Know the constellations to build your map of the heavens

Diagram courtesy of Marty Scott

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Finding the constellations

Let’s make our first step in learning the position of the constellations. Use the diagram and the instructions to see if you can find them the next clear night.

Finding the Walla Walla circumpolar constellations:

Find the Big Dipper, which is in the constellation Ursa Major.

Using the two stars on the side of the bowl opposite the handle as a pointer, follow a line connecting these stars and leading from the bottom of the dipper to a lone star about halfway up from the horizon. This is the star Polaris; it is the end of the handle of the Little Dipper in the constellation Ursa Minor.

Starting in the middle of the Big Dipper, move to Polaris and continue in a straight line about the same distance to find a W. This is the constellation Cassiopeia.

The top of the W faces the constellation Cepheus, which looks like a stick house with a squarish base and a triangular roof.

Follow the pointer stars in the bowl of the Big Dipper about halfway to Polaris. Follow the dim stars around the little dipper and then turn away from Cepheus. Use the chart to find the constellation Draco.

Stargazing apps

For iOS: Star Walk

For Android: Star Chart

On any given clear night, you can see more than 1,000 stars.

From the beginning of time people have been grouping the stars into images and objects. Six-thousand-year-old cuneiform texts from the Euphrates River Valley tell of the lion, the bull, and the scorpion.

By the fifth century B.C., these groupings had been associated with myths by the Greek astronomer Eratosthenes in his book Catasterismi. Today we call these groupings stellar constellations.

Many of our modern constellations can be found in the Almagest, a book written by the Roman astronomer Ptolemy in Alexandria about A.D. 150.

The Almagest listed 48 constellations divided into three groups — 21 Northern, 12 Zodiacal and 15 Southern constellations. These were the accepted constellations for more than 1,000 years.

But from Alexandria, Ptolemy could not see the extreme southern stars because they never rose above the horizon. It therefore fell to others to add these constellations.

From the 16th to the 19th centuries, astronomers added and deleted constellations to complete their own catalogs of the sky. There was no common set of constellations.

In 1919 a group of astronomers from around the world formed the International Astronomical Union.

One of their firsts tasks was to create an “official” list of the constellations. The list they approved in 1922, containing 88 constellations, is the one we still use today.

Six years later they improved the list by adding boundaries to each constellation. The entire sky was now divided into 88 regions, with each region bearing the name of the constellation in that region. Any object in the sky, such as a star, is in one and only one region.

If you know where the constellations are, you can use them to find stars and other celestial objects. For example, the star Polaris is in the constellation Ursa Minor; Saturn is currently in the constellation Virgo — planets move from one region to another.

Therefore, one of the first things a stargazer should do is to start learning the locations of the constellations.

From a given location on Earth you cannot see all the constellations. For example, the farther north you are, the fewer southern constellations you can see. Location is therefore one determining factor of what constellations you can see.

The other factor is time of year. We can only see the stars at night when our side of the Earth is opposite the Sun. As the Earth orbits the Sun during the year, our view of the night stars changes, resulting in winter, spring, summer, and fall sets of constellations.

You will never see Orion in the summer, for example, because it is a winter constellation.

As the Earth rotates during the night, the constellations appear to move from east to west. But constellations that are above the Earth’s poles, both north and south, will appear to circle a point in the sky above the pole.

They will not set; they are visible all night every night of the year. These are called circumpolar constellations, and their number depends on your latitude; higher latitudes have more.

In Walla Walla there are five circumpolar constellations: Ursa Major (Big Bear), Ursa Minor (Little Bear), Cassiopeia (Queen of Ethiopia), Cepheus (King of Ethiopia), and Draco (Dragon).

Marty Scott is the astronomy instructor at Walla Walla University, and also builds telescopes and works with computer simulations. He can be reached at marty.scott@wallawalla.edu.

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