General Observing Guide

[Fowad]

Hello Dear friends

In this topic we want to put useful points & experiences about how to observe & what can you do in an observing night to have good observations & results.

So be with us

***************************************
What Can we do to have a great Observation night (http://forum.avastarco.com/forum/showthread.php?675-General-Observing-Guide&p=15995&viewfull=1#post15995)?! (http://forum.avastarco.com/forum/showthread.php?675-General-Observing-Guide&p=15995&viewfull=1#post15995)
Find your way around the skies (http://forum.avastarco.com/forum/showthread.php?675-General-Observing-Guide&p=28987&viewfull=1#post28987)
Understand star co-ordinates and star charts (http://forum.avastarco.com/forum/showthread.php?675-General-Observing-Guide&p=29318&viewfull=1#post29318)
A guide to seeing and atmospheric transparency (http://forum.avastarco.com/forum/showthread.php?675-General-Observing-Guide&p=29651&viewfull=1#post29651)
Observing Jupiter's moons (http://forum.avastarco.com/forum/showthread.php?675-General-Observing-Guide&p=30933&viewfull=1#post30933)
How to… estimate star magnitudes (http://forum.avastarco.com/forum/showthread.php?675-General-Observing-Guide&p=31279&viewfull=1#post31279)

[gandom]

Fowad:

What Can we do to have a great Observation night?!

I ask all the experienced observers in the forum that please share your informations about this question here and this topic will help us to find out the important notes of being a successful observer!
I myself am not a real experienced one but i share with you what i know about it :)

First of all,you should specify your purpose of your observation and second, you look at your equipments and third,determine the specifications of the observation point you've chosen exactly and finally, determine the situation of the objects you are supposed to observe and also the moon and other highly annoying bright objects for the specified date!
Very obvious till now!?
I imagine one of these conditions and speak about it! Lets imagine that your aim is targeting some messier objects and you have a normal amateur telescope(from 4 to 12 inches for the Diameter of the main mirror)and you have chosen a place with normal sky(which is empty of clouds and dusts of course!)and there is no moon in sky!
Well,by this conditions,you can notice to these tips to enjoy and learn much more:
First try to adapt your eyes with the dark environment,at least for 20 minutes and then you find the sky full of stars!Shut your eyes down from any other lights except the red light which its low frequency,make the eye much less sensitive to it!A red head lamp is useful because of the freedom of your hands!!:D[/URL][URL="http://forum.avastarco.com/forum/images/smilies/guntootsmiley%5B1%5D.gif"]http://forum.avastarco.com/forum/images/smilies/guntootsmiley%5B1%5D.gif (http://forum.avastarco.com/forum/images/smilies/guntootsmiley%5B1%5D.gif)
If your aim is a little serious and you must manage your time to gather your needed data,you can make some sandwiches for yourself and the rest of the group for dinner!In this way you aren't supposed to spend a special time for dinner and you can have it fast.Also some hot beverages can help you warm up and concentrate on your work.:sSig_woohoo2:
‌Become sure that you gathered all your needed maps and eyepieces and the other small stuffs that i myself usually forget some of them!!(losing the screw of the mounting of the telescope is a nightmare!be careful!)especially the small stuffs of your Camera if you need one,like filters,mounting stuffs,lenses and etc.If there are some starter observers in the group,a green laser pointer is gonna to be a rescue!!
Depends on your aim,you can choose an appropriate map.for example if you need to make a photo of some fade objects and you have a short time you can use a map like the "observer's sky atlas" and if you are not in rush and don't need details,a map on A3 paper is sufficient!And if you have a laptop,you make it much more easier!
So,what else do you suggest?
I hope you enjoy your observation:thumbsup:

**************************************************
gandom:

to have a usefull observing,i think sketching of phenomenas is the best way...I've seen some astronomers that discovered a new planet,new supernova,new star by reviewing their sketch that they draw it before

[Fowad]

to have a usefull observing,i think sketching of phenomenas is the best way...I've seen some astronomers that discovered a new planet,new supernova,new star by reviewing their sketch that they draw it before

exactly!and some times photographing is more effective especialy in the low time situations,or in more advanced researches for the object's positions in the solar system.
I've read an article some times ago in the Astronomy magazine of Iran that was about an astronomer who discovered some supernovas by his own equipments and the point is its sketching activities which easily guided him to discover the alteration of the background stars, sooner than we
observe that supernova by eyes!what a cool job!

