Re: [ATM] What is a NEO scope?

[vorblesnak@peak.org]

I have Newt but found the Limiting Magnitude listed for an F4 scope of
various diameters to be lower than what others seemed to suggest.  A
search for LM in the archives brought up a discussion from April 2000 on
the limiting magnitude of the eye with a link to a Stellafane page
reproduced below ..

http://www.stellafane.com/atm/atm_select_scope/atm_scope_calc.htm

On that page the formula for LM is given as (cut and pasted) ..

Limiting Magnitude (ML) = Meye + 2.5 * log10( D2 * t / Deye2 )

Using some common constants it would be

ML = 8.5 + 2.5 * log10 * (D^2 * .70 / 49)

This assumes a limiting magnitude for the eye of 8.5 as stated on that
page,  70% light transmission for the scope and a pupil diameter of the
eye of 7 mm.

Using Google for the calculator and plugging the above in I get ..

16" D = 17.6 limiting magnitude
24" D = 29 limiting magnitude

So a 24" scope should be a good NEO diameter as far as limiting magnitude.
With CCD imaging it should be even better.

Comments?  Disagreements?  Expansions?

David Davis
Toledo, OR


>
> David,
>
>   Weeeeelllll, if an object that crosses Earth's orbit just happens
> to be big enough and crosses path with Earth, it could ruin your
> after-noon.
>
>   I ran the following magnitudes through ECU 4.0 (latest revision of a
> popular
> planetarium software). Should the info get line wrapped, I'm listing
> limiting
> magnitude and how many Near Earth Objects it can detect. ECU uses the data
> set
> available from
> http://cfa-www.harvard.edu/iau/Ephemerides/Unusual/Soft10Unusual.txt
> Mag 16   2
> Mag 17   4
> Mag 18   9
> Mag 19  27
> Mag 20  50
> Mag 21  80
>
> I don't have access to Newt or something similar that can translate
> telescope size
> and FL to limiting magnitude, but IIRC a 12 inch F6 limiting magnitude is
> 17.
>
> Tom

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