OAUSA Net - June 16, 2022 - Astronomy

[DaveK]

Astronomy

Time to find a camping spot away from city lights and enjoy the sky.

[AK6DH]

Many of us live in areas where the stars are washed out or not visible. One of the great things about driving or camping in the middle of nowhere, is the beauty of the night sky. If you are familiar with the look of the stars and constellations where you live, you will not recognize them out in the wilderness.

From the first time people looked at the sky, they have been naming the points of light they saw and grouping therm into shapes and figures from their mythology. A planisphere is a simple way to navigate around the sky, through these names and shapes. They are configured for various latitudes, you just dial in the month, day, and time, and hold it up in the air according to the compass points, to get an idea of what is up in the sky. I've been using this one for many years, it shows the naked eye and some binocular objects.

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https://www.davidchandler.com/products/ ... ar-charts/

A step up from the planisphere is a sky atlas, a set of maps divided into sections showing the visible objects. The Sky Atlas 2000 was one of the most accurate and popular in its day. I spent many hours using it to plan and observe nebulae and galaxies. It seems that electronic sky atlases, and telescope drives with built-in sky catalogues, have now taken over.

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Since the advent of smart phones, I have been using Astronomy software from Simulation Curriculum called "SkySafari." Like the planisphere, it shows you what is up in sky. It uses your phone's GPS to determine your location, for an exact view of what's up. You can set the magnitude (brightness) of the objects you want to show on the sky maps and set what name info you want to see about the stars, planets, and nebula. The constellations can be outlined, drawn, or pictured. If you touch an object, it will show a photo and more information about it, such as the Latin name, magnitude, and astronomical coordinates. In addition, if you know what you want to look at, you can search for it and it will show you its current location. You can advance the time to get a look at the sky later in the evening or any other time you like. It can also be put into "augmented reality" mode so you can identify the objects you aim the phone at. It is available in iOS, Android, and MacOS.It comes in 3 versions, Basic, Plus, and Pro. Each one has more stars and other objects in its database. The Plus and above versions can also control telescopes via WiFi. They make a WiFi telescope adapter for those scopes that do not have one.

Thu, Jun16, 2022 at 9:00PM

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https://skysafariastronomy.com

One of the fun ways to enjoy the sky is to see if you can make out the constellations. Each one has its own story of how it came about. On of my favorite constellations is Orion. In Greek mythology, Orion was a gigantic, supernaturally strong hunter, born to Euryale, a Gorgon, and Poseidon (Neptune), god of the sea. One myth recounts Gaia's rage at Orion, who dared to say that he would kill every animal on Earth. The angry goddess tried to dispatch Orion with a scorpion. This is given as the reason that the constellations of Scorpius and Orion are never in the sky at the same time. However, Ophiuchus, the Serpent Bearer, revived Orion with an antidote. This is said to be the reason that the constellation of Ophiuchus stands midway between the Scorpion and the Hunter in the sky.

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By Sanu N - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.p ... d=74939598

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By Mouser https://commons.wikimedia.org/wiki/File ... 8_huge.jpg

To view the stars, planets, nebulae, and galaxies close up, requires some magnification. The easiest, and cheapest, is a pair of binoculars. These are easily transportable and do not take up much room, so you can take them wherever you go. Binoculars with an objective diameter of 50mm are good for astronomy, due to their light gathering power. The larger the diameter of the lens, the more light is let in, so dimmer objects can be viewed, There s a trade-off, if you go too large, they will be too heavy to hold steady and require a mount to keep them still. Magnification also come into play in the ability to keep the image steady. 10 power is about the highest you want to go before a mount is needed. There's some debate on what magnification is best. Low-power advocates recommend staying with 7x or 8x, whereas the high-power types say that the increased detail and darker sky background provided by 10x units are worth the narrower field of view and extra jiggling.

Although the objective lens determines to a larger extent how much light enters the binoculars, it is actually the Exist Pupil that determines how much light enters your eyes, an important feature not be overlooked when one is selecting the best-suited binoculars for one’s self. In darkness and poor lighting conditions, the maximum pupil size of a human eye is on average between 5mm to 9mm for people below 25 years of age, 7mm being the average and the maximum size is 9mm, this number will decrease with age, what this boils down to is an exit pupil smaller than your pupil will mean that you will perceive the image as being darker than it actually is due to the limited amount of light entering your eyes.