[stargazer]

Find your way around the skies

by: Anton Vamplew

This article appeared in Sky at Night Magazine




[/URL][URL="http://www.skyatnightmagazine.com/sites/default/files/imagecache/490px_wide/main/Jon%20Hicks%20main.jpg"]http://www.skyatnightmagazine.com/sites/default/files/imagecache/490px_wide/main/Jon%20Hicks%20main.jpg (http://www.skyatnightmagazine.com/sites/default/files/imagecache/490px_wide/main/Jon%20Hicks%20main.jpg)



Image credit: Jon Hicks




To some people these days, the idea of star-hopping seems rather quaint. The idea that you slowly work your way around the sky using only your eyes to identify star after star, steadily building up the patterns of the constellations, surely belongs to a bygone age.


After all, today we have Go-To telescopes that can take you to any star or fuzzy nebula instantly. There you go – no knowledge of the sky necessary. Go-To telescopes certainly have their place.

For example, if you want to show the wonders of the night sky to a group of friends, it’s just a case of pressing some buttons and hey presto: deep-sky object after deep-sky object appears as if by magic. Certainly, with their computer databases of where each galaxy and nebula is located, Go-To telescopes are great for finding some of the more challenging, faint, fuzzy blobs.

However, there is something very rewarding in having a mental map of the stars, so that you
can glance up with confidence and point out Leo, Gemini or Ursa Major to whoever is within earshot. And that’s before you’ve pointed out the planets, which are sure to increase anyone’s fascination in the night sky.

It’s true to say that few people know their way around the night sky well enough. The only way of being able to gain this useful and entertaining knowledge is to learn the sky – and it is by star-hopping that you learn.

To be continued.....

[رخساره روشنی]

as my friends said, first of all we should chose what we want to observe , it means we should manage our observing night but chosing a good place for passing our observing night is very important , I know its importance because I have experienced a bad situation when i was out of the city for observing. the place I've chosen to observe was full of dangerous animals :crazy::scared:such as dogs and jackals. I was very scared and couldn't observe any more.

[stargazer]

A Universe to discover

Star-hopping really is fascinating. Not only are you recognising the patterns of constellations, you’re also learning about star distances, star colours, ages and names.

You’ll find that the whole of the night sky is an amazing mixture of space, time, history, science and world cultures. It’ll lead you off on all sorts of paths and you’ll learn things that will amaze others. Not to mention the basic reason – you’ll know what you’re looking at.

Now, you don’t need any optical instruments to begin star-hopping, but it does help to have a few things handy to make your evenings more enjoyable.

Firstly, let’s deal with the comfort aspect.Even in the summer, it will probably get chilly – at the very least – so wrap up warm.

Then, to get as comfortable as possible, set up a deck chair or sun-lounger – maybe we should call it a star-lounger in this case.

Just before you pop outside to try some real star-hopping, there are a couple of final useful things to have with you: a star chart or atlas, plus a red torch to see the charts, and also where you’re going, without ruining your night vision. And don’t forget a flask of tea and a few biscuits for when you fancy a break.

If you’re new to star-hopping, position your star-lounger north-south and sit with your feet pointing north. This will put you in an ideal position to see several key star-hopping points: the Plough, the North Star and the constellation of Cassiopeia as they’re all around the north part of the sky.

Why not practise star-hopping using the example shown below? Remember, take it easy, and you’ll be finding your way around the sky in no time.

to be continued.......

