Equipment
WHETHER YOU ARE new to stargazing and enjoying the night sky or a seasoned naked-eye observer, there will probably come a time when you want to take the next step and get a closer look at the celestial wonders you have been hunting down. To the inexperienced, the world of telescopes can be daunting, with a whole host of new terms and concepts that might be completely alien to you. Fear not, this chapter will teach you all you need to know, but perhaps it is worth considering first whether a telescope is the right tool for you as there is an alternative, cheaper option that will give you a closer look than the eye alone can offer.
Whether you should go straight for a telescope or not largely depends on your level of experience. I have seen newcomers spend thousands of pounds on a high-end instrument only to find astronomy is not quite for them: the result is wasted money. If you are a relative newcomer you may be better off buying a pair of binoculars first. If you then find stargazing is not for you, you have not spent lots of money and you can always use them for other more down-to-earth purposes.
All binoculars are described in a standard way, which is made up of two numbers, e.g. 7 × 50. This particular pair would offer a magnification of seven times (making objects appear seven times bigger) and have lenses that measure 50mm across. This last number is quite important as the lens diameter dictates how much light the binoculars will collect and therefore determines the faintest object you will be able to see. You can think of binoculars and telescopes as funnels for letting more light into your eyes than you would normally be able to detect.
When choosing binoculars it is better to have a bigger second number and therefore bigger lenses, and not so important to have a higher magnification as telescopes really are the instruments for higher-magnified views of the night sky. One downside to choosing binoculars with a larger lens or aperture is that they are larger and heavier and, while they will be magnifying the view of the night sky, they will also be responding to any movement your hands make. Tiny tremors or even your heartbeat will be picked up and magnified and will have an adverse effect on your view.
One solution to making sure you have a steady view is to mount the binoculars on a tripod. Many people own or have access to a camera tripod through friends or family and they can greatly enhance the experience of observing with binoculars. You will need to buy an adaptor that will fix the binoculars to the top of the tripod but these are not too expensive. The only downside is that fitting binoculars to a tripod makes looking at objects directly overhead very awkward if not impossible.
An alternative solution is to buy a pair of binoculars that use image stabilization technology. As its name suggests, this steadies the image you see through the binoculars. It will not mean you get a rock-steady image from a moving car but it will remove the slight hand tremors as you stand still and look through them. It is amazing how much more detail you can see when the image is nice and stable, so even if you do not want to spend the extra money on image stabilization, a tripod and adaptor are a worthwhile investment.
With a decent pair of binoculars it is possible to really open up the wonders of the night sky. They will not show a great deal of extra detail on the planets, although a higher-powered pair will just reveal a hint of the rings of Saturn and even the moons of Jupiter. The surface of the Moon will be enhanced nicely and you will be able to pick out smaller craters and finer detail in the lunar highlands, but it is not just the brighter objects that can be seen in greater detail. There are a whole host of deep-sky objects that now come well within your range. The March sky offers some great examples of easy-to-spot deep-sky objects for binocular-users. In the northern hemisphere sky the wonderful open Beehive cluster in Cancer is easy to find and is one of my favourites. Southern hemisphere observers can hunt down the Southern Pleiades, another stunning open cluster in the constellation of Carina. Both can just be detected with the unaided eye from a dark site but binoculars make them easy targets.
Eventually there may come a time when binoculars will not be enough and you will want to take an even closer look, so it is time to think about buying a telescope. If you have ever looked at telescopes on sale in either a department store or a specialist astronomy shop you will have seen a lot of phrases and words that probably did not mean all that much to you. Starting with the basics, there are three different types of telescope: refractors, reflectors and catadioptrics. Refracting telescopes have lenses inside and are of similar design to those you’ll see being used by sailors in films; reflectors use mirrors and catadioptrics have a combination of the two.
Most telescopes, regardless of their design, have a number of components in common: a tube to hold everything together, a mechanism – either a lens or a mirror – of collecting incoming starlight, an eyepiece to magnify the image, a smaller ‘finder’ telescope and a mount to hold the whole lot steady. The exact detail of each of these components varies from one telescope to another and with some it is possible to mix and match, or you could even build your own.
