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A GUIDE TO OBSERVING THE NIGHT SKY


BAZ
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I intend to hopefully provide guides to various aspects of Astronomy from a beginners perspective, so that people new to this amazing hobby don't make the mistakes that I, and possibly others have had to endure along the way.

This first page will be the contents page, listing topics of interest to you.

This thread will be locked, with access only to the Admin team, this is to stop it becoming cluttered and difficult to navigate.

There will be a separate thread for any questions, suggestions and feedback. If I make any errors, please point them out so that correct information is available.

I will try to start from basics and along the way deal with getting to know the night sky and how to find objects of interest. I will not deal too much with equipment as this will be covered in it's own relevant section, however I will mention what you will need to observe objects with.

1. IN THE BEGINNING

2. BEING WARM AND COMFORTABLE

3. MAGNITUDE

4. DARK SITE & STAR PARTY ETIQUETTE

5. STAR HOPPING & BASIC NAVIGATION

6. BATTERIES AND THEIR CARE

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A GUIDE TO THE NIGHT SKY.

IN THE BEGINNING.

There is no doubt that the sky is big and when you start looking for something, it’s very big indeed. It stretches from horizon to horizon and occupies the majority of your world view; well it would if we spent more time looking up. So how do we go about discovering the wonders of our universe and navigate our way round the night sky?

One of the problems is an idea of scale, just how big is the object you're after? Apart from the Sun and the Moon which are obvious to us, it becomes increasingly difficult to locate even the brighter Planets if you don’t know where to look. Some objects are that big, most telescopes are not capable of showing them due to their size, others are that small they need a good magnification to find and observe them. I won’t deal with equipment as that will be covered elsewhere in the forum.

In 1975, when I was 14, I got my first telescope, a 50mm Tasco refractor, and I went looking for M44, the Beehive Cluster. I spent weeks looking for it, failed and gave up; this convinced me I wasn’t cut out for this Astronomy malarkey. The truth was simple, I hadn’t been prepared either for knowing what to look for, nor where to look. There were also not the large amount of people into astronomy as there is now and no internet (as us old "duffers" were still busy inventing that for you back then).

So where did I go wrong?

One of the problems I had was poor information; I had a huge circular star map which was difficult to handle, and pointless to try using outside. It showed every star visible in the Northern Hemisphere, even if it was below the horizon. Other objects were red dots, giving no idea of how large a space they occupied. This led to my second problem... What was I looking for? I didn’t have access to the Astronomy books of the day, which were sparse and mostly technical books. There was and still is of course Sir Patrick Moore, but that was all. I may in fact have actually seen M44 on numerous occasions, but as I was using a scope, I was probably looking clean through it and would not have been able to make out its shape or structure. If I had taken up my Dad’s offer to use his battered old binoculars, I would have had a chance, as M44 is a large object.

I'm going to write this guide from the ground up so to speak, starting from the beginning, from the first glimpse of the sky and then moving on to locating objects. I'll be using star hopping as a method of finding our targets. I will start with the brighter and naked eye objects and progress in time to more difficult and challenging objects. This will be something for me to achieve as well, so should be of use to us all.

I will start with the most important observing tool we all hopefully posses, the “Mark One†eyeball. This has been responsible for all of the great Astronomical discoveries up until the invention of the telescope in the sixteen hundreds. The Arabic and Chinese astronomers were at the cutting edge for many centuries then and had a good understanding of how the Heavens worked, which is why a lot of stars and constellations have Arabic names. They would have had Chinese names as well, but were probably translated into Arabic as the information came west along the trade routes. They also didn’t have light pollution so would have all seen better skies than us.

An understanding of how your eyes works will get you better results when out observing and help you find even quite faint objects.

When you leave your brightly lit house and venture out into the garden, you are pretty much blind, unable to see anything but those objects that emit their own light, and then only the bright ones.

As soon as you move into a dark environment, your pupils will dilate, progressively getting larger and wider to allow as much light as possible into the eye, at this point a pigment called Rhodopsin, also known as Visual Purple is produced in the eye which enhances the sensitivity of the Rods on the Retina. Rhodopsin is synthesised from Vitamin A by the body, and Beta Carotene in carrots is a rich source of vitamin A, so it’s not just a myth! The Rods form the majority of your visual receptors, and “see†in black and white, where as the Cones which detect colour, form only a very small percentage of the sensors and sit in a small area around 0.3mm in diameter in the centre of the Retina.

