Getting Started in Visual Astronomy
The purpose of this Web Log is to pass on to other members tips that you have learned about visual astronomy. From time to time we’ll post entries from members of the club who have suggestions to help their fellow amateur astronomers in making their time at they eyepiece more enjoyable and more satisfying.
I thought I would start this blog with what are my top ten suggestions on getting started in visual astronomy:
10. Buy a Planisphere–skip the exploring the universe software for now. Begin at the beginning, get to know the night sky by learning the asterisms of each of the major constellations and where they begin and end. Start at the north and if you don’t have clear skies, or too much light pollution at home, come out to Bear Branch and use your planisphere out here. Look for one that is either printed on plastic or has laminated paper. A planisphere is a circular spinning sky map with the date and time printed on the outside ring and an oval shaped window that corresponds to what the sky looks like overhead, usually only the brightest stars are printed on the planisphere, and this enables you to quickly dial tonight’s date and time, and then hold it up, lie down on a blanket or a lounge chair, hold the planisphere up and compare the chart with the sky so you can see, distortion free, what each asterism is. An asterism is a collection of stars seen as a group, whereas a constellation is an area of the sky separated by official boundaries established and agreed upon by the International Astronomical Union (IAU). You are probably familiar with the asterism of “The Big Dipper” or in the UK, “The Plough” which is in the circumpolar constellation of Ursa Major, the great bear. There are many others. Across the pole, there is the famous W shape asterism that are the feature stars in the constellation Casseiopeia. This Asterism features prominently in WASI’s logo. The key to enjoying the night sky is getting to know the night sky.
9. The second thing you’ll need as you get started is a good red flashlight. I have a very bright 7 LED one my children bought me for Christmas one year, but I also have a couple of good headlamps that have red LED’s as well, I prefer the one that doesn’t make me flip through three white patterns before I get to the Red one first. Having a red flashlight will enable you to study your planisphere or star map without completely ruining your night vision, which is why the Boy Scouts, and the US Army always use red filters on their flashlights at night, your eyes are red-insensitive, so your pupil doesn’t constrict under exposure to red light the same way that it does under white light. Once you have one, you’ll probably want a second or third red flashlight. I have several of various brightnesses, and use the dimmest one which I’ve covered the inside of with red tissue paper to dim it down, is used only to consult a star map when I’ve attained full pupil dilation.
8. Buy a good star atlas. Once you have mastered the planisphere, it’s time to buy a good initial star atlas, such as Simon Mitton’s. Now out of print, you can occasionally find it on Amazon from a used book store. This simple atlas was staple-bound and had photographs from the 200″ telescope in the front. For maps, it had two circumpolar maps showing the top 40 degrees, from the pole to 50 degrees and then sectors of two hour wide swaths of the sky starting at 0 right ascension and continuing through 23 hours and 59 minutes, 59 seconds in a series of 12 maps. This atlas contains all the major asterisms, and stars down to 6th magnitude–all of the stars visible to the naked eye from most of the United States. It also contains the locations of all of the Messier and many of the Herschel’s NGC objects within reach of amateur astronomer’s telescopes.
Master the beginning star atlas, and you can move on to more enriching atlases, such as Wil Tirion’s spiral bound color Sky Atlas 2000. When I started my adventure in astronomy in 1980, nearly all star atlases were based on “epoch 1950.” In the 80’s we’d gotten closer to 2000 than 1950, so Wil’s work was vital–enabling updated views of the sky that take into account the “precession” of the earth. Because the earth actually “wobbles” on it’s axis, the exact position of stellar “true” north changes very slightly each year, and notably so after 50 years, requiring a change in “epoch.” The Sky Atlas 2000 will be accurate until 2030 or so, and then we’ll be entering “epoch 2050.”
There are a couple of different kinds of “atlas” available and are worth mentioning here. Back in the 1970’s and 1980’s you could get your sky atlas on individual loose legal size sheets and printed in inverse printing with dark pages and white stars, just like this paragraph. The advantage was that in our observatory, you could place the page you were interested in onto a light table, and illuminate it from behind with a red light bulb on a rheostat, so you could turn up the intensity of the stars to the dimmest possible level to still be able to read your map.
