2007/11/26

Introduction

Just like maps of the Earth help us find our way from place to place, star charts or sky maps help astronomers find objects in the night sky.  This article is the first in a series of four on learning to read a simple star chart and finding neat objects in the night sky.  Two star charts are included, one for parts 1 & 2, the other for parts 3 & 4.

Part 1 – Reading The Star Chart

The sky map was obtained free on the internet from www.heavens-above.com. It is set for Crowell, TX.  Anyone can visit the web site and select their city or town from the database.  The website will generate a star chart that you can then print out.  This map is good in September between 8-9pm, October between 7-8pm and early November, just after sunset.

The outer circle represents the horizon, where Earth and sky meet.  Notice the four directions N (north), E (east), S (south), and W (west) indicated around the outer edge.  To read the map, hold it over your head.  Or, face the direction you want to look and turn the map so that direction is at the bottom.  The stars on the map should match those over the horizon you are facing.  For example, face north and hold N on the map at the bottom, toward your feet.  The stars above the northern horizon in the sky should match those above the northern horizon on the map.

Part 2 – Planets and the Moon

Notice the location of the moon and any visible planets on the sky map.  See if you can find these objects in the nighttime sky.  What direction(s) do you have to face to see these objects?  Use binoculars or a small telescope to see the objects – how does your view differ?

Throughout each month, watch as the moon moves from constellation (star picture) to constellation (star picture).  As the year progresses, notice how the planets move against the background stars from month to month.

Map for Part 1 and 2

Part 3 – Stars and Constellations

You’ll notice dots on the map – these represent the stars.  The bigger dots mean brighter stars; smaller dots represent fainter stars.  Constellations are indicated by lines connecting these “dots.”  So constellations can be thought of as “Dot-to-dot” pictures.  These pictures are thousands of years old, and represent all kinds of animals, people, and objects that ancient humans saw in their patterns.  An easy star picture, or constellation, to begin with is the Big Dipper or Ursa Major.

The name Ursa Major means “big bear.”  You can find the Big Dipper on this map low in northwest, close to the horizon.  Notice the curved handle and the square bowl.  To find the bear, extend the dipper’s bowl to include the two stars in front of it – this is the body.  Notice the bear’s “nose” as the faint star forming a triangle off the end of the body.  Follow the curve of stars forming the front and back leg of the bear down to the NW horizon.  The handle is seen as the bear’s stretched-out tail, or sometimes seen as three hunters following the bear.

Part 4 – Star Hopping

Connect a line between the stars in the front end of the Big Dipper’s bowl, and go straight out the top.  You’ll come to a fainter star, all by itself – Polaris, North Star.  Polaris is special because it marks the direction north.  It is directly above the Earth’s north pole and never rises and never sets.  It is used in navigation to help explorers, sailors and pilots find the directions.

Polaris marks the tail end of the Little Dipper, or Ursa Minor, the “little bear.”   Follow the curved line of stars nearby for the handle of the Little Dipper.  The box at the end is the bowl of the Little Dipper.  You can imagine the body of the little bear is the whole bowl while the handle is its stretched-out tail.

Use the Big Dipper to find other objects.  Follow the curve of the handle – go diagonally across the bowl and out – go straight out the top of the bowl – what do you find in each of these directions?

Map for Part 3 and 4