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DSLR Astrophotography Untracked

Aug 15 2015 01:22 PM | project nightflight in Articles

With DSLRs and standard camera lenses astrophotography is on the verge of a new epoch, where tracking is no longer absolutely mandatory. When we heard about the technique described in this article, we immediately wanted to give it a try. It allows any stargazer using a modern DSLR to capture colorful, noise-free images of deep-sky objects, without an equatorial mount or tracking device needed.

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Blue Skies, Red Sunsets & Company: Part 3:...

Aug 02 2015 08:30 AM | Snickersnee in Articles

The time between sunset and night's darkness is divided into three intervals based on how brightly the sky is illuminated.

 

"Star light, star bright,

 First star I see tonight,

 I wish I may,

 I wish I might,

 Have the wish I wish tonight."

This familiar nursery rhyme is actually a good definition of civil twilight, which starts at sunset and continues until the brightest stars are first seen. It's the common legal meaning of twilight, as there is still light for many outside "civil" activities and most streetlights haven't been turned on. Technically it ends when the sun is 6 degrees below the horizon, or about 25-30 minutes after sunset for temperate latitudes most times of the year. Sunlight still streams 20 miles up. Nautical twilight continues from this point until the horizon blends with the sky, when the sun is 12 degrees below the horizon, about 50-60 minutes after sunset. The sun is setting at the top of the atmosphere about 90 miles (140 km) above you. Marine navigation using traditional visual methods such as sextants becomes difficult, since many of them involve a clearly defined break between sea and sky. The last interval, called astronomical twilight, starts with the end of nautical twilight and goes until the sun gets to 18 degrees below the horizon. This is the time about 70-90 minutes after sunset when no sunlight, either direct or scattered, illuminates the atmosphere above the horizon.

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The Best Telephoto Lenses for Astrophotography

Jun 27 2015 04:15 PM | rekokich in Articles

Over the years, I have tried more than two dozen telephoto lenses, until I finally found three or four perfect solutions. But first, there are several general rules which must be understood.



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How to Better Balance Big Binos

Jun 27 2015 03:03 PM | jtsenghas in Articles

Have you ever mounted large binoculars on a parallelogram mount, whether or not you built it yourself, and struggled with having it balance well at various angles, drifting up or down at various heights, but balancing perfectly at others? Here are explanations of the two-dimensional nature of this behavior and tips for minimizing it, along with a spreadsheet tool with graphical output which may help you to improve your existing setup or to design a better one.

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The World's Simplest Telescope -- Now you c...

Jun 27 2015 01:00 PM | ed_turco in Articles

This is a very worthwhile, instructive project for young and old. Try it and be amazed!

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A new Performance Index for Binoculars

Jun 13 2015 01:24 PM | Fomalhaut in Articles

Closing a gap in the technical literature on the topic of the visually accessible stellar limiting magnitude.

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Blue Skies, Red Sunsets & Company Part 2: S...

May 25 2015 02:19 PM | Snickersnee in Articles

When the sun is on the horizon, then the line between darkness and light created by the glowing sun and the shadow-casting earth is sweeping through your position. It's called the terminator as it terminates or ends the daylight. The terminator passes overhead twice a day with sunrise and sunset. At sunrise, the effects of the daily pageant play with darkness giving way to light, while for sunset the sequence is simply reversed. Descriptions here with the sunset will mean things that can happen at both times of day.



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The Definitive Newtonian Reflector

May 11 2015 12:30 PM | ed_turco in Articles

Amateur astronomers and telescope makers have debated from time immemorial the advantages and disadvantages of different telescope designs.  In particular, mountains of hard copy and electronic articles are available on the merits of refracting and reflecting telescopes, more recently, apochromatic refractors vs. Newtonian reflectors. This debate has become rather rancorous (Newtonian telescopes as APO "killers" comes to mind.) and unscientific, to say the least. And when all is said and done, in a discourse without loaded words and acrimony, a discussion devolves to one concerning perfect optics.  And isn't this what we all want or wish we had?



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Blue Skies, Red Sunsets & Company: Part 1:...

Apr 16 2015 02:37 PM | Snickersnee in Articles

Sunsets, sunrises and twilight, as well as clear blue skies and the less familiar crepuscular rays, mirages and green flashes are all examples of atmospheric optical effects that can be readily seen at many times of the year from many places on the earth. No special equipment beyond your eyes, a bit of patience and an openness to learn is needed to see and feel the beauty of the interaction of natural light and the air.

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A tale of two craters

Apr 15 2015 12:40 PM | skyaddict in Articles

Most craters on the Moon are named after famous individuals associated with our satellite, and those on Mare Crisium, the 'Sea of Crises' are no exception. After a little map reading, I decided to make the focus of my evening’s viewing a pair of craters named after the founders of two of the most famous Observatories on Earth.

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