Tools of the Trade
Since the advent of mass-produced astronomical equipment from the Far East, viewing the night sky in great detail has never been more accessible! Even a few decades ago, the only people who would be lucky enough to own a six inch telescope were members of universities and observatories. These days, there is a mind-boggling variety of astronomical equipment that can be purchased, such as binoculars of various apertures and telescopes of all sizes and specifications - even cameras with CCD chips for imaging almost Hubble Telescope-quality images from home! Night vision technology has recently been utilised by keen amatuer astronomers to view faint nebula in urban skies. Even for individuals who are more experienced in star gazing, purchasing the most suitable equipment can be confusing. This article will assist you in your own quest to get started in the exciting hobby of astronomy with the right equipment. Click the words below to read more:
Binoculars are the most mobile and easiest equipment you can use for exploring the night sky. A 10x50 binocular is considered to be a great starting point as the 10 times magnification and 50mm aperture will show hundreds of astronomical objects! Binoculars of this size can be held by most people without too much muscle fatigue. Anything larger, such as the 15x70 binocular, will show even more (almost double to the thoroughput of light to the eyes than a 10x50 binocular) but are quite heavy to hold for short periods of time. These can be connected to a good quality tripod with an adapter especially made to hold binoculars steady.
Although prices can vary from £50 to £900 for a decent 10x50 binocular, they can be satisfying to use at the lower price point. People have reported good results with the Olympus, Strasprey and Celestron brands. However, much cheaper models can have problems with prism alignment, lack of sharpness at the edges, general collimation (mechanical and optical alignment) and bad lens coatings which would be rendered useless when viewing the night sky.
A telescope is a great way to view objects in the night sky with greater magnification. However, there are also many pitfalls to avoid when considering a telescope purchase. General advice is to avoid purchasing your telescope from general catalogue retailers or department stores. These telescopes are often built with cheap materials such as plastic lenses and will boast of hundreds of times magnification. A bad purchase can be discouraging in any new hobby! It is also important to bear in mind that you will not see the incredibly detailed and colourful nebulae seen in photographs as the human eye does not have the light gathering ability that a camera has. Nevertheless, you will feel a sense of awe as you view celestial objects that are a vast, unimaginable distance away. For example, the star-spangled Hercules Cluster (M13) is around twenty-five thousand light years away!
Telescopes can be bought in various sizes and apertures. There are various technical factors to consider before making a purchase:
- the larger the mirror or objective lens size, the more light can be gathered. You will be able to view with higher magnification and therefore view fainter objects.
- you will notice that the technical specifications will state the focal length. Focal length is the distance between the primary mirror or lens and where the light is brought to a focus. It is a way of determining how long the telescope tube is, as with some larger telescopes, you may need a small step ladder to reach the eyepiece!
- focal ratio (f/) is important to consider; it is the speed of the telescope optics. This is another way of stating the focal length of the mirror or lens objective. The f/ratio is the focal length divided by the aperture. Telescopes with smaller f/numbers (fast) have a wider fields of view and lower magnification but produce brighter images. Focal ratios of fast scopes tend to be around f/3 - f/6.
For example, if you want to only observe Lunar, binary stars and planetary detail, a ‘slow’ scope of f/10 - f/15 is ideal as you can achieve higher magnifications and tease out more detail. A ‘fast’, brighter scope of f/4 - f/5 is better for DSOs (deep space objects such as nebulae, galaxies and more) and wide field observing. Anything in between those extremes is generally suitable for all celestial objects.
There are 3 commonly used types of telescopes:
This is the oldest design of telescope as it was invented in the 1600s by Hans Lippershey but used by Galileo Galilei. The basic form consists of an objective lens - nearest the object being viewed - which bends (refracts) the light to a focal point. An eyepiece containing another lens or lenses, takes the light and spreads it out across the retina of the eye. There are different types of refractors with a variety of lens configurations to eliminate issues such as chromatic aberration (colour fringing - such as seen when shining light through a prism).
A reflecting or Newtonian telescope consists of two mirrors; a larger disk of curved glass called a Primary Mirror and a smaller, ellipse (oval) disk called a secondary mirror. The primary mirror collects the available light in the night sky and reflects it to the angled secondary mirror and is brought to a focal point inside the tube. The secondary mirror reflects the light up to the eyepiece which contains lenses to magnify the image. This type of telescope is very popular as they are generally cheaper than refractors. Reflecting telescopes can come in all sizes; the larger the primary mirror, the more light can be gathered, which enables the viewer to see deep sky objects in more detail.
