"It’s about 500 light-years away in the direction of one of the spiral arms of the Milky Way." Directions like those sound good in a science-fiction story, but they won’t help you find anything in the night sky. In this article, we will explain the coordinate systems that are actually used in astronomy.
The need for a coordinate system is obvious: it’s a way of pinpointing the exact locations of celestial objects in the sky.
The first thing to get used to, as a skywatcher, is that the Earth is the center of your universe, though not of the real one. That is, you are always standing on the Earth, and that’s what everything seems to revolve around.
Great Ball of Stars!
Specifically, it’s convenient to think of the sky as a gigantic celestial sphere, a globe surrounding the Earth. The sphere is assumed to be infinite in size; the planets and stars are so far away that their distances don’t matter. When you step outside and look up, the sky appears as a dome, a hemispherical bowl. It isn’t, of course, but the illusion works for our purposes.
As the Earth rotates, this bowl seems to twirl around. The Earth rotates from west to east, which causes the sky seemingly to rotate from east to west, once every 23 hours and 56 minutes (one sidereal day). The stars stay in fixed positions on the celestial sphere (because they’re so far away); the Sun, Moon, and planets gradually move around it in their orbits, so it takes four more minutes (making a total of 24 hours) for the Sun to get back to the same position.
Latitude and Longitude, Astronomy Style
On the celestial sphere, astronomers use lines similar to those of latitude and longitude on the Earth. The astronomical equivalent of latitude is declination, measured in degrees (°) of arc, positive for north and negative for south. Each degree is divided into sixty minutes (’), and each minute is divided into 60 seconds (’’). (Seconds are used only when great precision is needed.) "Declination" comes from a Latin word for "bending" or "angle."
The celestial equivalent of longitude is right ascension (a rather clunky term, for sure). It is measured in hours (0 to 24), minutes, and seconds, rather than degrees, for reasons we’ll get to presently. For example, the pole star, Polaris, is at right ascension 2 hours 32 minutes, declination +89° 16’. The Table below shows the right ascensions and declinations of some other bright stars.
Positions of some bright stars (Epoch 2000.0)
|Sirius (in Canis Major)||6h 45m 09s||-16° 42’ 58’’|
|Regulus (in Leo)||10h 08m 22s||+11° 58’ 02’’|
|Arcturus (in Boötes)||14h 15m 40s||+19° 10’ 57’’|
|Altair (in Aquila)||19h 50m 47s||+8° 52’ 06’’|
|Fomalhaut (in Piscis Austrinus)||22h 57m 39s||-29° 37’ 20’’|
The strange name "right ascension" has to do with the rising of a star as viewed from the Earth’s equator, where stars with low declinations rise (ascend) vertically (straight up).
The right ascensions and declinations of stars are essentially fixed, although they shift very slowly because of precession, a gradual change in the direction of the Earth’s axis. The reason most star charts say "Epoch 2000.0" is that they show star positions for the beginning of the year 2000. Earlier, we had Epoch 1950 and Epoch 1900 charts. The rate of precession is 1° every 72 years, but different parts of the sky are affected to different extents.
On the contrary, the Sun, Moon, planets, comets, and asteroids are not fixed relative to the stars. They move around. You have to look up their right ascension and declination for a particular date.
The declination of Polaris, +89° 16’, is almost 90° north, which means Polaris is less than a degree away from the north celestial pole. That’s the point around which the stars appear to twirl (for Northern Hemisphere viewers). You can line up the polar axis of an equatorial mount by sighting on Polaris. If you live south of the equator, you can’t see the north celestial pole; instead, you see the south celestial pole, which is not marked by a bright star (although Sigma Octantis is close). An old astronomers’ joke is to report the discovery of some interesting object "about ten degrees south of Sigma Octantis" — there’s no such place, because declinations range only from +90° to -90°.
The point directly over your head, the zenith, has a declination the same as your latitude on Earth. The point directly south of you on the horizon has negative declination of 90° minus your latitude; for example, declination -50° if your latitude is 40 north. That’s why objects such as the Magellanic Clouds, at declination -65°, are never visible from the continental United States.
We mentioned already that right ascension is measured in hours (0 to 24) rather than degrees (0° to 360°). The two are interconvertible, of course; one hour equals 15 degrees of arc. If you want to give right ascension in degrees, you can; celestial navigators do, and they call it sidereal hour angle (SHA).
The reason right ascension is measured in hours is of course that the celestial sphere seems to rotate as the Earth turns. Its rotation period is called one sidereal day, or 24 hours of sidereal time, which runs slightly faster than mean solar time. If a particular star is directly above you, it will be directly above you again 24 sidereal hours later, or 23 hours and 56 minutes later by the ordinary clock. The sidereal time at any moment is the right ascension of the point directly overhead, as well as points directly north and south of it (along a line called the meridian).
At the same mean solar time — midnight, for instance, or 10 p.m. — the sidereal time will be 4 minutes later each successive day. That’s because the Earth orbits the Sun. The celestial sphere seems to "slip" relative to the Sun (actually, the Sun is moving on the celestial sphere), and that’s why we see different constellations at different seasons.
Most objects rise in the east and set in the west. Along the way, they follow lines of declination, which are circles centered on the north celestial pole.
Some objects near the celestial pole are always above the horizon; they just whirl around and around without setting. They’re said to be circumpolar. Above the Arctic Circle, the circumpolar region is so large that the Sun gets into it and doesn’t set, resulting in the Midnight Sun.
What Does the Coordinate System Mean For Amateur Astronomers?
An object’s coordinates tell you where it is in the sky. If you have a telescope on an equatorial mount, you can locate celestial objects to view by "dialing in" their right ascension and declination coordinates using the mount’s setting circles. (We won’t go into how to do it here.) The setting circles on most equatorial mounts, and the mounts themselves, are not accurate enough to land you right on an object consistently, but they’ll get you close; then you merely have to sweep the telescope a bit using the slow-motion controls until you spot the object.