The equivalent today, is to use an app for your phone that I’ve found that’s called Ad Astra which is Latin for “To the Stars.” Ad Astra has maps of each constellation with black stars on white, white stars on black, or in Professional Mode, it shows a much larger map of a large section of the night sky around the selected constellation with the stars and objects all in red on black–preserving your night vision. I’ll set Ad Astra up in Pro mode and then turn down the brightness level on my phone as my eyes dark adapt, and then place my phone on my telescope’s stalk next to my Nexus DSC, so both are ready references as the night progresses.
7. Buy a good set of binoculars. Before you invest in a telescope, it’s important to learn what objects are where, so you can see many of the largest and brightest deep sky objects with a good set of binoculars. Find a large bright object in your sky atlas such as the Andromeda Galaxy and then locate the object while lying on your back in your lounge chair and using your binoculars. See how much you can see, with BOTH eyes before resorting to a telescope. WASI Member and vice president Tony Falletta is a binocular expert–ask him for advice before he moves away…
6. If you’re not sure what your interests are going to be, then don’t buy a telescope right away. See the Member’s Benefits section of the web site, and then “check out” a telescope from the WASI Library. Curt Roelle, our club’s primary founder, and current librarian has a collection of scopes owned by WASI that you can check out, use and return. Some are simple Dobsonians with large bearings sitting on Teflon pads that you push to an object. Again, I would let simplicity rule the day. I’ve spent over 30 years in visual astronomy and only rarely had motorized scopes that tracked the object I was looking at, you really can get great views and learn the night sky with a “push to” telescope. You don’t have to let the computer controls get in the way of enjoying astronomy, and I’m a computer guy. So what kind of telescope will be right for you? It depends on what you’re interested in.
If you are really interested in studying the moon, our nearest neighbor in space, then you may never need a telescope larger than 8″. I have known lunar observers who are in their 70’s and never developed “aperture fever” because they can see and resolve objects on the moon with great accuracy.
If you are interested in the planets, and want to do planetary imaging, then the best telescope for that, and perhaps any kind of imaging is a high quality refractor with an apochromatic or ED objective lens. The larger the refractor, the more expensive the system. Stay away from low cost “department store” telescopes such as Tasco and Bushnell, and look for refractors from Celestron, Vixen, Televue, and Williams Optics among others. Refractors have no central obstruction, making the views brighter in general for the same diameter–they have higher performance than a reflector for the same aperture. Refractors also tend to have much longer focal ratios of f/15 or f/12 which provide much higher magnifications than the average Newtonian telescope at f/8 or f/6. Planets are bright objects that take this magnification well, so a refractor is a great telescope for planetary study. Consult the centerfold star maps in this month’s “Astronomy” or “Sky and Telescope” for updated positions for the planets as well as comets or other objects of interest, such as bright asteroids that refractors are also an excellent choice for. Refractors and Catadioptric telescopes (which also have slow speeds or high f-ratios) are also excellent for splitting binary stars, and doing variable star observing.
If you’re interested in open or galactic clusters then you need a wide field scope, such as a fast Newtonian with a focal ratio of f/6 or faster. Open clusters are groups of stars in our galaxy that are not necessarily physically close to one another, but they appear to be “together” because they line up optically where some of the stars could be much closer to us as in the foreground, and others are much farther away, in the “background” but they are visually pleasing and appear to be clustered. The “Double Cluster” in Hercules, and the three Auriga clusters, M36, M38 and M37, as well as the Gemini cluster M35, are all primary examples of open or galactic clusters.
Fast telescopes are also good for globular clusters such as M13 and M92 in Hercules, M4 in Scorpius, M56 in Cygnus, M71 in Sagitta, etc. Fast telescopes are also great for planetary nebulae such as M57 The Ring Nebula in Lyra and M27, the Dumbbell Nebula in Vulpecula, and dozens of others. Fast telescopes are also great for diffuse nebulae such as the Veil Nebula in Cygnus, the California Nebula in Perseus, and for galaxy work, pulling in faint objects that are several arc minutes across.