So down to a design flaw in the eyeballs design, we won’t be treated to Hubble like vista’s of the Universe, as nearly everything we are able to see will be monochrome, unless it’s a bright object such as a star or planet, it is usually very difficult to discern colour in fainter objects, there are exceptions to this rule and it is down to the visual performance of your own eyes as to what you will be able to see.

The downside to having become dark adapted, is any light other than a dim red glow will destroy your night vision immediately, you are again night blind. Your pupils will contract and the Rhodopsin disappears from the eye instantly, ready for the glare of a bright light. This is why people get grumpy when you use a white light torch or use headlights down an observing site. If you need to use a light any other than a red one to see what you are doing, then shout up and ask, it will save you a lot of verbal abuse. It takes between twenty to thirty minutes to become dark adapted, and anyone imaging won’t be the happiest person near you either.

As most of us live in urban areas, light pollution is something which really ruins our view of the sky, so we have to make the best of what we have available. To get dark adapted is simple, take out a beverage of choice, find the darkest spot available to you and make yourself comfortable for a while. You would hopefully have set up any telescope or other equipment beforehand, so it’s ready for use when you are. If you need light to see by, then you will need a red torch. A rear bike light can be pressed into service, but it does not need to be bright. You can judge how things are progressing by seeing which one is the faintest star you can see, this hopefully will get fainter as your eyes become accustomed to the dark. If you are in a really dark spot the Milky Way will become apparent if you are lucky. Make sure you wrap up in warm clothing as there's no point in being miserable when outside, even on a summer night you may need to put on warm cloths and a hat.

Its also worth pointing out that we humans have an instinctive fear of the dark, and it can get a bit spooky on your own even in your own garden, it’s amazing how tuned in you become and a small hedgehog can sound like a bowling ball crashing through the hedgerow. You are at greater risk of danger in a brightly lit town centre than your garden, but that doesn’t help much when you are out in the dark.......alone! Cats are nosey and will come and check you out in the dark, and if you are quite you might get a look at a fox if there are any that patrol the gardens around you.

This is a good time to learn the constellations, as you get to pick out the stars so we will begin here.

First steps

One of the essential items you will need is a decent and legible star map, I use and would happily recommend the Sky and Telescope Pocket Star Atlas. It’s a good useful size, covers the entire sky, great value for money and is laminated so it won’t go soggy when outside with you.

http://www.amazon.co...23600176&sr=1-2

I would also suggest the purchase of a compass, again not expensive and we will use this as we go along so I can give you a bearing to look for on the compass, then it’s just a matter of looking up from that bearing to the object we are after. I will give direct readings off the compass, so don’t worry about Polar Alignment, true or magnetic north. Bear in mind if you are reading this at a later date the compass bearings will not be accurate as this will move along with night sky. This is where Stellarium comes in handy, look in AZ/ALT coordinates, the first one is your compass bearing, and the second one is how far in degrees it is upwards.

http://www.amazon.co...23609875&sr=1-3

It should be noted I have no connection or interest in these products; they are just what we will be using.

Thirdly we will be using “Stellariumâ€, a really useful and free program which you can download here.

http://www.stellarium.org/

We will be using all of these to star hop to objects of interest. This will be a challenge to me as some of the objects we will be after, I may not have seen yet.

THE CONSTELLATIONS

A constellation is a name for a grouping of stars, put together so people had a standard map of the sky to use. This did vary between various civilisations, but has over time evolved into what we use today.

There are eighty eight constellations that all of the stars visible in the night sky are divided up into, this is so areas of the sky can be broken down into a manageable size and the patterns chosen are mostly mythological ones from the Greek and Roman and Arabic periods. They may not be that relevant today, but if it ain’t broke, don’t fix it!

There are newer ones as well that superseded some of the older and less distinct constellations, such as Canes Venatices, which was created by Johannes Hevelius in the 17th century.

They are a group of stars which are ranked by the brightest first and going down in order ranked by using the Greek alphabet.

http://en.wikipedia..../Greek_alphabet

Things change over time, so in some circumstances you may find the one ranked second or even third is actually the brightest star.

We will be dealing with Constellations along the way, as they are a major part in navigating round the sky, using them as “Sign Posts†to other objects. Two of the more prominent ones in the Northern sky are Ursa Major and Cassiopeia. They are both circumpolar, that is to say they never set below the horizon, and are used to find the Pole Star amongst others. Both have a lot of interesting targets residing in them.