The most common telescope for newcomers is the reflecting telescope (see illustration 1) as it offers more for your money, largely down to the optics inside. At the heart of a reflecting telescope is a circular mirror called the primary. It has a very accurate curve ground into its front surface, whereas inside a good-quality refractor (see illustration 2) are typically two or more lenses glued together, all of which have had curves ground into both sides. Much more work is needed to make the lenses compared to a single mirror and the glass has to be of higher optical quality. It is the greater production costs and quality of the refractors that drive their price up, so as a beginner consider reflectors as your first choice.
The primary mirror is the device that collects the incoming starlight in a reflecting telescope and the curve on the front surface of the mirror takes the incoming beams of light and focuses them to a point. The mirror sits at the bottom end of the telescope tube so it can reflect the incoming beams of light back up the tube. The converging beams are intercepted by another smaller, flat mirror called the secondary which is set at an angle at the top of the tube to direct the beams of light out of a hole in the side. It is at this hole that a special tube called a focuser is fitted to hold the eyepiece.
Refractors are designed differently, with the light-collecting device being a lens. Like the mirror in a reflecting telescope, the lens bends incoming beams of light to bring them to a point of focus. In the case of a good-quality refracting telescope the lens is actually made up of a number of lenses all glued together, usually two or more. The reason there are usually two or more lenses is that the incoming light, which is made up of different wavelengths, is bent or refracted by different amounts. Using multiple lenses ensures all wavelengths focus at one point for a sharp image. The lens in a refractor is fitted at the front end of the telescope tube so the starlight will pass through it and pass along the tube. On reaching the far end, the light passes through the focuser, where an eyepiece is held and the image formed.
The catadioptric telescopes come in many different forms but generally have a lens at the front end and at the other a mirror which reflects light back up the tube. It then hits a smaller mirror attached to the main lens before being reflected back down along the tube and passing through a hole in the primary mirror, where it encounters the focuser and eyepiece.
An important aspect of maintenance for telescopes, more so for reflectors and catadioptric than refractors, is the alignment of the optics. If they are not aligned accurately then there will be a significant reduction in the sharpness of the image seen. The process of aligning telescope optics is called collimation; rough collimation can usually be done in daylight with more precise fine tuning achieved by pointing the telescope at a moderately bright star at night. Due to the way the lenses are held they generally do not lose their alignment, but mirrors are susceptible to movement, so reflecting and catadioptric telescopes should be regularly checked for collimation. This is particularly true if you often transport your telescope to different observation sites.
There are many different types of telescope on the market, most of which have pros and cons, but all of them are described using the same terms. The two most important are aperture and focal length. Aperture refers to the diameter of the main lens or mirror and gives an indication of the telescope’s ability to collect light. The larger the aperture, the more light it can collect, and therefore the fainter the objects that can be seen.
A fairly standard beginner’s telescope will have an aperture of around 150mm and will show objects around a million times fainter than can be seen by the naked eye alone. There is a practical implication to this: if you want to see very faint objects like galaxies and star clusters, you will need a large-aperture telescope, whereas if you are hoping to track down brighter objects, like the planets, a big aperture is not of quite so much importance. For example, if you want to take a look at the galaxies M81 and M82 in Ursa Major then they will certainly be visible with a small 150mm telescope, but telescopes larger than this will collect a lot more light and reveal much more of the galaxies’ structure.
Not only does aperture determine the limit to which faint objects can be seen but, because it defines how much light a telescope collects, it will also define how much you can magnify the image. Magnification refers to how big an object appears compared to a naked-eye view, but as magnification gets higher so the image gets slightly darker. How high you can push the magnification depends on how much light there is in the first place, so a telescope that collects more light, i.e. has a larger aperture, will be able to take a higher magnification. To determine the maximum practical magnification a telescope can produce is a simple matter of multiplying the aperture in millimetres by two, so a 150mm telescope would give a maximum practical magnification of around 300x – any more than this and the image would generally become too dark.
Once the light has reflected off the mirror or been refracted through the lens it travels into another optical device, the eyepiece, which is a small tube that slots into the focuser of the telescope. Inside it is a series of lenses whose purpose is to magnify the image by an amount that is determined by something called focal length. The focal length is the distance it takes for incoming beams of light to be focused to a point and, perhaps obviously, a shorter distance means a shorter focal length.
