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Last updated: 6 December 2011

Subject:	Spreadsheets
Sent:	Monday, December 5, 2011 14:03:27
From:	Mike Scott (
You helped me out in a few email exchanges last year, and you help me
continually through your discussions on your Cassiopeia Observatory.
Thank you.
As a way of sharing, I have attached two very simplistic spreadsheets I
made for myself. There's nothing new or sophisticated here, I just made
these to make observing more organized and fun.

The EyepieceCalculations spreadsheet calculates the power, exit pupil,
and true field of view. I use it as a reference for the eyepieces I have
as well as any I'm considering. The spreadsheet shows the results for my
eyepieces and telescope, but others can simply change all the cell I've
marked in yellow to reflect their equipment (telescope focal length and
aperture, and eyepiece size and apparent field of view.
The ApparentMagnitudeAndBrightness spreadsheet is just a table showing
the brightness difference between two stars. I did see a similar table
in Burnham's Celestial Handbook, but it required making some
calculations for most of the magnitude differences I was looking at.
Here's what I posted a few days ago on my blog to explain why I made
this table and why it matters to me:
This is pretty basic information but I'm still sharing it for two
reasons. First, it has been completely overcast and windy for the past
two days, so what would have been observing time gave way to projects
like this. Second, even though Astronomy 101 teaches that a star with an
apparent magnitude of 5.0 is 2.512 times brighter than a 6.0 magnitude
star, these brightness differences amaze me.

That's particularly true when I apply these differences as I observe.
For example, my site's visual limiting magnitude is about 6.0. My
telescope lets me see stars with an apparent magnitude fainter than 13.
That difference of 7 magnitudes means the dimmest star I can see with my
naked eye is 631 times brighter than what I can see through my

Or consider a variable star that has a range of 4 magnitudes between its
brightest and dimmest. Small numbers like that are deceptive; they just
don't sound like that big of a deal. But a range of four magnitudes
means the star is 40 times brighter at its brightest. That's an
impressive change. 

Thinking about brightness when you look at apparent magnitudes or
magnitude differences puts what I'm looking at in perspective and makes
going out in the cold weather this time of year well worth the effort. 
Mike Scott

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