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A GUIDE TO THE NIGHT SKY.

BEING WARM AND COMFORTABLE

The first thing you should consider before venturing out is the clothing you are going to be wearing for stargazing. There really is nothing worse than having a clear dark sky above you and you are cold, shivering, and inevitably miserable. Seriously, Hypothermia is a real threat due to the fact that you, the victim, will not aware of its onset.

If nothing else it will cut short what could be an amazing night, and it makes you want to pack up and head indoors. So, how do you keep the cold at bay?

There is a good amount of evidence that wearing layers works, this is how people dress in colder climates and there are advantages to dressing this way. Firstly you don’t have to race out and spend a small fortune on the latest ski wear, save your money for telescopes! Secondly if you get too warm you can remove clothing, so plan for the worst; if you don’t take it in the first place you can’t do this.

There are available what is called base layer clothing, this is similar in appearance to the old style “Long Johns†but with modern fabrics that retain the heat, but breathes and wicks away any sweat you may generate. A set of these can be obtained for a reasonable price, and in fact one of the big four supermarkets stock them and is where mine came from. On top of these add tee shirts, sweat shirts, jumpers, fleece and a warm, waterproof coat for good measure.

Waterproof you ask?

You won’t believe how much water can be held in the air as it cools, and most of this tends to land on you and your equipment, being attracted to your prized optics almost as if it’s been poured on. This tends to happen mostly in the Spring and Autumn, as the days are a bit warmer, with it cooling rapidly as the Sun sets.

I have also worn base layer leggings, jogging bottoms and jeans, all at the same time, it’s a bit ungainly but you are able to stay out without getting chilled to the core. Wear two or even three pairs of socks, start with thin ones and then thicker and woolly ones, try and get them as long as you can so they keep your legs warm.

Wear good waterproof boots and unless its Summer, trainers are not going to do, they don’t retain heat and let moisture in, this will rapidly chill your feet.

The tricky one is your hands, as gloves are normally quite chunky and make operating equipment difficult, if it’s not too cold fingerless mitts might do the trick, if it’s really cold though once you have sorted out your kit, put your gloves on.

Don’t forget your head; wear a hat which will keep the heat in and be somewhere for the head torch to perch on.

You may not win any fashion awards, but then its dark and you are cosy.

There have been nights when colleagues and I have packed away our scopes and found 3mm of ice on them, we were able to take advantage of good skies and remained comfortable for what turned out to be a prolonged session.

You could find that a good night will be a long one; I have said to the wife that I will be out for a couple of hours and returned at four in the morning. Really clear and steady skies are rare in this country, so you may find yourself staying out longer than you thought you might.

So make the most of them.

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A GUIDE TO THE NIGHT SKY.

MAGNITUDE

When you first look skywards the first things you are bound to notice are the bright ones, primarily as they stand out in the darkness of the sky, you might be just having a look round, but if you are hunting something you need to know how bright it is.

This is where it all can get a bit confusing, as the Magnitude scale not only doesn’t have a set “standard†reference point; as all stars will vary in their output over time, it also uses positive and negative numbers. The Magnitude scale also has Apparent and Absolute scales.

No one is exactly sure who started the cataloguing of the brightness celestial objects, but Hipparchus, and then Ptolemy were at the forefront of sorting out a brightness scale. Bearing in mind there were no optical aids then and was all done by the human eye.

They started by dividing the stars up into six units, starting at 6 and then going up to 1, with each step up in number up being twice as bright as the previous one, magnitude five twice as bright as a sixth magnitude star, magnitude four twice as bright as a magnitude five one, and so on.

However this was a subjective scale as it relied on the ability of the observers eye’s to be able to decide on how bright a star was, so it was not terribly accurate.

In 1856 Norman Pogson set about trying to standardise the magnitude scale and adjusted it by stating that a first magnitude star is 100 times brighter than a sixth magnitude star.

They used Polaris originally as a magnitude 2 star, as this was convenient to most observers of the time and visible all year round, it did however put a spanner in the works when it was discovered that Polaris is actually a variable star, and therefore varies in brightness. Whoops!

This though seemed a good system, and over time Vega was adopted as the “Standard star†with a magnitude of 0 (now measured at 0.03).

So people started to work out the brightness of objects based on this system.

stars_mag.png

Magnitude six is the limit of the human eyes ability; this is of course dependent on the quality of the sky the person is observing. In a really good dark sky with reasonable eyesight you may be able to see things down to magnitude 6, but from a light polluted urban environment you may be lucky to see only down to Magnitude 4 or even only 3.

