As the dark nights creep upon us Christmas approaches and we begin to think about presents, and you may be flummoxed when you little ones spring on you they want a telescope. Astronomy is an expensive hobby when you start looking into telescopes but there is hope, as a starting point you don't need any equipment to enjoy the nights sky and the best meteor shower of the year, the Geminids peaking on the 14th of December of course a YA event is the best way to experience observatory grade telescopes, but if you're still wanting to get your first scope as a present we hope this little blog can help, read on!


The difficulty in buying a telescope for the first time is expectation, images in magazines and websites are a product of hours of stacking and processing and they aren’t anything like what you’ll see through a telescope! There are some things we need to be aware of when purchasing a telescope. Number one what are you hoping to see, number two, magnification, and number three resolution.


And then there are two real categories of things to see in the nights sky. What we'll all near Earth objects, the planets and moon etc and then Deep sky objects. The near-earth objects, although by our standards are not particularly near, astronomically they are our next-door neighbours! They are quite small and reflect light from the sun, as such they can be magnified quite a lot. To work out magnification in a telescope you take the focal length of the telescope and divide it by the focal length of the lens. So a telescope with a focal length of 900mm will come with two eyepieces, usually a 10mm and a 25mm lens. When using the 10mm lens the magnification will be x90, where as when using the 25mm lens the magnification will be x36. The urge is to magnify everything to the absolute max, but resist! Deep sky objects such as nebula in our galaxy and nearby galaxies such as Andromeda, magnification isn’t the issue, the objects are HUGE! This issue now becomes how much of their light can we ‘capture’. The large the opening in the telescope the more light collected and therefore dimmer objects can be viewed (dimmer objects being a galaxy far, far away!) our eyes are similar, in dim conditions our pupils dilate and we collect more light allowing us to see more in the dark. The next consideration is resolution, the bigger the opening then the higher the resolution. What I mean by resolution is if I drew two dots on a wall very close together and made you stand close to them you could resolve them as two points. If I had you walk backwards, eventually you would get to a point where the two dots would appear as one dot. To allow you to ‘resolve’ the dot as two dots I would need to ‘open’ your pupils more! When we look at the moon we can easily resolve the 'Man in the Moon', the Seas, which are large larva flows, this is because they are hundreds of kilometres in diameter. What we can’t resolve are the thousands of craters, they are too close together and too small.


So...Telescope Designs


There are many designs of telescope, but the main types you may have come across are

Newtonian, Refractors and Dobsonian and they all have their pros and cons.


Refractors are the typical telescope design we think of when picturing pirates! They rely on glass lenses refracting the light focusing it on our retinas. Refractors are solid, they don’t require adjustment, but because of the glass lenses the cost rises rapidly




Newtonians and Dobsonians are of a similar design, light enters the telescope, reflects of a circular or parabolic mirror back up the tube to a mirror set at 45 degrees which reflects the light into a lensed eye piece. . Dobsonians and Newtonians using mirrors, you can get more telescope for you buck!





So…what size telescope?


Telescopes come in a range of sizes, and size has two components, the opening and the focal length. An opening or aperture of 90mm will give a clear view of the moon and some of the close planets, mars, Jupiter and Venus, but, because of its relatively small aperture mars will appear as a dark red disk, Jupiter will be a grey disk and Venus, well Venus looks like a bluey disk anyway! You won’t be able to discern any surface detail in Mars and Jupiter, Mars’s polar caps and the banding in Jupiter won’t be resolved and the Nebula in Orion could be mistaken for a wisp of cloud, the Galilean Moons of Jupiter however will be just about resolvable. As the aperture increases up towards 5 inches (yes the change in units and use of Imperial is odd) the banding in Jupiter is visible with averted vision and clearer in a dark sky spot and some deeper sky objects can be viewed with the right conditions, The Great Nebular in Orion, the Andromeda Galaxy and a host of star Clusters. Now the problem with Astronomy, it can be an expensive hobby, as we progress towards 8 inches and up, the deepest of deep sky images begin to be within grasp but the price tag drags those objects away again!


Christmas Pressie Ideas:


As a starter, these are our recommendations, they can be passed on to siblings and friends once they have been grown out of. the links are for our friends at Rother Valley Optics.