[stargazer]

Star-hop from the Plough to Cassiopeia

http://www.skyatnightmagazine.com/sites/default/files/Plough1.jpg (http://www.skyatnightmagazine.com/sites/default/files/Plough1.jpg)

1 Find the Plough

The Plough is a shape or ‘asterism’ found in the constellation of Ursa Major, the Great Bear. It’s a good place to start because it’s a recognisable shape. It’s also close to the north pole of the sky, meaning it’s always visible in the night sky.

http://www.skyatnightmagazine.com/sites/default/files/Plough2.jpg (http://www.skyatnightmagazine.com/sites/default/files/Plough2.jpg)

2 Move from the Plough to the Pole Star

The two right-hand stars of the Plough are known as the Pointers. Extend an imaginary line between them and out of the Plough and they’ll point to the Pole Star, which is also called Polaris.

http://www.skyatnightmagazine.com/sites/default/files/Plough3.jpg (http://www.skyatnightmagazine.com/sites/default/files/Plough3.jpg)

3 Trace the shape of Ursa Minor

The Pole Star is the main star of the constellation Ursa Minor, the Little Bear. This is shaped like a smaller, fainter version of the Plough and you can trace its form arching off from Polaris. Well done, you’ve found a new constellation.

http://www.skyatnightmagazine.com/sites/default/files/Plough4.jpg (http://www.skyatnightmagazine.com/sites/default/files/Plough4.jpg)

4 Move on to Cassiopeia

Continue on in the same direction you took from the Plough to Polaris, for around the same distance again. You’ll find the distinctive ‘W’ of stars that make up the constellation of Cassiopeia. That’s it, a successful star-hopping session.

to be continued....

[stargazer]

Hopping with binoculars

Binoculars provide another way to star-hop. The trouble is, when you look through them it’s easy to lose your bearings because you’re only looking at a small piece of sky. A good trick is to work out how much of the sky your binoculars show you (their field of view).

To do this, take a look at the Plough, noting which stars are at the very edge of your binoculars’ field of view. Now find these stars on a starchart and make a ring out of wire and place it around them.

This ring is the field of view of your binoculars at the right scale to use on your starchart.You can then move your wire ring around the chart to plan each step of your star-hop and know in advance what the view should look like.

Try aiming for the Double Cluster in Perseus – it’s a great target through binoculars and it’s very close to Cassiopeia

[stargazer]

Understand star co-ordinates and star charts

by: Anton Vamplew

This article appeared in Sky at Night Magazine


When those early pioneers of science, the ancient Greeks, looked up at the night sky, they described it simply as it was seen. They imagined that the Earth was fixed at the centre of things, with the Solar System orbiting around us.

Beyond was the night sky, which they imagined as a sphere with the stars projected on the inside. This became known as the celestial sphere. It was the starting point for mapping the stars.

Even though we now know much, much more about our planet’s place in space today, we’ve held onto the celestial sphere because it’s such a useful way of thinking about the sky. Indeed, it even makes it possible to put all that starry-sky vastness onto a flat sheet of paper and make a starchart, with which you can find your way around the sky.

And just as latitude and longitude are used to find locations on the globe of Earth, the same idea works up there with the stars. The celestial sphere also has a grid system, which is simply a projection of latitude and longitude up onto this imaginary sphere.

The only difference with this celestial grid is that it has different names. Latitude – the lines that run around the Earth parallel to the Equator and give the north-south location – is called declination, while longitude – the lines that run up and down through the north and south poles and give the east-west location – is called right ascension.


http://www.skyatnightmagazine.com/sites/default/files/celestial%20sphere3.png


to be continued...

[stargazer]

Getting your bearings

Declination, often shortened to dec., is quite simple to get your head around because it uses the same units as latitude, degrees (°) and minutes (’), along with the smaller arcsecond (”). The ‘arc’ here is used to make it clear that this is a measurement of distance and not of time.

There are 60 minutes in one degree and, not surprisingly, 60 arcseconds in one (arc)minute. Degrees of declination start from the zero marker on the starry version of our equator, known as the celestial equator.

If you move into the northern sky hemisphere you’ll find a ‘+’ symbol is used before the figures, whereas you’d put a ‘–’ symbol first to show that the degrees and minutes are located in the southern hemisphere.

