REVIEW OF SUMERIAN OPTICS ALKAID 16” TRAVEL SCOPE
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For at least 10 years, observers have complained in forums about eyepiece barrel undercuts causing various problems, but especially catches. Because of my own experiences with catches occurring during insertion or extraction of an eyepiece when used with an adapter, I decided to do some investigation as to why. Catches, I found, are not a one sided issue.
If you watch enough sunsets, you'll eventually see one where, just as the last sliver of sun slips away, it turns green or reappears for an instant as a flash of greenish light. Congratulate yourself - you have just seen the famous green flash!
This is a description of my adventures with the fabrication of a 6” f/15 oiled achromat.It is assumed you will know all about grinding, polishing and figuring. It will discuss some problems I ran into and what I did to solve them in the easiest and most practical way, as well as things to watch out for. This is not a step by step description of the making of a refracting objective let alone the complete telescope.
If you’re mount setup seems a bit too wobbly in the wind, well this West Texan might have the answer. This will not make a woefully inadequate mount suddenly fine, but it should help someone whose mount is almost capable enough, but not quite. People write on CN that this is self-evident, and after reading this article you may agree, but I like pointing out the obvious. Hope someone finds it edifying.
In spite of its advantages, the HyperStar system is not quite as easy to use as a modern day apochromatic astrograph and many users have trouble achieving good results. The problem generally isn’t with the optical system; it’s often the result of not knowing how to properly align and use the system. Although Starizona provides user instructions for aligning and using the HyperStar system, the manual is fairly basic. This guide is intended to provide additional information to get the best performance out of the HypeStar System.
Refraction changes the shape of the setting sun. The oval shape most commonly seen is just the simplest example. Much more complex changes in appearance can occur because of refraction and these are called mirages.
I can’t tell you how many negative things I had heard about them, but in their day everybody wanted one. They were the first, each one was removed from the factory, had the electronics added on and shipped back for delivery.
In 1814 Bavarian optician Joseph Fraunhofer invented the modern slit spectroscope. He demonstrated bright emission lines when burning various elements, as well as numerous dark absorption lines in the spectrum of sunlight which are in his honor still called Fraunhofer lines. In 1821 he improved the diffraction grating first invented in 1785 by American astronomer David Rittenhouse. Fraunhofer then founded stellar spectroscopy by showing that spectra of several bright stars differed from each other and from the spectrum of the Sun.
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.
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.