[amsat-bb] Neked-eye viewing

n3tl@bellsouth.net n3tl at bellsouth.net
Thu Nov 6 07:23:23 PST 2008

Hey everyone,

I've followed with interest the recent posts about viewing AO-51 with the naked eye. With all due respect to previous posters, I'd like to offer a couple of thoughts.

First and most importantly, the relative magnitude of the celestial body in question - not its size - determines our ability to view it with the naked eye. I'm confident that everyone has, at one time or another, seen a meteor that was smaller than a 25cm cube. This is a case where size doesn't matter. More about that later.

Second, the relative darkness of the sky is the next most-affecting factor, I believe. Here in Athens, Ga., we don't have nearly the light pollution that folks who live an hour west of me must endure in the greater Atlanta area. But my skies aren't nearly as dark as those an hour east of me, in the rural areas of east-central Ga. and southwestern S.C. I see more here, routinely, than folks in Atlanta do. But folks another hour east see more, routinely, than I.

As was noted in a previous post, Orbitron shows the relative magnitude of satellites users ask it to track. With that in mind, I ran a 2-week prediction schedule for AO-51 to see how bright it would be in the night sky. Neither Orbitron nor any stargazing program takes relative light pollution into account. They provide predictions of magnitude. The more light pollution one has to deal with, the brighter an object will have to be for naked-eye viewing.

All of that being said - the brightest magnitude for AO-51 I was able to find for the next 2 weeks is 9.0. I suspect that others who run Orbitron predictions or those provided by other programs will find that a magnitude in the 9.0 range is about the brightest we'll get from the satellite.

When reporting magnitude, a lower number means a brighter object. I do not believe it is possible for anyone who lives even on the fringes of a metropolitan area to see (with the naked eye) any celestial body with a 9.0 magnitude. That includes the ISS. Naked-eye seeing in the night skies isn't about the size of the object, it's about its brightness (i.e., level of illumination). I just ran Orbitron's simulation mode and, using Los Angeles as my location, learned that during the 02:05-ish UTC pass of AO-51 (6:05 p.m., in southern California), it's brightest magnitude was 9.1. Based on that, I do not believe Clint saw AO-51.

On two occasions in the past year (i.e., since I finally picked up a halfway decent telescope!), I have been lucky enough to be looking at a star or planet when some satellite zoomed by in my field of view. It was pretty cool to see, and I consider myself fortunate. I recently picked up a pair of Nikon zoom binoculars (10x-25x x 50mm) for wide-field viewing, and I'm going to try to "find" our FM LEO satellites in the night sky with them in the coming days and weeks. I will not see them from here with my naked eye.

73 to all,

Tim - N3TL
AMSAT Member No. 36820
Athens, Ga, - EM84ha

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