http://www.straightdope.com/classics/a3_350.html
Uh, I think Cecil missed a few key points. All the constellations are stars that are in one galaxy, the Milky Way, in which, of course, we are located. The naked eye can see only our galaxy, and the Magellanic Clouds (and perhaps Andromeda?). Galaxies have vast numbers of stars, while constellations have a handful. This article should have had a lot more depth.
But I think Cecil’s column did a better job of making the central point: galaxies are an actual group of stars while constellations are stars that appear to be a group from a particular viewpoint.
I think that about lots of the the articles. It’d be great if they were more like the staff report lengths. However as I understand it, Cecil has to fit into a newspaper column first and foremost.
This seems to be saying that stars in galaxies are closer to each other than stars in constellations. Considering that constellations are all contained within one galaxy, that doesn’t make much sense.
If you assume that the person asking the question (or the person to whom the remark is addressed) is completely unaware of the nature of the night sky and the objects visible in it, pointing out that external galaxies are (for practical purposes) like what we see in our own galaxy, will likely leave that person confused. Being unable with the naked eye to see external galaxies and especially to make out individual stars in them, would require the uninformed sky watcher to get to a book or a telescope to verify what you would say about the difference between constellations and galaxies.
Showing that constellations are more or less arbitrary groupings of stars, and that asterisms are similarly arbitrary but may incorporate parts of the same constellation (such as the Big Dipper) or parts of several constellations (such as the Summer Triangle), may help to get across that these groups are purely to aid in identifying the stars we can see. Extending the grouping to all that we can see with the unaided eye (while explaining that there are a few naked-eye objects that are indeed extrnal galaxies) should help the novice to get a feel for the difference. The big problem is coming up with a rational reason for the constellations to start with. Attributing them to the ancients may work, but it may not persuade the really ignorant (or skeptical) novice.
This question was answered back when Cecil’s answers tended to be brief, if pithy. Often, more than one question was addressed in a single week’s column.
It wasn’t until later that Unca Cece decided to get both pithy AND verbose. 
That’s what I got out of it too.
I’m speaking from a few evenings of astronomy classes, but perhaps it might be better to say that a constellation is an arbitrary grouping of stars from within our own galaxy. This is as opposed to the galaxies we see outside of our own which are so far away that their finer details appear (to the naked eye where possible) as a mere smudge on the sky.
Well, maybe he should’ve been aiming for brief and useful, and if pithy happens to come along, woohoo.
Your basic premise here – that “[a]ll the constellations are stars that are in one galaxy, the Milky Way” – is flawed. A constellation is a region of the sky. A constellation doesn’t end within the Milky Way Galaxy, or even at the Milky Way’s edge; it extends to the ends of the universe. And while all the visible stars in some constellations may fall inside the Milky Way, some constellations include visible objects outside the Milky Way (for example, the Andromeda Galaxy, which is visble to the naked eye, lies within the constellation Andromeda), and all constellations contain extragalactic objects that are not visible to the naked eye.
This is an excellent distinction. The boundaries of the constellations are precisely defined by Right Ascension and Declination coordinates, in much the same way that states, countries, provinces, and other terrestrial entities are defined by their latitudes and longitudes. These boundaries are maintained for locating all objects, whether near enough to be within the confines of the Milky Way Galaxy, or as far away as the “edge of the Universe.”
So where the surface of the earth is how we normally think of the boundaries of countries and states and such, the analogous concept would be to call all the material beneath the surface, all the way to the center of the Earth, as being part of whatever geographic region is involved. This way, Spain is not just the portion of the Earth that appears on a map, but is all the three dimensional portion of the planet that goes from the surface to the center as delimited by those latitudes and longitudes.
This may be important to astronomers, but this column delas with just looking at the night sky with the naked eye-
So for our purposes, we’re dealing with classical constellations. That is, an apparent grouping of stars that outline a mythological character. That outline may encompass celestial objects that are not necessarily part of the constellation. And the vast majority of constellations do not have extragalactic objects visible to the naked eye. There is a vast difference in scale between that concept of constellation and galaxies. Even by your definition, the column comes up short.
