The Sky and What You See in Astronomy

Seeing is the term astronomers use to describe the condition of the atmosphere and the things we look at in space when stargazing. The atmosphere over us is very active, changing from moment to moment. This is why we see the stars twinkle, and why we can see things with our eyes when we learn to see actively that we wouldn't see otherwise.

We live in the lowest part of the atmosphere, even those of us living at high altitude. Within that lower portion there are many layers that swirl and churn invisibly over our heads. That activity becomes visible when we look at light that passes through it, especially light that comes from a "point source", that is, a star.

Each of these layers has a different temperature. The temperature differences affect how they interact at the boundaries between layers. If you've ever seen a layered fluid, with each layer a different color, as you might get in a layered drink, this is similar to the layers in the atmosphere.

Image courtesy of Morpheus1703

In the case of a drink in a glass, the layers are static. There's no wind, no forces pushing them one way or another. They lay quietly one on top of the other. In the atmosphere, however, the layers are constantly in motion. Heat radiating from the ground, accumulated from the daytime sunlight, rises from below. Winds blow. And each time that narrow line of light that we see coming from a star passes across the boundary between two layers, its straight line path is disturbed.

Refraction is the word for that disturbance. It's the same effect that we use in lenses to focus light. The ordinary type of telescope that people think of, that has a large lens facing the sky and a small lens near your eye is called a refractor telescope because it uses refraction to create its image. Its lenses are made of glass that doesn't change shape much, which refracts light by only so much--no more no less. The atmosphere, however, is like a lot of liquid lenses all flowing over and around each other, constantly changing shape and position.

Seeing is the word used in astronomy to describe how good or how bad the atmosphere is affecting the view of the sky outside the atmosphere. When we say the seeing is good, we're saying that the air is relatively still, the images are steady. When we say the seeing is bad, we're saying the turgid atmosphere is making it hard to see a clear image of the astronomical objects we're looking at.

Seeing can be different at different times of the night, of course. Once the ground has cooled hours after sunset after a sunny day, the seeing can improve dramatically. Or if the weather becomes still. The hours after midnight are the best for seeing in most places. But we can't all choose to engage in our hobby at that time if we have responsibilities in the morning.

Image courtesy of Philipp Salzgeber

Fortunately, we have a built in solution. Our eyes have been built to actively adapt to differences in seeing conditions. Normally we use that without thinking about it when viewing normal terrestrial objects under varying conditions of lighting, at different distances, of different colors and materials. We learn to make out objects in shadow when we're standing in sunlight, see differences of texture where there's not much difference in color or lighting is low enough to hide detail. We adjust naturally between something held in our hands to objects in the distance. But many of these conditions don't exist when we're doing astronomy.

Everything is infinitely far away so far as our eyes are concerned, when we're doing astronomy. The difference between the Moon, at a mere quarter million miles or about four hundred thousand kilometers, and the Andromeda Galaxy, which is eighty trillion times further away than the Moon, is indistinguishable to our eyes. Everything might as well be equally far away. Our eyes can't distinguish details using the means that we normally use distance to give us cues when we're looking at things on Earth.

There is no apparent color for most things in space, with a few exceptions. At that, any color that does exist is pale and washed out by daytime standards. If we see color, it is usually more a matter of contrast between colors of objects that are near each other with significant differences.

We need to learn a new set of cues for actively seeing with our eyes for astronomy. It's not difficult, it just takes a little awareness and practice. Knowing what's happening is part of the solution. Aside from color and distance, we have to look hard to see many of the differences in lighting in astro objects, textures are subtle. Instead, we have to learn to use our eyes to "capture" images during moments of good seeing among the bad.

Relaxing the eye is key to capturing those moments of clarity. If we're straining to see, we're focusing entirely on the image we see now, trying to pick out detail. Instead, we need to relax and take our time, hanging over the eyepiece for a while, waiting for that moment of clarity to come.

The changing of the atmosphere can enhance as well as degrade the image we see, either with our eyes, or through the telescope. If we're waiting for that moment, relaxed, when it comes our eyes will "capture" those moments of superlative clarity. Sure, it's really happening in the brain, where all the image interpretation and processing is happening.

