EYEPIECE AND APPARENT BRIGHTNESS CALCULATIONS
Last updated: 6 December 2011
Subject: Spreadsheets Sent: Monday, December 5, 2011 14:03:27 From: Mike Scott (email@example.com) 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 telescope. 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. Sincerely, Mike Scott http://redmountainobservatory.blogspot.com
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