It’s important, very important to get to know the different kinds of telescopes and their mountings before you spend a lot of money on a telescope. And maybe, just maybe you’ll decide that you’d like the learning experience of building a telescope yourself from scratch. We have the Amateur Telescope Making (ATM) Corner blog set up just for that purpose. You’ll find tips for everything from finding sources for optical glass to grinding your own mirror, polishing and figuring, to how to construct your mount or dew-heater system in the ATM Corner.
5. Start inwards and work outwards. As you get to know the sky you should learn to know and identify objects closest to the Earth and work outwards from there–so begin with studying the moon and it’s cycles, and seas and craters, focus on the terminator, and see what features you can see. The larger your telescope, the finer the details you can resolve on the moon. A 6″ scope can see details such as craters down to around 3 miles in diameter. An 18″ telescope can see and distinguish between craters a half a mile in diameter, this is known as resolving power.
Next study the planets, and learn their wandering habits, where the ecliptic is in your local sky and at Bear Branch. The “inferior” (in orbit diameter only) planets Mercury and Venus are interesting objects that must be observed very close after sunset (when they are at greatest eastern elongation), or just before sunrise (when they are at greatest western elongations). The inner planets make great public night objects, and Venus varies greatly in appearance from a small but nearly fully round object at conjunction to first and last quarters and then to very large slender crescents as we pass it in opposition. The outer planets: Mars, Jupiter, Saturn, Uranus, and Neptune each present different challenges, and respond differently to visual tools such as color or polarizing filters or apodizing screens. I will write a future blog post on apodizing, as it is a powerful technique for increasing sharpness while decreasing glare.
Then learn the open clusters such as those mentioned above, or the Beehive or M67 in the spring. These are clusters inside the Milky Way galaxy. Planetary nebulae are also internal to the Milky way, primarily nova and supernova remnants, each season has planetaries to share, in the winter and spring we have the Crab Nebula, M1, and in summer and fall, M57 and M27 are the largest and brightest, but there are many others. Learn the diffuse nebula, such as the Orion Nebula (M42), and the Rosette in winter, the Helix in the spring, and the Eagle nebula, the Omega or “Checkmark nebula”, the Lagoon nebula (M8) and Trifid nebula (M20) in the summer months. Dimmer diffuse nebulae, such as the Eastern and Western halves of the Veil Nebula require larger and larger telescopes to see well, as you exhaust objects within reach of your telescope, it’s easy to develop “aperture fever” wanting larger and larger telescopes to see dimmer and dimmer objects with your own eyes.
Lastly there are the other galaxies and galaxy clusters, and again, the seasons present different viewing opportunities, with summer being the best time to take in the Whirlpool galaxy M51 in Canes Venatici, the hunting dogs, and M101 the Pinwheel galaxy in Ursa Major. In the fall and early winter we have the Andromeda galaxy and her neighbors, M32 and M110, and the Triangulum galaxy M33.
4. Buy good eyepieces. This may seem like a no-brainer, but even before you invest in a telescope, you should look to buy some good eyepieces, and by good I don’t mean that you have to shell out a large amount of money to get high quality eyepieces.