This is why the mount of the telescope becomes so important. It needs to be there for our eye, silently doing its job, keeping the telescope on the object we're viewing. We can't be stressing about the fact that the thing we're looking at is sliding out of view. We can't be using our built-in image processors to compensate for a wobbly, weak, or shaking mount--we want to save that capacity for dealing with the thing we can't do anything about, the cylinder of atmosphere that lies between the end of the telescope and the edge of outer space.

So, remember:

1. You can get your eyes used to seeing with as much skill as night as during the day, but it'll be unfamiliar at first, and will take a little practice.
2. You need to relax, and take your time at the eyepiece (even if there's a line of people waiting to look behind you. Take your moment and make it count. I guarantee, you're not going to be there as long as you fear you have been.
3. The support for the instrument needs to be stable, reliable, and out of your mind when you're at the eyepiece.
4. The atmosphere is going to do what it's going to do. Even if it is wild, and the image is bouncing around in the scope, there will still be occasional moments when the object you're viewing snaps into clarity. The difference between good seeing and bad is how long you have to wait for that to happen, and how long those moments of clarity last.

Your eyes can't tell that the stars are a few hundred million times as far away, except for Saturn to the lower left of the Moon, which is only 3,500 times as far away as the Moon.
Image courtesy of Ragesoss

We're lucky to live in a world like this. We don't need to have a view of space to live. Our atmosphere could support us perfectly well as we are, and have constant cloud cover over the entire planet. We could live in a world where the only things we're aware of in space are the Sun and the Moon, and those only as hazy lights in the clouds. Stars, planets, nebulas, and galaxies could all be completely abstract things to us in daily life. They'd be nothing more than scientific oddities, discovered by chance with the invention of radio. Instead, we have an atmosphere that allows us to look directly into the infinite when local conditions permit. We can see the wonders of the universe, the greatest physics laboratory ever, by just looking up. With simple, inexpensive instruments we can get views of these objects that bring their natural detail and beauty into our view.

A few objects show enough to even the unskilled eye to be magnificent. The Moon, Saturn, Jupiter. Other objects require a little more from us to meet them halfway. The Orion Nebula, Hercules Cluster, Andromeda Galaxy are relatively bright objects with details strong enough to enjoy easily, and there are several dozen more like them. Those object prepare us, and our eyes, for the next level. When we want more.

The good news is, that as your viewing skills increase, each dimmer, more subtle level of objects that you learn to appreciate has even more objects. From a handful of objects to a couple of dozen, we go to a few hundred. Once we have trained our eyes to appreciate those, objects such as the Black Eye Galaxy, M65 and M66, and the Little Dumbbell, we reach a point where there are not merely hundreds, but thousands of objects waiting for us to see them and appreciate their beauty. A lifetime pursuit opens up.

Many amateur astronomers specialize in a particular type of sight they seek, over the course of a season or for a few years. I myself spent a couple of years collecting new galaxies that I had seen. I shifted from that to globular clusters. First, in our own galaxy, then to those visible in other galaxies. Double stars and nebulas of particular types have also been among my "current interests" at different times of my life and under different sky conditions. The eruption of Mount Pinatubo in 1991, and the dust it put into the upper atmosphere, brought my galaxy-seeking to an end at that time, and for a few years afterward. That was when I shifted to globular clusters, which "shine through" the dust better than the faint details of a galaxy's halo.

That was also one of the times it struck me how lucky we are to have the sky that we have. Frustrating as it can be at times, our atmosphere is a wonderful thing, and our first gateway to the universe.

Image courtesy of Michael J. Bennett

Planetary Nebulas

Planetary nebulas are one of my favorite objects in the sky to observe. The way they look, and the way they respond to magnification, make them unique among the different types of nebula.

The Owl Nebula doesn't look so dramatic in my telescope as in this image, but it's still one of my favorite objects in the sky.