This type of telescope is an almost ideal combination of the best features of refractor and reflecting telescopes and falls somewhere between the two also in price. Catadioptric telescopes have two mirrors (one at the back and the other in front) with the addition to a lens which corrects issues such as colour fringing and optical errors that can occur in large reflecting telescopes. Light passes through the correcting lens before being bounced off the curved primary mirror, to a secondary mirror, and finally to the eyepiece. The light path is folded within and creates detailed images, considering how small the telescope tube is. The enclosed tube lessens the amount of dust getting inside, but it needs to be cleaned occasionally. There are two types of compound telescopes: Schmidt Cassegrain and Maksutov Cassegrain. The Maksutov uses a smaller mirror and thicker lens than the Schmidt. Though this makes it slightly heavier, the Maksutov produces slightly sharper images.
Without these, you will not be able to bring the light gathered inside the telescope to focus. Most telescopes bought today come with supplied eyepieces but often they are only of barely sufficient quality and you’ll be eventually wanting to increase your collection to include different focal lengths. These little ‘magnifying glasses’ can adjust a telescope’s magnifying power. The focal length of eyepieces can vary; the shorter the focal length, the greater the magnification of the telescope. To calculate the total magnification, you divide the telescope’s focal length by the focal length of the eyepiece. The eyepiece itself can be made of a combination of lens elements to provide a wider field of view, or reduce aberration. Simpler designs such as the Plössl-type eyepieces are very acceptable for long term ownership and prices can range from £30 to £200.
Finderscopes are mainly small refractor-type scopes that are mounted on the telescope with a lower magnification, wide field view that will enable you to accurately pinpoint your target. These scopes are nearly always supplied with the telescope you have bought. There is a large variety of ‘finder’ apparatus, such as red dot finders, but for beginners, a refractor style finderscope is best.
This equatorial mount is more complex than an alt-azimuth mount as it moves along the natural path of objects in the sky, centred about an imaginary line through the North and South celestial poles. Celestial objects travel across the sky in a combination of altitude and azimuthal movement. An equatorial mount turns on a single axis and tracks the natural motion of the stars. To ensure proper alignment, the mount is aligned with the Pole Star in Ursa Minor as the star appears to be stationary as other objects move around it. The reason for this is that is it near the North Celestial Pole which is above the Earth’s North Pole.
When the “polar axis” of an equatorial mount is aligned to the celestial pole, objects can be tracked with the movement of only the polar axis. Because only one axis needs to be moved, equatorial mounts can be more easily motorized to track celestial objects and keep them in the field of view. To get an object in the field of view in the first place, the telescope must still be moved in both axes.
After the mount has been aligned, the right ascension and declination parts of the telescope are used to find objects in the sky, similar to the longitude and latitude co-ordinates on Earth.
An alt-azimuth type of mount is easier to use but the movement does not emulate the natural path of celestial objects. The telescope moves up and down (altitude), left and right (azimuth). This can be a bit annoying for users but the set-up time is minimal. The mount can come in different configurations, such as the photo tripod style mount or Dobsonian style which is a fork-type mount and extremely popular due to its simplicity. However, it is only suitable for observational astronomers. It is possible to take planetary and lunar images with this type of mount but for deep sky objects, an equatorial mount with a motor drive is required.
Solar observing is a satisfying way to ‘do astronomy’ during the day, if clouds and bad weather are stopping you from getting out there at night. Our nearest star is a fascinating object to watch as there is so much going on! Sunspots, prominences, filaments and flares can be observed through the right equipment.
It is imperative at this point to make you aware that viewing the Sun is VERY dangerous if the wrong equipment is used. Never look at the Sun with any optical equipment without appropriate solar filters. Do plenty of research before you buy, as incorrect viewing of Sun’s light through optical equipment can permanently damage the retina of the eyes and may lead to permanent blindness. However, you can use the equipment you already own with accessories that are designed to filter out the sun’s radiation (heat) and virtually all its light.
Solar filters can be attached to your telescope and can be purchased from reputable astronomy retailers. Baader is the recommended brand. The filters can be either made of a special film or treated glass and can be bought in different sizes to attach to the end of your telescope. This will enable you to view sunspots in white light.
Solar telescopes are designed like a traditional refractor with purpose-built filters (etalons) to observe the Sun’s surface with different wavelengths. The user tunes, or isolates the desired wavelength the telescope has been built for, such as Sodium-D, Hydrogen Alpha and Calcium-K. The broadest wavelength is Hydrogen Alpha, which is the most popular amongst solar observers.