One of my favorite Eyepiece suppliers, it may surprise you to learn, is Russell Optics. Russell Optics and Machine is located in Meadview Arizona, in very dark sky country. Mr. Gary Russell purchases research grade, and US military surplus optics and machines 1.25″ and 2″ eyepiece barrels for them in black Delrin(R) plastic. This makes eyepieces that are light weight, corrosion proof and inexpensive. Because he sells direct from his machine shop, there is next to no markup and the prices are very reasonable. His specialties are very low power super wide angle Plossl and Konig and achromatic Plossl (AP) style eyepieces with 60, 65 and 70 degree apparent fields of view. His lowest power eyepiece is an 85mm Super Plossl with a 70 degree field of view, and he also makes similar Super Plossl’s in 80, 72, 65, 56, 52, 50, 40 and 32 mm. Gary also makes mid-range eyepieces in the 26-18mm range in the AP and Konig style, and has, in the past made 2x and 3x Barlow lenses as the optics are available, and has also made research grade Konig eyepieces with 1/20th wave rated lenses in 12, 8 and 7mm focal lengths, but alas, these are all sold out and no longer available (except occasionally on Cloudy Nights or AstroMart). So for low power eyepieces, you don’t have to shell out a lot of money to get eyepieces that will provide years of pleasure and hours and hours of sharp clear clean and crisp images, from the center to the edge of the field. As I like to say “sharp is sharp” and I’ll compare Gary’s eyepieces with anything from Televue or even Explore Scientific. Those brands DO give you a much wider angular field of view (AFOV) but at the premium of a price tag that is 6 times the cost of a similar focal length eyepiece from Gary Russell.
Because the eyepieces normally bundled with a telescope are junk, it behooves the neophyte astronomer to start off by buying some good low power and mid-power eyepieces and use those in several different loaner telescopes looking at different objects as you decide what interests you most about astronomy.
3. Get good filters. Another no-brainer, but given the current light pollution situation we find ourselves in, it just makes sense to get the best filters that you can afford. There are several types of optical filtration that you can apply to your telescope, so let me briefly cover them here, and I’ll go into them in much greater detail in a future blog post.
Probably the earliest filters used in astronomy are the Kodak Wratten(R) filters that were developed for hard film cameras in the era of black and white photography. Back in the 1950’s these filters were developed to help enhance daytime photography. A dark red filter, for instance applied to a film camera, would produce a dark sky and high contrast with white cumulus clouds in a black and white image. That would be very disturbing in color, but for black and white it produced a nice effect. Kodak standardized these gel filters which were little more than a layer of dyed plastic film sandwiched between two layers of plano glass the diameter of the camera lens. You can buy color gel filters in several different colors in both 1.25″ and 2″ diameters and they screw on the bottom of your eyepiece (or in an “accessory drawer” tube into which you insert your various eyepieces) and they work to enhance contrast on the bands of Jupiter, the dust storms on Mars, or the rings of Saturn.
The next important kind of filter is the neutral density filter (NDF), usually a smoke grey or brown color, NDF’s reduce glare, and bring out detail on both planets and the moon, and NDF’s do that, like wearing sunglasses, do not unduly disturb the color of the planet, so you still can see what natural color is there. The common 13% transmission “Moon” filter is an example of an NDF that reduces the moon’s light amplitude by 13% making extended viewing easier on the eyes.
A third kind of filter are polarizing and variable polarizing filters. Polarizing filters work by shuttering light into parallel grooves so that light waves can only enter the filter in a specific plane. A variable polarizing filter consists of two polarizing filters, with one fixed to the eyepiece, and the other capable of rotating freely so that when it’s at 90 degrees to the fixed filter, no light comes through at all, and is adjustable so that only a small percentage of light comes through, so you can adjust the transmission level to one that provides the optimum balance between transmission and contrast.
Beginning in the early 1980’s companies such as Lumicon began offering astronomy-specific transmission filters designed to block out artificial light while allowing band-pass transmission of stellar wavelengths. Without getting too technical, their offerings were called the “Lumicon Deep Sky Filter” and the “Lumicon Ultra High Contrast” filter. After their patents expired, the market has been flooded with cheap imitations and knock off “Light Pollution Reduction” filters, and your mileage may vary using them, which is why it pays to buy a good one from reputable brands such as Baader Planetarium, or from Lumicon, which is now part of Farpoint Astronomical Supply, but their filters can still be bought elsewhere, such as from High Point Scientific as well. Today there are even more narrowband filters than the UHC available, which focus on only a few nanometer wide bands around specific stellar frequencies such as Hydrogen Alpha (which is a very dark red filter used primarily in astrophotography as it’s too dark for visual work), Hydrogen Beta, and Oxygen-III. Each of these have their own applicability and I’ll get into these in a later blog post.
