Seeing Stars . . . and Light Scattering
Written by: Kyle Butz
This spring, my wife and I took a vacation to Hawaii during which one of the highlights involved looking at the night sky near the top of Mauna Kea. Mauna Kea is the tallest peak on the big island towering over 13000 feet in the air. It is known around the world as one of the best places on the planet to star gaze and numerous high powered telescopes are stationed there looking into the depths of the universe.
High above the clouds on a bumpy, gravel, winding mountain road, the summit of Mauna Kea seemed to be a drive not worth making for much of the ascent. However, upon reaching top, the reasons for the rave reviews we had read became crystal clear. Watching the sunset with telescopes opening and the moon and stars rise was amazing.
Well below the summit at 9000 feet, the visitor center below comes to life each night with several telescopes set to see different night sky features. When we were there, we saw Venus, Mars, Saturn and the moon up close and more stars than I had ever seen at a distance.
It was then that volunteers from the center come out with laser pointers in hand and provide a tour of the night sky. From the Big Dipper to the Southern Cross and everything in between, constellation and bright stars in the night sky were pointed out.
During this tour, I couldn’t help but notice the laser light scattered from dust particulates in the air (much to the annoyance of my wife) from the cars descending the mountain. The resultant light scattering off of dust particles is a clear example of laser diffraction. With the proper detection in place, one could examine the particle size without a problem.
While this may seem irrelevant, it actually may be more relevant if we think of the telescopes at the top of the mountain. The road to Mauna Kea’s summit is mostly gravel, and with gravel comes dust. However, the final half mile splits into two segments, one neatly paved, the other a gravel road. This gravel road has a speed limit of 5 mph I can only postulate is based on dust generation from vehicles. The paved portion obviously generates minimal or no dust at all. Dust into the air near telescopes can impact the multi-million dollar devices effectiveness. Dispersed dust settles anywhere and everywhere, including telescopes that open every night. By limiting the dust generation every night, the scopes will work more effectively. The dust’s ability to disperse itself in air is a particle size question that can be monitored by a laser diffraction measurement. The result of this particle size question was likely paving a path near the top of the mountain while leaving nearly all the bottom rough gravel road untouched.
If you get a chance to visit the Mauna Kea, I would highly recommend it. And when you do, I hope you keep your eyes open looking for stars and keep your mind active on how and why things are the way they are. Sometimes you’ll find something in the details that relates.