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Observing an old moon - tips?

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#1 zleonis

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Posted 11 September 2019 - 10:16 AM

October's S&T noted that October 27th could be a good opportunity to spot a very old moon. I'll happen to be in Virginia's Blue Ridge in late October during the last few days of next month, and it looks like there will be a window just before civil dawn to catch the moon about 16h30m before conjunction.

 

I'm planning to attempt the observation from an overlook with a clear view to the east/southeast that's about 2000' above the surrounding valley. I'll try to get there around nautical dawn - I'm hoping Mars and some of the brighter stars in Virgo are still easily seen so I can get familiar with the area and how it relates to terrestrial landmarks. I may try to use rough atl/az offsets to get my scope pointed at where the moon will be and then sweep start sweeping slowly when it rises.

 

Are there techniques that are more effective? What instrument is best (I have a 4" F/6 achromat and 10x50 binoculars)? How difficult an observation would this be - akin to a threshold nebula or something, or will it be reasonably obvious if it's in the FOV.

 

Thanks for sharing any thoughts or experiences!



#2 Tom Glenn

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Posted 11 September 2019 - 12:27 PM

If you can see the horizon clearly during twilight before the Sun is rising, then you should be able to find the nearly 1% illuminated Moon using binoculars.  Your challenge will be that you have a short period of time to catch it.  Using Roanoke, VA as a reference, the Moon rises at 6:49am local time, which is already after nautical twilight has begun.  Civil twilight begins at 7:12am local time, and at that time the Moon will be nearly 4 degrees above the horizon.  From this point until the Sun rises at 7:39am, it will become increasingly difficult to locate the Moon, so your best bet is to try and catch it as soon as it is above the horizon provided you can see all the way to the horizon clearly at some point in between 6:49am and 7:12am.  The earlier the better as far as sky darkness.  Binoculars will be easiest, although if you do have a clear view of it, you can locate it in the scope as well.  With clear transparency along the horizon (always iffy), it will be very obvious when you see it (even naked eye).  Good luck!  


Edited by Tom Glenn, 11 September 2019 - 12:28 PM.

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