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| Plan your observing session | Science and Religion | Meteor page | Fractal images | Links | |
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| Plan your observing session | Science and Religion | Meteor page | Fractal images | Links | |
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I have several of my astronomy pictures posted at my desk at work. It is like having a billboard that say's "Ask me about astronomy" and people do. One of the most common questions asked is "How powerful is the telescope that you used to take those pictures?" Another common one is "My kid likes astronomy, what type of telescope should I buy?" This my attempt at answering questions like these. I do not claim to be an expert in astronomy, but what I do have are kids and a limited budget with a little experience in photography and star gazing. I hope there is something in here that is worth while for you.
My first word of advice: DON'T BUY ANYTHING (yet). I have heard several people tell me about the "600 power" telescope that they bought on sale at some department store. These types of telescopes are just toys, so they are not that good for astronomy.
So, what do you do first? Keep surfing the net. Start at the Sky and Telescope or Astronomy magazine home pages. After your kids kick you off the computer, go buy one of the magazines. They are full of great information that ranges from beginning stargazing to advanced "what the heck are you talking about?" On the way home from the magazine store stop off at the library and check out a good book on astronomy. The Backyard Astronomers Guide by Dickerson and Dyer is the best book I have checked out so far.
Find a friend who owns a real astronomical telescope (like the ones advertised in the magazines) and look through it several times. Ask your friend to let you set it up and take it down. Dropping several hundred or even thousands of dollars on a telescope without trying it out it is like buying a car without knowing how to drive it. You should test drive a few scopes before you buy one. Believe it or not, you do have friends with telescopes, lots of them. There are astronomy clubs everywhere. The Sky and Telescope site has a list of them. Go to a star party with these good people and they will be happy to share their scopes with you (unless they are taking pictures, photography is a one-person sport). Some clubs own telescopes that they will loan to their members. The one I belong to has a variety to try out. In fact, the pictures on my home page were taken with a borrowed club telescope.
If you have to buy something, buy binoculars. After you have read the books and magazines and have a full understanding of the cosmological constants (just kidding) take a pair of binoculars, with a star map, outside and look around the night sky. You will be surprised at what you can see with binoculars. In fact, things like bright comets and lunar eclipses look best with binoculars. It is also the best way to familiarize yourself with the sky. Many of the faint, fuzzy objects that you look at through a telescope are seeable with binoculars. 7x50s or 10x50s work well. Anything over 10 power (that is 10x50) requires a tripod or something to hold it steady.
Don't expect too much the first time you look through a scope. My first experience through a telescope was at a star party. I knew about the great Andromeda Galaxy M31, seen it in pictures and I could find it with binoculars, so I asked a guy with a fancy computer controlled scope to slew to it. I was very disappointed. It looked like a piece gray lint or an out of focus star. I was expecting to see color and dust lanes, like the pictures. Now I find it to be one of most beautiful and interesting objects out there. I had to learn how to look and what to expect.
It helps to have an understanding of what you are seeing. What is it? How far away is it? How did it get there? One of the best things about astronomy is the information that is available about it. From the myths associated with the constellations (kids like them) to the creation of the universe you can go as deep as you want. I used the word "creation" on purpose. Astronomy reinforces my religious beliefs.
After you have learned what you can see through a telescope, you can then make a good choice about buying one. What do you want to do with it? How much money do you want to spend? Are you going to try photography? Photography requires a telescope with an equatorial mount so that it will follow the stars across the sky. These types of telescopes are more expensive than simple Dobsonian mounted telescopes. A Dobsonian telescope works great for casual back yard type observing.
What about power? Power is not as important as optics and aperture. Compare the eclipsed moon with M42, the Orion nebula. In the picture, the nebula is just a little smaller than the moon. Deep space objects do not require a lot of magnification but they do require a telescope that can gather light. That is where aperture plays its part. Larger telescopes gather more light so that you can see these dim objects. On the other hand planets do require high magnification, but remember when an object becomes highly magnified it becomes dimmer so again optics and aperture come into play. That is why a "600 power" department store telescope is pretty much worthless for astronomy.
So go out and buy a $5000, 20 inch killer scope, right? Well, maybe, but probably not. Where will you be doing most of your observing? If you are like me it is from your back yard somewhere in the suburbs where there is a lot of light pollution. A 20 inch light bucket is for gathering light and it doesn't care where the light is coming from. In light polluted areas, the contrast between the background sky and a faint object is not very good. In the country, where the sky is dark, a 20 incher will allow you to see much more than you would see with a small scope. Other factors to consider in telescope selection are ease of transportation and ease of set up and take down. Big telescopes are not easy in those areas. The bottom line is this: buy the scope that you will use. If you dread setting it up or hauling it then you have the wrong scope, you wont use it.
In my opinion 8 inches is about the right aperture. For casual observing a Dobsonian mounted Newtonian telescope does just fine.
There are generally two types of telescopes, refractors and reflectors.
