4. Finding stuff in the night sky
(part 1, using a starchart or planisphere)
In the last section we got a bit of a head start by finding the Big Dipper and the North Star, so now we know where north is. But what about finding other stars and constellations? It helps to use a starchart of some kind. There are lots of different ones, some simpler and some more detailed. For now, you'll want a simpler chart. Let's start off with a basic skychart that appears in many magazines or that you can print from the internet.
Fig 1: Examples of monthly starcharts available online and in magazines.
Star Charts online
There are several websites that provide simple starcharts. Some may require some setup (input your location, time zone) so that a more accurate chart can be generated.
These starcharts are often only good at certain hours on certain nights because the Earth is spinning on its axis and moving around the sun. But don't worry about that now. Notice the chart. The flat piece of paper (the chart) is supposed to represent the dome of the night sky (so some of the figures (patterns) near the edge of the circle will appear mushed on some of the charts). The circle's edge represents the horizon, the line between the sky and ground. And the center of the circle, though unmarked, represents the zenith, the point directly overhead. So the closer the patterns are to the center of the circle, the higher they are in the sky. If there is a pattern very close to the edge, then it is down low near the horizon and may not be visible because of trees or buildings. Now notice the directions are marked along the edge of the circle. Looks like East and West got printed backwards, but if you hold the chart overhead so that 'north' on the chart is north, then you'll see that the directions line up just fine.
So how to read the chart? Let's say that as you are holding the chart overhead, you happened to be facing south. If you bring the chart down, notice that 'South' is at the bottom of the circle. Patterns between the lower edge of the circle and the center are in the sky in front of you. Without rotating the chart move it back overhead, and you rotate under it -- the chart stays still but you turn underneath, say to the west. Now bring the chart down and you'll see that west is at bottom. Again, patterns along the lower edge of the circle are near the horizon in front of you. As you look at patterns closer to the center, you are looking higher in the sky. Now as you are facing west and looking at your chart, you see a pattern just above center, where in the sky is it? Well, it is past overhead, ie look overhead and then start leaning backwards to see the sky behind you! It would be easier to reorient (take the chart back to overhead, turn yourself under it, bring chart down in front) yourself to face east. Now that pattern is between the lower (eastern) edge/horizon and center (overhead) so you can look up high in the sky and see the pattern without breaking your neck!
A more permanent but still simple kind of starchart is a planisphere. Basically, you can adjust it for whenever you are observing. If you have a planisphere, first match up the time on one ring to the date on the second ring. Now the stars that are visible through the window are the ones visible in the sky. And this window, whether circular or oval in shape, is like the circular monthly starcharts from the magazines or internet. Once the date and time is setup, the planisphere works just like the simpler starchart. What about that little grommet thing the two pieces spin around? Go ahead and play with the planisphere. See how as you spin the window, different stars come into view. Pay close attention and notice that near one side, close to the grommet, some stars never really disappear or set. And that grommet is not at the center of the window, it's off to one side. The grommet is right at the North Celestial Pole and effectively 'hides' the North Star. Remember, the Earth's axis is pointing out into space and happens to be pointing at a star, so that as the earth spins, that point (the star) seems to sit still like the center of a CD while all of the other stars spin around it.
Okay, okay, reading a starchart or planisphere is one thing but how do the dots on the chart relate to the stars in the sky? Well, on the charts we usually represent brighter stars with bigger dots. And since these charts are meant to be used for just simple visual observing (no binoculars or telescopes), then really only the brightest stars that are visible to the eye alone are presented on the chart. In addition, on charts we connect the dots to help us visualize the patterns but of course those lines are not really up in the sky so we just have to imagine them. Let's orient ourselves to the north, ie stand so that you are facing north and the chart has north at bottom. You'll see that Polaris, the North Star (if you are using a planisphere, the grommet hides it but it is there!), is between the lower edge of the circle or window and the center.
When are you observing?
