18 Apr 2011
A couple of weeks ago I had the pleasure of driving up the great slopes of Mauna Kea on the big island of Hawaii with my astronomy club. We traveled to the top of one of the biggest mountains on planet Earth to visit some of the world’s premiere telescopes.
It was very cold, it was oxygen-depriving, and the UV levels from the sun were intense - the summit of Mauna Kea is a very inhospitable place at nearly 14000 feet above the paradisal shores of Hawaii. Then why do universities and corporations spend hundreds of millions of dollars for real estate on the arid, lifeless top of a remote island in the middle of the Pacific, a place that looks more like a Martian landscape?
Well, the reason is clear. No, really, that’s the reason - it’s the clarity. They are built up high and away because up there we can see the skies best.
Think about what interferes with our viewing the heavens from down here near sea level. We are at the bottom of an ocean here, an ocean of air. The atmosphere, although life-giving, is a nemesis for those trying to decipher the information of our celestial sphere. It bends and distorts the path of the light we are trying to get. It is like trying to talk under water - a lot of information gets garbled. Get high into the atmosphere and the heavens' speech becomes clearer.
Up at those great heights we can also get above much of the cloud layer. Every time we drive up to the summit of Mauna Kea we drive through banks of clouds only to break through to crystal-clear skies. Of course, clouds and water vapor cannot be completely avoided every day, but the higher elevations increase our chances of clear, steady skies.
A look at the locations of these observatories will reveal one more advantageous characteristic - they are away from the bright lights of humankind.
It is for that reason that a high mountain is not enough, it must be at least somewhat desolate, as well. The observatories on Mauna Kea, being on the less populated Big Island, are drenched in darkness. No awful, interfering light pollution to ruin a dark sky there.
And it’s not just Mauna Kea, of course. Look around at the great observatories of the world. They are located on isolated mountaintops in Chile, Arizona, South Africa, Russia, and the Canary Islands.
And of course the magnificent Hale Telescope is built atop our own Mount Palomar. When it was planned in the early 20th century there was essentially no light pollution there. Nowadays, sadly, city lights creep in around the mountain like some ghostly beast.
Observatories are great edifices revealing the secrets of the skies and are built in those isolated locales for a reason. If you get the chance, visit some. But dress for the occasion; it is not a stroll on the beach.
04 Apr 2011
We have two interesting questions from readers this time - one about planets twinkling, another about telescopes cheating.
The first is from Mrs. Crouch Madden of Oceanside. Her question has to do with why planets don't seem to twinkle, at least not like the stars do.
Why stars twinkle at all was handled recently, so I won't repeat it all here. (Recall it had to do with the redirecting of the star's light through tiny pockets of air of different temperatures up in our sky.)
Stars will "twinkle" because they are so unbelievably small in the sky. Obviously stars themselves are huge, but are so far away they are really nothing more than points of light in our skies above. So anything that bends the star's light makes it appear like the whole star itself is jumping around.
But planets, although smaller comparatively, are way, way closer to Earth. They are far bigger than mere points in the sky. So, if the light from - let's say - the "left" side of the planet gets bent one way, light coming from the "right" side probably won't get bent in the same way. In that way, the zillion photons coming from all over the planet's surface can effectively compensate for each other and cancel out the "twinkle" effect. Thus planets appear relatively calm in the skies compared to their hyperactive, jumpy cousins, the stars.
A second question comes from Darrill Andries of Lake Elsinore. He wonders if since telescopes can see so well for so far, if they might not also see events out there before we can, we poor souls who have not the benefit of big lenses and mirrors.
It sounds like a perfectly logical question. Scopes see way "farther out" into the universe, so why shouldn't they see a supernova long before our naked eyes ever see it?
That is until you realize that the ability of the big scopes to make things appear closer has nothing to do with them actually being closer. They are stuck on or around Earth just like we are.
When those telescopes show us monstrously big images of distant beauty they have no benefit of being closer - but they do have the benefit of gathering a lot of light and magnifying images.
Bottom line: They receive their light - their information - at the exact same time we do. They are the same distance from those events and objects, so they have absolutely no advantage over our simple eyeballs as far as "when" things happen.
But, oh my, what they do show us are cosmic masterpieces invisible to our naked eyes.
Keep the questions coming and until next time, clear skies!