This week’s question was asked by a third grader.
QUESTION: Why do stars form pictures in the night sky?
ANSWER: Stars patterns in the night sky are referred to as constellations. There are 88 officially recognized constellations. Some constellations are only visible in the northern hemisphere, while others are only visible in the southern hemisphere.
In our part of Wisconsin, we can see about 53 constellations in the course of a year. We can’t see about 35 constellations unless we go to the southern hemisphere.
The earliest official record of constellations was made more than 3,000 years ago by the Babylonians, an ancient civilization based in what is now modern-day Iraq. Half of the 88 constellations in the night sky were named by Ptolemy (100 AD-170 AD), who lived in Alexandria at the mouth of the Nile River. He wrote in Greek but held Roman citizenship. In his book, Almagest, the constellations and the names he gave them exist to this day and are the basis for all the 88 official constellations listed by the International Astronomical Union.
The most famous constellation is the Big Dipper or the Big Bear (Ursa Major) located high in the north sky. In England, the Big Dipper is known as the Plow (Plough). The Big Dipper is visible year-round in the Northern Hemisphere, so it is known as a circumpolar constellation.
You can use the Big Dipper as a guide to find six or seven other constellations. For example, the two end stars, nicknamed the Pointer Sisters, point to the Pole Star or Polaris, in the handle of the Little Dipper.
Orion is the highlight of the winter sky in our area of Wisconsin. The Orion constellation contains the bright super giant stars Betelgeuse and Rigel. Overhead and to the west you’ll find the Andromeda constellation which contains the Andromeda Galaxy, the most distant object that can be viewed with the naked eye. It is humbling to realize that the light we see tonight from the Andromeda Galaxy left that celestial body over 2.5 million years ago, for Andromeda is 2.5 million light years distant.
Star formations change over the centuries. The stars are moving and changing positions in the sky, which can make them look less like what they were originally named and more like something completely different. The constellation Cassiopeia originally looked like a W, but today it appears to be a squiggly line. Astronomers believe that the Big Dipper will look like the number 5 in 50,000 years.
One way to learn the night sky is with a star chart. It gives a snapshot of what the night sky will look like at any one time and at any one location. These maps may seem rather baffling and confusing at first but they’re actually very simple to use.
You will notice that east and west seem to be reversed. The chart is designed to hold above your head. The outer edge of the chart indicates the horizon, so the further the stars are from the edge the higher they will be in the sky. The center of the chart shows the stars and constellations that will be directly overhead.
There are several useful apps for cell phones and tablets, and they cost just a few bucks. Star Walk is very good, showing stars, constellations, comets, planets, satellites, and the ISS (International Space Station). Star Walk is GPS based, so you just hold your cell phone or tablet up to the night sky, and it shows on the screen exactly what is in the sky. It’s an amazing tool for learning what’s up there!
A worthwhile Internet site is heavens-above.com. You put in your latitude and longitude and the program will generate a screen showing your current night sky. It will also produce a table showing when and where to look for the International Space Station and the Hubble Telescope. The coordinates of 43.98 N 90.52 W are good enough for Tomah and Sparta.
Over the past decade or two, the ISS has added many modules and solar panels. It’s fairly large and reflects a lot of light from the Sun. The ISS is visible in the early morning before sunrise and in the evening right after sunset. As it traverses the sky from west to east, the sun is not visible for us on the ground, but the sun’s rays strike the ISS and reflect down to a viewer on Earth. It’s worth looking for.
Send questions and comments to: firstname.lastname@example.org.
Larry Scheckel is a retired Tomah High School physics teacher.