Suffice it to say for now that a UHC or LPR is a filter that suppresses the emission spectra bands present in the nuisance pink/yellow high pressure sodium and the blue-green mercury vapor streetlights that have been commonplace from the 1970s through today. Fortunately these are being replaced by LED lamps, but due to the lower initial cost of LED’s over the price of HPS bulbs, municipalities that had few streetlights in HPS before are adding more and more lighting on less important streets in LED lights, so the net effect may actually become worse and not better, and LED light has a broad and uniform spectrum closer to broad daylight, which means we can’t easily filter out artificial light from LED streetlamps the way we can with element lamps.
The UHC filter is a narrowband transmission filter allowing H-A, H-B and O-III through specifically, and blocking nearly all other visible light out, resulting in much darker background sky–blacker blacks, but this filter requires good seeing and for your eye to be fully dilated for it to help. In contrast, the theory behind the “Deep Sky” filter is to maximize transmission of all light frequencies, but comb suppress NA-1, NA-2, Hg-1 and Hg-2 bands from High Pressure Sodium and Mercury vapor lamps, so it blocks nearly all light in those specific frequency bands + or – 10 nanometers. This enables planetary nebulae, globular clusters, and galaxies to “pop” in the eyepiece.
2. Use Averted Vision: This one is not as obvious for the beginner to learn, and it takes some getting used to. When looking through the eyepiece, you shouldn’t try to just stare at the center of the eyepiece. The reason for this has to do with the anatomy of the eye itself. Our eyes have a screen of light-receptor cells at the back of the eye called the retina. The retina consists primarily of two types of cells named for their structural shape–rods and cones. Rods are sensitive to the volume of light, and are necessary in perceiving the subtle gradations between one shade and another, being able to see differences in the schist or basalt on the moon, for instance. The other cell type are called cone cells, and it is these cells that are responsible for our perception of color in the world around us. The cones also require a higher threshold or intensity of light to be gathered in order for them to start working. In astronomy this is around the 16″ or larger diameter telescope looking at a star or open cluster to perceive the red from orange from yellow from blue stars in that cluster. At the very center of the retina, however is a blank spot, this is where the optic nerves are bundled and they leave the eye itself out the back of the eye and connect with the opposite lobe of the brain–the right eye connecting with the left brain, and the left eye connecting with the right brain. The brain is constantly adjusting for the missing cells over the optic nerve by “filling in” what it “thinks” is there based on previous input from the eye. So when we observe, if we stare at an object in the center of the eyepiece, we’re not really seeing anything at all. To properly see the object in the eyepiece, we need to look not directly at it, but if it is in the center of the eyepiece field of view, then we should look toward the edge of the eyepiece field, and allow the maximum amount of light to accumulate on our retina as possible, this will enable our perception of the object to be brighter, stiller and sharper than if we tried to stare directly at it and had to have our brain “make up” what the object looks like.
1. Phone a Friend. You made the right move by becoming a member of WASI. No matter where we are in this hobby, there’s always someone with a little more experience. If you need help getting started, or just want to learn where an object is, there’s no better way to get started than to ask a fellow WASI member for help. Observing is fun, and observing together in a Star Party, open house or outreach event is even more fun. You can see a lot more when everyone is looking at and for a different object, and you can take a peek through someone else’s scope in addition to what you see in yours.
Our outreach team loves sharing the night skies with everyone from neophyte to old salt. Kids from 8 to 80 can and do find astronomy to be a hobby that is full of satisfaction–keep looking for things that you haven’t seen before. You will deepen your satisfaction by keeping a log book of your observations and make note of the people who stop you on the street for a peek through your eyepiece, and share with them what it is that you’re looking at, how far away it is, etc. I will write more on how to keep a log book, and what I’ve got in mine.
–Tom Milley,
WASI Webmaster & Outreach Team Member