In refracting telescopes, the light path passes though a lens in the front of the telescope on its way to the eyepiece and eye. These types of telescopes are what most non-astronomy people think that a telescope is. Camera lenses are refractors.
In reflecting telescopes, the "lens" is a concave mirror in the bottom of the telescope. The light path is reflected and diverted to the eyepiece and eye. The Hubble Space Telescope is a reflector, along with most of the other telescopes used by professional astronomers.
It is hard to say which type of telescope is best for the amateur; there are many things to consider. Generally speaking, good quality refractors are best for high powered and high contrast looks at solar system objects like the planets and moon. It is tough to beat the crisp, quality view of a good refractor.
Some refractors have a wide field of view with a fast focal ratio so they are good for photography.
Good refractors are expensive compared to their reflecting counterparts. They run about $1000 an inch, so at that kind of money they are generally smaller than reflectors. "Big" amateur refractors can be 8 inches in diameter. "Small" ones are 2 inches.
Reflectors are the most common telescopes used by amateurs and I am sure economy is a big reason for that. "Big" amateur reflectors can be 36 inches. "Small" ones are 6 inches.
Another reason that larger reflectors more popular is that they are better for looking at faint deep space objects.
A little about etiquette at star parties
The first rule is to have fun. Move around and visit all of the scopes. Pay close attention to the young astronomers. Let them show you the sky.
Be very careful with light. Use flashlights that have give off red light. Keep the car headlights off.
Keep young children under control. There is a lot of expensive hardware around for them to run into.
Sound carries well at night. I enjoy music but not everyone has the same tastes as I do, so I leave it off. Even that cosmic new age stuff can be an imposition on some people.
A key to success at any observing session is to plan on it getting colder than you might think it will be. Always dress warmly, even in the summer.
Seeing is the ability see through the atmosphere. It has more to with the stability of the sky than the clarity of it. The night can be perfectly clear, but when you look through a telescope the image may be dancing and shimmering so much that you can hardly see anything. If you have seen a "heat wave" you have seen a cause of bad seeing. Looking over a housetop can make an image shimmer. Poor seeing is also caused by turbulent air overhead. The steadiest seeing is often when the sky has high and very thin clouds, or when there is a high pressure haze.
Many of the objects in the sky are so faint that it takes some effort to see them. It can take as much as a half hour for eyes to adjust as much as possible to darkness. It only takes a split second for a careless light to mess things up. Red filtered flashlights allow you to have enough light to see a star map without destroying dark adaptation.
Averted vision allows you to see very dim objects just slightly better. What you do is look a little off to the side of what ever faint object you may be looking at and you may be able to see more light coming to you. I think the reason that you are more light sensitive a little "off center" has to do with eyeball color receptors verses black and white receptors and how they are located in the eye. We have more black and white receptors than color and the color ones are located at the center of the retina. With averted vision, you are using those black and white ones off to the side. (I think).
There is no question that sky watching is better in a dark area than from the city, but there is still much to be seen from the city. The convenience of your own bed and kitchen make it worth while to understand what can be seen from the city. It is best to start out by shielding yourself as much as possible from the lights around you. This will help your eyes to stay a little more dark adapted and keep a stray reflection from entering the instrument you are looking through.
Obviously, the moon do not pose a problem in the city. In fact, the moon can be so bright that you may want to use a filter, or obstruct the telescope, so that it is a little easier to look at. Planets are great city targets. Double stars can keep you entertained for hours. Bright open clusters, like the double cluster, are another good target group. Bright nebulas like the ring and Orion nebulas are good targets, but nebulas along with galaxies and globular clusters are seen much better under dark skies. The sky map in Sky and Telescope seems to be structured for viewing in the suburbs so it is a good reference for your observing session.
I am willing to bet that one reason you are reading this is that comets Hyakutake or Hale-Bopp has sparked an interest in astronomy within you. How blessed we are to see these two events within a year of each other! It is very possible that we will never see another comet like these in our lifetimes. On the other hand, maybe one more will pop up in the years to come. Besides, there is usually a "telescope size" comet around to look at.
Comets have been described as "dirty snowballs" and that sounds good to me. Their long elliptical orbits around the Sun take them way beyond the orbit of Pluto. The time that it takes them to make their orbits divides them into two categories, short period and long period. Short period comets take less than 200 years for one orbit while long period comets are more than 200 years.
The method used to observe comets depends on how bright the comet is and how big it is the sky. To observe Hale-Bopp I simply had to go outside and look. When I used binoculars in the city the tail doubled in length. At a dark site, the tail was four or five times longer. After "city watching" Hyakutake and then seeing it at a dark site I was awe struck. That tail stretched 45 degrees across the sky. I've never seen anything like that. Everything in the night sky looks better from a dark area.
So, eyes and binoculars work well for "monster" comets like Hale-Bopp, but that comet also had some very interesting telescopic features as well. Through a scope you could see what looked like bow shocks, or rings, around the comet. Most comets are only observable through a telescope.