You may also want to consider if you are older than 50, you may not need the 7 mm exit pupil provided by 7×50’s, therefore you may consider 8×42’s which will give a slightly larger image. If you don’t mind a little more weight, a pair of 8×56’s or 10×50’s are a great choices for stargazing. 10×50 being about the perfect balance between conformability and viewing quality. Any more than 10x magnification, and the image will get a little shaky. Any bigger than 63 mm, and the binoculars will get too heavy to hold for long periods. A good pair of binoculars will allow you to find double stars, star clusters, galaxies, nebulae, craters on the moon and the moons of Jupiter. On a clear, dark night you can see about 3,000 stars, With smaller binoculars, like the standard 7x35 that everyone seems to have, you can see over 100,000 stars. Even in the middle of the city, binoculars will allow you to explore the heavens.

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Telescopes are not required to view the heavens, but that’s what most people use to see the many objects in the sky. There are 3 main types of telescopes, with varying light paths to magnify the view and shorten the tube. The refractor is what a lot of people think of when they see a telescope. It is made up of several lenses lined up in a tube. They combine to magnify the image. These are more expensive, due the double sided grinding of the lenses. They are, however, sealed and not prone to getting out of alignment due to vibration. This makes them better for taking with you off-road. Another familiar type is the reflecting or Newtonian telescope. It consists of 2 mirrors, 1 to gather the light and the other to reflect it out the side. This double path shortens the length of the telescope, and the mirror surfaces are easier to grind into shape. Many amateurs make their own, including the mirrors. As with binoculars, the larger the diameter of the objective, the more light gathering power you have. The reflecting telescope, since it is less expense to make, gives you the best size for the money. They are generally open tube, so dust can collect on the mirrored surfaces. There are many tube designs that allow you to break own the larger ones for easy transport. The 3rd type is the catadioptric telescope, it has a primary mirror to gather the light, and a secondary mirror to reflect it back to the bottom of the telescope, through the primary mirror. There are various types of catadioptric telescopes. A variation, called Maksutov, uses a spherical mirror, instead of parabolic. This shape is easier to grind, but now a corrective lens is required to make the stars look round and colors normal. A mirrored spot is put in the center of the corrective lens to reflect the light back down to the bottom. This has the advantage of making the tube sealed, which keeps out the dust. Another type of sealed catadioptric is the Schmidt-Cassegrain. This also uses a spherical primary mirror and a lens on the front to correct for spherical aberration.

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Once you’ve decided on a telescope, it’s time to determine the mount to use. There are basically 2 types, equatorial and alt-az. The equatorial mount has 2 axes that move along the celestial coordinate system of right ascension and declination, which is like our longitude and latitude. Once properly oriented to the North pole, it generally only needs to move in right ascension to follow an object and keep it in the eyepiece. The alt-az mount moves in a circle around the ground and up and down. The zero point of the azimuth mount is pointed North. It is not following the celestial coordinate system, so it has to move in 2 directions to keep something in the eyepiece’s field of view. Since it does not actually follow the relative motion of the object, it will rotate in the eyepiece. This is OK for viewing, but not for traditional long exposure film photography. Modern digital photography uses shorter exposures and field rotation can be accounted for in post processing.
In the photo of the telescopes above, the refracting telescope is on an equatorial mount, the catadioptric is on an alt-az mount, and the reflecting telescope is on a type of alt-az mount called a Dobsonian mount, after John Dobson, who wanted astronomy with telescopes to be inexpensive and accessible to everyone. These mounts can easily be made with scrap wood lying around the house.