Given that magnification is determined by focal length, changing the eyepiece will actually give you a higher or lower magnification, but the exact amount achieved is calculated by dividing the focal length of the telescope by the focal length of the eyepiece. For example, if a telescope has a focal length of 1000mm and we are using an eyepiece that has a focal length of 20mm, the magnification would be 1000 divided by 20, which is 50x. You will see that an eyepiece with a longer focal length will produce a lower magnification than an eyepiece with a shorter focal length. The easiest way to remember this is that an eyepiece with a big number means a smaller image and an eyepiece with a small number means a bigger image.
It is easy to draw the conclusion from all this that as a new telescope owner you need to have a number of different eyepieces to give a range of different-sized images. The eyepiece you choose will depend on the object you are observing, e.g. low power for deep-space objects and high power for planets. You will also find that not only will the telescope determine which eyepiece you can use but the weather will often force you to use a lower magnification because of unsettled conditions. My eyepiece collection consists of eyepieces of various brands but has a good spread of focal lengths at 56mm (53x), 24mm (125x), 12mm (250x) and 6.4mm (469x), but of course on a different telescope you would get different magnifications. A good starter set might be a 24mm and a 12mm eyepiece or similar. You can also get devices called Barlow lenses which double, triple or even quadruple the magnification achieved with an eyepiece; for example, using a 24mm eyepiece on my telescope gives 125x magnification and I could use it with a 3x Barlow lens and get a magnification of 375x. These are a good addition to your kit as they will effectively double the number of eyepieces, but plan carefully as you will not want to duplicate your magnifications.
As with telescopes, there is a huge range of eyepieces on the market of different makes and focal lengths and prices vary significantly. If you are new to the subject it is best to go for medium-priced eyepieces as you will still be getting reasonable quality but not breaking the bank. Newcomers often make the mistake of buying a good-quality telescope followed by cheap eyepieces, but be warned: a cheap eyepiece can totally ruin an otherwise fantastic view.
One final word about eyepieces. There is a term called eye relief, which is the distance your eye should be from the eyepiece to get the optimum view. This is of particular importance when it comes to observing if you wear glasses. Short- or long-sighted observers can remove their glasses and adjust the focus of the telescope to suit. If you suffer from astigmatism then you will need to keep your glasses on so a long eye relief will allow you to observe more comfortably.
There is another telescope term called the focal ratio, which is written as, for example, f/x. It brings together the focal length and aperture of a telescope and its value is reached by dividing one by the other. Using the 150mm telescope earlier described, if it has a focal length of 900mm then its focal ratio is 900 divided by 150, which is 6, i.e. f/6.
Before looking at the mount that telescopes are fitted to it is worth just briefly mentioning the mini-telescope that fits to the side of a main telescope, called a finder telescope. Because the main telescope magnifies the sky by around 50x or more, it is incredibly hard to find your way around. For that reason a smaller, less powerful telescope is fitted to its side; it usually magnifies around 10x, giving a much wider field of view. By lining up the two telescopes so they are pointing in exactly the same direction, it is a simple matter to find an object with the finder telescope (or its location, as it is not always possible to see the object itself through the smaller finder) and it should be centred in the main telescope. This will take away the frustration of locating objects in the sky. Modern alternatives to the finder telescope are available which project a tiny red dot onto the sky and by aligning this to the main telescope you can again easily home in on your target.
We’ve now covered the optical components – telescope, eyepieces and finder telescopes – but none of these will be any good if they are fixed onto flimsy, wobbly mounts. A mount is the word used to describe the thing the telescope sits on and generally it is more elaborate than a camera tripod.
Telescope mounts come in two basic types, alt-azimuth and equatorial. A normal camera tripod can be considered to be an alt-azimuth mount as it moves around two axes: up and down (in altitude) and left and right (in azimuth). An astronomical mount of this type is not much different in that it moves around the same axes but in design and rigidity they do differ. A classic example of this type of mount is the Dobsonian style, which is a rather strange-looking box device that the telescope sits in, designed by the American amateur astronomer John Dobson. Just like the camera tripod, it allows the telescope to move in altitude and azimuth and is probably the best telescope mount for a beginner as there is minimal set-up time and it is very easy to use.
