Saturday, December 6, 2008

Arizona Observing Session

We made two trips to the Riparian Preserve in Gilbert while I was in Arizona. The first trip was actually on Saturday evening, the night before the butterfly and bird photos were taken. We wanted to have a look at the small observatory set up on a slight rise in the middle of the park which houses a 16-inch Meade telescope. Called the Gilbert Rotary Centennial Observatory, it is open free to the public every Friday and Saturday night, weather permitting. The East Valley Astronomy Club manages the observatory for the reserve and two volunteers were in attendance when we arrived and before the evening was over, about 60 people dropped by to have a look through the scope.

I had sent an email to the member of the club responsible for events, to ask him if we could join the club's Deep Sky Observing session which was scheduled for that evening. Thanksgiving night was a new moon and the skies should have been very dark. Unfortunately, I sent the email too late to receive a reply in time to make plans to drive out to the site the club uses for their dark sky viewing, but I did make the acquaintance of several members of the club who were very friendly and said they would be very happy to have me join them with my scope the next time I am in AZ.

In talking to both the volunteers at the observatory and the third club member that I contacted by email, it appears that they have the same problem in AZ that we do in LA, i.e., light pollution, although we have to drive further to escape the city lights than they do. The Riparian Preserve was a great place for birdwatching, but not so great for astronomy. I was surprised that the sky was not as dark as I was expecting and only part of the problem was glow from the city lights. The park itself had dozens of lamps lighting the paths, especially the path around the lake which was next to the observatory. These lamps were attractive but not the kind that aim the light down at the ground, but instead in all directions including up. The light in the photo above is not one of the more offensive ones. It has a shade which aims the light down.

The volunteers explained that they had the key to turn off these lights, but that they were afraid to do that due to safety concerns. I suggested that they plant some bushes on the hill on the lake side that would come up to the mid-point of the observatory. The scope could not look down in that direction anyway, and the bushes would block some of the light from human eyes. All the light prevents your eyes from becoming dark-adapted which allows you to see fainter and fainter objects. It takes half an hour for your eyes to fully adapt to the dark and any bright light you look at, like passing car headlights, starts the process over again.

The other problem was all the water surrounding the observatory. Water creates water vapor, especially in the desert, which reflects the light, which makes the sky a grayish color instead of a deep black. So while the scope was very capable of bringing in some fairly faint objects (the Andromeda galaxy, the Ring Nebula, the Orion Nebula and Trapezium, etc.), the background remained gray. This was most disappointing when we viewed M45, the Pleiades, which is stunning when the "Seven Sisters" and their companions shine like diamonds on a black velvet background. I was surprised to find that we actually have darker skies here in LA when looking out over the ocean. The volunteer commented that he thought the clear, clean, ocean air, free of particulates of all kinds, would offer a better background for the stars than AZ skies.

Meanwhile, back home, the guys in my own club (SBAS) had to cancel their dark sky observing session due to high Santa Ana winds. Sigh. It's a wonder that any astronomy ever gets done.

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