FCUHOMESCHOOLING ASTRONOMY CLASS
Learning Constellations
Learning the constellations is fun and easy. Moreover, knowledge of the night sky can provide hours ofenjoyment whenever you look up on a clear night. In the exercises below, you will learn how to use a star chart to identify the brighter stars and constellations that are visible at a given time of year.
Once you know the basic pattern of the constellations, you can then test your knowledge of them on a simulated sky in a series of four seasonal quizzes. In these quizzes, you will be asked to point out a constellation or star. Then, by clicking on the sky map where you think the constellation or star is, you will get the name of the constellation and a picture of it.
The exercises consist of three parts:
-How to use a Star Chart
-What the Night Sky looks like at Different Times of Year.
-Constellation Quizzes to test your recognition of constellations and
bright stars.
One caution:
These exercises do not show the planets or Moon. In looking at the real sky, it will help you to know where the brighter planets are so that you don't confuse them with stars. Check with your instructor, a planetarium program, or website to learn where the planets are on a given night. Eventually, you will recognize the planets in the sky from their appearance in constellations whose pattern you know
http://www.astro.umass.edu/
USING A STAR CHART
A star chart is a map of the night sky. With it, you can identify and
locate constellations and stars. A typical star chart (see below) shows
the relative positions of the stars and their brightness.
Chart of Winter Sky
To use a star chart to identify stars and constellations, you must
first
find the one appropriate for the time of year you are observing. Notice
that
the chart above is labeled "Winter." Picking the chart appropriate for
the season is important because as the Earth orbits the Sun, the Sun's
glare hides many of the stars.
FINDING THE PROPER CHART
In the back of the text book and on the inside front cover, you will find four charts, one for
each season of the year. (These seasons are labeled for the northern hemisphere). Thus, if
you want to learn the winter constellations, pick the winter chart, which is sketched in very rough outline above.
Because each night the stars move across the sky, rising in the east and
setting
in the west, you also need to consider the time of night. The charts we
will discuss below show the sky as it appears about 8 PM local time.
Once you have found the appropriate chart, you need to match it to the
sky. First, you should match direction. That is, if you are looking
south, you need to orient the chart so it shows the southern sky.
You will notice that the chart has labels north, south, etc. If you hold the chart so that south
is at the bottom, it shows the sky approximately as you would see it looking south, with the
center of the chart being approximately overhead. Referring to the chart sketched above, it
therefore shows the sky as you would see it looking south at about 8 PM in December.
(Keep in mind that this is only a sketch. Most of the stars are omitted.)
With the correct chart in hand you are now ready to match it to the night sky.
Two steps are helpful here. First, look for star patterns. Second notice
the relative brightness of stars in the pattern. The chart shows the
relative brightness of the stars by their size. Dim stars are shown as tiny
dots. Bright stars are shown by big dots. With that in mind, let's try to
identify Orion.
Notice that the chart shows that Orion has two bright stars on either
side of a dimmer line of three stars, which form Orion's belt.
Exercise #1
Use the sketch of the chart to find the constellations Orion and Taurus on
the actual chart in the book.
Exercise #2
What direction should you look to see the constellation Orion? What
direction should you look to see the constellation Cassiopeia?
LEARNING THE CONSTELLATIONS
To learn the constellations you need to learn not only their shapes but
also their relative sizes. Let's start with shapes. Find Cassiopeia on
the Winter Chart and notice its shape.... roughly a "W." (You can
remember this if you think of the "W" as the chair or throne on which
Cassiopeia, the Queen, sits). The sketch below shows the outline of the
constellation Cassiopeia.
The Constellation Cassiopeia
Exercise #3.
Find Orion the Hunter. He is usually depicted as a standing
figure with raised arms, one arm holding his shield, the other his club
to defend himself against the bull, Taurus. Orion thus has a roughly
"H" shape.
The Constellation Orion
Exercise #4.
Find Taurus on the Winter chart. Taurus the Bull is easy to find
if you think of his bright red eye (the star Aldebaran) and his horns
that form a "V."
You have seen that Orion, Taurus, and Cassiopeia each have a different
shapes (H, V, and W). You can also see that they differ in size. For
example, Orion is much larger than Cassiopeia. But how much of the real
sky does Orion cover? For example, could you cover it with your thumb
at arms length?
DESCRIBING SIZES OF CONSTELLATIONS
When we talk about the size of a constellation, we are referring to how big it looks to us. That is, how much of the sky does it span. Technically, we measure size on the sky by angular measure.
Astronomers traditionally use angles to measure sizes and distances on
the sky. To understand how, imagine two sticks joined at one end with a
nut and bolt so they can be spread apart. If you hold these sticks up
to your eye and sight along one to a given star and along the other to
another star and then measure with a protractor the angle between the
sticks, you will have found the angular distance between the two stars.
The figure below shows how that angle can be found for the size of the "bowl" in the star grouping we call the Big Dipper. The figure shows that this distance is about 20 degrees.
The Angular size of the Big Dipper
The above technical definition works well, but for ordinary sky
watching, it is helpful to start with a simpler scheme using just your
hand at arms length. If you hold your arm out straight and spread your
fingers, the angle from tip of thumb
to tip of little finger is about 20 degrees for most people, as the
sketch below shows.
Thus, your spread hand will span slightly more of the sky than the width of the Big Dipper's
bowl. Similarly, if you make a fist, then the angle between the knuckles at arm's length is
about 5 degrees. These are of course only approximate, but will help you estimate relative size and distance in the sky.
SOURCE:
http://www.astro.umass.edu