70mm refractor by Skywatcher

700mm Focal Length

Eyepieces: 10mm & 25mm

£99

https://www.rothervalleyoptics.co.uk/skywatcher-mercury-707-telescope.html



76mm Skywatcher mini Dobsonian

300mm Focal Length

Eyepieces: 10mm & 25mm

£69

https://www.rothervalleyoptics.co.uk/skywatcher-heritage-76-mini-dobsonian-telescope.html




114mm Newtonian Skywatcher

1000mm Focal Length

Eyepieces: 10mm & 25mm

£135

https://www.rothervalleyoptics.co.uk/customer-return-skywatcher-skyhawk-114-reflector-telescope.html



There is then an alternative, the trusty binoculars, for a relatively smaller outlay a really good pair of 70mm aperture bins can be purchased, these can be used to get to know the seasonal changes in the night sky and can be passed on when you’re convinced your little astronomer is going to take up the hobby and the investment in a telescope is worthwhile!

https://www.rothervalleyoptics.co.uk/celestron-skymaster-15-x-70-observation-binoculars.html



There are many different variations of telescope and a huge range of budgets available, but be aware, some may appear too good to be true and they most often are. With our continued impact on the environment its so important we conscious when doing our Christmas shopping. If looked after, a telescope will last years and can be passed on to siblings and friends, the very cheap, plastic bodied scopes from toyshops will not last, and more often than not the lenses are made from plastic meaning the image you’ll see will be distorted and potentially put off a budding astronomer and resign your present to the shed and eventually the landfill.


YA Astronomers are keen to help, so if you see something send a pic over and we’ll give you all the advice we can and if you want further recommendation get in touch! To sample the delights of astronomy, check out our events and get to see observatory grade equipment in your community!


www.yorkshireastronomy.co.uk/events


Clear Skies!


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The Camera

First is to focus your camera at infinity, this is where the rays of light enter almost

parallel to each other. You can do this on auto by focusing on something a long way

away, when the camera focuses switch to manual. If the lens you're using doesn't

have an auto focus option. Zoom in as close as you can to a star and adjust the

manual focus until the star appears as a point. Your camera is now focused.

There are two things you'll need to look at, the exposure and the ISO. The exposure

is how long the shutter remains open. the ISO is effectively the sensitivity of the

sensor. Set the camera to manual (look for the symbol 'M' on the top of the camera)

when you look through the camera you will be able to cycle through the exposure

times using the scroller normally located on the top of the camera near the settings

wheel. the ISO needs some trial and error. but for Milky Way shots typically around

800 - 1200 works well.


The Lens

The Lens is the most important part of the camera! there are two aspects to search

for; how fast it is and the focal length. Typically the focal length gives you an idea of

the field of view. The shorter the focal length the more you can fit in the picture. for

Milky Way photos 14mm is perfect. For a deep sky shot of Andromeda or the

Nebula in Orion 135mm is ideal. Its also useful to have some lenses in the middle; a

50mm and 100mm would be perfect. These lenses are 'prime' they only have one focal length, they tend to be better for astrophotography than the variable telephoto-lenses which are

excellent for nature and day time photography.

The next thing is the speed. It will be labelled as a 'f number' this, in affect, tells you

how much light will be let through the lens when you open the shutter. Normal day

time lenses have an f value of around 4 - 6. for astrophotography anything less than

three is ideal!

Lenses I recommend are the Samyang 14 f2.8 - My go to Milky Way lens.

Canon 50mm f1.8 - a really good and cheap lens if you want to zoom a little on an

aspect of the Milky Way

Canon 135mm f2.8 - I use this for deep sky astrophotography.


The Rule of 500

Because the camera is on earth and the earth is spinning, the camera is therefore also

spinning now the stars you're trying to photograph are stationary, this means that

when the shutter is open the sensor will capture the light but as the earth moves the

stars will appear to move in the sky. the result on the photograph is 'streaking' the

stars appear to elongated. the rule of 500 is a rule of thumb and it allows us to work

out how long we can open the shutter without the stars streaking. take the focal

length of the lens and divide by 500.

For example the Samyang 14mm; 500/14 = 35.7

This means you can open the shutter for 35 seconds and the stars will still appear

as points of light.

an issue arises when we work with the 135mm Canon. 500/135 = 3.7. so the lens

can only be opened for 3.7 seconds before stars streak. to capture enough light to

make the deep sky objects pop out 3.7 seconds is not long enough, well need to

compensate for the earths rotation. you'll need a star tracker. I use a Skywatcher

Star Adventure. this is needs to be aligned to the pole star and then the camera can

be attached to it. exposures can run for up to three minutes.