Conversely, you can use the setting circles to identify objects you happen upon in the sky. By noting the right ascension and declination values of an object your scope is pointed at, you can then look up the values in a star atlas or catalog to find out what it is.
Other coordinates are useful for other purposes. The most obvious are altitude (distance above the horizon, in degrees) and azimuth (compass direction; north = 0°, east = 90°, south = 180°, west = 270°). Computer programs can convert right ascension and declination into altitude and azimuth for a particular place and time.
Also important are ecliptic coordinates. The ecliptic is the line in the sky that corresponds to the Earth’s orbit around the Sun. The planets are always near the ecliptic, in a narrow band called the zodiac. Planetary orbits are always computed relative to the ecliptic, and ecliptic coordinates take the ecliptic as their "equator." Ecliptic latitude is the distance of an object from the ecliptic, and ecliptic longitude is measured along the ecliptic from the place where it passes through declination 0°.
There’s yet another set of coordinates that uses the center line of our galaxy as the equator. Galactic longitude is reckoned in degrees from the galactic center in Sagittarius; galactic latitude is the distance north or south of this center line. These coordinates are used in the study of the structure of our galaxy, but not for finding objects in the sky.
Even the smallest telescope will reveal breathtaking close-ups of the Moon’s rugged, battered surface. New features are highlighted every night along the terminator, where the light and dark portions of the lunar disk meet. Craters, smooth lava plains, and jagged mountains abound, providing endless fascination.
Venus, Mars, Saturn, and Jupiter make great subjects for study with a telescope. They’re very small, even at high magnification, but are bright enough to see even from light-drenched city skies. Any size telescope can show Mars’ pale red disk (and often a polar ice cap), Saturn’s pale yellow orb and picturesque rings, and Jupiter and its bright moons. In good seeing conditions you’ll see Jupiter’s colorful cloud bands and its Great Red Spot.
No telescope shows stars as more than tiny but colorful pinpoints. Double stars, like the famous blue-gold pair Albireo, are a popular target. There are also numerous star clusters of different sizes and brightness ... the jewels of the sky. It’s fun to hunt them down using a star map and see how many stars you can resolve.
Like snowflakes, no two of these ghostly clouds of gas and dust look alike. All are faint and in a telescope will appear mostly gray or greenish in color. But their shapes and structure are revealed with patient observing. Dark-sky observing sites will let you see much more.
Incredibly distant and challenging faint subjects, dozens of galaxies are visible in backyard telescopes of modest size, hundreds or thousands in bigger models. In dark skies with a 6" scope, you can discern hints of structure in the brightest galaxies. The more time you spend observing them, the better trained your eye will become at seeing faint details.
Pictures vs. Viewing
Human eyes are not sensitive enough to detect colors in faint light. Long-exposure photos of nebulas and galaxies show their true colors. It’s impossible for a photo to depict the real-time, low-light image you will see. Fortunately, the eye is often better at revealing glimpses of detail on the planets than the typical photo can catch.
When it comes to buying or using a telescope, there are a lot of strange terms to learn. Not all of them are critical to actually using a telescope, but most will help you better understand your telescope and how it works. One of these terms is focal length.
Generally expressed, focal length is the distance (given in millimeters) between the telescope's primary lens or mirror and the point where the light rays come together in focus. Why is this important? Focal length is the major determining factor of any given telescope's magnifying power. You might think that using a lot of magnification would be a bonus when looking at a small object, but all telescopes have a practical limit. At lower magnifications, the image is small, bright and well-resolved, but too much magnification makes for nothing more than a big, blurry image. Why? Telescopes can only gather so much light and high magnification means you're just spreading that same amount of light over a larger area - resulting in useless or "empty" magnification. So how do you determine a telescope's practical magnification limits? It's easy. Just multiply the objective lens or mirror's diameter (in millimeters) by 2. For example, a 100mm telescope would have a practical magnification limit of 200X.
Knowing your telescope's limitations will help you to choose accessories, such as eyepieces and barlow lenses wisely. First let's learn about a telescope's focal length, and then we'll look at eyepiece focal length.
How To Determine A Telescope's Focal Length
Most telescopes list the focal length in the manufacturer specifications. However, there might be a circumstance where you don't have access to this information. So what do you do if you have a mystery telescope? There are two ways to get a rough idea if you have some information. It might be printed on the telescope's body or perhaps on an instruction manual or box. If you have the telescope's focal ratio (f/number) you can measure the diameter of its primary optic - either the large mirror for a reflector telescope, or the large lens of a refractor telescope. Now, multiply the focal ratio by the diameter of its primary optic. Viola. You now know the telescope's focal length. The second method is if you know the magnifying power of your telescope. This circumstance might occur if you have a telescope or spotting scope with a known, fixed eyepiece. Look for any marking which might tell you it has a specific magnifying factor. If you have this value, then you can multiply the focal length of eyepiece by the magnification. This will also give you the focal length of the telescope.
You can also determine the focal length of a reflector telescope in another manner, but you'll have to remove the mirror (This method is very risky and could void your telescope's warranty). Chances are you'll only use this method if you encounter a home-made reflector telescope or an old one which no longer has an instruction manual. Carefully mount the mirror so it is held securely vertical and place it in a darkened room. From the other side of the room, shine a flashlight on the mirror and place an impromptu projection screen between the two - slightly off to one side. Move the screen until the light is focused in the smallest possible point. Mark that distance and measure it. Now, divide that measurement number by two to determine the focal length.