So, you have a sky map and it's dark outside, what should you do first? Grab the map and some binoculars and see what you can find. Pick a bright deep space object, like M31 or the Double Cluster, and see if you can track it down by star hopping to it. Use the "W" of easy to find Cassiopeia to point the way. Don't expect too much. If you are in the suburbs, you will see what looks like a spot on your binocular lens. Binoculars are the best way to learn the sky. After you have found an object with binoculars see if you can find it with a telescope. Make an open cluster one of your first deep space targets. Some are bright, beautiful and easy to find, especially if you can find one with binoculars first. Double stars are another beautiful group of objects to see. Albero in the head of Cygnus the Swan is a spectacular site. Double star hunting can be done from the suburbs and is a fun way to learn the constellations.
Be sure to reserve judgment on deep space observing until you do it at a dark site. It is tough to see many of these faint objects in light polluted areas. The moon will also wash out a faint object, so it is good practice to observe within a few days of a new moon.
The Moon is an object well worth your time, unless it is full. The most interesting part of the moon is the terminator, the area between light and dark, and full moons don't have a terminator, so they are best looked at with something other than a telescope. There are a lot of cool mountains and craters to learn about on the moon. It is also fun to learn how the moon passes through its phases. When you understand the phases of the moon, you can make good plans for deep space observing because you will know where the moon is in the sky and when it will rise and set.
Planet observing offers some interesting and entertaining challenges. When you look at Saturn the rings are the first thing that jump out at you, but try to see its satellites, especially Titan, the largest satellite in the Solar System. Use the chart in Sky and Telescope to identify them. Look for areas of light and dark on the planet and in its rings.
When you look at Mars, can you see the polar ice cap? What other features can you see on the planet? Mars needs to be relatively close to Earth before you can see any detail on it.
I think Venus looks best with the naked eye. It's fun to watch it move higher or lower in the sky as our positions in the solar system change. Through a telescope you can watch its phases change... a little boring if you ask me.
Mercury, like Venus, is fun to watch as an evening or morning star.
My favorite planet is Jupiter because it changes with every observation. The first things to notice are the four Galilean satellites. Like Saturn, they can be identified by looking at the magazine chart. Sky and Telescope provides times for when the satellites transit across the face of Jupiter and when they cast their shadows on to the planet. These events only last a few hours so you can view them in one night. You can also watch them disappear and reappear in the shadow of Jupiter. The Great Red Spot is a fun challenge to spot, and yes, Sky and Telescope tells you when to look for that as well. Finally, look for the bands on the planet and see the turbulent swirls that separates them.
Meteors are bonus entertainment during a night of observing. Meteors occur when small pieces of space stuff plow into the earth's atmosphere. They hit the earth's upper atmosphere at tremendous speed and burn up instantly. These meteor chunks are mostly about the size of a grain of sand. You can usually see a handful of sporadic meteors during an observing session. They are not very bright but they do brighten the spirit when they zip overhead. On rare occasions, a sporadic fireball will have you wondering if the Martians are invading.
Meteor showers are annual events that occur when the earth passes through debris left by comets. Their regularity gives us the opportunity to plan for the events and even report to each other what we saw. Meteor showers are named for the constellation from which they appear to be coming. That area is the leading edge of the earth as it moves through space.
The Persied shower is the best annual meteor shower. The shower lasts for days but it peaks on the morning of August 12. At its peak, it has a rate of about 100 meteors per hour.
The November Leonid shower occasionally outshines them all and that occasion may happen again in 1999 and 2000. It is always good to go to a dark site when looking for meteors but this one is packed with bright fireballs that can be seen from almost anywhere. For the 1998 shower I could see them through high thin clouds from my front yard in the suburbs. I even read a report of daylight sightings. The Leonids are also famous for their lingering, glowing trails.
Good luck, Mother Nature has a way showing who is boss in the middle of the night. The first line of defense is a good offense, go out on a dry night. You will know as soon the scope cools if the night is dry. A dew shield will hold it off for a while and many times "a while" is long enough. The key to dew is to keep the scope slightly warmer than the air. The reason that a telescope (or a car) can become colder than the air around it is that heat radiates away from it into space. Hold your hand up to a window on a cold night and you can feel the heat being sucked out your hand. Dew shields put a barrier between the scope and empty space so that it slows the radiation down. Blow dryers may be used to heat the scope but they are not the best idea because may over heat the scope and distort the optics, plus their effects don't last long enough and it is tough to find a place to plug one in on the top of a mountain. I have used a 10 foot dryer vent hose taped to my car heater outlet to blow warm air on to the scope, but much caution should be used to avoid over heating which causes tube currents and distortion. Buying a dew zapper is always an option. Dew zappers (or whatever they are called) use resistors to keep the scope slightly warmer than the air.
That's it for now. I've been watching the hits on this page and I'm surprised to see that most of you are more interested in the information sections of my site than you are in my pictures. With that in mind, I will try to add more information when the urge hits.
Email Keith at astrokeith@yahoo.com or use this feedback form