Nebulas
Nebulas, or, more properly, nebulae, are cloudy-looking objects in the sky. The word nebula is Latin for 'mist', 'cloud', or 'fog'. There are a lot of different types of things that look like a patch of cloud or fog in the sky. To give a brief list, there are reflection nebulas, emission nebulas, supernova remnants, and planetary nebulas. Each is different, and looks like a bit of cloud in a modest sized telescope. Even galaxies were once considered nebulas, before it was discovered how far away they are, and that they're made of stars like the Milky Way.

Planetary nebulas were given their name by William Herschel. He was trying to build a fairly comprehensive catalog of things in the night sky that aren't stars. He included a description of them in the Philosphical Transactions of the Royal Society, Volume 75 starting on page 263. You can read it, without pestering your local reference librarian, thanks to Google Books.

He chose the name because, though he knew they were nebulas, he also noticed that they tended to be somewhat round and that when magnified their brightness across their visible surface they tended to act like the illuminated disk of a planet, rather than like the other nebulas he had been observing. Sometimes it's implied that the name was given out of a mistaken sense that the objects have something to do with planets, but that's clearly not the case.

Stellar Remnants

Today, we know that planetary nebulas are made up of material that's been cast off a star when it goes from being a giant star (like a red giant) to being a white dwarf star. When this happens, the outer parts of the star that aren't involved in the nuclear reaction of the star (which happens at the core of a normal star) are blown off into space by bursts of energy from the core. The core collapses to form the white dwarf, the outer areas of the star, usually called the "atmosphere", though it's nothing like our atmosphere except that it happens to be the outer part of the star just as the atmosphere is outside the solid and liquid part of the Earth.

There are two basic types of planetary nebula, spherical and bipolar. The spherical ones appear to be stars that have blown off their atmosphere in a fairly uniform fashion.

Abell 39 is a perfect example of a spherical planetary nebula.

Bipolar planetary nebulas are ones where the material appears to be spread into two halves on opposite sides of the original star. Usually, each side looks like a mirror of the other half. One of the mysteries of planetary nebulas is why this happens, and how some of these beautiful forms come into being.

One of the brightest bipolar nebulas in the sky, the Dumbbell Nebula.

The bipolar nebulas appear to take on a wide range of shapes. In some cases, probably in many of these cases, the nebulas themselves are the same shape as each other, but look very different when seen from different angles. Dr. Bruce Balick has a great web page on this that includes lots of other information about planetary nebulas.

Seeing Planetary Nebulas for Yourself

Many planetary nebulas are bright enough to be seen easily. A few can be seen by eye, but they don't look as spectacular that way. The Helix Nebula is the closest known planetary nebula, and it can be seen by eye about 1/3 of the size of the Moon (when I look at it, it actually looks closer to half the size of the Moon, but that's probably just an optical illusion.) But it's very dim, because its light is spread out over such a large area. It looks more like a slightly light patch of sky than like a nebula.

The Helix Nebula is visible by eye but it's not this dramatic and colorful.

Binoculars do a great job of bringing it out and making it look brighter. You still won't see what the Hubble Telescope sees, but it will be worth your while.

A modest sized telescope will bring out detail in about another one or two dozen planetary nebulas in the sky. The Dumbbell, above, shows its "apple core" shape to even a small telescope at low magnifications.

The Future of Our Sun

Present thought is that our own sun will create a planetary nebula of its own in the far future, several billion years from now. First it will become a red giant by puffing up its outer parts, then the core will collapse and the outer gases will be blown off into the space around it.

I've heard mixed predictions of whether the resulting planetary nebula would be visible from within the solar system. Since the Earth will be destroyed during the red giant phase of the Sun, unless a future project relocates it somewhere to move it outside the space that the Sun will swell up into as a red giant, it'll be pretty much an academic question, anyway.

I recently gave a talk on Planetary Nebulas to the Nevada County Astronomers. You can see the slides from my talk on my website.

What is a Galaxy, Anyway?

Though we can't see it directly, the sky is full of galaxies. A few can be seen directly, like the Andromeda Galaxy, and some others under excellent viewing conditions. A pair of binoculars will show more of them, and in fact is one of the best ways of viewing Andromeda. Andromeda covers such a large area of sky that few telescopes will show all of it at once--it takes the wide field of view of a pair of binoculars to see it all.