How To Determine Your Telescope's Magnifying Power
Now that you understand the importance of your telescope's focal length, you can determine the magnifying power of any eyepiece you use in it. All it takes is a little math. Take a close look at your telescope's eyepieces and you'll see they also have a focal length. It is usually printed on the barrel and it is also expressed in millimeters. All you need to do is divide the focal length of the telescope by the focal length of the eyepiece. For example, if you have a telescope that has a 1000mm focal length and you are using a 20mm eyepiece, you will be getting 50X (1000mm/20mm = 50X). If you place a 20mm eyepiece in a telescope with a 500mm focal length, you'll get 25X (500mm/20mm = 25x). That is why the same eyepiece appears to behave differently in different telescopes! As we learned earlier, there are practical limitations to a telescope's magnifying power, so choose, and use your eyepieces by focal length accordingly.
Magnification can be a wonderful thing. It can reveal amazing planetary features, subtle details in nebula and galaxies, split tight double stars and make you feel like you are walking on the Moon. However, high magnification also has some drawbacks. If you aren't using a telescope with a drive unit, you will constantly have to use your slow motion controls to "track" your subject as the Earth moves. This can be very frustrating when viewing. Also, when you magnify, you are magnifying sky conditions (How to Judge Sky Conditions). For example, if you are using 200X on a night with poor clarity and stability, you are magnifying those conditions two hundred times as well. Just remember your telescope's practical limits and how to determine its magnification - and enjoy pushing those limits on good nights!
With so many modern stargazers relying on computerized telescopes to locate objects, learning to read a star chart might seem like a lost art form. However, using a star chart is very easy, and it helps you really understand what you're looking at and the way the sky works. Additionally, not all telescopes have on-board computers and not all star gazers want to use them. There's a lot of satisfaction to be gained by learning to use a star chart and manually locating objects. By knowing a few simple instructions, you'll find using a star chart is like a recipe. All you need to know are some common measurements and how to find the key ingredients! Let's start with the basics.
Planispheres and All Sky Chart
The first type of star chart you'll probably encounter is a planisphere or an All Sky Chart. These are normally presented in a round format which depicts the brightest stars and constellations as they are seen during specific times of the year. A planisphere is printed on a wheel with dates and times to help you select a key "window" showing the general night sky for the selected time. Like the planisphere, the seasonal All Sky Chart is designed to be held over your head and aligned with the cardinal directions. Unlike a terrestrial map, all star charts have east to the left and west to the right - the correct orientation to match Earth's movements and the apparent movements of the celestial sphere. To help you understand the concept, hold an All Sky Chart over your head and face south. You'll notice east, the direction of sunrise, is to the left, north is behind you and west, the direction of the setting Sun, is to the right. Now all you have to do match up bright star patterns with what you see and identify the primary constellations. These types of star charts are like gathering together the ingredients.
Formal Star Chart
Once you have familiarized yourself with the constellations and key stars that you see, it is time to get more specific. First, choose an area of the sky in which you'd like to work. You'll notice two sets of numbers along the margin of the formal star chart. Like on a terrestrial map, which uses the alphabet in one direction and numerals in the other, these sets of numbers divide the map into sections. In reading from left to right - which (unlike a terrestrial map) represents east to west - you'll see hours, numbers and seconds. These numbers along the top margin are called Right Ascension and it is abbreviated in celestial coordinates as RA - the equivalent of terrestrial longitude. Each celestial "day" is divided into 24 hours (of rotation of the Earth) and begins on the point of vernal equinox. This "zero hour" is the place in the sky where the Sun crosses the celestial equator during the March equinox (equal times of day and night). The second set of numbers reads from top to bottom - north to south - and they are either positive or negative. This set of directions is the Declination and is abbreviated as Dec. It is the celestial equivalent of latitude. Positive numbers are located above a line on the charts, and an imaginary line in the sky, called the celestial equator. This is the dividing line between the northern half and southern half of the night sky. Negative numbers lay to the south.
Why are these numbers important? All astronomical objects, even stars, are given a set of celestial coordinates which use right ascension and declination. These coordinates remain constant. If you are looking for a specific object, you can use its assigned directional value as a recipe to help you find it! For example, if you wanted to view the Crab Nebula you might ascertain its coordinates from a resource such as an astronomy magazine, an astronomical catalog or an observing book. In this listing you would see the directions: RA 05 34 31 - Dec +22 00 52. This means you can locate it both on your star chart and in the sky at 5 hours, 34 minutes and 31 seconds in right ascension and north of the meridian at +22 degrees, 00 arc minutes, 52 arc seconds. Begin reading your star chart at the zero hour and count the hours across to the west (right) until you reach the fifth hour. Use the declination scale along the side margin and locate positive twenty-two degrees. By looking at the larger scale, you can determine the constellation in which it is located and the general area in which it can be found. Until you have become familiar with the night sky at all seasons, you may need to use a planisphere or All Sky Map to make sure the constellation where your object is located is visible. Once you've determined this, it's time to go on to the next step.
Take a look at the large, printed stars around your object on the map. These primary stars are the ones you'll be looking for when translating map to sky. Note they also have a designation. If you're thinking "That's all Greek to me!" then you'd be correct. Very bright stars are given a Greek letter designation such as Alpha, Beta or Gamma. These designations are not only stellar names, but indications of the star's brightness - starting with Alpha as the most luminous and descending in order. Most good star charts will have a key to these letters as well as a magnitude key where the printed star size is also given a brightness value. Common numerical designations on stars are called either Bayer or Flamsteed numbers. These are stellar catalog numbers assigned to bright stars and were originally created by historical astronomers, Johann Bayer and John Flamsteed. Most ordinary star charts use Bayer numbers - along with Greek letters - but Flamsteed numbers are used where no Bayer designation is given.
From Star Chart To Sky
The next step in using a star chart is to match what you see on the map with what you see in the sky. Begin with the constellation, and then identify the very brightest of the stars you see around your designated target and locate that pattern in the sky. For example, you know from looking at the map that your object is located about ten degrees west of Alpha X. The key is to start big and get smaller, but how do you translate degrees from a book to degrees in the sky?!
