Monday, November 5, 2018

Last night I saw Neptune...

... and thought about horizons.

("Last night" was actually last Saturday, but I did start to write this on Sunday.)

I grew up in Arizona in the 1950s and 60s. I took for granted that the horizon was 30, maybe 40 miles off, and the sky overhead was an infinite expanse of blue, blue, blue. I have vivid memories of topping a rise on one of my many family trips "up north" (to Payson or Flagstaff) and seeing revealed to my eyes range after range of mountains receding into the distance, each one 30 to 40 miles further away that the one in front of it.

How different it is here "back East" (as we used to say). Here the horizon is seldom more than one or two hundred yards away. On rare occasion (usually on a highway when you're paying no attention to such things) you might actually see a mile or more in front of you, but that's not so often and you're almost always distracted from enjoying the view by the need to watch the traffic right next to you.

I remember (when I was old enough to see the humor in such things) laughing whenever the weatherman said that "visibility is 10 miles at BWI" when I could plainly see the Moon overhead. I wanted desperately to shout at the radio, "No! Visibility is one quarter million miles!"

Neptune, as seen from Voyager II

Neptune is not the easiest target to find in the night sky, especially for someone like me who resolutely (some would say fanatically) eschews any and all electronic or mechanical aids to observing. My "finder scope" is a pair of 8X56 binoculars hanging round my neck. And, no matter how faint the objective, I stick with starhopping as my one and only method of navigation. Last night, it was find the Water Jar in Aquarius. From there, it was a fairly easy slide down to Lambda Aquarii, a star on the ragged edge of naked eye visibility in light polluted suburban Maryland. Then scan westward until I have a kite shaped asterism centered in my field of view. Neptune (in my mirror imaged view) hung off the left side - a tiny blue dot with just a hint of a disk. Switch to a higher powered eyepiece and the non-stellar nature of the dot became more apparent.

A quick check with the ephemeris and one finds that Neptune is currently two and three quarter billion miles from the Earth. Knowing full well that I will never see Pluto or any other Trans-Neptunian object with even my largest telescope (a 102mm refractor), I acknowledge that this electric blue dot in my eyepiece is the furthest thing I will ever see within our Solar System with my own eye. And I cannot tear myself away from it. I care not that there are hundreds of DSOs clamoring for my attention on this rare evening of perfect conditions. I can't get enough of this sight, this "dot".

I don't care how silly this sounds, but 2.75 billion miles I can understand. But interstellar distances? They defeat me. Oh, it's easy enough to say the words, "This star is 840 light years away," but we all know that such words don't really mean anything to us. The distance is simply too great to comprehend. And don't get me started on intergalactic distances!

I think I spent maybe all of 20 minutes drinking in the view and pondering what I was seeing. Then it was on to some double stars that I really wanted to observe that evening. But it was Neptune that haunted my thoughts all the way home, and Neptune that first came to mind the following morning.

We don't think much about horizons in suburban Maryland - not when houses, buildings, and trees restrict our view to a few yards around us. Stargazing can be a useful corrective to our everyday perspective on things.

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