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The right equipment, site, and techniques can make all the difference when you're observing from the city. W henever I leaf through an issue of Astronomy magazine, I am amazed at the variety of telescopes, eyepieces, and accessories available to today's amateur astronomer. We have never enjoyed such a rich assortment of equipment for viewing the universe.
But then, we have the other side of the coin. Even though there are more telescopes for sale today than ever before, many people interested in astronomy never buy one simply because they can't see the stars. Runaway light pollution is robbing us of the night sky. I haven't seen it in years. But take heed; all is not lost. Many amateur astronomers who live in and around major cities enjoy wonderful views through their telescopes any clear evening they wish. They just have to know a few tricks to pull out the best their equipment has to offer. First, let's look at the problem of light pollution and define a few terms.
Light pollution comes in two varieties: sky glow and local, or line-of-sight, glare. Sky glow refers to the sickish orange glow we see rising above our horizons, the combined effect of hundreds, even thousands of lights on buildings, in parking lots, and along roadways all casting some of their light skyward.
The net result extinguishes faint stars and washes out the sky.
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Localized, or line-of-sight, light pollution can happen anywhere, in the largest cities and in the smallest rural towns. Most often, it is caused by one or more poorly designed or placed lights, either from a neighbor's house or possibly a badly located streetlight.
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By itself, line-of-sight light pollution may not wash out the sky like sky glow does, but it can blind an observer to faint starlight by sneaking into the corner of the eye. The good news is that it is possible to deal with both of these problems, lessening their impact and increasing your enjoyment of observing from your home.
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Here are some tips and tricks to try. Equipment Let's begin the discussion of which telescopes are best for viewing from a city by putting an urban legend to rest. The oft-repeated advice of "If you observe from a light polluted area, small telescopes are better than large telescopes" is just plain wrong. That old myth was based on the premise that because larger apertures gather more starlight, they must also gather more sky glow, which in turn must wash out the field of view. This simply is not the case. A larger telescope will gather more starlight regardless of where it is located.
A inch telescope will show more stars than a 6-inch telescope from downtown Chicago just as it will from Smalltown, USA. It is true, however, that larger apertures are more sensitive to heat currents and turbulent atmospheric conditions. There have been nights when I couldn't focus my own inch reflector due to turbulence, while images in my 4-inch refractor and 8-inch reflector were sharp.
But that has nothing to do with light pollution. When considering which telescope to purchase, many people think only in terms of budget. Depending on where you live, your number one concern should be storage. Where will the telescope be kept between observing sessions? Unless a telescope is convenient to use, it will quickly become relegated to a dark corner. Many a stargazer's zeal has turned to apathy by the harsh reality that setting up a telescope can be hard work. I'll just wait until tomorrow night.
Hmm, I wonder what's on TV. If you live in a three-story walk-up apartment, you do not want a large telescope that requires several back-and-forth trips to carry everything out. In that case, an ideal solution would be a small grab-and-go instrument that can be carried in one hand, while a guidebook and chart are held in the other. If, however, you live in a house, perhaps with a garage that has room for storing a telescope, then a larger instrument could serve you well.
I know two amateur astronomers who live in areas that are severely impacted by light pollution. Jack owns a 90mm refractor on a small German equatorial mount.
Evolution of the optical telescope
He uses it just about every clear night. Because of its size, however, Carl only uses it three or four times a year. So, which telescope would you say is better? To my mind, the answer is clear. The small refractor, modest as it is, takes Jack into the universe far more often than Carl's huge reflector. What matters most is that, be it a small, inexpensive instrument, or a pricey, advanced scientific device, the best telescope in the world is the one you use often and enjoy to its fullest.
Urban astronomers gain great advantage from using computerized telescope mounts. While star-hopping is a wonderful way for locating targets from a dark-sky site, it is difficult to do if the sky is so bright that reference stars are few and far between. But keep in mind that inexpensive computerized telescopes often divide their strengths between electronics and optics, in the process compromising both.
Be sure to optimize the telescope you own, no matter the size or type. One of the most effective ways to improve the view is to add a tube extension in front of the telescope. Installed in , it remains the largest refracting system in the world. The reflecting telescope predominated in the 20th century.
The rapid proliferation of increasingly larger instruments of this type began with the installation of the 2. The technology for mirrors underwent a major advance when the Corning Glass Works in Steuben county, N. This borosilicate glass , which undergoes substantially less expansion than ordinary glass does, was used in the 5-metre inch Hale Telescope built in at the Palomar Observatory. Pyrex also was utilized in the main mirror of the 6-metre inch reflector of the Special Astrophysical Observatory in Zelenchukskaya, Russia.
Since then, much better materials for mirrors have become available. Cer-Vit, for example, was used for the 4. Almost as important as the telescope itself are the auxiliary instruments that the astronomer uses to exploit the light received at the focal plane. Examples of such instruments are the camera, spectrograph, photomultiplier tube , charge-coupled device CCD , and charge injection device CID.
Each of these instrument types is discussed below. American John Draper photographed the Moon as early as by applying the daguerreotype process. The French physicists A. Fizeau and J. Foucault succeeded in making a photographic image of the Sun in Five years later astronomers at Harvard Observatory took the first photographs of the stars. The use of photographic equipment in conjunction with telescopes has benefited astronomers greatly, giving them two distinct advantages: first, photographic images provide a permanent record of celestial phenomena, and, second, photographic plates integrate the light from celestial sources over long periods of time and thereby permit astronomers to see much-fainter objects than they would be able to observe visually.