Don't panic. A simple way of measuring the sky is to use your hands. Hold your hand outstretched at arm's length. From the tip of your little finger to the tip of your thumb is approximately 20 degrees. If you make a fist, that is about 10 degrees. The width of your thumb is somewhere around 2 to 3 degrees. This easy way of measuring will assist you in finding the general location of what you're looking for. Take an even closer look at your star chart and you'll notice it is also divided into other, smaller sections - usually 10 degrees. While this might seem a little confusing at first, you can learn if you practice!
Now, look at your star chart again. You have found the primary stars around your target and your telescope is aimed in the general direction. Use your optical finderscope to assist you in locating and identifying even fainter stars which match the pattern on the star chart. By knowing how many degrees your finderscope reveals, you can even further refine your hunt.
If you use an equatorial mount, you're also in for a big surprise. Once you have reasonably polar-aligned your telescope and set the axis at least close to your latitude, take a close look at those numerical dials on the mount. Do those numbers look familiar? Darn right, they do! One set is Right Ascension and the other is Declination. It might be like comparing an abacus to a calculator, but these handy tools can also get you very close to the perfect recipe for a starry night!
Budding astronomers today have a greater variety of telescopes to choose from than ever before. Some are complex, computerized marvels, while others offer a more basic approach to stargazing. But even with all of these to entice us, none is more versatile than a pair of binoculars. Indeed, when it comes to touring the universe, two eyes are better than one!
Advantages of Two-Eyed Touring
Observing the night sky with binoculars has many advantages. One of the greatest is how friendly and comfortable binoculars feel. Perhaps this is because they can be used either while standing up or sitting down. What could be more enjoyable than casually scanning the heavens with a binocular while lying back in your favorite chaise lounge?
Another great advantage is their portability. Astronomy on the go! While a telescope can be bulky and takes time to set up, binoculars are compact, lightweight, and ready instantly, either for a casual glance at the night sky or for an in-depth study of the universe.
Binoculars show the "real" sky. Astronomical telescopes flip the sky around one way or another, either upside-down, left-to-right, or both. Thanks to both their upright image and wide fields of view, binoculars keep everything as it was meant to be, making it easier to find your way around when comparing the view you see to a star chart.
The wide fields of binoculars also let us enjoy some sky objects that are simply too large to fit into a telescope’s limited field of view. You are probably familiar with some already, such as the Pleiades and the Coma Berenices Star Cluster, but that’s just the start! Dozens of sky sights are better appreciated through binoculars than through telescopes.
Research: Binocular Vision is Better
Beyond aesthetics, research shows that an observer’s visual acuity is greatly improved by using two eyes instead of only one. Binocular vision enhances our sensitivity to subtle differences in contrast, resolution, and color. Some people experience up to a 25 to 40 percent increase in their ability to detect faint objects through a binocular than through a conventional telescope!
That’s a dramatic improvement, but why? Light entering the eye is focused by the lens onto the retina, which converts the image into electrical pulses and sends them onto the brain. The brain then interprets the pulses into the image that we sense. By relying on only one set of pulses (i.e., using one eye), any inconsistencies in the signals will interfere with the final image. With two sets of signals to interpret, however, the brain will merge the pair of electrical messages. The result is the ability to see fainter, lower-contrast objects.
Yes, there are many benefits to touring the universe through binoculars, but perhaps the greatest is that the binocular universe seems much more personal than that viewed through a telescope. By extending our natural, two-eyed view, the cosmos seems drawn to us, and us to it. It is a feeling, a sense of oneness and belonging, that cannot be duplicated any other way.
Choosing Binoculars for Astronomy
The nighttime performance of binoculars depends on the aperture (diameter) of the front (objective) lenses and the magnification provided by the eyepieces. The wider the objective lenses, the more light the binocular will collect and transmit to your eyes. For astronomy, objective lenses of 50mm diameter or larger are recommended. Indeed, 7x50 binoculars (7x power and 50mm objective lenses) are ideal stargazing glasses because they offer plenty of light gathering, good power, bright images, and a wide field of view (which makes it easier to find things). A 10x50 binocular, also a popular size, has the same light-gathering capability but provides higher magnification (10x). The higher magnification may result in a slightly shakier image if you’re holding the binoculars by hand. But for astronomy, it’s advisable to mount the binocular on a tripod anyway, to prevent arm and neck fatigue from prolonged overhead viewing.
Even better for stargazing are "giant" binoculars with 70mm, 80mm, or 100mm objective lenses. Because they admit more light, they can reveal fainter objects. But beware: such binocs are heavy and will require a tripod for support. Big binoculars often come in higher powers such as 14x, 16x, 20x, or even more. With smaller binoculars, high powers like that would yield very dim images, but larger apertures take in enough light to maintain good image brightness as magnification is increased.
Ten Favorite Binocular Targets
1) The Moon — Wow! You’ll see an unbelievable number of craters and rocky mountainous features, all in stunning clarity. Because its surface is so bright, the Moon is best observed during its crescent phases.
2) Jupiter and its Moons — Binoculars will reveal the bright disk of this giant planet, flanked by its four largest Moons, whose positions change nightly.
3) The Milky Way — Scanning along this dense band of stars on a summer night is immensely pleasurable. You’ll see countless clusters, knots, vacant dark patches, and nebulous puffs.
4) Sagittarius Star Clouds — The part of the Milky Way near the constellation Sagittarius ("the Teapot") reveals the richest detail in the night sky. It teems with interesting objects, including the Lagoon, Swan, and Eagle Nebulas, the M24 Star Cloud, and a wealth of open clusters. Use a star chart to help identify them.
5) The Pleiades — This sprawling cluster in Taurus appears as six or seven bright stars to the naked eye, but blooms to several dozen in binoculars.
6) The Andromeda Galaxy — Easy to spot with the unaided eye under a dark summer sky, this majestic "island universe" fills a good portion of the binocular field. You’ll see its bright core and faint disk, perhaps even the dark dust lane around the edge.