Right ascension, or RA for short, is slightly more complicated because it uses hours (h), minutes (m) and seconds (s) as units. One hour of RA is the same as 15º of longitude – that’s movement left or right. Time is used as the unit here instead of angles because it represents the Earth’s rotation: in one hour the sky turns 15°. You’ll see this all adds up perfectly for one day and night, or 24 hours worth of rotation: we have 24 hours x 15 degrees, which equals 360° and one complete rotation of the Earth.

Here’s how we’d write the position of the brightest star in The Plough, Dubhe: RA 11h 04m 15s, Dec. +61° 42’ 03”. You’ll notice that RA comes first (it always does) and that there’s a ‘+’ sign in front of the Dec. number, showing that the position of the star is in the northern hemisphere. With the position of a star written like this, you’ll be able to find it on a chart (see photo below).


http://www.skyatnightmagazine.com/sites/default/files/starchart2.jpg


to be continued...

[stargazer]

Star magnitudes

Of course, when you find Dubhe on your chart you won’t see it shining brightly. Instead, starcharts show the brightness of stars (their magnitude) by having bigger dots for brighter stars.
We know that all stars are the same-sized single points of light in the real night sky, but
it’s impossible to show their brightness any other way on a printed page.

Also, don’t forget that starcharts will show north as up and east to the left, instead of to the right. This is different from normal maps because the starchart is showing you the sky from below, while a normal map shows you the land from above. To align the starchart and begin using it, hold it up over your head and you’ll see that the directions fall into place.

From alpha to omega

As we’ve seen, the beginnings of astronomy in the west were in evidence during ancient Greek times, from the 5th century BC. In homage to these early Greek astronomers, German astronomer Johann Bayer published a starchart called Uranometria in 1603, in which he labelled the brightest stars of a constellation with Greek letters for the first time.

This stuck, and it has become the standard way of referring to stars in constellations. Usually, but not always, the brightest star in each constellation was designated as Alpha, the next-brightest as Beta, then Gamma, all the way to Omega. The Greek symbols for these letters can be seen below.

Ursa Major is a good example: the main star, Dubhe, is not the brightest, but Bayer labelled it Alpha anyway, so it became known as Alpha (α) Ursae Majoris. You’ll notice the last two words are spelt differently. This is because they are the Latin possessive for the name – they mean ‘belonging to Ursa Major’.

All constellations have a Latin possessive, with some sounding grand indeed, such as Geminorum, which means ‘belonging to Gemini’.


http://www.skyatnightmagazine.com/sites/default/files/Alpha-gamma.jpg

[stargazer]

A guide to seeing and atmospheric transparency

by: Anton Vamplew

This article appeared in Sky at Night




http://www.skyatnightmagazine.com/sites/default/files/imagecache/490px_wide/main/Setting_Sun_2007.png


THE BASICS

What Moving air in the atmosphere can spoil our views of the stars, making them shimmer and dance in the eyepiece

How toRate the stillness of the atmosphere and your view of the stars

Where Find observing locations with the stillest views

Tricks Techniques to create placid air around your scope

The weather is generally considered to be the biggest hindrance to astronomy. What’s the betting that the night you decide to use your Christmas telescope is the night that spell of fine weather changes for the worse? So you’d have thought that when the skies finally clear, your problems would be over. Surprisingly, though, even a clear night may not be the best time to go out and observe.

The issue is the ‘seeing’. In astronomy, this doesn’t mean how you look at something. It’s a term that describes how much the view you see through your telescope is disturbed by what’s going on in the atmosphere above you.

At moments of good seeing, you’ll get sharp, steady views through your telescope. But bad seeing produces turbulent, unstable telescope views of the Moon and shuddering, shaky images of stars. This is thanks to the layers of moving air between you and the object you’re looking at, the effects of which are magnified by your telescope. On the other hand, deep-sky objects like galaxies and nebulae aren’t that affected by bad seeing.

In the atmosphere, air at different temperatures is always moving around and mixing together. Light travels through hot and cold air at different speeds so it is continually bent this way and that before it finally arrives at your scope all shaken and stirred. Sometimes there are very few moments of clarity. One of the best ways to see this distortion is to watch the Sun setting on a clear horizon. It will have a jagged appearance, thanks to the sunlight moving through layers of turbulent air.

to be continued...