One downside with using an alt-azimuth mount is that it is difficult, though not impossible, to attach motors to enable it to follow objects across the sky. When objects in the night sky move their position changes in both altitude and azimuth as they arc across the sky. To follow them, it is necessary to fit a motor to both axes of the telescope and this will allow you to freeze their motion. It will not, however, stop them rotating in the eyepiece. As they rise and set they follow a curved path and as a result appear to slowly spin while we look at them. This apparent rotation is not an issue in visual observation, but if you want to try your hand at photography it becomes a problem, as exposures can last for some minutes and in that time the object will have rotated, leaving you with a blurred image.
The solution to this is a different type of telescope mount, the equatorial mount, which differs from the alt-azimuth style in the orientation of the axes. With the alt-azimuth mount, a vertical axis allows the telescope to swing horizontally around the horizon, in azimuth. With the equatorial mount the same axis (the polar axis) is tilted so it is parallel to the Earth’s axis of rotation. This means that as the telescope is moved around that axis, it follows the same arc across the sky as the objects. With this type of mount it is possible to attach a motor to just one axis, turn the telescope in the opposite direction to the Earth’s rotation, but at the same speed, and objects remain in the centre of the eyepiece and do not spin. This means you need only one motor to follow or track objects across the sky and also allows for long-exposure astronomical photography without any blurring.
This all sounds fantastic, but the key in getting an equatorial telescope to accurately track objects across the sky is in a process called polar alignment. As its name suggests, polar alignment is the act of aligning the polar axis to the axis of rotation of the Earth. Advanced amateur telescopes will have small telescopes within the polar axis allowing it to be aligned to the north or south celestial pole. The mounts are designed so they will work for any location on Earth but they need adjusting for your specific location. Very rough polar alignment can be achieved by aligning the axis north–south and setting the adjustable angle of the mount to be the same as your latitude. If you are observing visually then that will be enough to keep the object in the field of view for a short while, but for astronomical photography more precise methods like ‘drift alignment’ are needed; that is too detailed for this book, but further information is readily available on the internet.
My choosing the right telescope system for you is a bit daunting, but for newcomers I would always recommended a 152mm or 200mm Dobsonian reflecting telescope around f/6 or f/7, which will be a pretty good all-round telescope and not cost a crazy amount of money. In your search for a telescope you might also see computerized telescopes that have the ability to control the motors and point at objects for you. These are fantastic telescopes but unless you are prepared to spend lots of money you will find the optical quality of the entry-level computerized instruments to be lacking. I would suggest steering away from them as your first telescope and upgrading to one in a few years.
One final piece of advice: before you spend your hard-earned cash pay a visit to your local astronomical club. It is one thing to understand the words written in this chapter but nothing quite beats the experience of seeing telescopes for real and taking a look through them. It is not just the price you should consider when making your purchase but portability, future expansion, potential upgrades and build quality, so seeing them for real and speaking to owners will soon have you homing in on the ideal telescope for you. There are plenty of specialist astronomical equipment suppliers in most countries, and they are also a great place to go for advice. It is best to keep away from the telescopes in department stores unless you are buying for children as they are pretty poor quality. Take your time though, try a few out with friendly local astronomers, and you will eventually know which one to buy and, who knows, before long you will be giving advice to other newcomers and sharing your experience.
March: Northern Hemisphere Sky
March is a great time of year for getting out under the stars and for picking out faint fuzzy objects like clusters and galaxies, because the obscuring stars and dust of the Milky Way run low around the northern part of the sky. This gives us an unimpeded view out in the other direction, into deep space. We start the March guide in the constellation of Virgo, which straddles the celestial equator in the south. Virgo is not the brightest of constellations but it can be found to the south-west of the easily identifiable bright red star Arcturus, in Boötes to the east, and to the south-east of Leo and its brightest star, Regulus, to the west.
