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موضوع: General Observing Guide

  1. Top | #1
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    General Observing Guide

    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?!
    Find your way around the skies
    Understand star co-ordinates and star charts
    A guide to seeing and atmospheric transparency
    Observing Jupiter's moons
    How to… estimate star magnitudes
    ویرایش توسط stargazer : 03-17-2012 در ساعت 01:49 PM

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  3. Top | #11
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    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’.


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  5. Top | #12
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    A guide to seeing and atmospheric transparency

    by: Anton Vamplew

    This article appeared in Sky at Night


    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...
    امضای ایشان
    برگ در انتهاي زوال مي افتد و ميوه در ابتداي کمال … بنگر که چگونه مي افتي ؟!

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  7. Top | #13
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    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...
    امضای ایشان
    برگ در انتهاي زوال مي افتد و ميوه در ابتداي کمال … بنگر که چگونه مي افتي ؟!

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  9. Top | #14
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    Feb 2011
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    1,588
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    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.



    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...
    امضای ایشان
    برگ در انتهاي زوال مي افتد و ميوه در ابتداي کمال … بنگر که چگونه مي افتي ؟!

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  11. Top | #15
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    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.
    امضای ایشان
    برگ در انتهاي زوال مي افتد و ميوه در ابتداي کمال … بنگر که چگونه مي افتي ؟!

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  13. Top | #16
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    Feb 2011
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    Observing Jupiter's moons

    Anton Vamplew

    This article appeared in Sky at Night


    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 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...
    امضای ایشان
    برگ در انتهاي زوال مي افتد و ميوه در ابتداي کمال … بنگر که چگونه مي افتي ؟!

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  15. Top | #17
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    Moonwatch

    The next step in viewing Jupiter is to use a small telescopeone 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...
    امضای ایشان
    برگ در انتهاي زوال مي افتد و ميوه در ابتداي کمال … بنگر که چگونه مي افتي ؟!

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  17. Top | #18
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    عنوان کاربر
    کاربر ممتاز
    تاریخ عضویت
    Feb 2011
    شماره عضویت
    584
    نوشته ها
    1,588
    تشکر
    20,144
    تشکر شده 12,837 بار در 1,573 ارسال

    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.
    امضای ایشان
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  19. Top | #19
    کاربر ممتاز

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    How to… estimate star magnitudes

    By Dave Eagle


    This article appeared in
    Sky at Night




    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...
    امضای ایشان
    برگ در انتهاي زوال مي افتد و ميوه در ابتداي کمال … بنگر که چگونه مي افتي ؟!

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  21. Top | #20
    کاربر ممتاز

    عنوان کاربر
    کاربر ممتاز
    تاریخ عضویت
    Feb 2011
    شماره عضویت
    584
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    1,588
    تشکر
    20,144
    تشکر شده 12,837 بار در 1,573 ارسال

    General Observing Guide         
    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...
    امضای ایشان
    برگ در انتهاي زوال مي افتد و ميوه در ابتداي کمال … بنگر که چگونه مي افتي ؟!

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