Processing

Once you have your photos you'll need to process them. it may sound like cheating

but you aren't adding light to you photo. you've captured all the ancient photons its

just they aren't very concentrated so the light appears to be dim in comparison to the

light of closer objects e.g. light pollution. processing removes the unwanted photons

and allows the ones we want to be seen.

free online applications are Gimp and Photopea, although the easiest and best is

probably Photoshop which you unfortunately have to pay for a subscription to.

part of the processing is to 'stack' photos. This involves taking hours of short

exposure photographs and stacking them on top of each other. this reduces noise

and allows you remove photos with aeroplanes or satellites in. programs which can

do this for free are 'Starstax' and 'Deep Sky Stacker'


But above all get outside and look up, you don't need lots of expensive kit, a reasonable camera a tripod and you're away!! Good Luck and Clear Skies

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The National Park Dark Sky Festival for the Yorkshire Moors and Dales…




In the UK we’re getting more and more detached from what the nights sky looks like, we have a knowledge of some of the constellations and asterisms. Some know the plough and its use to find the pole star, many can find Orion during winter with his distinctive belt, but what the sky looked like to our ancestors and how it changed during the year indicating the coming of seasons is something we have lost, how the appearance of the Summer Triangle, made of the stars Vega, Altaire and Deneb and its significance relating to the return of the summer months.

The encroachment of light pollution has such a significant effect on how we live our lives, it makes us feel safe in dark cities, but nature of the design and shear number of unnecessary lights is drowning out the night. The Bortle scale is a measure of light pollution and what we should be able to see. The scale runs from Bortle 9 to 1. 1 being a perfect dark sky sight, the spiral arm of our galaxy, the Milky Way, should be able to cast a shadow on a moonless night all the way to Bortle 9, which would be equivalent to looking up at the sky in the middle of a major city.


The glow of Halifax as Orion rises

You can judge the levels of light pollution in your local area by finding Orion the Hunter. Look south east from around 19:00, the later the better! Orion appears as a rectangle with three stars making up its belt. The top right star is Betelgeuse (the subject of our previous Blog!) the top right is called Bellatrix; the bottom line of the rectangle is Rigel and Saiph. Count the stars within the rectangle, you can include the belt and the rectangle forming stars. To see no more than 10 indicates you are in a heavily light polluted area. In a dark sky site, you expect to see thirty, a remarkable sight!

There are some amazing dark sky sites around the UK, the Brecon Beacons, the Lake District, Dartmoor, Kielder Forrest, Snowdonia and The Yorkshire Dales to name a few, they’re locations where we can get a feeling of what our night sky would have looked like in the past. To see a fuzzy band of stars which make up our own galaxy and then to look between Peruses and Cassiopeia to see a faint smudge, our nearest neighbour Andromeda.


The National Park Dark Sky Festival is an event that aims to claim back the night, to bring awareness of the level of light pollution. The festival begins on the first of February and runs through to the end of march is an amazing opportunity to reconnect with our ancestors and see the wonders of the universe, simple to observe the number of stars makes finding the constellations a challenge! For this Dark Sky Festival, we have teamed up with Go Stargazing and The Tan Hill Inn, the highest and best (probably) pub in the UK. A location where the aroura is visible! Go Stargazing and their astronomers aim is to make astronomy accessible for all. We’ll be at Tan Hill on for the week beginning the 17thof February and on Friday the 21stand 28thof Feb.

To combat light pollution, you can find different filters for your telescope or camera. It should be warned that these won’t make objects brighter, only increase the contrast between them and the sky! How filter work is…. our streetlights work via florescence, that is the gas is excited which emits photons of light of a very particular frequency. The Filters work by absorbing photons of a similar frequency thus removing the photons of light emitted from the fluorescence of that particular element! All good you may say, but! The light from distance stars, galaxies or nebulae will have to pass through the filter regardless, meaning light will be absorbed, the result? Objects will appear dimmer although the contrast will be higher. The best method to see distant objects either with binoculars or a telescope or the naked eye is to get away from all streetlights and other sources of artificial light. There are some fantastic locations to do this, dark sky discovery sites or Dark Sky Parks. Visiting these locations, you’ll not only be amazed at the number of stars that will appear as your eyes acclimatise to the low levels of light, but it will also give you the opportunity to form a bond with our past, our ancestors as little as 50 years ago but also as far back as we have been able to look up! Comets, galaxies, the Milky Way have all been immortalised in some form, Hailey’s Comet appearing in the Bayer Tapestry, something many of use many not see in the future (2062/2063) due to its reflected light being drowned out from photons emitted from artificial sources.

To find out more about dark sky sites in the UK or what events are taking place in the National Dark Sky Festival visit www.gostargazing.co.ukfor a comprehensive list of nearby events.

Or you can join astronomers from Yorkshire Astronomy and Go Stargazing at Tann Hill Pub, the highest and (probably) the best pub in the UK, situated in the Yorkshire Moors, a dark sky discovery site in February. Look out for our article in Sky at Night in February!

Clear Skies!

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