In pictures taken by space telescopes, we can see fields filled with galaxies. The galaxies are scattered across the image like stars. These images cover a ridiculously small area of the total sky above us. If the number of galaxies in these pictures is multiplied by the number of pictures that it would take to cover the entire sky, we learn that there are more galaxies in the sky than there are stars that we can see with our eyes, even on the darkest of nights.

Our view of a galaxy has not always been the view we have now, though. The word "galaxy" has had, historically, a rather slippery sense of meaning.

The Galaxy as a Place of Myth and Legend

Before the telescope was turned on the heavens by Galileo in 1609, there was only one Galaxy. The Galaxy. Galaxy referred to the Milky Way. Known for as long as anyone has looked upward, it's a part of the sky that appears to be a stream of milky light. Exactly what it was couldn't be known, of course. Myths gave it various forms, such as milk from a great godlike cow, or a path of the gods.

Galaxy comes from the Greek galax, the word for milky. Galaxy is a combining form. To our ears, it falsely suggests the sound of lacto, or the Latin for milk, but it's actually unrelated. To the Romans, the Milky Way was Via Lactea. Milky Way is a literal translation of that.

When Galileo turned his telescope on it, he was the first to see it as stars rather than as a milky cloudiness. The stars in it are so close together and so numerous that there's no way our eyes can make it out as stars without the resolving power of the telescope. The telescope not only magnifies the view, but improves the contrast we see, making it easier to see the individual stars by magnifying the spaces between them and allowing us to pick them out from the general glare.

The Galaxy as Nothing Special

From that time on, the Milky Way, or the Galaxy, became a name for an area of the sky with most of the stars in it. In the book Elements of Astronomy by Simon Newcomb, published in 1900, the terms "galaxy" and "Milky Way" do not even appear in the index. The Milky Way receives only one short mention in the book, describing Galileo's discovery. The 1886 book Recreations in Astronomy by H.W. Warren has "Milky Way" in the index with two citations, but "galaxy is absent. The greater of the two passages cited reads:

Every one has noticed the Milky Way. It seems like two irregular streams of compacted stars. It is not supposed they are necessarily nearer together than the stars in the sparse regions about the pole. But the 18,000,000 stars belonging to our system are arranged within a space represented by a flattened disk. If one hundred lights, three inches apart, are arranged on a hoop ten feet in diameter, they would be in a circle. Add a thousand or two more the same distance apart, filling up the centre, and extending a few inches on each side of the inner plane of the hoop: an eye in the centre, looking out toward the edge, would see a milky way of lights; looking out toward the sides or poles, would see comparatively few. It would seem as if this oblate spheroidal arrangement was the result of a revolution of all the suns composing the system.

Lessons in Astronomy by Chales A. Young, from 1896, contains one entry in the index under "Milky Way, the", and one under "Galaxy, the", both giving the same citation. The description given is as follows:

The Galaxy, or Milky Way.--This is a luminous belt of irregular width and outline, which surrounds the heavens nearly in a great circle. It is very different in brightness in different parts, and is marked here and there by dark bars and patches, which at night look like overlying clouds. For about a third of its length (between Cygnus and Scorpio) it is divided into two roughly parallel streams. The telescope shows it to be made up almost entirely of small stars from the eighth magnitude down; it contains, also, numerous star clusters, but very few true nebulae.

The galaxy intersects the ecliptic at two opposite points not far from the solstices, at an angle of nearly 60 degrees, the north of the "galactic pole" being, according to Herschel, in the constellation of Coma Berenices. As Herschel remarks,--

"The 'galactic plane' is to the sidereal universe much what the plane of the ecliptic is to the solar system,--a plane of ultimate reference, and the ground plane of the stellar system."

It further describes the distribution of the stars in the heavens as being non-uniform, but that with what is known can give some information about the structure of the Stellar Universe:

The great majority of the stars we see are included within a space having, roughly, the form of a rather thin, flat disc, like a watch, with a diameter eight or ten times as great as its thickness, our sun being not very far from its centre...As to the Milky Way itself, it is not certain whether the stars which compose it form a sort of thin, flat, continuous sheet, or whether they are arranged in a sort of ring with a comparitively empty space in the middle, where the sun is situated, not far from its centre.