Some people have exceptional eyesight and are able to see down to magnitude 6.5, and some have even claimed to be able to see the Moons of Jupiter without any optical aid. This in fairness is entirely possible as Ganymede, the largest of Jupiter’s moons, has an apparent brightness of 4.38. It is not generally visible due to the glare from Jupiter itself, this varies in magnitude between -1.61 up to a maximum of -2.94.

So using this system the brightest star visible from Earth is Sirius, at -1.46, followed by Canopus, Arcturus, Alpha Centauri, and Vega in descending order.

It wasn’t until the eighteen hundreds that it was decided to measure the brightness of the Sun at -26.7 and Moon at -12.7, and more accurately, the Planets, as these vary in magnitude with their fluctuating distances.

Here’s a list of the 26 brightest stars.

http://www.astro.wis.../brightest.html

What you notice from this table is that there are two scales of magnitude listed, apparent, and absolute.

Apparent magnitude is the brightness of a star viewed from Earth; absolute magnitude is how bright it would appear at the standard distance of 10 parsecs, or 32.6 light years.

The parsec is a unit of length used in Astronomy. (Not Starwars! It is a unit of distance, not time). It is about 3.26 light years, or just under 19 trillion miles.

The name parsec is "an abbreviated form of “a distance corresponding to a parallax of one secondâ€. It was coined in 1913 at the suggestion of British astronomer Herbert Hall Turner. A parsec is the distance from the Sun to an astronomical object which has a parallax angle of one arcsecond.

This is to show you how bright the stars would be if all were placed at an equal distance away from the observer, and if we had some of the brighter stars nearby it would be really amazing.

Rigel in Orion would be -8.1, Deneb in Cygnus would be – 7.2, these would be about half as bright as the Moon, and would cast shadows at night and also be visible in the daytime sky. Anything brighter than -4 in a clear sunlit sky, would be visible.

As of 2006, the star with the highest known absolute magnitude is LBV 1806-20, with a magnitude of −14.2. This star is at least 5,000,000 times more luminous than the Sun. The least luminous stars that are currently known are located in the NGC 6397cluster. The faintest red dwarfs in the cluster were magnitude 26, while a 28th magnitude white dwarf was also discovered. These faint stars are so dim that their light is as bright as a birthday candle on the Moon when viewed from the Earth

Sirius would though only be 1.4 as this appears brighter to us as it is closer at 8.6 light years, our own sun would appear as a magnitude 4.83 so even at that distance visible to our naked eye, which is somehow comforting to know.

We then have to consider deep space objects which we would like to see. This is again a confusing area, such as the brightness for an object like M31.

At an apparent magnitude of 3.4, the Andromeda Galaxy is notable for being one of the brightest Messier objects, ( and one of the first on a list of things to see) making it visible to the naked eye on moonless nights even when viewed from areas with moderate light pollution.

Although it appears more than six times as wide as the full Moon when photographed through a larger telescope, only the brighter central region is visible to the naked eye or when viewed using binoculars or a small telescope.

This is a magnitude reading for the entire object with all of its surface brightness taken into account, and in reality only the core is seen. So if you were looking for M31, and expecting it to be as bright as a third magnitude star, this is where things start to get confusing and disappointing.

There are quite a lot of larger but fainter objects, which when they have their brightness measured scientifically, don’t measure up to what the lay person would expect to find.

There is also the limiting magnitude of what you can see; this is governed by the weather, where you are sited and it’s light pollution, and the equipment you are observing with. Getting out to a dark site with good seeing really does make a dramatic difference to the performance of your eyesight and the binoculars or telescope you are using.

This is what you can expect to see down to with:

Naked eye limit Mag 6

Average Binocular (7x50’s) limit Mag 9

A list for telescopes and different conditions;

scope_size_mag_limits.png

The faintest object detected to date is magnitude 36, by the European Extremely Large Telescope.

The weather plays a major part in how faint a star or object you can detect will be. It is not only the clouds, but also the amount of water vapour, and dust in the atmosphere when you are looking upwards through it all.

On a really cold and freezing night, there will appear to be millions of stars visible, and the transparency of the sky is good, but the downside to this is everything will be twinkling like mad, as the heat from the Earth disappears out into space, causing turbulent air currents. Although you may be able to see more, the view through any telescope is likely to be moving as if seen through a clear jelly.