7) The Orion Nebula — One of the most beautiful gems in the sky, this expansive winter nebula glows brightly, displaying intricate wisps and tendrils. At its heart is an easily-split double star and a luminous quadruple star, called the Trapezium, which can be resolved with binoculars of 11x or more.
8) The Double Cluster — Residing halfway between the "W" of Cassiopeia and the constellation Perseus, these side-by-side stellar splashes are a true delight to behold in binoculars.
9) Albireo — A bright double star in the head of Cygnus the Swan, notable for its gorgeous color contrast: one star glows yellow, the other blue. Ten-power binoculars will split the pair cleanly.
10) Scutum Star Cloud — This impressive star field contains the compact open cluster called the Wild Duck and some dark, starless patches.
The question of which telescope is best for the beginner is asked a lot. Here are our thoughts on the best beginner telescope - it really depends on what is important to you! There are many factors, most of which can only be answered by you, to pick the best beginner telescope. Here are some general guidelines to help steer you in the right direction.
Price, portability, what you can see with your new telescope and features such as computerized and GoTo functionality are the common attributes for the beginner to consider.
Price is a very important factor, especially if you are a beginning enthusiast. You may not be sure that you or your family will stick with the hobby for the long run and want an entry-level price just to get you started. Of course, you may find that in no time at all you're ready to step-up to a larger, more feature-rich telescope. Or, your high level of interest in astronomy and desire to have a high-quality, more capable telescope right from the beginning may make the investment in a higher-priced telescope your best choice. No matter your budget - Orion will have the right telescope for you!
The design and size of the telescope has a lot to do with portability and what you can see.
Refractors are the telescope design that most beginning astronomers consider first. A refractor uses a lens that provides a clear, quality view and tends to be smaller and more portable. Refractors can be used for both astronomy and scenic viewing (with a correct-image diagonal). A small 60mm-70mm refractor is one of the most inexpensive investments you can make to get into the hobby. You will be able to see the Moon in great detail, the rings of Saturn, and a cloud belt or two around Jupiter. Smaller telescopes are very portable and inexpensive, but lack the aperture (size of optics/light-gathering capability) needed to see much outside of the solar system like faint nebulae and galaxies.
Some great refractor choices from Orion can be found in the Refractor Telescopes For Beginners category.
If you're looking for the next step up to a more capable, feature-rich refractor, you can explore these Intermediate Refractors.
Reflectors use a primary and secondary mirror to gather light from the universe to your eyes. Mirrors are more economical to manufacture and are available in larger sizes to gather more light and see beyond our solar system. Reflectors are used exclusively for astronomy and tend to be a larger, less portable telescope.
There are relatively inexpensive models that will allow you to enter the realm of deep-sky objects, as well as give excellent views of the planets. A 4.5" to 8" Dobsonian is perhaps the best "bang-for the buck" beginner choice.
With a scope like this, you can see things like the Orion nebula in nice detail, the oval structure in the Andromeda Galaxy, the Ring Nebula in Lyra, and many more deep sky objects. Best of all, these telescopes are big enough in aperture that they will probably last many years before being out-grown.
Of course you can spend more to include computerized capability found in the GoTo and IntelliScope Dobsonians.
Cassegrains make a great portable telescope using a combination of mirrors and lenses. They are very portable, can be used for scenic viewing during the daytime with a correct image diagonal, and are available in larger aperture with less weight to manage.
Here are some great, entry-level Cassegrains for Beginners.
If price isn't quite as much of issue and you want to invest more but still don't want something overwhelmingly large, consider these Intermediate Orion Cassegrains.
As you can see, there are many different types of scopes that can be a great first telescope - consider a few of the factors we've described here before you make your decision and you can't go wrong.
Or just send us an email at firstname.lastname@example.org, contact us via live chat, or give us a call Toll-Free at 800-676-1343 and we'll help you find the right telescope!
A telescope wouldn’t be terribly useful without something to hold it steady. Telescope mounts come in two general types: altitude-azimuth (or altazimuth) and equatorial.
The simplest type of mount is the altazimuth version. It has two perpendicular axes of motion, vertical (altitude) and horizontal (azimuth). Standard camera tripods have altazimuth mounts.
Because they are easy to use and cost less than equatorial mounts, altazimuth mounts are ideal for smaller, inexpensive, beginner telescopes. They’re also the mount of choice for terrestrial observing with spotting scopes. Some altazimuth mounts are equipped with slow-motion controls, which allow fine adjustment of the telescope’s aim to help zero in on target objects.
The Dobsonian Mount
One new version of altazimuth mount used widely by amateur astronomers is called the Dobsonian mount. Invented by San Francisco telescope-maker John Dobson in the 1970s, this boxy mount is constructed of wood and sits low to the ground. Besides being inexpensive, Dobsonian mounts are inherently strong — capable of supporting giant Newtonian reflectors. Teflon and other low-friction materials used on the bearing surfaces allow very smooth adjustment of the telescope’s position.
The equatorial mount is the preferred type for astronomy. It also has two perpendicular axes, but they are called right ascension (RA, or polar) and declination (Dec). When the RA axis is aligned parallel with the Earth’s rotational axis, objects can be easily "tracked" as they drift across the sky (due to Earth’s rotation) by turning just one of the slow-motion controls (RA) instead of two, as is required with an altazimuth mount.
An equatorial mount offers other advantages as well. A motor drive can be coupled to the RA axis for automatic sky tracking-a terrific convenience. Also, with better equatorial mounts, astronomical objects can be located by their celestial coordinates (found in observing guides and star atlases) using the RA and Dec setting circles.
When it comes to astronomical observations, it is important to note what your sky conditions are. The reason is simple enough - sky conditions affect how you see things. You may find, like most amateur astronomers, that you'll enjoy keeping a record of your observations. Understanding how to assess and log factors such as transparency, limiting magnitude and stability are important contributions as to how, and when, you can see certain astronomical subjects. By reading the tips below, you'll be better equipped to more accurately record sky conditions in your observing journals.
