Unaided Vesta and a Moonbow

See a naked eye asteroid? Why not? I had never seen an asteroid with the unaided eye before and here was a good chance. Was it worth setting the alarm clock for 2am? Sure, you cannot answer that with a no if you are truly an amateur astronomer.

Off goes the alarm… wife starts grumbling… throw a few things in the vehicle… a few more complaints from my wife now up and awake… feed the cats… A kiss… and off into the dark. I setup at the end of the development where the streetlights have yet to be turned on, at the end of a dead end road surrounded by lots that have been graded but not yet built on. While setting up the gear I discover I am not quite alone, listening to hooves clattering up the road towards me. Someone riding by moonlight? No, just three feral donkeys that wander past. Later, the calm was broken by a male donkey being, ah, quite energetic, just up the hill, and willing to tell the world about it.

Conditions could have been better, Jupiter was a swimming ball, so much for a little planetary viewing to pass the time awaiting moonset. Transparency was only so-so with the usual low altitude tropical haze and the occasional cloud scudding through. So just sit back and enjoy the night for a while, and try to ignore the loud braying that occasionally disturbed the otherwise peaceful night.

As I waited for the moon to set I noticed a bank of clouds approaching from the northeast. The usual cloud bank over the Kohala volcano was reaching out a little further than it usually does. This was a bit of a concern, when the trade winds are blowing this cloud bank usually forms over the Kohala and with it a heavy misting rain that drizzles constantly in Waimea. I looked about at my gear and decided to cover some of it up in case this cloud bank got closer.

And it did, and as usual the mist was falling ahead of it driven by the steady breeze. Combine a wall of mist and a setting bright moon and the unexpected can occur. I looked out to check the cloud’s position and quickly did a double take. Hanging there in the wall of mist was a beautiful, ghostly moonbow. Grab the camera time!

Camera, tripod, remote shutter release… dash 50yds to where the big power lines would not dominate the picture… hope not to find the donkeys that are around here somewhere… find a spot on the rocks of the ancient lava flow where I could setup the tripod without endangering the camera or my ankles… in the dark… focus the camera… in the dark… frame… program the shutter release for a one minute shot… fire! Time for two frames before the moonbow faded from sight. A quick check of the frames and victory! Got it!

Waimea Moonbow
Moonbow! 1min, Canon 20Da, 17mm@f/4 with the lights of Waimea at center

With the fading moonbow and the setting Moon I was able to return to my mission objective, Vesta without optical aid. Finding the asteroid was trivial, just starhop up from Jupiter or down from ζOph and there is was. Swung my little TV-76 to the correct location and there it was, right on the location plotted. Easy to see at about 5.5 mag. a little brighter than HIP80793 at 5.6 mag. that was located about 1°sp. Naked eye was tougher, there was a line of 4-4.2 mag. stars coming up from Sco that was relatively easy, but it took averted vision to find Vesta and then only occasionally as it would appear and dissapear before my eye. I was clearly being hampered by the lousy seeing and poor transparency down lower in the sky. I am sure from a better site, possibly up on the side of Mauna Kea without the moonlight it would be quite simple to spot. I will need to try again before this opposition is over. That will have to wait a bit until after full Moon.

Vesta 28May2007
Vesta (marked), Jupiter and Summer Milky Way, 40s, 17mm@f/4, fixed tripod

Author: Andrew

An electrical engineer, amateur astronomer, and diver, living and working on the island of Hawaiʻi.

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