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A GUIDE TO THE NIGHT SKY.

STAR PARTY GUIDE LINES

AND DARKSITE ETIQUITTE.

There are few “Golden Rules†that really apply to being at a star party or a dark site with fellow stargazers, but here are a few that apply, other than just being courteous.

If you can, get there before sunset in the summer, as it’s easier to set up in the light. Relax and plan your evenings viewing with a brew and a chat with your neighbours.

If it’s dark in the winter month’s try to all agree on a time when you will all get there, so you can set up together with white light’s and then agree a time for white lights to be turned off. Someone may be trying to get something that sets quickly, so communicate and let others know if you need it to be dark a bit sooner.

When you set up, if possible, leave plenty of room between each other. It is more comfortable spreading out, you won’t trip over other peoples gear and it allows viewing of low objects without trying to see round cars or other peoples heads.

Always drive slowly; there might be hazards that are not easy to see in the dark.

The first rule of Astronomy Club is NO WHITE LIGHTS

Any use of white torches or lights will earn you unwanted verbal abuse; this is of course allowed if you have an emergency.

Although when at a large autumn star party, an ambulance had to attend someone who was too ill to be moved, even they got abuse from some of the more fanatical attendee’s.

Use a red light and try not to use one that’s too bright, as it can affect sensitive imaging equipment and its owners.

Don’t shine your red lights into other peoples faces if you can help it, I know it sounds obvious, but some folks just like to see your face, aim away if you have a head torch on.

Cover laptop, net book, and tablet screens with a red screen, if you are some distance from one, they are bright. Even if you think you have hidden it in your car, they glow. Laptops etc should also have a red screen on even when inside your tent, the whole tent lights up without one, the fabric casts a glow.

Red lights are also need inside a tent or caravan, and not a bright one if it can be helped. Caravans have the benefit of being able to black out the windows, so white lights may be used inside, but check you don't get light leakage before setting off, and be careful of opening the door.

Car headlights are obvious pollution, so if you turn up late, turn off your main lights and use side lights if you can, if not come and get someone to guide you with a red torch. People are more than willing to help you, and will help you with setting up as well, just ask for help, you will get it.

Dark sites are a bit more relaxed and no one would expect you to drive down a pot holed road without lights, just be careful when approaching observers.

Don’t forget the interior and boot lights, or when you lock your car that all the indicators will flash.

If you have to leave early, let everyone else know, they can have five minutes and a brew while you leave. Reversing lights are white and bright!

People understand that others have to get up early and leave early, just shout up and let people know, so imaging gear can be stopped without causing any problems.

Do not touch or even look through some one else’s equipment without first asking. Again it sounds obvious, but I have seen people even move other folks scopes without them being present.

This is more than often the case with imagers, who set up their equipment, and then go to bed. Only joking!

Try not to walk in front of someone’s pitch without checking you are not obscuring the view of their scope. If they are imaging they may not seem like they are paying attention, but in the mean time you could be in the shot.

Try not to take pictures of the evening with the flash on your camera, not without letting people know you are going to do this. You will not be popular.

Ladies, or gentlemen, please don’t wear mascara when attending an observing session. Iam not being picky, but trying to get it off an eyepiece is not easy.

It has happened, so Iam pointing it out to save cleaning later.

When people are leaving, try to make sure the last person is not left on their own, so that everyone is able to leave the site safely.

If you are last and your car won’t start you could be stuck. Just check.

It is a fact we are not perfect, and we make mistakes, so if some one is doing something that is spoiling your time at the darksite, please ask politely to see if matters can be resolved to everyone’s satisfaction.

Failing that see or contact one of the Admin team and the matter will be resolved or sorted out later.

If some one is doing something that really is out of order they may be asked to leave the site.

Fortunately this is very rare as astronomers are a decent bunch of people, who help and look after each other.

If you are not sure about anything, please ask.

Star parties and get together's at dark sites are a fantastic way to not only meet the people you may have chatted to via computer, but are a way of gaining hands on knowledge of how to get the best out of the equipment you already own, or ogling kit you would like to own.

They are also great places for picking up good second hand equipment, which you know has been looked after.

I know, I can't resist.

A few hours with friends always makes the world a better place.

This is just so we can all enjoy the hobby that we follow, as good nights are in this country so few and far between.

Look after each other, and have a great time.

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  • 3 weeks later...

A GUIDE TO THE NIGHT SKY.