Following this comes a section asking whether the stars form any sort of system, mentioning that it is unlnown whether gravitation operates between the stars and whether there might be some sort of orbital motion that defines the overall form of the Stellar Universe, with a concept called Maedler's Hypothesis being somewhat more likely, that there is motion about a common center of gravity. It goes further in naming Alcyone, in the Pleiades, as a star described as closest to that center and therefore the possible "central sun", but discards the idea as having no proof to sustain it.

Over all, the subject is treated lightly, though in great thoroughness for the books of the time. After two pages on the Stellar Universe, the book returns to the serious discussion of the solar system.

The Revolution

In these same books, in sections which are practically appendices to the important main matter of the nature and operation of stars and the solar system, there are brief mentions of nebulae, "clouds" in space. Among these are some unusual ones taking the form of spirals. The spirals go unmentioned in Newcomb's book. In Warren's book, they are only listed as one of many possible shapes of nebula:

"Nebulae are of all conceivable shapes--circular, annular, oval, lenticular, conical, spiral, snake-like, looped, and nameless."

Young's book takes advantage of the very latest work in photography and spectroscopy. It has a more extensive section on nebulas, stating that photography reveals features which, for example, reveal a regular annular structure in the Andromeda nebula. Conclusions formed by the new information are absent, however. There is only the excitement that comes with new information to be studied.

The 1923 book The Wonders of the Stars by Joseph McCabe is an exuberant popular book on astronomy that leaps into the subject of the spiral nebulas, however:

Some astronomers think that spiral nebulae may be stages in the formation of solar systems like ours. It is estimated that if two stars approached within a few million miles of each other they would raise such tides (analogous to the ocean-tides raised on the earth by the moon) of metal that a vast quantity would be shot out into space. We are imagining, remember, a volcanic outpour streaming thousands of millions of miles into space. If two such mighty streams were shot out opposite sides of a star, its gravitational power would cause them to wind round the central mass, and it is said the resulting structure would be like the spiral nebula in the photograph. The arms and the star would continue to whirl around, like a gigantic Catherine-wheel. The next stage would be that the matter contained in the spiral arms would begin to gather round the denser centres, and ultimately it would be all (except, perhaps, for a little residual matter, to make meteors) collected in a large number of smaller globes circulating around the star.

Even at this stage, however, questions appear. The rotation of the spiral nebulas has been observed, and questions about their size and distance from these measurements can not be answered, but at the very least some boundaries can be established. As mentioned in the McCabe book, what is known about the spirals would seem to make them too large for solar systems, as they were then understood.

The Island Universes

About the time of McCabe's book, astronomers were beginning to establish distances to these spiral nebulas. In Young's book, it was an open question whether they were part of the same system as the stars around us. In McCabe's book, he notes that some feel they are outside the system of stars but discounts the idea himself.

The controversy about the size of the Milky Way and its relationship to the spiral and other nebulas which appeared to be at exteme distances was known as "The Great Debate".

This work found that the distances to the spiral nebulas, and many others that were not of spiral form, were greater than those to any of the stars known in our "Stellar Universe." This placed them outside that universe and made them ambiguous objects, compared to those nebulas that had been established as being within the Stellar Universe.

The name "Island Universe" arose for these objects, though it was an abuse of the term "universe." They appeared to be islands of stars and nebulas that fell outside the main system of which we are part. The falsehood of our own system being the primary among them fell away quickly as measurements revealed the sizes of these "islands." Their extent was as great as that as the circle of stars about us in the Milky Way.

In 1932 Robert H. Baker revised the popular book Astronomy for Everybody written in 1902 by Simon Newcomb. He updated it with the vast quantity of new understanding that had arisen. It includes a new chapter titled "Galaxies."

In the description of the Milky Way we have noticed some of the star clouds, in particular, the great Sagittarius cloud whose center is 50,000 light-years away, and the somewhat smaller and nearer Scutum cloud. According to the view recently set forth by Shapley, these and other star clouds are galaxies, that is to say, vast assemblages of stars and nebulae. They average 10,000 light-years in diameter. Some are considerably smaller, while the largest are three or four times greater in diameter.

