[AZ-Observing] Re: MM date limits (again)

  • From: AJ Crayon <acrayon@xxxxxxxxxxxxxx>
  • To: az-observing@xxxxxxxxxxxxx
  • Date: Wed, 17 Mar 2004 19:50:23 -0700

Tom, funny you should mention this topic - last night I took a much 
closer look at M30s elevation at twilight.  Actually it is about 1/2 deg 
above the horizon at the 5:07am MST time given for astronomical twilight.

Why did you pick the sun at -10 deg?  Is this from experience or a gut 
feeling?  Could it be from some actual calculations that balance M30's 
magnitude and sky brightness.  One would also have to factor in not only 
the mountains, but the elevation of the site plus sky glow from Tucson 

Actually the site Gerry Rattley used in 1985 was down Dugas Rd, about 
five miles north of Cordes Junction and at that time had a very good 
eastern horizon - much better than the rock quarry of today.

As far as the 1996 feat - I remember it quite well.  There were several 
of us trying to see M30, including David Fredericksen who called to me 
to come see it in his telescope.  I didn't go for two reasons, one it 
was 200' away and I was trying to see it in my 8" but never did.  Never 
the less many of us had a chuckle over the incident.

Finally, while I don't think one can say M30 can't be seen, it will take 
a lot of luck and depends on not just the above mentioned factors but 
also on instrument, experience and the fatigue factor.

Tom Polakis wrote:

>The subject of the date range of a perfect score in a Messier marathon
>lends itself well to comparing observations with desktop planetarium
>software results.  Naturally, I can't resist analyzing it to death.
>On the morning side, 25 people at the 2001 Arizona marathon saw M30 as part
>of their perfect score.  This one was held on March 24/25.  And on March
>23/24, 1985, Gerry Rattley was the first documented case of somebody seeing
>all 110.  This is the earliest date for M30 documented on the SEDS site,
>with the exception of one outlier.  There is one observation of M30 from
>the Arizona marathon on March 16/17, 1996.
>Here's what the software shows.  With the sun at an altitude of -10
>degrees, the altitude of M30 is:
>March 16/17: 3 deg. 23'
>March 20/21: 5 deg. 13'
>March 23/24: 6 deg. 35'
>I am not so certain that M30 will not be visible from the Arizona City site
>next Sunday morning.  I don't know the altitude of those distant mountains,
>but they can't be more than a couple degrees (it's always much less than
>you estimate during daylight).  The marathon window for our latitude may be
>as long as 10 days.

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