Star Hopping and Basic Navigation.

As we humans go about our daily routines, the one thing common to us all, is how we relate to our environment, and find our way around.

This could be something simple, such as a trip to the supermarket, and then finding a specific item on the miles of shelves: We simply need to know how to get there. This eventually gets to be instinctive, and you just get your teabags, and its job done: You know where the shop is, and which shelf the teabags are on.

Star gazing doesn’t have to be more complicated than that. After a while, you can find your favourite objects simply by knowing where to point the scope, and by a quick look through the finder.

What you need, either terrestrial or celestial, are maps and signposts, and a way of working out which direction you are going to go in.

The first task is to find out in which direction you are looking. In the Northern hemisphere this is convenient for us as Polaris is pretty much bang in the centre of the Northern celestial pole. Not sure which one this is? Then we need to look for and use the “signpostsâ€.

This is where your map is needed, a Star map in fact.

You may have come across Planisphere’s which are sold as beginners guides, but they are not maps, and to be honest they are only good for showing you what is visible above the horizon; it is difficult to work out which stars are which on such a small disc.

What you need is a decent Star Atlas; these don’t have to cost an arm or leg either. A good number of us use, The Sky and Telescope pocket Star Atlas; it retails at around ten pounds, is affordable, a useful size, and has both Northern and Southern constellations. This is your map book.

The stars are divided into eighty eight constellations; these are groups of stars which form a pattern in the sky. There are reasons why they are this way, but that is a whole new subject.

The constellation is then divided further, starting from the brightest star in that group, and then in descending order of brightness, and marked using letters of the Greek alphabet. It’s worth learning at least the first six or seven of these, as you won’t get far not knowing what the different symbols mean. It’s a sort of galactic Highway Code.

Look at constellations as star cities. On a terrestrial map you need to know where the nearest city is to where you are heading, then the town, village, street, house number.

So start by breaking it down like that. First of all you need to find north, particularly if your mount is an equatorial one. You could use Ursa Major and Cassiopeia as signposts for this, as well as a compass to confirm it, and this will get you pointing in the right direction.

So you know where north is, and by turning around you are facing south. The line that runs from north to south through the sky is called the Meridian. When an object passes this point it’s at its highest point in the sky and after that it begins to set. This is because the Earth is rotating, so the whole sky appears to move left to right. It’s also important to remember that the constellation will change it’s orientation as it moves over the sky. As it rises, it may look similar to your star map, but as it sets it would appear to be upside down.

Another important “line†through the sky is the Ecliptic plane. This is the path that Solar System objects tend to follow; by looking along this line you will find planets, the Moon, and the Sun. However they aren’t always on this and can be up or down of it depending on how they are inclined to the Sun in their orbits.

The Ecliptic is usually shown on Star maps.

So now you are ready to locate the constellation you want look for, and this is where it starts to get a bit tricky. Some constellations are really faint, and were sorted out before the advent of light pollution. Some of the zodiacal constellations such as Aries, are no more than a few dim stars, and difficult to locate from even a dark site. What you need to do is use a brighter pointer and aim towards the fainter ones by drawing an imaginary line through bright stars to get there.

Find a really bright star somewhere in the sky in the rough direction of what you want to see.

Then locate the “Alpha†star of the constellation you need.

Use your star map to work down the stars in a chain like manner, using other stars to form geometric shapes, such as triangles, squares, and arcs. The reason for doing this is that our brains are very good at recognising patterns. If you see a triangular pattern on the star atlas, look for that in the sky and confirm you are going in the right direction by looking from another direction, to check that you are not veering off course.

Now this is where your Star Map programs come in useful. If you cannot take your screen outside with you, make a rough sketch of the bright stars to get you in the area. Make another sketch, showing the faint stars around the object you are after. Or just print off a finder chart. Most finder charts show a general view of the area, followed by a detailed map, showing stars down to quite low magnitudes. This again depends on how bright the object you are seeking is and what stars are available nearby.

It isn’t easy to try and describe how to master what is a practical skill. It’s similar to trying to teach someone how to ride a bike by writing down instructions; but like bike riding, once you have mastered it, you don’t forget it.

There isn’t any prescribed method to finding things, you might find a system that works for you, doesn’t for someone else. This is a skill that develops over time and with practise. Start with something easy, and work towards fainter and more difficult objects to see. Finding faint objects is also something that takes practise; it really is something that you get switched on to, and you may amaze yourself by how faint something is and how you came to spot it.