The brightest star in Virgo in the northern hemisphere of the sky is called Epsilon Virginis, or Vindemiatrix, and is easy to pick out as it lies to the east of the most easterly star in Leo, Denebola. It is the third-brightest of all the stars in Virgo, is classed as a yellow giant and is a little cooler than our Sun. It seems to be a strong source of X-ray radiation, which is thought to be the result of strong magnetic activity at its surface. Just to the west of Vindemiatrix, not quite halfway to Denebola, marks the location of two galaxies, M58 and M87.
M58 is a barred spiral galaxy but at magnitude (brightness) 9.7 it is definitely a target for telescope owners. It is a great example of how a larger telescope will show finer levels of detail; in other words, it ‘resolves’ more detail. A telescope aperture of 100mm or more will start to reveal its spiral arms and one larger than 200mm will reveal the bar structure. It lies a staggering 68 million light years away from us and, of the 2000 or so members of the Virgo Cluster of galaxies, it is among the brightest.
Just to the west by about 5 degrees in the direction of Denebola is the largest, brightest and most dominant member of the Virgo Cluster, M87. This goliath of an elliptical galaxy is just visible with binoculars and easily seen through telescopes. Visually the galaxy does seem large and astronomical images show that it appears in our sky larger than the full moon, which is due partly to its proximity to us, at an estimated 52 million light years.
Moving directly north of Virgo is the fainter constellation called Coma Berenices and one of its brightest stars, Diadem, is found just to the north of Vindemiatrix in Virgo. There are only three main stars in Coma Berenices, arranged in a right-angled triangle, but there are many more fainter stars. The majority of the fainter stars make up part of a stellar cluster called Melotte 111, which is only 270 light years from us. Like Virgo, Coma Berenices is rich in galaxies; of particular note is the edge of spiral galaxy NGC4565 just south of Gamma Comae Berenices, the star on the constellation’s western border. Telescope owners should search out this galaxy and, with a 200mm telescope or larger, its dark dust lane can be seen running along the disc of the galaxy.
To the north of Coma Berenices is another small constellation, called Canes Venatici, which has only two prominent stars in it. They can be easily found as they are parallel to the last two stars in the handle of the Plough to the north and point directly to Arcturus, the bright red star in Boötes. On a line between the brighter of the two Canes Venatici stars, Cor Caroli, and the last star of the Plough’s handle, Alkaid, is the spectacular galactic collision known as the Whirlpool Galaxy, or M51. Starting from Alkaid, it is found about a quarter of the way to Cor Caroli and can just be seen in binoculars together with NGC5195, the galaxy it is interacting with. It is thought that NGC5195 passed through the main disc of M51 from behind around 500 million years ago before returning, for another ‘collision’ 400 million years later, to its present position, slightly behind M51. The two are believed to be entwined in a gravitationally bound dance which is likely to lead to an ultimate merger.
Just the other side of Alkaid, at roughly the same distance as M51, lies another fine example of a spiral galaxy, M101. Observations of Cepheid Variable stars inside M101 have allowed its distance to be calculated at 27 million light years. It is just beyond the limit of visibility to the naked eye so binoculars are needed to pick it up from dark skies, but a telescope of 100mm or bigger will start to show the structure of the spiral arms.
The stars of the pan of the Plough act as pointers to a lovely pair of galaxies. Imagine a line between Phecda at the south-east corner of the pan to Dubhe at the north-west corner and extend the line on to the north-west for the same distance. Scanning the sky in that area with binoculars will reveal the stunning contrast of the symmetrical spiral galaxy called M81 and, in the same field of view, the ragged form of M82, an irregular galaxy. There are many other fine examples of galaxies in the March sky, particularly around Virgo and Coma Berenices, so do not be restricted to the objects already covered – have a wander around the sky and discover more galactic surprises.
March: Southern Hemisphere Sky
Spica, the brightest star in the constellation of Virgo, is dominant in the southern hemisphere sky during March and it provides a useful pointer to a stunning galactic treasure, the Sombrero Galaxy. In appearance it resembles a large, wide-brimmed Mexican hat and it also goes by the name of M104. The galaxy can be found about half a degree to the west of Spica but telescopes will be needed to see it. A 100mm telescope will show it as a smudge of light, 200mm will show the disc and bulge, while 250mm or above is needed to pick out the dust lane which gives it its characteristic appearance. It is hard to tell the shape of the galaxy because we are looking at it almost edge-on. Observing M104 is a great example of how different eyepieces affect the view through a telescope. It is always tempting to pump up the magnification by using shorter-focal-length eyepieces to try and reveal more stars, but doing so means the image gets fainter. M104 illustrates how a compromise between image size and brightness needs to be found.
