What Can I Expect to See?
By Way of Introduction
It’s a very easy mistake to make.
You see those spectacular images of colour and shape which show the beauty of the Universe and just how fortunate you are to live within it and you think to yourself, perhaps a telescope will show me something similar?
Time passes and one day you hear about some astronomical phenomenon that’s going to occur. You’ve read the reports in newspapers and seen something on TV about the breath taking sights in the superlative that will appear in the night sky.
So you decide to ask about what telescope you should buy and from an astronomer’s natural enthusiasm and well meaning intention you are informed that telescope x, or p or q will give you the most fantastic and awesome views. And so you purchase your telescope. The clouds and rain pass, you set up with batted breath and at long last you take a peek at the night sky, and your heart sinks.
The meteor shower wasn’t that promised firework display after all. The giant planet was the size of a pea in the palm of your hand, and the spiral galaxy, and the cosmic clouds of nebulae were mere smudges in various tones of bland grey.
You feel let down, disappointed. Somewhere in your mind you expected to see these Hubble type images, at least a little colour on those huge cosmic galaxies and if you don't feel ripped off, then perhaps at least a little deceived.
Some may argue that there ought to be a warning on every telescope box and advert and image: This Telescope Will Not Show You A View Like Those in Magazines or Taken by Camara.
Others, perhap partkaking in the casual ideology of cynicism, will blandly inform you that such warnings are pointless. You don’t expect to buy a guitar with a sticker on it saying, ‘Buying this guitar will not make you play like Jimi Hendrix.’ Nor do you buy some perfume with a label saying, ‘Buying this perfume will not give you the sex appeal of Brad Pitt.’
But somewhere in this jumble there is a middle ground we can tread upon. Some words of advice we can offer up so that new comers of the future never have the occassion to feel unnecessarily deceived or ripped off in any manner.
The primary function of a telescope is not necessarily to make things look bigger but ultimately to concentrate more light to your eye. Distances are so vast in the universe that the more light a telescope can gather, the more powerful it is. This power makes the object brighter which makes it easier for you to see distance features. It is measured in terms of aperture whose light gathering capacity increases with the square of its radius.
Typical beginner’s telescopes range from about 4” to 8” and the typical distance these little bits of glass and mirror are looking at is anything between a few hundred or so million kilometers to many millions of light years. And what you will see will depend on many factors. These include but are not limited to, sky conditions, the quality of your telescope and eyepieces and your own level of experience.
It’s worth pointing out at this stage that in general, you’re not going to be viewing over 200x magnification. If the telescope box tells you otherwise, don't believe it for the simple twofold reason that average sky conditions don’t allow for this to happen and that many objects are so far away that if you up the magnification too much you’re simply making them too dim.
Assuming that for now the first two factors (quality of optics and sky conditions) are out of your immediate control, then a lot of what you are able to see in the night sky depends on your own observing skills and this requires time and patience.
Typically, a beginner wants to see a bit of everything: The Moon, some planets, galaxies, emission and planetary nebulae, globulars and open clusters.
The first part of this thread will concentrate on typical solar system objects viewed by the beginner. The second part will concentrate more on Messier objects and other deep space phenomena.
Part I - The Solar System with 4" to 8"
The Moon - you should be able to make out typical lunar features such as craters and riles. An 8” should be able to tweak out details about 2 to 3km in size. Bigger the aperture, brighter the image and the more detail you will see.
Mercury and Venus - you’re going to see these planets as small disks, a lot bigger than the brightest stars but they will generally have a total lack of detail to be seen and you will only be able to observe their phases.
Mars – again, you’re going to see this as a small red disk and if you want to see anything else you’re going to have to not only spend a lot of time at the eyepiece, but also have realtively high magnification which in turn requires some decent atmospheric conditions. After time, you might be able to make out a tiny white-ish area at its pole, perhaps a tiny dark marking or two. And all this in an object no bigger than a lentil in the palm of your hand.
Jupiter - a 4" will reveal some detail on Jupiter and an 8" will reveal more. But in either case you need time to observe. If you look casually through the 4 or 8", have a quick five minute gander, you'll say to me in both cases, 'I saw a white-creamy disk about the size of a pea with one or two orangy-brown bands on it.' And yes, that is the first impression we'll all get, but to go beyond that you will need to work. An 8” will reveal a significant amount of detail but you need to sit quietly for quite some time, relaxed in a comfortable position and allow your eyes to respond to the faint delicate markings, the subtle whisps of differing shades which are present on the Jovian disk. You’ll also see the four big Jovian moons which will look like very bright stars. Visual observing is quite hard work but the more you do it the better you get and the more you see.
Saturn – a similar story unfolds for Saturn. There are no easy wins in astronomy and you need to take your time. With a 4” to 8” telescope you should be able to see the rings of Saturn (it may just appear as the one), subtle bands on the planet itself, four or five of its moons that in some cases will appear like brightish stars and on a good night, Cassini’s Division which will look like a thin black circle drawn inside the rings.
Uranus and Neptune – these will appear as tiny objects. With enough magnification you might be able to garner a pale blue or greenish colour and the appearance of a disk-like shape.
The Sun – with the proper white light filters in place you will see sunspots and the structure within, namely, Umbra and Penumbra; you will see faculae, granulation and limb darkening. Do not ever look at the Sun without proper filtration.
An Approximation of an Eyepiece View
Here are some approximations of what you might see through your eyepiece which will hopefully ground expectations.
Jupiter as taken by Voyager 1.
Jupiter as seen in a 4" frac.
Saturn as seen by Cassini.
Saturn as seen in a 4" frac.
Uranus a taken by Voyager 2
Uranus as seen through a 4" frac.