Use averted vision. That is looking to the side of an object and not directly at it. This is so the more sensitive part of your retina is able to pick it up. The blinking nebula blinks for this reason, look to the side it's there, look directly at it, it disappears.

Try to look at what you have found for a while, making a note of the star field around it, so that you have made a mental map of where it is, and this can then help you to find it next time. However this is dependant on the “Seeing†on that particular night; you might find it difficult or impossible to locate again, either due to the weather, or if you are using a different site. But if you are familiar with the star pattern around your object then you will know it’s not your failure to find it.

Here's a link to a site, which gives detailed finder charts for all of the Messier objects, including the Telrad circles. A very useful resource.

http://avila.star-shine.ch/astro/messiercharts/messierTelrad.htm

There are extraordinary people who are able to memorise absolutely thousands of stars, down to the faintest magnitudes visible.

George Alcock of Peterborough memorised what is thought to be in the region of 30,000 stars in the area of the northern Milky Way. By doing this he was able to notice any changes in the sky, and in doing so, he discovered five comets and five novae. He did all this using just binoculars, a truly astounding feat considering the British weather and light pollution.

Edited by tuckstar
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BATTERIES AND THEIR CARE.

Most Astronomers will at some point require a battery or power supply to run the Mount, dew control, imaging gear, or other devices that needs power.

The most popular solution for this is the “Power Tankâ€, which has various other bits on it such as a torch, radio, and compressor and so on.

These generally have a 7 amp/ hour, or 17 amp/hour batteries inside, which if cheap, don’t last long, won’t hold a charge, and come with inadequate chargers.

So, what do you need, what type of battery is going to suit your gear, and pocket, not to mention your back!

SEALED LEAD ACID BATTERIES (SLA)

These are the most common ones on the market, and come in a large range of sizes and capacities. They range from a couple of amp/hours to hundreds of amp/hours.

I would suggest if you need more than 38 a/hr, consider a leisure battery.

They are also known as Valve Regulated lead acid batteries. As they are sealed, leakage is usually non existent, but not impossible.

These batteries are capable of giving you good service over a long time, but they need some care. Using a mutimeter set on DC voltage will be able to give you a reading of the open voltage across the terminals. This will give you a rough idea of its state of charge, but not its performance. For this you will need to perform a load test, where a meter measures the voltage drop against current draw.

You can have a battery that indicates a full charge, but due to its age and other problems, may cause it to go down hill fast.

12.7v and above – 100 %

12.5v - 90%

12.1v - 50%

11.7v - 30%

11.5v - 20%

If you want to keep your battery in good shape, never use it below 50 % charge.

Do not let batteries get discharged by being left without topping them up. They will lose charge just by sitting there, approximately 4 percent per week, so charge them at least every four weeks, or buy a smart charger and leave it connected, these cycle the battery through a slow charge/ discharge cycle and helps maintain it.

Most Power Tanks are just casings with various bells and whistles attached to a battery. They were sold for the auto market, to aid battery boosting a car. On their own, they are not capable of starting the car, and should be attached and left connected to the main battery of the car for at least fifteen minutes. This helps boost the condition of the main battery, giving it that bit more capacity.

Various scope manufacturers sell their own brand of power tank, and these will run a mount, but start to struggle when asked to power dew control.

Another factor is the ambient temperature, the colder it gets, the greater the internal resistance of the battery increases, and in a short space of time your battery can be flat.

In my own experience you will need at least a 17 amp/hr battery if using dew control. Just on my Dob, with no mount to supply, they last all night. I have a Secondary mirror heater, finder, Telrad, and eyepiece heaters. With all of these on full I get a current consumption of around 4.5 amps. At this rate on a cold night I would get about three hours use.

So to conserve your battery, turn the controller down so that the temperature is just above the ambient temperature, this prevents dew forming. On my scope I get about six hours on a cold night, but the battery is in a box lined with a camping mat to help it keep warm.

If you can, buy a battery bigger than you think you need, as you may add things in the future and also take cold nights into consideration.

THINGS THAT KILL BATTERIES

SULFATION

Lead acid batteries will lose their ability to charge, and retain a useable charge when left discharged for too long. This leads to a process called sulfation taking place

The lead and lead oxide that the plates are made from react with the sulphuric acid in the electrolyte to produce lead sulphate.