These descriptions will work for mid-northern latitudes. If you live much further north, then some of the northern constellations will appear higher in the sky and the southern ones closer to the southern horizon. If live further south, but still in the northen hemisphere, the constellations will be shifted with northern ones being closer to the northern horizon and southern ones appearing higher in the southern sky. If you live in the southern hemisphere, please check with your local astronomy club, observatory or planetarium to learn which constellations are visible and where in the sky they are.
Let's say you're out at about 9pm in January. Notice on the chart that the Big Dipper is standing on its handle and is to the right of the North Star. So in the sky, look to the northeast (right of north) and midway up in the sky. Once you see the Big Dipper, use the pointer stars in the bucket to pinpoint Polaris in the sky. In the opposite part of the sky (northwest), you should see a backwards crooked '3' or Cassiopeia. Now compare what you are seeing on the chart to what you are seeing in the sky.
It's winter, so let's look at the winter constellations. So turn around and face east, making sure the chart is oriented east (ie, east is at the bottom of the circle). Look at the center of the chart. See there's a big dot very close to center. Now look directly up, you should see a bright star overhead. That's Capella in the constellation Auriga. Turn and face south. About midway up in the sky is the constellation of Orion the Hunter. There are three stars of about equal brightness and evenly spaced that mark his belt. A bright orange-red star above marks one shoulder and a bright blue-white star below and right from the belt marks one of his knees. Hanging from the belt are three dim stars that mark his hunting knife or sword. Use a pair of binoculars to zoom in on the sword. Notice that the middle star is no longer one star and that it looks a little fuzzy. That's the Orion Nebula.
Looking back at Orion's belt, the three stars point down and left to a really bright star. That is Sirius, α Canis Major. Sirius is the brightest star in the night sky. What is the brightest star in the day sky? Up and left from Sirius is Procyon, the brightest star in Canis Minor. Up and slightly right is a pair of bright stars that is almost above Orion. The pair of stars is Pollux and Castor and they are in Gemini. Match up some of these constellations with the chart and then try to identify the Pleiades and Hyades, two open star clusters. Hint: Most people think they are looking at the Little Dipper when they see the Pleiades.
Let's say you're out at about 9pm in April. Notice on the chart that the Big Dipper is above the North Star and Little Dipper, so look high in the north to find the Big Dipper. Notice how the handle points off to the east at a sort of bright orange star. That is Arcturus and it is part of Bootes. To remember that name, note that the handle of the Big Dipper is not straight, it curves -- you 'arc' to Arcturus. Now if we could punch holes in the bottom of the Big Dipper, the water would leak out onto another constellation. You might want to turn and face south. Look on your chart (make sure south is at bottom) and find the constellation of Leo the Lion. There is one group of stars that looks like a backwards question mark (it might be labeled as 'the Sickle') followed by a triangle a little ways to the left. The question mark marks the head and mane of the lion. The triangle marks the back leg and tail. During the spring (2007), there will be an extra 'star' just ahead of Leo. That is the planet Saturn. Pay attention to the position of Saturn and you can watch as it slowly moves against the background stars over several weeks and months.
It's spring, so let's look at the spring constellations. So turn around and face east, making sure the chart is oriented east (ie, east is at the bottom of the circle). Find Arcturus again. Look around. Below Bootes, there is a circlet of stars. That's Corona Borealis the Northern Crown. And just below that is a squashed square that marks Hercules. If you look over toward the west, you might just be able to see Orion setting with Gemini the Twins standing above him.
Let's say you're out at about 9pm in July. Notice on the chart that to the left of the North Star is the Big Dipper. So in the sky, look to the northwest (left of north) and about halfway up in the sky. Once you see the Big Dipper, use the pointer stars in the bucket to pinpoint Polaris in the sky. Now compare what you are seeing on the chart to what you are seeing in the sky. Go back to the Big Dipper on the chart. Look at the handle and follow it. Sure looks like it is pointing at another big dot way to the left. Okay, look at the Big Dipper in the sky and follow the handle till you see a bright star off to the left. You might notice that you are looking far enough left where it might be easier to turn and just face west. That star you (hopefully) found is Arcturus. It's easy to remember because you follow the arc of the Big Dipper's handle -- you 'arc' to Arcturus. Arcturus is in Bootes, which is mainly a Spring constellation, meaning that it is easier to see in the evening sky in the east in the Spring. Here in the summer (9pm in July) it will be low in the west and setting, getting harder to see as it disappears in the evening twilight.