I hope this part of the thread has helped a little in getting an idea of what to expect from your telescope. The second part will follow shortly dealing with some of the more popular Messier and NGC celestial objects.
What Can I Expect to See...Galaxies and Nebulae
A Truism or Two
There’s an old truism that runs around the boards: a galaxy or a nebula is a faint, grey fruzzy in a 4” and a 6” and a brighter grey fuzzy in an 8” or a 10”.
There’s also another truism which rings truer to an astronomer’s heart beat. All things being equal, you will see more tomorrow than you did today, and so it follows that you will never see less than you did this evening. Each evening with a galaxy or nebula you are training your eye and brain to notice more than what you have already seen. And that takes time; it takes patience, a little love and care at the eyepiece.
Size, Magnitude & Brightness
When beginning to observe deep space object such as globulars, galaxies and nebulae it is handy to bracket them into three intertwined classes:
The size of the object
The object’s magnitude
And its surface brightness
We do this so as to have a rough estimate of how well we may be able to view a given object, and by doing so not only arming ourselves with useful knowledge, but also lessening the impact of frustration and disappointment.
As a frame of reference, we can argue that the angular diameter of the full Moon viewed from Earth is about 0.5 degrees, or 30 arc minutes, or 1,800 arc seconds.
So a galaxy like M 31 is over 3 degrees in diameter. An emission nebula like M 42 in Orion is over 1 degree in diameter. A globular cluster like M 13 is about 16 arc minutes in diameter and a planetary nebula like M 57 is just over 1 arc minute.
The object’s magnitude is the total sum of all the light stemming from the object. There are differing ways this can be measured but for the observer the most useful guide would be the apparent magnitude. This scale starts on the minus side for bright objects and travels up into the plus side for dimmer objects.
Most of the stars you see making up a constellation’s pattern have an apparent magnitude of about 1 or 2, M 31 about 3.5, M 42 around 4, M 13 about 5, M 57 about 8 and at a dark site the naked eye should be able to see stars down to about 5 or 6. Looking just at these figures, then, it would appear that M 31 and M 42, for example, are a lot easier to see than M 13 or M 57.
But this is where it may get confusing.
If we say that the object’s apparent magnitude suggests the the overall light output of an object, then by comparison surface brightness is a measure of how bright an object may appear. Although it isn’t necessary for the given discourse, we can point out that apparent magnitude is not measured in any unit but surface brightness is actually measured in magnitude per square degree. Again, lower the number, brighter the object. M 31 has a surface brightness of about 23, M 42 around 22, M 13 about 21 and M 57 about 18. Looking at these figures, then, contrary to what we have just said, it now seems that M 13 and M 57 will be easier to see.
So what gives?
For something like M 31, although its apparent magnitude is relatively quite high making it one of the brightest deep sky objects in the night sky, its light is spread over a colossal area, that light is being thinned out and so the galaxy is very dim to see. By comparison, M 57 or M 13, although having a poorer apparent magnitide, are a lot smaller so the light, the magnitude per square degree, is more concentrated and therefore they have a higher surface brightness making them easier to see.
Rule of Thumb
As a general rule thumb, then, we can say that apparent magnitude is a good indication of how well you may see an object where we are dealling with point sources of light such as planets or stars, but for large extended objects such as globulars, galaxies and nebulae, surface brightness and size are the tools you want to be using. Take this as an indicative, not a definitive rule of thumb.
Other Factors to Bear in Mind
No matter what has just been said above when it comes to observing deep space objects most of what you will be able to see will depend on a myriad of other factors, not limited to, the quality of your optics, atmospheric conditions and inevitably, your own experience. Nevertheless, we can suggest a number of pointers to bear in mind when preparing for a deep space session:
Whereas planets and the moon are bright and largely unaffected by light pollution, being large and extended and very faint, deep space objects depend entirely on dark skies. If we say that a comfortable seat will add ½” to 1” of aperture to your telescope, then the impact of dark skies is unprecedented. It’s probably not much of an exaggeration to say a 6” under dark skies will blow away a 10” or 12” in an urban setting. Galaxies and nebulae and globulars are some of the faintest deep-sky objects and dark skies are everything when viewing them.
Whereas good seeing conditions are essential to good planetary and lunar observing, deep space objects are more dependent on clear, transparent skies.
Whereas detailed planetary and lunar observing require high magnifications, there's no ideal magnification in which to view deep space objects. It’s a case of trial and error. If you want to view M 31 in its entirety, you’ll need extremely low powers but if you want to see a little more detail, you will need magnification. Some planetary nebulae, some globulars take magnification well, some don’t. It’s a case of trial and error.
Whereas colour filters aren’t really that useful when viewing planets, nebulae often benefit from filters, in particular, narrowband ones like UHC and OIII filters. They improve contrast and make faint details apparent. There aren’t filters to improve your views of galaxies and even if there were, any improvement would be negligible.
An Approximation of an Eyepiece View
Here are some approximations of what you might see through your eyepiece. Bear in mind that the sketches were generally not made in a hurry and in many cases took a good hour or so sitting at the eyepiece.
M 31 - Galaxy. Hubble Image.
M 31 - 4" Sketch.
M 51 - Galaxy. Hubble Image.
M 51 - 4" Sketch.
M 27 - Planetary Nebula. Hubble Image.
M 27 - 4" Sketch.
M 3 - Globular Cluster. Hubble Image.
M 3 - 4" Sketch.
M 42 - Emission Nebula. Hubble Image.
M 42 - 4" Sketch
I hope this had helped a little.
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P.S: Thank you everyone for your kind replies and support. I'm sorry I haven't replied to each of you but it's been a busy day and I just haven't had the time. Seriously. Please don't think me rude and I will make ammends this weekend.
I will try to post up a little on open clusters and doubles with a shorter and final third part.
Thank you again to everyone