If you think that his columns were “useful”, you didn’t read many of them. 
Take the analogy of where Spain ends below. For most purposes, Spain is an area of the Earth’s surface. We might be a pilot or miner, in which case rights above and below the ground matter, but for the vast majority of the world, Spain is a bit of the Earth’s surface.
Similarly, I would agree with Great Dave that the column deals with people simply looking at the sky with the naked eye. That’s how the people who first settled on the idea of the constellations in the first place viewed them after all 
Constellation V. Galaxy
A constellation is a group of stars that seem to form a picture in the night sky. The Greeks recognized and named forty-eight constellations. Many of these constellations were also recognized by the Arabs, Egyptians, and the Babylonian. In 1928, the International Astronomy Union fixed the boundaries of the eighty-eight constellations in the sky. Twelve constellations lie on the ecliptic and are known as “the Zodiacs.” Part of Ophiuchus lies on the ecliptic, so that makes thirteen ecliptic constellations. Twenty-nine constellations are between the ecliptic and the North Celestial Pole plus the remainder of Ophiuchus. Forty-seven constellations lie between the ecliptic zone and the South Celestial Pole. The names of the constellations are given in Latin, because Latin was once the language of learning. The names used by the Greeks, Egyptians, and other people were translated into Latin. For convenience, the ancients named the constellations after a certain figure that it seemed to form in the sky. They refer to mythological or legendary men, women, and animals. For thousands of years, people have used their knowledge of the constellations to guide them from place to place. By knowing the positions of the constellations, it is possible to locate stars, planets, comets, and meteors. The constellations appear to move westward as the Earth rotates around the axis. For this reason, certain constellations can be seen only during one of the seasons of the year.
A galaxy is made of billions of stars, dust, and gas all held together by gravity. Galaxies are scattered throughout the Universe. They vary greatly in size and shape. Not all galaxies look alike. Galaxy’s can take on several unique shapes. One such shape is a “spiral”. The stars, dust, and gas swirl around in perfect spiral form. The spirals seem to be made up of “arms” that swirl around a central point. Spiral galaxies are some of the most beautiful galaxies in space. Our own galaxy is spiral shaped!
There are three other types of galaxies: lenticular, elliptical, and irregular. Generally speaking, galaxy types that are not spiral or elliptical are considered irregular. Irregular galaxies have no defined shape and can be very small. Elliptical galaxies are shaped like eggs or footballs. Some of the largest galaxies in the universe are elliptical. Galaxies range in size from a mere 1 million stars to 1 trillion stars. Our own galaxy packs an impressive 100 billion stars. Our galaxy gets its name from the light produced by all the stars inside it, which from Earth, looks like a band of milky-white light across the night sky.
Constellation V. Galaxy
Constellation: As a wee tot I flew to Toledo in one of these monstrosities.
Galaxy: The bowling alley my mom and dad use to call home every Wednesday, Friday and Sunday night.
No no, its supposed to be Star Destroyer V. Galaxy!
Ai ai ai… this article made my head hurt. I want to thwap people upside the head when the topic comes up. Constellations are not scientific in nature at all, it was just a bunch of old dead guys playing connect the dots. And if you went to live on some other planetary body, they’d be all messed up anyway. Constellations are merely the appeared location of a star, and mean nothing. IMO, it’s really not even important to note that all the stars in a given constellation are in one galaxy. From a scientific standpoint, the important thtings to note are that galaxies are natural clusters of many many stars, can have different shapes, and are relatively far apart with relatively empty space between them.
That depends on the planetary body. From anywhere in our Solar System, you wouldn’t be able to tell the difference, and from Alpha Centauri, only two or three differences would be big enough to be noticeable (Centaurus would of course be missing a star, Casseiopeia would have an extra star, and Sirius would be slightly displaced).
I wouldn’t say that galaxies are “relatively far apart”… The Milky Way and the Andromeda galaxy, for instance, are separated by a distance about 15 or 20 times the diameter of either. I don’t think you’ll find any other category of objects in astronomy which are typically that close, relative to their sizes.
Not so. The naked-eye stars (except the Sun 
) are all officially named for the constellations they are in.