[stargazer]

The Antoniadi Scale

It’s very useful to note down what the seeing is when you’re observing. Many astronomers use the Antoniadi Scale as a measure of what the atmosphere is up to. It’s a five-point scale using Roman numerals. I indicates the best conditions, while V describes the worst.

I Perfect seeing without a quiver of turbulence at all.
II Slight shimmers; moments of stillness last several seconds.
III Average seeing; larger air tremors blur the view.
IV Poor views with a constant and disturbing swell.
V Bad views with severe undulations; so unstable that even quick sketches are out of the question.

The other factor that affects observing conditions is the transparency of the night – just how clear the sky is. After it’s been raining, the sky is completely transparent because the rain clears away particles of dust and smog from the air. However, when it’s been raining it also tends to be windy, which means that the seeing is bad. You’ll notice that the stars are twinkling because of the bad seeing.

to be continued...

[stargazer]

How faint can you see?

Atmospheric conditions have an impact on the faintness of the stars you can observe. Use the chart below to check the faintest stars you can see by looking at Ursa Minor on a very clear night to work out your limiting magnitude. This is the faintest star magnitude, or brightness, that you can see from your location – higher numbers mean fainter stars.


http://www.skyatnightmagazine.com/sites/default/files/chart.png


Transparent conditions, though, are good for larger, fainter objects like nebulae and galaxies, which really benefit from the better contrast. Poor transparency generally means the air is steady with good seeing, but dust and particles are sitting in the atmosphere because the air is still. These conditions are good for looking at the Moon and stars.

A good way to think of it is to imagine a swimming pool with a penny coin on the bottom. The water represents our atmosphere and the coin the starry object you’re looking at. Through completely still water (ie no air currents), the coin looks still, crisp and clear. In this case the seeing is perfect and so is the transparency. If the water is made to move – causing ripples – the coin’s image will shake around; the transparency is still good but the seeing is bad. And if some milk is spilt in the pool so you can’t see the coin very clearly, the transparency will be reduced.

It goes to show that you’re at the mercy of the atmosphere, and moments of clarity are a wonderful thing.

to be continued...

[stargazer]

Improve your seeing

You can’t do anything about ‘high-level seeing’ – the air currents far above you – but you can influence the ‘low-level seeing’ to create steadier air conditions immediately around you and your scope. Here’s how:

1 Leave your scope outside to cool to the ambient temperature, getting rid of air currents in the tube.

2 Observe on grass rather than concrete. Concrete absorbs more heat from the Sun and radiates it out to the air above it for longer.

3 Air currents tend to stay low to the ground, so it can be a good idea to raise up your scope on a platform

4 If you build an observatory, make it using thin materials like wood that can cool quickly.

5 The geography of your observing site affects how air behaves. Being near the sea gives you calmer air than near a range of hills, where air is forced up, causing turbulence.

[stargazer]

Observing Jupiter's moons

Anton Vamplew

This article appeared in Sky at Night


[/URL]http://www.skyatnightmagazine.com/sites/default/files/imagecache/490px_wide/main/mAINjUPiMAG.jpg (http://www.skyatnightmagazine.com/sites/default/files/imagecache/490px_wide/main/mAINjUPiMAG.jpg)

Image Credit: Pete Lawrence


The Solar System is truly an incredible place, but one world in particular stands out and truly deserves the title King of the Planets: Jupiter. It is grandiose in all respects. Not only is it the largest of the planets – it would take 1,321 Earths to fill the volume of Jupiter – it’s also more than likely that it keeps the largest entourage of moons.

It’s the massive gravitational effect of Jupiter that does the trick, attracting more than 100 moons into orbit around the planet at the latest estimate. Many of these satellites are fairly small and can’t be observed from Earth, but the biggest four are easy to spot with just a small pair of binoculars.

A minimum size pair for spotting these four moons would be [U]7x50s, which magnify what your eyes see seven times and have front lenses that are 50mm in diameter. You can certainly catch glimpses of these Galilean moons (named after Galileo, who first observed them) with hand-held binoculars, but your view will be much improved by resting the binoculars on a wall or fence, or even attaching them to a tripod with an inexpensive bracket. With binoculars though, Jupiter itself will not appear as anything more than a large, slightly oval-shaped disc.

to be continued...

