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There are two things to note when using this chart, one: you should use averted vision to determine the faintest star visible, and two: you should add a tenth of a magnitude to the figure so determined to actually figure out how dark the sky is at the zenith (i.e. if 5.6 is viewable at Polaris¡¯ altitude, 5.7 is visible at the zenith).

Obviously the darker the sky is, the fainter the objects that can be seen. A Dark Site is considered one where stars of magnitude 6.2 or fainter can be seen.

Even worse for the urban observer, every magnitude lost due to the brightness of the night sky loses more than a magnitude of light grasp in the telescope because of contrast reduction. Since each magnitude is 2.512 times as bright as the next one, this means that you have to increase the light gathering area of your telescope by more than that (actually closer to 2.9 times!) to compensate for one magnitude of light pollution in your area. It¡¯s multiplicative, too¡ªtwo magnitudes of light pollution would require a telescope almost 8.5X as large in area to see the same as a smaller telescope at a dark site.

The good news is that the opposite is true¡ªgaining a magnitude by having the sky get darker (as when traveling away from a city toward a darker place) has the effect of increasing the size of your scope¡¯s area by nearly 2.9X. That¡¯s a VERY good reason to travel to the dark sites frequented by your local astronomy clubs, and a VERY good reason to take your telescope with you when going on vacation to the National Parks. Sometimes just traveling a few miles away makes a big difference in what can be seen. It¡¯s good that amateur telescopes are all quite transportable.


Our night skies weren¡¯t always this bright. In the US, the population has approximately doubled since 1950, yet the use of outdoor lighting has increased more than 10,000 times! It was once possible to see the night sky in the middle of our cities but today we can only make out the Moon, the planets, and a hundred or so of the very brightest stars. No doubt this growth was due to the lower prices of energy in the past. But energy isn¡¯t cheap anymore. Additionally, this surplus lighting is injurious to our safety and even health.

Today, there are organizations like the International Dark-Sky Association (http://www.darksky.org/ida/index.html) that are working with cities and states to revise our lighting to provide the same light on the ground (for our safety) without sending light upward where it is not needed. The Win-Win situation that will come about by the use of intelligent lighting is that we will light our cities with less than 50% as much power, provide the same (or better) light on the ground, and at the same time darken our skies once again so that we will go back to seeing the stars in the sky at night.

Many states and cities have already gotten in line with the idea of intelligent lighting--you can read all about it at the link provided.

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Lumicon #82A Light Blue 2 inch
Lumicon #82A Light Blue 2"
Item No. 735-22070
Manuf. No. Lumicon LF2075

MSRP: $38.00
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LUMICON #23A Light Red Filter - 2 inch
LUMICON #23A Light Red Filter - 2"
Item No. 735-22030
Manuf. No. Lumicon LF2035

Increase contrast and detail on the moon and planets! For use with standard 2'' eyepieces and accessories.
MSRP: $38.00
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Lumicon # 8 Light Yellow 2 inch Filter
Lumicon # 8 Light Yellow 2" Filter
Item No. 735-22005
Manuf. No. Lumicon LF2010

MSRP: $38.00
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LUMICON #23A Light Red Filter - 1.25 inch
LUMICON #23A Light Red Filter - 1.25"
Item No. 735-21030
Manuf. No. Lumicon LF1035

Increase contrast and detail on the moon and planets!
MSRP: $25.00
Our Price: $19.95
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