As the battery is charged and discharged through its life, lead sulphate will recombine back. But if poorly maintained, or due to old age, an increasing amount of this sulphate converts to a more stable crystalline form, which will no longer revert back, and slowly causes degradation of it’s charging ability, and capacity.

This is the fate of lead acid batteries, as over the years the active material is consumed by this natural wasting process.

This can be better managed if the battery is regularly charged, especially in the warmer months, as it will naturally discharge faster due to less internal resistance.

Also charge the battery as soon as possible after a session with the scope, try not to use it one night, and then the next, without a charge in between, it just speeds up the wastage process.

SHORTING THE TERMINALS

This is usually accidental, unless you have the desire to vaporise parts of your body. The bigger the battery, the bigger the bang!

The 12v will not kill you, but you might feel a jolt, it depends on your bodies own resistance.

Whilst working for the Coal Board, my colleague turned half of my thirty millimetre spanner (2ft long) into vapour when he shorted a Five ton loaders battery box. This was an accident, he just absently minded grabbed onto the box with the spanner in his hand.

It also blew open a number of cells on the batteries, caused by arcing between the plates.

Just be very careful, as a lot of stored energy is available very quickly, and even a small battery is capable of causing a nasty burn.

DEEP DISCHARGING

If you find that when using your battery, it completely discharges, this will cause rapid failure of the battery. If you check your battery with a meter, and you have less than 11.5 volts, the days of your battery are numbered. Less than this failure is very likely.

Batteries don’t like to be discharged by much more than fifty percent, more than this degrades it more rapidly.

So what do you do if you have a power need bigger than you thought?

LEISURE BATTERIES

These are bigger, and more tolerant of being discharged more often than a SLA battery. Their construction is more robust, their plates are thicker, and have a gap under the plates to allow some build up of debris without affecting the plates.

The down side is they weigh more, and are larger. They are available in sizes from around 75 A/hr to a monster 170A/hr battery.

That said if you run an imaging rig, which requires the laptop running off it, these are the ones you might need to consider.

The cost of these has come down and these are worth looking at if you need a large reliable amount of power.

Fuses.

As already discussed, there is a large amount of energy just waiting to be used. When ever you connect equipment to a battery, always put a fuse in the line, and where possible, protect other individual items with their own fuses.

Most “Cigar lighter†plugs have fuses built into them.

If they haven’t, go to a retailer like Maplin’s and change them. It will cost a lot less than a fried controller or other valuable item.

One of the unfortunate side effects of a short is called “Spikingâ€; the surge may indirectly kill other vulnerable bits of kit caused by the surge generated by the initial fault.

CHARGERS

Most of the power tanks come supplied with an inadequate plug top style transformer type charger. These are unfortunately cheap, and cause premature battery failure. They struggle to charge a discharged battery, and I have seen on a number of forums, people asking for advice when their power tank has been on charge for three weeks and still not charged up from new.

The other fault they have is that when the battery achieves full charge, the less current is drawn from the charger. The effect of this is that the voltage supplied rises; I have measured one at 17 volts.

This may cause overheating and distortion of the plates, and also the production of gases, namely hydrogen and oxygen.

A voltage of around 14.5volts at room temperature is capable of causing gassing.

If you have one of these, monitor the battery, and when it has reached full charge, disconnect the charger.

There are on the market reasonably priced smart chargers. These monitor the voltage in the battery, and adjust the charging voltage and current accordingly. They range from around £12, to a C-Tek one at around £40.

Keep your eye’s open, as Aldi do one for £14, and it is very good value. I have had one for three years now, and it charges both my vehicle and Astro batteries.

Smart chargers can usually be left permanently connected, as they cycle the battery through a slow discharge/charge regime.

Read the supplied instructions!

Using a smart charger is simple to connect to a power tank, just connect the same colour croc clips to each other, (red to red, and black to black) the croc clips are normally directly connected to the battery.

Please do not use car battery chargers on sealed lead acid batteries, they supply far too much current, and can overheat the battery with nasty consequences, if not just a dead battery.

If they are charged too fast, with either too high current or voltage, hydrogen and oxygen is produced from the liquid electrolyte in the battery. This largely recombines back into water – but if gas production is more rapid than recombining can accommodate, the valves will vent the over pressure.

THIS IS EXTREAMELY DANGEROUS!

The gases being vented is a mixture of hydrogen and oxygen, these are very volatile, and are capable of a large and dangerous explosion.

With a bit of care, your battery will last years, and give you many happy dew free nights with your scope.

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