It's summer, so let's look at the summer constellations. So turn around and face east, making sure the chart is oriented east (ie, east is at the bottom of the circle). Look at the center of the chart. See there's a big dot below center. Now look up, you should see a bright star nearly overhead. That's Vega in the constellation Lyra. Match up some of the stars nearby and you have the Summer Triangle. The Summer Triangle is an asterism consisting of stars from three constellations - Vega from Lyra up high, Deneb from Cygnus in the northeast and Altair from Aquila towards the southeast. If you are in a very dark location, you might notice there is a strange strip of cloud or milky glow rising out of the south going through the Summer Triangle and disappearing in the northeast. If you look on your chart, you might even see some markings for that milky haze - it's the Milky Way -- our galaxy!
Looking towards the south are two fun constellations, but they are sometimes harder to see in light-polluted and hazy skies. The first is Scorpius. It looks like a capital letter "J" with the top bent over to the right. Some people see a giant fishhook. During 2007, there's an extra star in the area. It's the planet Jupiter. Watch it over several days and weeks and you'll be able to see how it moves against the background stars. A bit further east is Sagittarius. It's supposed to be a centaur, but most people see a teapot with the Milky Way appearing as steam coming out of the spout.
Let's say you're out at about 9pm in October. Notice on the chart that below the North Star is the Big Dipper right along the edge of the chart. So in the sky, look low in the north near the horizon. Oops, you might have trees or buildings blocking your view so seeing the Big Dipper might be tough. Instead, notice on the chart that there is a crooked '3' up and right (in the northeast) from the North Star. That's Cassiopeia.
Let's start in the west. On the chart, you should see a bright star about halfway up in the sky. That's Vega. If you look in the sky, Vega should be pretty obvious over in the west. If you look up from Vega, there will be another bright star Deneb. Towards the SW, at about the same level as Vega is Altair. Those three make up the Summer Triangle. They were way over in the east during the summer, but now that it's autumn, the sky has shifted. On your chart, find Deneb (it's in Cygnus the Swan), above it you'll see a big square or triangle, but if you are facing west, you'd have to bend over backwards to see it. So turn around and face east (and be sure to adjust the chart so east is at bottom) and now that square looks more like a diamond. It's called the Great Square of Pegasus. On the chart you'll see a double strand of stars hanging from 3rd base of the Great Square. Look in the sky at the Great Square, find the star at 3rd base and see how there are two strings of stars going down into the northeast? Those stars make up Andromeda. If you look high in the northeast you'll see that crooked '3' again. Look very carefully and you'll see how the top half of Cassiopeia is like an equilateral triangle and that it points towards Andromeda. Use some binoculars and scan the sky and you might find a fuzzy, the Andromeda Galaxy. Another way to find it is the start from 3rd base in the Great Square of Pegasus and go down to the second star in the brighter string. It's orange in color. Above that is a dim star (from the dimmer strand making up the constellation of Andromeda) and above that is another dimmer star. Note that this is where Cassiopeia is pointing. Use binoculars and right close to this dim star is the Andromeda Galaxy.
Asteroids and Comets
So that's how you find stars and constellations in the sky using a starchart. But what about a bright (naked eye, almost don't need a chart!) comet? Occasionally, you'll see in the magazines or on the internet, or even on these pages, a graphic showing a chunk of the sky as if you were facing the direction noted usually along the horizon line in the graphic. Well, face that direction and then match up the patterns as you learned above!
With most comets and asteroids that require binoculars or telescopes to be seen, a wide angle image is usually provided so that you can get your bearings, and then a zoomed in view that you would match to what you see in binoculars or a telescope, depending on how faint the asteroid or comet is.