[stargazer]

Moonwatch

The next step in viewing Jupiter is to use a small telescope – one with a front lens 3 to 6 inches in diameter. As this gathers more light, it can magnify the view more, so the Moons will appear brighter and fill more of the field of view.

Don’t necessarily expect to see all four, however: as the moons travel around the planet they may be behind or in front of Jupiter when you’re looking.

It’s by using a larger scope with a front lens over 6 inches in diameter that you really start to see detail on the planet itself: not only the darker belts and lighter zones, but features within the gaseous atmosphere as well. At this level of detail, observers can also see the occasional dark spot caused by the moons casting their shadows onto Jupiter’s atmosphere. The joy of Jupiter is that whatever your level of equipment, there’s always something to see.

Happy observing, and remember – what seems like an easy amateur target today made history at the start of the 17th century. When Galileo first saw Jupiter’s moons, it proved scientifically that the Earth was not unique and wasn’t at the centre of the Universe.

to be continued...

[stargazer]

The Galilean Moons

Io
Diameter: 3,650km

The tremendous gravitational pull of Jupiter on this innermost of the four Galilean moons, together with its closeness to the planet, means Io whizzes round Jupiter in just 1.75 Earth days. This fast orbital speed is easily seen in a small telescope: it visibly shifts position in just a few hours. Physically, Io is the most volcanic place in the entire Solar System. The whole world is covered in sulphurous lava flows and volcanoes erupting in plumes more than 500km high.

Eurpopa
Diameter: 3,140km

The second Galilean moon out from Jupiter, Europa, should theoretically be visible with the naked eye since it shines at magnitude +5.3. But Jupiter’s overwhelming brightness makes it difficult to separate the moon from the planet. Europa’s brightness is due to its surface being smooth and icy. Scientists suspect that underneath is a liquid water ocean, leaving open the possibility that life may lurk in the depths.

Ganymede
Diameter: 5,260km

The third major moon out from the planet is not only Jupiter’s biggest, but it is also the largest moon in the entire Solar System. This is a world with a cold ice surface, a large warm ice (possibly water) mantle, a rocky interior and a liquid iron core. It measures a tremendous 5,260km across, which is bigger than Mercury. Indeed, if Ganymede was released into space, it would be classed as a planet.

Callisto
Diameter: 4,820km

The last of the four giant Galilean satellites is Callisto. It is the third largest of the Solar System, after Titan, the biggest of Saturn’s moons. Callisto ranks as one of the most cratered worlds known – its entire icy, ancient surface is covered with impact craters that date right back to the time of the early Solar System, when the moon formed. Like Europa, it is thought that beneath the surface may lie a watery ocean.

[stargazer]

How to… estimate star magnitudes

By Dave Eagle

This article appeared in Sky at Night



[/URL][URL="http://www.skyatnightmagazine.com/sites/default/files/imagecache/490px_wide/main/Star%20magnitudes%20MAIN_0.jpg"]http://www.skyatnightmagazine.com/sites/default/files/imagecache/490px_wide/main/Star%20magnitudes%20MAIN_0.jpg (http://www.skyatnightmagazine.com/sites/default/files/imagecache/490px_wide/main/Star%20magnitudes%20MAIN_0.jpg)


Work out the brightness of celestial objects for yourself using a simple procedure

Even to casual stargazers it’s pretty obvious that the stars are of differing brightness. Astronomers always like to catalogue and classify objects in the sky, and the brightness of stars is no exception. Over 2,000 years ago, the Greek astronomer Hipparchus devised the system we use for this purpose, called the magnitude scale.

In Hipparchus’s magnitude scale, the brightest stars were known as first magnitude and the faintest stars were sixth magnitude. He gave a higher number to the faintest stars, which sounds a little topsy-turvy until you swap the word ‘magnitude’ for the word ‘class’. Looking at it this way you start to see them as ‘first class’ stars, ‘second class’ stars and so on as the stars get fainter, putting the scale into perspective.

