FreeLists / az-observing / [AZ-Observing] Re: R: 2008 All Arizona Messier Marathon - results

[Andrew Goodwin <a.goodwin1@xxxxxxx>]

     Two other points of consideration:   according to my GPSr the last 
two outings where I set up the altitude was 1,719' at N32 27.664 W111 
43.880  and 1,708' at N32 27.669 W111 43.819.   There is a mountain 
range to look over at the horizon though I do not know the hight of 
these mountains perhaps some one could add this data to the mix.

Andrew



Tom Polakis wrote:
> Did Lorenzo really view M77 at astronomical twilight, when its altitude was 
> only 1 degree, or did he pick it up some minutes before then?  When several 
> of us spotted M74 on March 29, 2003, the time was about midway between 
> nautical and astronomical twilight.  The sun was around 15 degrees below the 
> horizon.
>
> Jeff, since the Earth is not flat, the 1/cos(zenith angle) approximation for 
> airmass breaks down at low altitudes.  Check out the plot in this Wikipedia 
> article.
>
> http://en.wikipedia.org/wiki/Airmass
>
> The plane-parallel curve does indeed go to  57 airmasses at 1 degree, but a 
> more realistic model would give 26 airmasses -- still a huge number.  My 
> guess is that Lorenzo found M77 when it was a few degrees higher, and it was 
> extinguished by 10 or 15 airmasses (only 3 or 4 magnitudes).  Since M77 is a 
> Seyfert galaxy with a very bright core, perhaps he saw only the core.  That 
> would count!
>
> Tom
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