good enough to be home to 8 or 10 meter wide telescopes worth hundreds of millions of dollars. Mauna Kea, a dormant volcano in Hawaii, the foothills of the Andes mountains in Chile, the island of La Palma in the Canary Islands all have large observatories housing many of the world’s largest telescopes. They are all within 30 degrees of latitude of the equator, above 2500 meters altitude, and far away from city lights. Well over 70% of nights are clear enough to make observations, and depending on the season, there can be stretches of clear nights that span weeks.
Now these are just the best places in terms of these four limiting, albeit important, factors. There are other large telescopes around the world that trade off some of these advantages for other things. Some telescopes are located closer to cities, or in the countries that are funding them. There may be more light pollution or further from the equator, but they aren’t as remote. Some telescopes have been built near the North and South poles. They’re able to see less stars over a year, but the stars they do see can be observed for hours on end during the long, deep, polar nights during local winter.
It should also be noted that these locations are the best places on Earth to put a telescope. That doesn’t mean they’re the best places ever. You can get darker skies, better weather, look through less air, and see all the stars in the sky in other locations: Namely, in space. There are observatories like Hubble and Spitzer that orbit up in space, where none of these problems exist. However, new problems pop up, like space radiation, orbiting, and extreme remoteness, which makes them extremely expensive to design them, launch them, operate them, and heaven forbid, fix them.
So in the end, there’s no single place that’s the best location for our best telescopes. If there was, all of our telescopes would be there. This I think is a good thing. It allows people all over the world to be a part of the discoveries and excitement the telescopes in their home regions bring, it keeps all of our telescope eggs out of the proverbial basket, and creates opportunities for cooperative projects across the globe, adding some humanity to the seemingly serious and scientific task of observing the cosmos.
That brings me to the end of the podcast. I hope you learned something, and thanks for listening. Until next time, this is Robert Berthiaume wishing you all clear skies and good times.
End of podcast:
365 Days of Astronomy
=====================
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.