The galaxy of which our sun is a member is known as the local system...These star clouds are grouped nearly in one plane in the supergalaxy which we call the galactic system. For the past century and a half, astronomers have been trying to determine precisely the form and extent of this system whose principal feature, as we see it in projection in our skies, is the Milky Way.

At this point there was still uncertainty about where to draw the lines. Were the various star clouds that we now call the Milky Way Galaxy all part of one galaxy, or several galaxies in an interacting system? Were the external galaxies part of this system, or were they entirely independent?

Over time the consensus became that the external nebulas, the Island Universes, were full independent galaxies in their own right, and that the various star clouds around us in the near distance were different components of a single spiral structure like that seen in Andromeda and Triangulum.

The word galaxy became a general term for the "Island Universes" or assemblages of star clusters independent of our own. In spite of the fact that the word itself means "Milky Way", it was extended to include those structures in space like our own Milky Way, as well as describing the Milky Way itself.

The Spiral Path

The galaxy began as a thing in the sky. Unique, mysterious, and unexplained. It was an object of legend, where gods tread, that led from one storied place to another, with a story behind its unique existence. Then, with the telescope, it was seen to be nothing more than an aggregate of common objects. No longer was it a mystery. It was just a bunch of stars. Like pebbles in the aggregate of a path, their number was nothing of greatness, just a result of their proximity.

Then, with a closer look at the star clouds within the Milky Way, and anomalous objects outside it, it was found to be one of a number of immense associations of stars in our universe. As we dream of and seek other civilizations like our own, the galaxy, as its own mini-universe, has become a place of legend again. Where so many stars come together, we infer many planets. Where so many planets lie, there lie the greatest chances for other life like our own. New places for others with consciousness to arise and to experience their own epic sagas.

Once again, "galaxy" has become a place of myth and legend. In 1977 we were treated to the line "A long time ago, in a galaxy far, far away..." Since then, the land of galaxies has only extended further and become more mysterious and colorful, thanks to the amazing images provided by our astronomers.

'Galaxy' has gone from naming a thing, to an area, to a span of stars that fills a small universe (by present standards) to a thing that is scattered in unimaginable plurality through a far, far larger universe. A universe that is once again large enough for stories of strange peoples and strange things that reflect our view of the vast unknown.

What Can I See Tonight?

This summer I was at a star party, showing the sky to interested non-astronomers, as I do many nights each year. One participant came armed with the knowledge of a number of the finest objects to view in the sky. They asked me to show one, then another. They and the others there all enjoyed seeing each of these objects as I put them in the telescope's view.

Then they said "How about the Orion Nebula? I hear that's really beautiful!"

It is, but I couldn't show it to them. I had to apologize, then explain that we couldn't see Orion that night.

Why?

The Sun blocks part of the sky from the Earth's view. Here, the area near Pisces is behind the Sun. Image by Tau'olunga.

As the Earth travels around the Sun during the year, there is part of the sky behind the Sun that is not visible. The part of the sky that is behind the Sun from our point of view changes depending upon where we are in our orbit. In the image above, Pisces lays on the far side of the Sun from the Earth. The other constellations nearby will also be hidden since they are only visible during the daytime. Pisces would be high in the sky at noon, but you can't see stars at that time because the atmosphere will be lit by the Sun.

Even if you were outside the Earth's atmosphere, there will still be stars hidden behind the Sun. But you would be able to see more of those close to the Sun since the Sun's glare wouldn't be spread out the way it is when you're looking from within the atmosphere.

Six months later, the Earth is on the other side of the Sun. At that time Pisces will be high in the sky at midnight. But the stars in Virgo and the area around it will now be hidden by the Sun.

The Orion Nebula. Impressive, but don't expect to see it in summer. Image by Filip Lolić.

Orion is called a "Winter" constellation because it is highest in the sky at midnight during winter. It's close enough to the ecliptic that it's hidden by the Sun during summer. That means the nebulas in it, including M-42, the Great Orion Nebula, will not be visible in summer. They are visible at other times of the year. Though only in winter are they visible at relatively convenient times of the night, near sunset. At other times you'll need to either get up early or stay up late.

