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Some notes on Visual Urban Astronomy

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#1 Charlie Hein

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Posted 19 January 2013 - 08:50 AM

Some notes on Visual Urban Astronomy

By Tom Bryant

#2 rmollise

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Posted 19 January 2013 - 09:33 AM

Nice review and very well written. Only one nit to pick: FILTERS. Filters are extremely valuable tools for the urban astronomer. But you have to have the right filter and use it in a manner which allows it to do its thing properly. Forget broadband filters. They are of use to imagers and that is it. The place to begin is a UHC filter. AND...you must prevent ambient light from entering the eye lens end. Do that with a UHC or an OIII, and you will, like I did, find yourself seeing many nebulae you thought impossible.

Finally, many galaxies that are not point sources look great from the city. You just have to experiment with optimmum magnification, which can vary a lot, and wait for the object to be as well placed in the sky as it gets.

Great article. :cool:

#3 PhaedrusUpshaw

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Posted 19 January 2013 - 12:09 PM

Comprehensive and concise, well written Sir.
Keep looking up!
Bill

#4 Philip Levine

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Posted 19 January 2013 - 12:31 PM

Hi Tom,
I enjoyed your article very much. The link to the dark sky map was also helpful.
Regarding the Night Assistant program, I have Windows Vista and downloaded the recommended files, but could not find the "BrightStarsDB.zip" file. Is this the "naData12.zip" file?
Ran "java GetParams" via command line in the "classes" subdirectory, to test the program, and just got a blank observing screen, not a configuration screen.
Did not see a ".bat" file anywhere.
What am I doing wrong? :question:
thanks, Phil

#5 chbau

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Posted 19 January 2013 - 04:51 PM

I found BrightStarsDB.zip at:
http://download.poly...pub/sourcefo...

Chris

#6 3c_273

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Posted 19 January 2013 - 04:59 PM

On Night Assistant: The Windows interface does not work as advertised.

It works fine on my Linux box, so the broken interface never became apparent!

I'm going to fix it over the next couple of days, so watch this thread for updates.

Sorry for the inconvenience!

#7 Urban Observer

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Posted 19 January 2013 - 07:52 PM

I really loved your article! Outstanding! Inspiring!
I immediately had very similar thoughts as Uncle Rod. That is; the only thing I don't agree with, is the part about some filters not being useful. I've been an urban observer for a while. And, see, I love nebulae filters. And, if loving nebula filters is wrong, then I don't wanna be right :)
Seriously, though, in my opinion they are (all) must have's. Even the lowly, barely useful, SkyGlow/Broadband types.
I wish you Good Seeing!
-Al
urbanastronomy.blogspot.com

#8 NigelR

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Posted 20 January 2013 - 07:34 AM

Greetings from Benoni in South Africa :-)

Thanks for a VERY interesting article - APPRECIATED!

Am guessing the 'bug' you mention is reason why when trying to configure / set-up version <nightAssistant09_62.zip> I only get blank screen?

As an aside, I also assume (very dangerous!) that naming convention for the database file differers between article and the Source Forge listing? The title of the required files reflecting the Bright Star (naData12.zip 2012-12-26 312.7 MB) or Feint (naData16.zip 2012-11-10 2.9 GB) data?

Awaiting 'fixed' Windows release soon!

#9 3c_273

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Posted 20 January 2013 - 09:59 AM

To all who have responded to the article, thank you for your kind comments and clear insights.

I've made several improvements to Night Assistant, and neglected to update the documentation, which many of you have pointed out. Many thanks for this. I've again updated the documentation, and it now reflects the current version of Night Assistant.

I *think* the Windows interface is right now, but won't be testing it until my Windows Guru (Kathie) tries it on her machine. I'll keep you posted...

Night Assistant was written because, 5 years ago, none of the available "Planetarium" programs did what I needed for my observing program. Things like finder charts to 12mv (now 16mv, mostly because Tom Corbin has an Obsession 18) and accurate double and variable star information at the click of a mouse. There are things it doesn't do, like control your telescope (My C-11 does a fine job on its own, and my C-8 has no computer interface), or show solar system objects (I can easily find the bright planets in my Telrad).
As I say in the notes, the source code *is* included, and you are encouraged to expand the program.

As to the notes about filters. Based on your comments, I'll be buying a UHC filter soon. Lumicon, TeleView, Celestron, or Baader? I'd like to hear what you think about these. Based on my experience with Tom C's O-18 with and without the UHC, I've concluded that the filter really helps emission nebulae, but little else. If we called them "nebular filters" it might be a bit more accurate. Again, I'm interested to hear your take on them.

#10 Project Galileo

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Posted 20 January 2013 - 07:48 PM

Great article. Thank you. Very interesting.

#11 3c_273

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Posted 21 January 2013 - 12:15 PM

The Night Assistant program runs flawlessly on Linux, but only brings up a tiny window on Windows. That window, when expanded, is a large black square, totally useless.

A quick Google search did not find an easy answer. I'll keep working on it.

So much for the Oracle/Sun/Java claim of "Write once, run anywhere"

#12 3c_273

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Posted 21 January 2013 - 08:53 PM

The continuing saga of Night Assistant

-or-

There's nothing like software development to allow you ample opportunity to make a chump of yourself.

I've got it working in command line mode on Windows. From the classes folder, run "java GetParms" and it should come up. I'll revise the documentation tomorrow. Promise!