Transparency or Clarity
If you have ever taken notice of a blue sky, then you know there is more than one shade of blue. One day it might be pale, the next day a break-your-heart shade that seems like it almost has purple in it. This is caused by transparency - the volume of moisture in the atmosphere - and the amount of thin cloud cover (or even pollutants) at any given time. This same transparency factor carries over into the night. While it might be dark, just how dark is it? Darkness or transparency is judged on a scale of one to ten, with one representing totally cloudy and ten representing maximum clarity. For example, a slightly hazy sky would have a transparency of around five or six. A partly cloudy sky might be considered a three. A perfectly clear night high in the mountains with no Moon, where stars seem to have a life of their own could be a nine! You can even have a moonlit night where very little light is scattered by thin clouds... a seven! The most important thing is to be consistent on the numerical value you assign to any given evening's transparency factor because it affects limiting magnitude.
The next factor to help you judge sky conditions is limiting magnitude , which indicates the faintest star you can see without optical aid. To assist, you will need to know the magnitude of several stars visible at the time of your observation. You can find this information on almost all star charts. For example, if you were viewing during the summer in the northern hemisphere, you might use such stars as Alpha Cygni (Deneb) with a magnitude of 1.2. Now take a look at Beta Cygni (Albireo). It has a magnitude of 3.1. Next, try 61 Cygni, which has an apparent magnitude of 5.2. If you can see this star, then the limiting magnitude of your sky is at least 5. These stars are only examples, and you can use any star for which you have a given magnitude. Take your samples from various positions around the night sky and list the faintest you can see! Always be sure to wait until you are fully dark adapted.
The next factor in judging sky conditions is stability. This is how "steady" the sky - and the image in your eyepiece - appears to be. Stability can be attributed to atmospheric conditions, or it may be nothing more than rising heat. Using your telescope, take a look at several stars in different locations in the sky. You will be judging stability, like transparency, on a scale of one to ten. Stars seen near the horizon will almost always appear to twinkle, wink in and out and move around. This is an unstable viewing condition and would rate around a two. If you are looking high above the horizon and the view looks like it is under running water, you might have great clarity, but poor stability. To help you further refine your reading, take a look at something which relies on stability to be seen, like the reasonably close double star Polaris. Does the image split into two stars easily? Do you have to focus and refocus again? If so, you might have a slightly unstable sky. However, don't make a hasty judgment. Ask yourself two very important questions: (1) Are your telescope optics at ambient temperature? And (2) Is your telescope set up in a place that might cause temperature "waves" like a concrete or blacktop surface? These two factors also play a very important role in how you see things. An unstable sky won't stop you from viewing, but never being able to come to perfect focus because of image waiver could cause you to miss small details which would otherwise be visible.
Putting It All Together
Now that you've judged your sky conditions and marked your field notes, don't stop there. While you might have great transparency, great limiting magnitude and poor stability when the evening begins, these conditions can change in a short period of time. Sometimes you'll find the most unusual combination of conditions, too. For example, a night with poor transparency might be the most stable. After you have logged sky conditions for awhile, you'll also be able to judge what types of nights work best for certain observations. For example, very stable nights are great times to shoot for tight double stars and planetary details, while nights with exceptionally good limiting magnitude could be the time to find that extremely faint galaxy you've been craving!
There are three ways to observe a comet: with your unaided eye, with binoculars and with a telescope. For all three types of observations, you will need a few simple tools to help you get the most from what you see. Before you begin, the most important thing you will need is a good locator map or the coordinates of where the comet will be at the time of your observation. There are several online sources which provide general charts, such as Heaven's Above . You can also get the ephemeris (a table which lists a comet's position over a period of time) from official websites, such as the Harvard Minor Planet Center. Once you have this information, you can use them to locate the comet on a star chart, enter the coordinates into a planetarium program to generate a map, or enter them into a computer-assisted telescope. Remember a comet can move a degree or more each night and you have to update your location information accordingly! Ephemeris information often lists the comet's magnitude as well. This will assist you in knowing if it can be seen visually, with binoculars, or if it requires a telescope. Generally, a comet will need to be at least magnitude 4 to be seen without optical aid, while larger (10X50) binoculars will reach to about magnitude 8 and an average (150mm) telescope can easily detect a magnitude 10 to 11 on a dark night with excellent seeing conditions.
The next step is to gather your observing materials and choose a location where you'll be able to see the comet over a period of several days. You'll need a red flashlight to read your chart (How Do You Read a Star Chart?) and to aid you while sketching. Before you panic at the thought of doing a little art work, this is essential to record keeping. It's fun and easy, too! Just use an ordinary sheet of white paper and trace four circles on it. These circles will be your eyepiece, binocular or visual field of view. You will need to label each of your little "mini sketches" with the date, time, location, equipment used, magnification factor and sky conditions. It may seem like homework, but it's really quite simple. It's not that hard to translate what you see onto paper when it is only a few dots and some symbols. Use large dots to denote bright stars and small dots to represent dimmer stars. The comet might be a dot which approximately represents the size and brightness of the nucleus with shading around it for the coma and shading for the tail. Make the comet sketch size as accurate as possible in relation to the star field in the eyepiece, binocular field of view or unaided eye section of the sky. These sketches will let you keep track of the comet's position over a period of time - allowing you to determine the direction in which it is going or how its appearance (such as the size of the coma and tail) may change. You might even catch an exciting event, such as a close pass to a planet or deep space object!
Now, let's get down to business.