There's a myth about Orion and Scorpius. It's said that they were mortal enemies and would always fight. In the sky this is reflected by the fact that they are at opposite sides of the sky, and are never in the sky at the same time. So, while Orion cannot be seen in summer, the wonderful sights of Scorpius are not visible in the Winter. So if Scorpius is up, Orion isn't, and vice versa.

The M-4 Globular Star Cluster, in Scorpius. See it in the summer, you won't be able to in the winter. Image by Ole Nielsen

How much does the sky change each night? A reasonably accurate rule of thumb is that the stars rise three minutes earlier each night. Note that this doesn't apply to the Moon, it moves in an entirely different way, coming up about 40-some-odd minutes later each night. Another rule of thumb is that the sky changes by about 1 degree each night. This is because the Earth moves about 1 degree in its orbit about the Sun each day. This means that something that is up tonight by about 10 degrees above the western hemisphere will disappear in about a week and a half. So see it while you can!

Likewise, if you see the Pleiades just above the horizon at sunset, you have less than an hour to wait before the rest of Taurus, including Aldebaran (the Eye of the Bull) and the Hyades (another nice star cluster in Taurus) are visible.

How Far?

When I show things off at a star party, we usually look at things that cover a long range of distances, from near to far.

Very Close: 1-2 Light Seconds Away

During the day, we'll sometimes put a telescope on a nearby landscape feature such as a mountain top or a cell tower. The distance to these objects is familiar to most people. It's usually fractions of a mile to a few hundred miles. Astronomically speaking, these objects aren't at all distant.

Close: 1-6 Light Hours Away

We also show off the Moon both in day and night. It is only a quarter million miles away. It takes light about one and a quarter seconds to go this distance, so we might say that it is just over a light-second away.

The Sun and bright planets range in the millions of miles. The sun is about 93 million miles away, planets range from a bit under half this distance to several times this distance. The distance to the sun is about eight light minutes. The planets range from about three light minutes (a very close pass with Venus) to just about six light hours (Pluto and Eris.)

Nearby: 4-25 Light Years Away

The next step in distance takes us from measurements in light hours to measurements in light years. The nearest star is a component of the triple-sun Alpha Centauri system, called Proxima Centauri. It's just over four light years away. This is about 37,000 light hours away. The nearest stars are a whole lot further away than the solar system's planets, the visible comets, the asteroids, the Moon and Sun. Sometimes in art you'll see a star shown in front of the Moon (or within the horns of a crescent Moon.) This can never happen, they are millions of times further away than the Moon. (Yes, except for our own star, the Sun. But it's still hundreds of times farther away than the Moon.)

Nearby stars include Altair, in the Eagle, Sirius in the Big Dog, and Procyon in the Little Dog. Near range out to about 25 light years away or so.

Middle Distance: 25-100,000 Light Years Away

Stars in our galaxy range from these nearby neighbors to the stars in the globular clusters. These are about as far away as you can get while still being in the Milky Way galaxy. The ones you can see can be about as far away as 80,000 light years. Most of the stars you'll see at night are far closer, however, from the nears stars above out to distances of a few hundred light years.

This range includes the nebulas, like the Ring Nebula, Orion Nebula, and Lagoon Nebula. It also includes the star clusters.

Far: Millions of Light Years Away

Here we get to the galaxies. The nearest galaxy to ours (not counting small companions to the Milky Way, like the Magellenic Clouds) is the Andromeda Galaxy, at about 3 million light years distance. A whole bunch of galaxies in the Virgo Cluster is about 50 million light years away. These objects are all far further from us than any of the individual stars, clusters, or nebula you will see through a telescope that are part of our galaxy. Telescopes with mirrors or main lenses larger than 10 inches or so can show individual items in the closest galaxies, like the globular clusters and nebulas in the Andromeda galaxy. But normally any of these you see are in our galaxy, and normally over 100 times closer than even the nearest galaxy.

If you want an idea of what you can see in different sizes of telescopes, see What Can I See in My Telescope?