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Sky Watcher - Mark Thompson

Stargazing - Mark Thompson

Astronomy is perhaps the oldest of sciences and most people, at some point in their lives, have marvelled at the sight of a dark star-filled sky.  Choosing a telescope to get you up close and personal with the many astronomical wonders can seem like a daunting task but here at Jessops we have teamed up with Stargazing Live's Mark Thompson to bring you the all the advice you will need to get started.


If you are new to astronomy then you are probably struggling to tell your refractors from your reflectors and with all the new terms like aperture, focal length and focal ratio your head will probably be spinning.   So lets start by looking at the basics.  There are three main types of telescope; refractors which use lenses to collect light, reflectors which use mirrors and catadioptric  which use a combination of the two. If you get into really advanced astronomy then there are subtle differences and benefits between them but for most general users the important difference is that you can get more telescope for your money if you get a mirror based reflecting telescope.


There are loads of new terms that you will come across as well but they are really pretty simple to understand.  Perhaps one of the most important is the telescope's aperture.  The aperture is the diameter of the main lens or mirror and in the case of astronomical telescopes, bigger is better. You can think of a telescope as a funnel to collect loads of light and concentrate it into a tiny beam that will fit inside your eye, this means you will be able to see objects fainter than your eye alone can detect.   If you wish to look at fainter fuzzy, so called 'Deep Sky' objects then go for a telescope with the largest aperture.  If on the other hand you want to look at the planets and Moon which give off plenty of light then you might wish to consider a smaller instrument.


The focal length of a telescope is the distance that light is brought to a focus from the main lens or mirror so a telescope with a focal length of 500mm will bring incoming light from the stars to a focus after 500mm.  This is an important consideration for determining magnification and length of exposure for astronomical photography.  To determine the magnification of a telescope you need to divide the focal length of the telescope by the focal length of the eyepiece that you are looking through for example a 500mm focal length telescope when used with a 10mm focal length eyepiece will give you a magnification of x50.  The eyepieces in telescopes are interchangeable so you can increase or decrease magnification by changing the eyepiece.  If you are using a telescope for astronomical photography then you will need to use longer exposures on telescopes with longer focal lengths.  The 'speed' of the telescope is also described by its focal ratio which is written as f/7 or f/5 (pronounced 'ef seven').  Telescopes which have a lower focal ratio are considered to be fast and more suited to deep sky astronomy and will mean you can use shorter exposures than a higher focal ratio which are slower and better for planets.


Deciding which telescope to get amongst the multitude of different options is a challenge even for the experienced observer.  For the newcomer there are some great options such as the Skywatcher Skyliner 150 or the Skywatcher Explorer 130.   If you have children who are interested in zooming in on the planets then these telescopes might be a little big for them so instead take a look at the Heritage 76 or the Infinity 76 instruments. They are easy to use and great for transporting your little ones to distant worlds.   With access to so many sensitive DSLR  cameras it is possible for beginners to get wonderful shots of the constellations and Milky Way.  the Heritage 114P is a great tracking platform for cameras to enable you to get stunning long exposure shots.   Once you have mastered basic DSLR photography then you can really zoom in on planets, galaxies and star clusters with the Explorer 200, perfect the budding astrophotographer or experienced visual observer.


With your chosen telescope it is best to set it up outside before nightfall.  This allows the optics to cool down with the atmosphere.  If you wait until night time then plunging your nice warm telescope into cold night air will lead to dew forming on the optics.  If you do find yourself in this unenviable position, use a hair dryer on its lowest setting to gently blow warm air over the optics to get rid of the dew.  Before it gets dark it is a good idea to make sure the tiny finder telescope is aligned with your main telescope. You can do this easily by pointing the main telescope at a distant object like a chimney or aerial and then adjusting the finder telescope so that it points at exactly the same view.  You need to make sure that whatever is in the centre of the finder telescope is also in the centre of the main telescope so it is best to start out with a low power eyepiece (higher focal length) in the main instrument before fine tuning with a higher magnification.


Once night falls, give your eyes a chance to adjust to the darkened environment. It takes about an hour for your eyes to get adjusted to seeing in the dark and letting them adjust will give you the best views through the telescope. Once you are dark adapted, try not to expose your eyes to bright lights until you are finished, even for the briefest period of time otherwise you will have to wait a full hour again to adjust.  Use a red torch to give yourself a little light at night if you need so that you can adjust equipment or read star charts.


If you find that you are getting a rubbish view through the telescope you might want to check the collimation or alignment of the optics.  Reflecting telescopes are the most susceptible to this so you will need to refer to the instruction manual for details of how to collimate your particular telescope.  You can get an idea if you need to collimate by 'de-focussing' the telescope on a bright star.  You should see a bright disk with a dark disk in the centre.  If the dark disk is not perfectly centred then you will need to collimate, if it is perfectly in the centre then it is more likely that the atmospheric conditions are poor and not suited to high magnification astronomy so nights like these are best left to the deep sky objects.


If you wish to take astronomical photographs through a telescope then you will need an equatorial telescope mount.  These mounts will enable your telescope to easily follow objects across the sky. Without it, you will get strangely blurred images. Equatorial mounts need to be polar aligned to accurately track objects as they slowly move across the sky. Polar alignment can be a little time consuming but is essential to get good pictures. To achieve good polar alignment, the polar axis of the mount needs to point at a place in the sky called the north celestial pole which is the point about which, all objects seem to rotate around. Some telescopes mounts come with polar axis telescopes that help you to achieve that.  For really accurate tracking then drift alignment is the technique to go for and this relies on watching what happens when you point a star at in the south and then low in the east.

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