You'll need to download the latest version, 09_7:

https://sourceforge....bservethestars/



#13 WRAK

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Posted 22 January 2013 - 04:58 AM

Great call for visual amateur astronomy despite light pollution I can only support. What I do not buy is keeping full telescope magnitude limit with heavy light pollution - there is some loss due to the brighter background to calculate on a logarithmic base depending on the value for the naked eye magnitude limit like for example:
TLM = 9 + 5 * log10(D_in) - LN((6.5/NEML)^2.512) giving a TML loss of about 2mag for an 8" scope with NEML of 3.
This formula does not base on any optical theory and is only an approximation based on own observations under heavy light pollution so it might very well be possible to do better under specific conditions but when it comes to split double stars you will have a hard time with companions fainter than this value.
Wilfried

#14 Ed D

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Posted 22 January 2013 - 09:33 AM

Well written article that serves as a guide for visual astronomy in light polluted environments.

Ed D

#15 Philip Levine

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Posted 22 January 2013 - 12:43 PM

Hi Tom,
With the most recent download and info I was able to get the Night Assistant program to run on Windows. "java GetParams"
Thanks for your hard work and patience.
I'm sending a pm.
thanks again, Phil

#16 3c_273

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Posted 22 January 2013 - 04:26 PM

Night Assistant should work on Windows now. That said, I never run in on Windows, so I'm looking for intrepid souls to try it out and get back to me with what works and what doesn't. Of course, there SHOULD be no difference, but I'll believe that when your reports are in. Please get back to me on my hotmail account:

rkk_529 (At sign) hotmail.com

Many thanks in advance and Clear Skies to All!

#17 Starman1

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Posted 25 January 2013 - 11:35 AM

The limiting magnitude of a scope cannot easily be defined by just a simple formula.
The sky brightness is only one concern. Other factors include (and I may be leaving some out):
--altitude of star
--cleanliness of optics
--extinction factor (related to altitude of site and transparency of the air)
--color of the star
--experience of the observer
--age of the observer
--magnification used
--etc.
So the limiting stellar magnitude of an 8" scope can reach as deep as 16 in a pristine site with all other parameters optimum, or as little as 12-13 if conditions are not optimum.
My normal limit in an 8" (I used Roger Clark's excellent star cluster charts) was 15.1-15.3 in a dark, but not pristine, site, and I reached 15.6 once in a near-pristine site.

So I was interested in seeing how deep I could reach here in L.A. in my backyard (a "white zone" light pollution area) and I regularly discovered that though the sky measured (with a Sky Quality Meter) between 3.5 and 4 full magnitudes brighter than my dark site, the dryness of the air and the often excellent transparency of the bright sky air enabled me to get to magnitude 13.5-13.8, or 1.5-1.6 magnitudes poorer than my dark site.

What it usually meant was that I had to use higher magnifications in the city than were needed in the dark site to see fainter stars. And Seeing conditions often interfered with that. Poor seeing can make the faintest stars invisible by smearing them out.

But it pointed out, as was pointed out to me by other observers, that you don't actually lose exactly the same magnitude in stars at the limit as the difference in magnitude between a dark site and a brighter one.

That's stars, however. Extended deep sky objects like galaxies are wiped out by small amounts of light pollution, reducing contrast, in many cases, to zero and making the objects invisible.

Narrowband filters can make many many nebulae and planetaries visible in even the brightest skies, but don't expect miracles--the faint outer envelopes of many nebulae simply disappear. Even in the extremely narrow bandwidths of those filters, contrast is reduced by the brighter skies. But I have seen, and viewed, the Orion Nebula in a sky so bright the stars in the sword could not be seen at all! And though M57 doesn't really need a filter at a dark site, it's still amazingly good with a filter in skies so bright <100 stars are visible in the sky and it looks like early twilight AFTER it's gotten "dark".

The point is that you should never take for granted that any object is invisible in a city environment. Many factors influence the limits we see, and Tom rightly pointed out that there is still a universe of objects to look at. There are over 5500 star clusters that are named, in the Milky Way, and the vast majority of them will be seen in an 8" scope. And don't forget the "star clusters" that aren't really clusters but appear to be (there are thousands of these and hundreds have names), called asterisms.

One could spend every clear night observing and barely dip into what's visible in even the brightest of cities.

Good summary Tom. Hopefully you've encouraged others to go looking from their urban backyards.

#18 JimP

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Posted 25 January 2013 - 07:07 PM

Excellent article. I enjoyed it very much. I have almost always lived in an area with significant light pollution, some areas worse than others. That is, of course, one reason I have spent most of my 47 years of observing viewing and imaging the Moon, planets and double stars. I have observed other objects and star clusters in particular, as you point out, can be really beautiful from light polluted areas and there are plenty to observe!
I also enjoyed looking at your log book. I write in a log book and have always been disappointed that my log is more a diary and I cannot quickly compare objects observed on different nights (and years) with different scopes. Your log allows you to add an observation made in 2012 between one made in 2006 and 2010. I like that very much. My only suggestion is that you write more, make it more enjoyable to read. What was the night like? Cold? Hot and Humid? What were some of your thoughts while observing? I suspect your kids and grand-kids and others down the line would be interested in your thoughts while you were out there observing.

best,

JimP

#19 3c_273

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Posted 27 January 2013 - 01:38 PM

Upgrades of Night Assistant Continue.

For all of you who've tried, and failed, to get Night Assistant working, my apologies! It had been 2 years since I had upgraded the documentation, and changes had been made.

I've reintroduced the "Help" button, and tried to upgrade both the FAQ:

http://observethesta...ourceforge.net/

and user's manual:

http://observethesta...sersManual.html

There have been several tweaks to the program as well. You no longer have to click a button to display a preformatted list or make a finder chart of a named object. Just fill in the text box and hit the Enter key.

Please try using it again, and I'd appreciate any feedback you can give, either in this forum or directly to me:

rkk_529 (at sign) hotmail.com

Thanks!

Tom

PS: What is the technical term that Microsoft uses for their test team?

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