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Surface Brightness

It is an unfortunate fact that many viewing locations skies are becoming less "dark", which is why I think this next request is increasingly crucial. I'm personally in Brooklyn (by the beaches where it's a bit darker) using an 18" Teeter f/3.7 and of course it's still challenging for DSOs beyond the popular object lists. So, it would be extremely helpful to add Surface Brightness (SBr) to the 'Object Info' screen but also to be able to Sort/Filter by that information. One of the formulas I have seen (from one of my favorite astronomy books "The Urban Astronomer's Guide") is as follows:

SBr = m +5 x log(d) - 5 x log(70)         where     SBr =Surface brightness, m=Visual magnitude, d=object size in Arcseconds

The popular example used is M101 -listed w/ a visual mag of +7.9 However, for most people viewing from local sites, a challenging SBr of 14.2.

So, it would also be really nice to sort the observing lists and searches by SBr (or SBr equivalent -whatever works for the programmers best). This way a person can begin to arrange a "Challenge DSO" list for themselves. When you combine this, w/ other requests (like for Filters, SQM, etc) observers can more quickly learn to stretch the perceived limitations of their scope & location -and improve their observation techniques to be able to bag those faint fuzzies.   

Thanks so much!

FYI - I'm adding (and have already added) a bunch of requests only b/c I want to be able to drop my supplementary apps and save time at the scope. There's no disrespect intended - I love the program and in addition to SkySafari Pro, I also own Starry Night, SkyFi3 -and even SkyBT (which I rigged to use successfully w/ my Android phone back in the day).  So basically, I'm your best customer ;-)






  • 0
    Bill Tschumy


    We have thought about this many times.  I'm somewhat skeptical of relying on that formula for the surface brightness calculation.  It works reasonably well when the object has a uniform brightness over its entire area.  It works much less well when the object has a bright core and an extended dimmer area.  The core can easily be seen although the formula might say the overall surface brightness is to low.

    Another example is that our sizes for globular clusters are close to the true object's size even though the outer halo is generally not visible though the eyepiece.  The formula would give it a much lower SB than is justified and might cause people to neglect an object that is definitely visible.

    I wish I had a good solution for this.

  • 0
    Jeffrey Herrera

    Hi. I do respect the difficulty as I agree with your examples, and understand these types of formulas work best for diffuse objects. It's definitely not a definitive measure but then again the problem is that neither is visual magnitude for many Nebulae, Galaxies -and even Globulars from my smaller scope. However, IMHO, seeing the two next to each other in 'Object Info' , which is already next to "Size", would be very helpful because the mind will quickly create a ballpark expectation over time (no matter what formula is used for Surface Brightness). A label like "Suggested Surface Brightness" might also tip the user this is not rock solid -though in a 'Pro' app, users already know better than to Not try something based on a single field description. The astro apps I've seen use a measure like this do vary from each other [I guess differing formulas] -but one gets used to the internal consistency of each apps' SB attempt -so I still find it useful when combined with visual magnitude. I'd even settle for just Nebulae and Galaxies having it. I understand if you decide not to, but I'd love for SkySafari to put their best SB formula out there and go for it - people will use it. Thanks

  • 0
    Bill Tschumy


    We can consider it and see how it goes.  I would love to have good SB estimates.

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