Once you have located the comet, record the information for that night onto your observing sheet. This important information includes the date, time, your observing location (latitude and longitude), instrument used, magnification or eyepiece used and sky conditions. (How to Judge Sky Conditions). Now you are ready to begin sketching. You don't have to include every star that you see in the eyepiece, binocular field or sky into your sketch - just the major ones. Remember to use larger dots for brighter stars and smaller dots for dimmer ones. For example, the comet might be located to one side of a triangle of large stars with a Y-shaped asterism of smaller stars to the other side. You will need to label at least one star with a proper Greek letter or catalog number. This information is usually provided on your printed star chart. Look for a star which has a symbol or number printed beside it. If there isn't one, don't worry. Draw the field and use an arrow to the outside and label it with a direction towards a known star on your chart which has a symbol or number. Now, sketch the comet and label the outside of the sketch circle with the cardinal directions. Which way is which? That's easy. Turn off any drive units and watch which way the stars "drift" to the outgoing edge. That's west! Since this is your first sketch, you can't place an arrow which shows the direction the comet is headed just yet. That's why we need to do three to four observations. This same sketching technique holds true for all three types of observations. For the unaided eye, the sketch field might be something as large as a constellation. For binoculars, it's around three or four degrees of sky so choose a bright pattern of stars and label the primary ones.
Once you've done your paperwork, then it's time to have some fun! Try switching around eyepieces in your telescope to see which one gives the best view. Ask yourself some questions! If you'd like to determine the size of the comet, try locating an object which has a known size. For example, your observing catalog tells you globular cluster M80 is approximately 10' in size. How does the comet compare? Is there a tail visible? If so, how far does it extend? By knowing how many arc minutes a comparison object is in size, you can judge these simple measurements for yourself.
If you'd like to determine a comet's magnitude, you can do that, too. Just choose a star for which you have a value. Most star charts have a key to the edge which gives a magnitude. Just put the known star in the eyepiece and defocus. Compare what you see with the comet. For example, if you think the comet is brighter than its listed value of 5, try locating a 4th magnitude star and defocus your eyepiece. Is the star brighter than the comet - or the same? While this isn't a professional grade observation, it's certainly a good way of telling from night to night how a comet changes.
Be sure when you observe a comet to note how it appears. Does it have a stellar nucleus - a central "body" which appears as bright and as sharp as a focused star? How large is the coma - the fuzzy halo around it? How bright is the tail? What color does it appear to be? Does the tail split into two components? If so, you may be observing a comet with an ion tail and a dust tail!
Lather, rinse and repeat. For many observing programs, you'll need to observe a comet at least three or four times before your observations become "official". While it might be tempting just to head out with binoculars and take a quick shot at the sky, remember the lessons learned by Charles Messier - there's a lot of things out there that may look like a comet, but aren't. Even if you don't submit your records, you should still be very proud of yourself for being a real comet hunter!
At one time, comets were referred to as dirty snow balls. Then they became known as dusty ice balls. Now they are considered icy rock balls. No matter what set of adjectives you use to describe them, what we have learned recently is that comets are as individual as, well, individuals!
Astronomers have hypothesized that comets began their lives as part of the solar nebula and orbit the Sun in two distinct periods - long or short. Comets which have short orbital periods are thought to come from the Kuiper Belt, an area of the Solar System beyond the planets, extending from the orbit of Neptune and similar to the asteroid belt. Comets with longer orbital periods may originate from the Oort Cloud, a suspected region of comet bodies that's located about a light year from the Sun. These comets might have orbital periods which last hundreds, or even thousands, of years, and some may just take a direct route towards the Sun when nudged by the gravity of the larger planets or a wandering star. There are even a handful of comets - hyperbolic - which make only one pass through our Solar System before being flung out into deep space.
Periodic comets which have an established orbital period of less than 200 years have the designation "P/" added to their name. For example, Halley's Comet is officially designated as 1P/Halley. This means it is the first periodic comet discovered and it was named after its discoverer, Edmund Halley. Non-periodic comets - or ones for which an orbital period hasn't yet been confirmed - are designated with "C/". Many non-periodic comets are located and named for the equipment which reveals them, such as ones discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) and Solar and Heliospheric Observatory (SOHO). These may be less famous, but often turn into spectacular telescopic objects.
Hyperbolic comets make only a single approach into the Solar System and only a few hundred of them are known. A famous example of this type of comet is C/1980 E1 discovered by Edward L. G. Bowell. It left the Solar System faster than any natural object known!
These little icy bodies are somewhat similar to asteroids - measuring anywhere from tens of meters to a hundred or more meters across. They are composed of very ordinary materials, such as rock, water ice and dust. Another major component of a comet is frozen gases, such as ammonia, methane, carbon monoxide and carbon dioxide. Comets are even known to hold key organics, such as amino acids. While they might appear round when viewed through a telescope, comets are very irregular in shape due to their lack of mass.
While comets are distant in the Solar System, they remain frozen and most of their volatiles - frozen gases or liquids - are suspected to be hidden beneath a dry, dusty surface. Because of their small size, they are almost impossible to detect. As they near the Sun, they begin to warm and vaporize, causing the volatiles to stream away from the comet's nucleus and carry the dust away with them. This action creates a thin, visible atmosphere around the comet's body and is called the coma. The radiation pressure of the Sun and the solar wind causes the coma to extend away from the nucleus into the highly visible tail. This is what makes a comet so beautiful to view and creates its distinct shape. A comet's tail will always point away from the direction of the Sun.
As a comet passes through the inner Solar System, both the coma and the tail are illuminated by reflecting sunlight and can often be seen from Earth. Most comets are very faint and require a telescope to be seen, but there are a few which reach unaided eye visibility. Some may develop a dual tail, one from dust and the other from ionized gases. There are even a few comets which have unexpected outbursts of gas which can cause them to suddenly brighten and increase in size. While it doesn't happen very often, it's quite exciting when it does!
Comets can be very exciting for other reasons, too. Some have been known to break up into fragments for unknown reasons - while others have been observed smashing into planets or diving into the Sun. Some even "run out of gas" - a condition where the volatile material contained in a comet nucleus evaporates away.