The plate or film consists of glass or of a plastic material that is covered with a thin layer of a silver compound. The light striking the photographic medium causes the silver compound to undergo a chemical change. When processed, a negative image results—i. Since the s the CCD has supplanted photography in the production of astronomical images. Newton noted the interesting way in which a piece of glass can break up light into different bands of colour, but it was not until that the German physicist Joseph von Fraunhofer discovered the lines of the solar spectrum and laid the basis for spectroscopy.
The spectrograph consists of a slit, a collimator , a prism for dispersing the light, and a focusing lens. The collimator is an optical device that produces parallel rays from a focal plane source—i. The spectrograph enables astronomers to analyze the chemical composition of planetary atmospheres, stars, nebulae, and other celestial objects.
A bright line in the spectrum indicates the presence of a glowing gas radiating at a wavelength characteristic of the chemical element in the gas. A dark line in the spectrum usually means that a cooler gas has intervened and absorbed the lines of the element characteristic of the intervening material. The lines may be displaced to either the red end or the blue end of the spectrum.
This effect was first noted in by the Austrian physicist Christian Johann Doppler. When a light source is approaching, the lines are shifted toward the blue end of the spectrum, and when the source is receding, the lines are shifted toward its red end. The slit of the spectrograph is placed at the focal plane of the telescope. The resulting spectrum may be recorded photographically or with some kind of electronic detector, such as a photomultiplier tube, CCD, or CID. If no recording device is used, then the optical device is technically referred to as a spectroscope.
The photomultiplier tube is an enhanced version of the photocell, which was first used by astronomers to record data electronically. The photocell contains a photosensitive surface that generates an electric current when struck by light from a celestial source. The photosensitive surface is positioned just behind the focus. A diaphragm of very small aperture is usually placed in the focal plane to eliminate as much of the background light of the sky as possible.
A small lens is used to focus the focal plane image on the photosensitive surface, which, in the case of a photomultiplier tube, is referred to as the photocathode. In the photomultiplier tube a series of special sensitive plates are arranged geometrically to amplify or multiply the electron stream. Frequently, magnifications of a million are achieved by this process. Here we show how to do it without risking losing your eye sight!!
Please subscribe to my channel for more video guides and keep updated! How to improve visual performance of an Achromat Refractor RE EDITED Read more Owners of Achromatic Refracting telescopes will find that the Chromatic aberration effect or false colour creating deep purple halos around planets, bright stars and the moon may be detered from these effects. Here in this video guide we A4B we here to show you all what can be done to help reduce these effects and help improve on your telescopes performance. This is the only video guide on the net which is available which demonstrates this CA problem.
A guide to Barlow Lenses Read more A brief intro into Barlow lenses and their uses, in this video guide I show variety of Barlows that I own and my views on each one to give you some idea to pick a perfect barlow for yourself! This unique webcam is used to deliver fantastic high res images and providing multi functionality. Here not only a review, I show you how to use using Sharp Cap 2. Yet again we A4B are the first to bring a video guide on this great camera!! How to make a DIY Solar filter Read more Are you wanting to view the sun through your telescope, but realise yourself that these glass solar filters are far too expensive!
Look no further as in this video guide I show you that making a DIY solar filter for your telescope doesn't have to be expensive! So please enjoy watching my video guide and please subscribe!! How to clean a Refracting telescope Read more Here's a video guide to show how to clean the optical objective lenses on Refractors of all types including Achromats. Here I show you my method of cleaning them safely without damaging the delicate coatings.
Here there many methods out there on the internet, but this my approach!! Please enjoy the video and please subscribe onto my channel and support us at A4B!
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Here I give you a step by step guide on how to do it, It's a long video but, I show many things including images taken with the camera itself, and show proof of the modification works to reduce the camera's noise, which is the biggest drawback for this camera, The camera is more suited for imaging planets at high res images, but I find that the camera can be used as a cheaper alternative to a CCD, and you can take amazing images of Deep Sky objects like Galaxies and Nebula, using the chip's high performance hi-res image and pixel size!!
And please subscribe onto my Channel!! How to attach a DSLR camera onto your telescope Read more In this A4B video guide I give advice on connecting a DSLR camera to your telescope, unlike most Youtube videos I cover all telescopes and give hints and tips on connecting a DSLR and I explain reasons why certain telescopes operate differently, due to their designs, and I explain how you can compensate the focus problems involved with these telescopes to ensure you pick the right correct equipment and save money in the process!
The development of the telescope and auxiliary instrumentation
Please enjoy this video and please subscribe onto my channel. Also we are available at a Face book group so please join us today!! The complete detailed guide to CCDs Deep space cameras Read more This video guide highlights the basic info regarding CCDs, as these are widely used as dedicated long exposure deep space cameras. Here I cover variety of CCDs ranging from basic to the advanced imager. And point out key elements to CCDs. Please enjoy the video and please subscribe today. How to take pictures of the International Space Station ISS Read more Here I take you to complete video guide like no other, Yes I know it's long but it covers everything you need to know about taking pictures and videos of the International Space Station.
We are fully aware that there are some ISS imaging films out there on the internet, but not many. Also the A4B video guide highlights how to make images more stunning using freeware software, Here we help the best we can so that you can successfully find ISS and image it!! Again please watch and enjoy, as we A4B will make happen for beginners and we care for our A4B members as at the end of video, again like myself and many others who started out as beginners have successfully imaged the ISS in one night alone and got fantastic results. How to take pics of the Perseids Meteor showers Read more Here I take you on a tour on how to take pictures of the Perseids Meteor showers, which happens between July and August months every year, Being the most active meteor shower of the Night sky year in the Northern Hemisphere.
The most active period at the moment is between 11th of August to 25th of August Here I show you how can you take great pictures using basic equipment within budget for most amateur astronomers. Please subscribe on to my channel so that you are kept up to date for the latest A4B video guides.