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

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!


A Supernova in Orion!

The constellation of Orion, the Great Hunter, a collection of stars that is instantly recognisable. Orion’s belt comprising of three stars with his sword hanging by his side is an asterism that many of us are familiar with, particularly at this time of the year when Orion is high in the night’s sky from about six o’clock. But what is with the stories reporting that Betelgeuse, a bright orange star found in the left shoulder of Orion, is about to explode in a supernova?

Firstly, Betelgeuse is a super red giant located about 640 light years away from earth, 640 light years means it will take light 640 years to reach earth and so when we look at the star we are seeing it 640 years in the past. Similarly, when we look at our own star, the sun, we see it 8 minutes in the past. Betelgeuse is a massive star; if it was in the place of our sun it would take up the space up to the orbit of Jupiter. Betelgeuse is classified as alpha Orion or a Orion, this means it is the brightest star in the constellation Orion. It is also a ‘runaway star’ A star that is travelling faster than the interstellar medium it is sitting in, for Betelgeuse to be travelling faster than the matter that’s surrounding it something must have either pulled it or pushed it away from its position. This could be gravity; something with mass pulling it, like a galaxy or other body. Or it could be an explosion that is pushing it away - a supernova, one of its neighbouring stars exploding.


Super massive stars burn through their fuel (hydrogen and helium and their isotopes; helium and hydrogen but with different numbers of neutrons) incredibly quickly. In the prime of its life, Betelgeuse would have been fusing hydrogen and making heavier elements whilst emitting immense amounts of energy. Because of its huge mass the gravitational force trying to squash it down would have been battling the thermonuclear force trying to blast the star apart. As the fuel in its core is exhausted the force of attraction, due to gravity, begins to win this battle compacting the star. This causes the temperature to skyrocket and the hydrogen and helium in the outer core and any heavier elements in the core fuse to release incredible amounts of energy. This tips the battle of gravity and thermonuclear force in the other direction, causing the star to swell. The side effect of this is that the star cools and takes on a red colour. When we see Betelgeuse now, it has a orange, red appearance to it, a Super Red Giant. The colour change of a star relates to its temperature and gives us an idea of what is happening in the core of a star and where it is in its life cycle. Our own sun is in its Main Sequence.


Eventually the force generated from the nuclear reactions in the star’s core will not be able to hold up gravity. At that moment the core will instantaneously collapse. The shockwave will obliterate the outer layers of the star; this is a supernova - and what will be left?



The Crab Nebula - A remnant of a Supernova.

The core, a body of immense density. Our sun will meet a similarly sticky end; only the shock wave will not be anywhere near as impressive! The core of Betelgeuse will have two pathways. The matter will be squished together creating a body made of neutrons. These neutrons, according to uncertainty and something called ‘neutron degeneracy’ should not be able to get any closer together, but if the core has a mass of 3.4 times that of the sun at this point then the neutrons won’t be able to hold up gravity. The result? The phantom of astrophysics…the singularity or BLACK HOLE!!


Betelgeuse is a variable star with a regular pattern in its dimming. The cycle has a period of just under 6 years. There is also a faster cycle with slight changes in its brightness of around 550 days. The current dimming of Betelgeuse is greater than previously observed but it could be that these two cycles of dimming have overlapped and as a result we are seeing a more obvious change in brightness than what we usually see. It is also very unusual for a star to undergo a dimming stage prior to a supernova. Betelgeuse will supernova and when it does it will outshine a full moon and be visible during the day. In astronomical times this will happen very soon, but unfortunately for us, very soon is 100,000 years away!

Find Orion and Betelgeuse by facing east after the sun has set and its dark. The Belt is the easiest thing to find. Three stars in a line, around the belt there appears to be four stars making up a rectangular box. Betelgeuse is the top left. Check out events and workshops page to find more wonders of the night’s sky and join us for an astronomy workshops night walk!

https://www.yorkshireastronomy.com/hebden-bridge

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