How often do we see a comet? Comets visible to the unaided eye don't occur very often, but telescopic comets happen several times a year. Sometimes there is even more than one visible at any given time. How they appear is mostly due to their composition and how close they get to the Sun. While a comet's movements are fast compared to other astronomical objects, it appears slow when seen through the telescope eyepiece. Don't count out seeing movement, though. By patiently watching over a period of hours, it is very possible to physically detect the distance a comet has moved by the relationship with the surrounding background stars. Observing a comet (How Do I Observe A Comet?) is easy enough, but locating and tracking a comet takes some work. They can often move several degrees from night to night! Always be sure to use a good locator map to help you correctly identify a comet - or enter the proper coordinates into your telescope's computer control.
The year 2013 might just be a very good time for comets. Right now, there is one headed our way which should make a good apparition for the southern hemisphere - Comet C/2011 L4 PanSTARRS. It is projected to come within 45 million kilometers (28 million miles) of the Sun on March 9, 2013. This is close enough that it should have a visible tail. But hold on... An even more exciting new comet is expected to rock the mid-latitude northern skies! It is named Comet C/2012 S1 (ISON), and it was discovered by a Russian team, Vitali Nevski and Artyom Novichonok, at the International Scientific Optical Network (ISON). Currently Comet ISON is located about the distance of Jupiter's orbit, but it is expected to come within less than 2 million kilometers from the Sun at perihelion (its closest pass) by November 28, 2013. Will it be spectacular? No one knows for sure because comets are very unpredictable. It could be as breathtaking as Comet Hale-Bopp, or it might be a dud like Comet Kohoutek. If Comet C/2012 S1 (ISON) continues on its anticipated trajectory toward the Sun and doesn't break apart, it might even be visible during the day!
When it comes to astronomy, you will find the term "arc second" used in three ways: (1) to express a given distance in declination on a star chart, (2) as a given unit of an astronomical object's size, and (3) as an expression of telescope's resolving power. Let's take a look at each use of the term in more detail.
First, we'll examine how an arc second is expressed when applied to a star chart and to the visible night sky. Picture the entire dome of the night sky as the face of a clock. The clock is divided into hours, minutes, and tiny seconds. Much like this imaginary clock, the celestial dome is divided into degrees and each degree is comprised of arc minutes and arc seconds. There are 60 arc minutes in each degree, and each arc minute is made up of 60 arc seconds. But, just how big would that be? Let's use the full Moon as an example. It covers approximately 1/2 a degree of night sky - which equals 30 arc minutes or 1800 arc seconds. These measurements are abbreviated into a type of astronomical shorthand. Terms for the Moon's apparent size would read 30' for arc minutes or 1800" for arc seconds.
When you look at a star chart (How Do I Read a Star Chart?), you'll see degrees of declination - measurements from north to south - marked along the edge. Each degree of sky contains 60 arc minutes, or 3600 arc seconds. When using an astronomical catalog or observing instructions, you'll be provided with an "address" of coordinates to celestial objects which utilizes arc seconds. This address may read something like RA 12h 22m 13s - Dec +22° 44' 11". Look at the second set of numbers. This means your object is located twenty-two degrees, forty-four arc minutes, eleven arc seconds north of the celestial equator. Although a single arc second would be too small to visually determine when looking at the sky, it is very important to celestial surveys and catalogs. It is like assigning a celestial "house number" to a specific target and allows astronomers to locate targets with precision.
When expressing the size of an astronomical object, it is often given in terms of angular diameter as seen from Earth - not its true size. Most of the time, these angular diameters are very small since most objects are very far away from Earth, so they are expressed as arc minutes, or more frequently as arc seconds. An astronomical catalog or observing guide will provide an object's size to help observers better understand what to expect from a target before they try to locate it with a telescope. This is helpful if you have never seen a particular object. Let's use two samples to illustrate this concept - a globular cluster and a double star. For example, globular cluster M80 is listed as 10' (ten arc minutes) in size. A good star chart will show this object printed to scale in relationship to the stars around it. This makes identifying it from the surrounding stellar patterns seen in the eyepiece much easier. You knew in advance the cluster would cover a certain amount of distance between identifiable stars. However, the angular distance measurement between double stars is much smaller and is always expressed as arc seconds. A good example is Polaris. The main bright star, Polaris A, is separated from small faint star, Polaris B, by 18" (eighteen arc seconds). By knowing a double star's separation in advance, you can test your telescope's ability to resolve small distances and aid you in determining sky conditions (How Do I Judge Sky Conditions?). Most general star charts don't print separations that small, so you'll need to rely upon your astronomy catalog as a resource for those numbers.
Another place in which you will encounter arc seconds is in a telescope's specifications - the resolving power. This is your telescope's ability (under ideal observing conditions) to "see" or separate a given size or distance. While there are lengthy mathematical expressions used to determine arc seconds of resolution for telescopes, a simple way to understand is to use the known separation of a double star as an example. Let's return to Polaris. If a telescope has a stated resolving power of 1.0" that means it is capable of clearly resolving an object - or distance - of one arc second. That's just 1/18th the distance between Polaris and its companion! With this information, you know our example telescope with a resolving power of 1.0" (one arc second) will be able to "split" the double star Polaris under ideal observing conditions.
While these measurements might seem a little confusing at first, you'll soon understand and appreciate them. Knowing an arc second's distance on a star chart will help you better locate objects by further refining their positions. Being able to add arc minute and arc second directional numbers to a telescope's computer aiming system will make it far more accurate. Understanding an arc second in size will assist you in relating what you see to others. For example, you might observe a comet and want to record its size in your notes. If you know a given object's size in arc minutes or arc seconds, you can compare the two and make a more accurate assessment. By knowing your telescope's resolving ability in arc seconds, you'll also know if you're able to "split" a given double star in advance - or know if your telescope is capable of "seeing" very small separations, such as revealing individual members in a star cluster. Arc seconds might be tiny, but they're very important!
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