At the brighter end of the scale, magnitudes become a little awkward as some stars and other objects are brighter than first magnitude. There are stars with zero magnitude – wrongly suggesting they have no brightness – and in cases where the stars are even brighter, they have a negative magnitude, as you can see in these examples:

The Sun –27
Full Moon –12
Venus (at its brightest) –4.4
Arcturus –0.04
Vega +0.03
Polaris +1.99
Pluto +13.9

With telescopes and imaging equipment like CCD cameras, you can go way beyond the sixth-magnitude objects on Hipparchus’s original scale and capture objects like Pluto, which is far too dim to be seen with the naked eye. The Hubble Space Telescope has managed to image objects as faint as magnitude +30. Don’t forget that the magnitude doesn’t tell you how luminous an object really is in itself; it’s a measure of the apparent brightness of a star as seen from our vantage point here on Earth.

The great thing about star magnitudes is that by getting to know the brightness of stars and carefully observing them, you’ll be able to estimate the magnitudes of other objects you see in the sky. This is handy when you see a meteor streaking across the sky, or a passing comet. You might also want to keep track of the changing brightness of a variable star so that you can let others know how bright it is.

to be continued...

[stargazer]

Know your sky

The first step in learning how to estimate magnitudes is to make sure you know what you’re looking at. Print out a detailed star chart showing star magnitudes near your chosen star from planetarium software such as Redshift, or from one of the websites in ‘Find out more’ on page 80. You need to identify the field of view correctly. In our step-by-step guide using Ursa Minor over the page, this may seem easy, but when you’re tackling fainter stars in star fields that you haven’t observed much, it can take some time to find where you are.

When you’ve got to grips with what you’re looking at, use your chart printout to find two stars in the same field of view as the one you’re interested in, to compare it against. These ‘comparison stars’ need to be on either side of your target star in terms of brightness – one brighter and one fainter. You also need to make sure that both comparison stars are not variable stars, which change in brightness. Now decide how bright your target star is when compared to the two comparison stars. Is it halfway between them, or is it somewhere else in between, being of a more similar brightness to one than the other? Use your own judgement and be consistent in how you make your comparisons.

Once you’ve decided, it’s time to put a figure on the target star’s magnitude in comparison to your two other stars. Look up the magnitudes of the comparison stars on your star chart. Knowing this will help you make a reasonable estimate of your target star’s magnitude. Let’s say the two comparison stars are of magnitudes +4.0 and +3.0. If the target star is two-thirds of the way from the faintest star to the brightest, this gives you an estimated magnitude of about +3.3. Don’t worry if you’re a little unsure; practice makes perfect.

to be continued...

[stargazer]

Give it a go

Now let’s try a real example. Imagine now is July. High up at this time of year is the constellation of Draco, the Dragon. The stars you’ll need are marked on it in the image below. It’s a constellation meandering between the two bears, Ursa Major and Ursa Minor, and it has a distinct pattern of four stars marking its head, known as the Lozenge. We’re going to estimate the magnitude of one of those stars, Grumium (Xi (ξ) Draconis). The comparison stars we’re going to use are Etamin (Gamma (γ) Draconis) and Kuma (Nu (ν) Draconis), at magnitudes +2.2 and +5.0 respectively.


http://www.skyatnightmagazine.com/sites/default/files/Draco%20INSERT%202.jpg (http://www.skyatnightmagazine.com/sites/default/files/Draco%20INSERT%202.jpg)
The constellation of Draco is high this time of year. Use the stars Gamma (γ) and Nu (ν) Draconis to estimate the magnitude of Xi (ξ)


Observe carefully and try and work out where the brightness of Grumium lies between our two comparison stars. You should see that it’s roughly two-thirds of the way from Etamin towards Kuma, which will then give you a rough estimate for this star’s magnitude of about +4.0.

With your newfound skill you’ll be able to work out the brightness of a host of different objects, including variable stars. You’ll also be able to use binoculars or a telescope to estimate the brightness of really faint objects such as minor planets or comets. Make sure you record your findings in a log book – you never know what you might find.