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Since the Dobsonian mount is not computer aimed or motor driven, and aiming device needs to be used to point the telescope. The most commonly used one, is the Telrad finder (TELescope Reflex Aiming Device) invented by Steve Kufeld. It projects 3 concentric circles into the sky, that are .5, 2, and 4 deg in diameter. It is so popular, that a Telrad template came with my Sky Atlas 2000 to assist with finding objects. It’s basically a red dot finder for astronomy, similar to those used on firearms. The Telrad is longer so it can house larger batteries and be collimated. The Telrad is also used on systems with other types of mounts, even those that are computer driven. Sometimes we like to eschew the technology and aim it ourselves. They even make a white light Telrad for use in the movie industry for aiming lights without having to turn them on.

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One of the most important items in your aresnel is the eyepiece. It is analogous to speakers on your home stereo. A good eyepiece can make a mediocre telescope look good, but a bad eyepiece will make a great telescope look terrible. For a long time eyepiece design remained stagnant. In the late 70's Al Nagler, who designed the Lunar Landing simulators, used optical ray tracing and design to improve on the telescope eyepiece. He wanted a view through telescope to look like a panorama. His eyepieces immediately became the success of the astronomy world, and many others have starting using his techniques to improve their eyepieces as well.


What to Look At

What is there to look at once you have binoculars or a telescope? There are generally 3 things people view the moon, planets, and deep sky objects. Generally most people start viewing things in that order with the first telescope. The moon is easy to find and can be fascinating to look at with just a pair of binoculars. Planets are next as they too are generally easy to find. Deep sky objects are what most amateur astronomers like to view and are best appreciated from the dark remote locations to which we find ourselves when off roading or overlanding.

Moon

Lunar astronomy is a specialty of some amateur astronomers. Exploring the surface of the moon from your back yard can be fun. The challenge is being able to find obscure features. Some of these features are only visible when the lunar lighting conditions are just right.

Planets

Planets can be enjoyed with binoculars or a moderate size telescope. Many people’s first exposure to amateur astronomy is looking at Jupiter and its moons or the rings of Saturn with a through a telescope at a public astronomy event.

Deep Sky Objects

Beyond the moon and planets are the so called deep sky objects. These are objects well beyond our solar system. Thousands of deep sky objects have been cataloged and are generally considered more interesting to observe by serious amateur astronomers.
Once you graduate to astronomy with binoculars or a telescope there are a great many more things to see in the night sky. Favorite amount amateur astronomers are the so called Messier deep sky objects. These were the first deep sky objects cataloged and the easiest to see since they were discovered using 18th century telescopes.
Charles Messier was a French astronomer who lived from 1730 to 1817. Messier was primarily interested in finding comets. He kept running across other fuzzy diffuse things in the sky that didn’t change position like a comet. He made a catalog of these objects so he wouldn’t waste time on them searching for comets. This became known as the Messier catalog. Today these are among the most interesting targets in the sky for amateur astronomers.

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Pictorial Messier Catalog

Today the catalog of celestial objects has been greatly expanded in the New General Catalog (NGC) list of objects. The latest version of the NGC lists almost 8000 celestial objects.

Solar Astronomy

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Observing the sun is something I like to do. There are now many safe ways to do so. Coronado makes a purpose built solar telescope with the proper filters to reject the harmful wavelengths and filter the image so that sunspots and solar flares are visible. The key to safe solar viewing with modern solar telescopes is the H-Alpha filtering system they use. Typically there is a deep red filter that removes most of the unwanted wavelengths of light and reduces the overall intensity. Next is a special tunable bandpass filter called an etalon which works like a radio frequency tunable bandpass cavity filter except for light frequencies. Finally there is the H-Alpha filter itself which is sophisticated optical filter made with 50 or more different coatings.
These filters are so narrow that the speed of the rotation of the sun needs to be taken into consideration if you want a clear view of the entire solar disk at once. More expensive solar telescopes include 2 separately tunable etalons. These are called “double stacked” telescopes.

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You can also get white light solar filters that fit on regular telescopes. These look like Mylar discs and reflect most of the light, to prevent it from entering the telescope. Only .001% of the light gets through.

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There is another form thread about traveling to the solar eclipse in 2024, so I thought I would throw these I from 2017. They were taken by the late Jim Mettler using a white light filter.

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This is a good reference site for star maps, ISS and other satellite transits.
https://www.heavens-above.com

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