Heading a little further to the south-west from Spica is a relatively faint constellation called Corvus, which is made up from four moderately bright stars forming a four-sided shape. Its brightest star is called Gienah Corvi and it marks the north-west corner of the constellation.
Starting from Spica again, an imaginary line to the south will reach the third-brightest star in the sky, Alpha Centauri, which has a distinctly yellow colour to it. It is a member of the nearest star system to the Sun at around 4 light years. Halfway between the two, and on the southern side of the last two stars in the tail of Hydra, the snake, is the position of one of the nearest and brightest galaxies in the sky, known as the Southern Pinwheel, or M83. It is a stunning face-on spiral galaxy which is just beyond the limit of visibility to the naked eye, but binoculars will reveal the nucleus and a modest beginner’s telescope will start to show some of its spiral structure.
Continuing on to the constellation of Centaurus, Alpha Centauri is its brightest star with the second-brightest, Beta Centauri, or Hadar, in the west. These two stars form a triangle with what is now the third-brightest star in the constellation, Epsilon Centauri, or Birdun. Taking the line between Hadar and Birdun and continuing on for the same distance again leads to a galaxy called Centaurus-A. Also known as NGC5128 this galaxy is close, at just over 14 million light years, yet even at this distance it is still necessary to use a decent pair of binoculars or telescope to spot it. Through larger telescopes it will appear as an elliptical galaxy with a dark dust lane superimposed against it, but radio telescopes reveal something quite surprising: it has two huge lobes of radiation extending out of its polar axis. It is thought the galaxy is the result of a merger event with the disruptive force of a black hole at its centre. Studies from the Spitzer Space Telescope have confirmed that its unique appearance is the result of an elliptical galaxy which is in the process of merging with a spiral galaxy.
Glancing a little to the south of Centaurus-A, it is easy to spot a faint smudge of light which is perhaps one of the most amazing sights in the night sky, Omega Centauri. It is known to be the largest and brightest globular star cluster orbiting the Milky Way and is home to several million stars. In reality it was once a dwarf elliptical galaxy that became captured by our own galaxy, with the discovery of a black hole in its core supporting this theory.
Arching through the southern part of Centaurus, running from east to west, is perhaps the most spectacular galaxy of them all, our own, the Milky Way. Measuring a staggering 100,000 light years from one side to the other, it is vaster than we can easily visualize, although it is fairly average in size compared to other galaxies. Our Solar System is around 30,000 light years away from the centre, which lies in the direction of Sagittarius over in the east at this time of year. The band of light we see as the Milky Way comes from the combined light of up to 400 billion stars that make up the galaxy, but scan along it and it is possible to pick out dark patches which are huge interstellar dust clouds that one day may form the next generation of stars.
Head back towards Alpha Centauri again, the bright yellow star inside the Milky Way, and just to its west is the constellation called the Southern Cross, or Crux. It does not only point towards the South Celestial Pole but also to a couple of faint smudges in the sky that could be mistaken for disconnected parts of the Milky Way. They are actually two of the satellite galaxies of the Milky Way, the Large and Small Magellanic Clouds, named after the explorer Ferdinand Magellan, who observed them on his voyage in 1519, although they were known about long before that. In reality they do not orbit the Milky Way but instead are galactic visitors, thought to have arrived here around 2 billion years ago.
The Large Magellanic Cloud lies in the constellation of Dorado, is easily visible to the naked eye and at 14,000 light years in diameter is about twice the size of the Small Magellanic Cloud found around 20 degrees to the west in the constellation of Tucana. The Large Magellanic Cloud shows evidence of high levels of star formation, hinting at its gravitational interaction with the Milky Way. The Tarantula Nebula is a fine example of one of these star formation regions and is just visible to the naked eye at the eastern end of the galaxy.