Light Show

As you know, I have a great love for science and cosmology. I seem to have a very technical side that enjoys unraveling mysteries, or at least following the work of those who do so.

But I also love beautiful things, and very often the tools and findings of science are beautiful themselves, even as they reveal the beauty of the universe.

A great example of this beauty is pictured above. The twin Keck telescopes which are perched atop an extinct volcano called Mauna Kea on the big island of Hawaii, at an elevation of 14,000 feet.

The Kecks are masterful designs, true testaments to human creativity. And they are also beautiful. From the graceful domes that protect their delicate instruments to the huge sectioned hexagonal mirrors at their hearts, they just leave me in awe. And can you think of a more beautiful location? They don’t sit there just so astronomers can work in a paradise though, Mauna Kea is a perfect location for a telescope: high elevation to minimize atmospheric distortion, no close mountains to stir up the air, very clear skies, and a thousand miles of temperature-moderating ocean all around to provide stability.

These instruments are designed to “see” in both the optical and near-infrared parts of the spectrum. The 36-section hexagonal aluminosilicate ceramic mirrors are the largest optical/Infrared mirrors in the world.

The two Kecks can work together to form what is called an astronomical interferometer with an effective mirror size of 279 feet, or they can each take observations separately.

The Kecks have one amazing feature that sets them apart from other telescopes and it’s an awesome piece of technology. Because of manufacturing issues and the warping effect of gravity on large heavy objects, segmented mirror designs are needed to produce mirrors larger than about 200 inches (the previous largest telescope, which held that title for many years, was the 200 inch Hale at Mt Palomar). So the Keck uses a set of 36 hexagonal mirrors interlocked to make one big mirror. But these mirrors have to be aligned to each other nearly perfectly. An alignment error of 1 millionth of an inch would be catastrophic to the observation. The Kecks have the most advanced alignment and drive mechanism of any telescope. The mirrors are aligned by a computer that checks their relative heights in hundreds of places twice every second. Minute corrections are made nearly instantly to bring the mirrors into alignment.

That’s all amazing, but there’s more. Because these mirrors can move independently, they can also be used to correct for atmospheric disturbances that hinder the clarity of all ground-based telescopes. The initial design of this system worked like this: the telescope has an optical sensor that locks on to a bright star (which is called the guide star) close to the site in the sky being observed. By measuring the changes in the brightness of the guide star caused by atmospheric disturbances, the system can calculate the corrections required in the mirrors and send that information to the mirror alignment computer which then corrects for them. This is called Adaptive Optics, and as implemented it was an ingenious system but it had a huge limitation: only about 1% of the sky is close enough to a star bright enough to use as the guide star. So the system was re-imagined in a very novel way

The Keck telescopes can now create their own guide stars.

“In the upper part of the Earth's mesosphere (90±10 km altitude), there is a 5-10 km thick layer rich in Sodium atoms, deposited by the ablation of micrometeorites. These atoms can be excited and caused to radiate by spontaneous emission by projecting a pulsed laser tuned to the Sodium D atomic transition (589 nm) in the direction of the science target.”

Laser Guide Star (LR)

So, using powerful lasers, the telescope can excite particles in the extreme upper atmosphere to the point that they radiate light. This light can be used as a substitute guide star for correcting atmospheric disturbances. It’s genius. This new system is called LGS AO (Laser Guide Star Adaptive Optics). You will notice that the guide star laser is a pretty orange-yellow color – that’s the color of a laser tuned to the 589 nm wavelength as needed to cause this effect on Sodium.

LGS AO works so well that the Keck telescopes now routinely produce images that are sharper than the Hubble Space Telescope.

The Kecks have produced some of the greatest discoveries in astronomy during the last decade, including the discoveries of more planets than any other instrument, including the Kepler spacecraft.

All that and of course, I think they really are beautiful to look at.