star MapDraw a star map of the constellations that circle around the North Star and use it to note the changes in the sky from hour to hour.

What to do: To make your star map, copy the illustration below onto your circle of cardboard. Then tape the cellophane over your flashlight. (The red covering will prevent it from being too bright for you to see the stars.)

At 9 o’clock on a dry moonless night, take your star map and the flashlight outdoors. Turn the chart so that the month in which you are observing is on the top. Hold the chart above your head and look for the same pattern in the sky.

On another night, go out at 7 o’clock or at 10 o’clock and match the star map with the sky.

What happens: At 7 o’clock you have to turn the chart one month clockwise to match the sky. At 10 o’clock you have to turn it a half-month counterclockwise.

Why? The North Star remains at approximately the same place in the sky—far, far away, but directly above the North Pole. This is because the Earth’s axis points to it throughout the year. All the other stars and constellations, however, seem to wander around the North Star once a day, moving counterclockwise. As the Earth rotates, it looks as if the entire sky is rotating, although the stars do not change position relative to each other. Since one turn of the Earth takes only 23 hours and 56 minutes, a star seems to rise and set about four minutes earlier than the day before. This adds up to two hours (30 x 4 = 120 minutes) in a month and, of course, one hour in half a month.

What you will needCircle of cardboard

FlashlightRed cellophane and tape

If you are ever lost in a forest at night, you can use the sky to find your way. Face the North Star, which is the brightest star in the northern sky, and you are facing north. Look 180° across the sky to the horizon. That is south. East is 90° to the right and west is 90° to the left.

On a clear night, ask an adult to help you practice finding the North Star.

the sky as compass

164 Fruit of the Vine and Other Places

A constellation is a group of stars that long ago people named for heroes and gods and animals that they thought the patterns looked like. There are 88 constellations. We still use many of these names in Latin and in the English translation. And we still use the stars as a calendar and a direction finder.

The equator is the only place from which all 88 constellations can be seen during the course of a year. In other latitudes, you can see perhaps 60 at different times, and about 24 at any one time.

In the United States, Canada, the United Kingdom, and Europe, you can see the constellation of Leo, the Lion, with the bright star Regulus high up in the sky in the middle of April at about 9 p.m.

In August, as it gets dark, high in the southeast section of the sky you will see three bright stars—the Summer Triangle. Directly overhead are Vega, in the constellation Lyra, the Harp; Deneb of the constellation Cygnus, the Swan; the Altair of the constellation Aquila, the Eagle.

In the evening skies of October, just below the W-shaped constellation Cassiopeia, you will find four bright stars arranged in a square making up the body of an upside-down horse with wings, the constellation Pegasus, the flying horse.

In the Southern Hemisphere, the Southern Cross (the Crux) is the easiest constellation to recognize. You can see it in the evening skies of Miami and the Florida Keys in May and June, but its four stars are always visible below the equator. Looking south, observers in Australia, southern Africa, and South America can see the Crux just below the two bright stars Alpha and Beta Centauri. Some think it looks more like a kite than a cross.

Get a book from the library about stars and constellations and on a clear night, ask an adult to help you practice finding constellations in the sky.

some timetelling stars

Fruit of the Vine and Other Places 165

The following experiment will help your recycling efforts by giving you more room in the collecting bin.

What to do: Pour hot water into the bottle until it is about half-full and swish it around for about a minute. Then pour the water out and, quickly, put the cap on and twist it tightly.

What happens: The sides of the bottle suddenly collapse inward!

Why? The hot water heats the air inside the bottle and, with the cap left off, it fills to the brim with warm air. When the hot water is poured out and the cap is replaced, the air inside of the bottle quickly starts to cool. Since cooler air takes up less space than the same amount of warmer air, there’s now extra room in the bottle!

To fill that extra space, the sides of the bottle are pushed in by the force of the air pressure outside the bottle, which is constantly pressing in every direction.

What you will needPlastic 2-liter bottle

with capVery hot tap water

The Collapsing Bottle

12 Why Is There Air?

The Talking CoinYou may have heard somebody say that money talks, but until you do this experiment you have probably never actually seen it speak.

What to do: Put the quarter in the cup of water and place the empty bottle in the freezer for five minutes.

When the time is up, remove the bottle from the freezer and, immediately, cover the mouth of the bottle with the wet coin. (It is important to completely cover the bottle’s mouth with the coin.)

What happens: The quarter becomes a tongue for the bottle and begins to chatter at you.

Why? When the bottle was put into the freezer, the air molecules inside of it cooled and moved closer together. Since the air in the bottle then took up less space, it left room for extra air to flow in—so it did.

When the bottle was removed from the freezer, however, the air molecules inside of it began to warm up and spread out again. It’s a great example of, “There was enough room for everyone to sit comfortably in the car until we all put on coats and it was crowded.” Suddenly there was no room for the extra air molecules.

It is that “extra air” that is being pushed out of the bottle as the air warms that makes the coin move up and down as if it were talking.

What you will needPlastic 2-liter bottle

QuarterCup of water

FreezerKitchen timer or watch

Why Is There Air? 13

Can you turn a piece of wood into a whistle? Sure you can. It’s a great experiment, and fun, too.

What to do: Use the hammer and nail to make a hole in the narrow end of the stirrer or paddle. Put one end of the string through the hole and tie a tight knot. Now, make two or three holes in the wider end of the wood. You can put the holes all in a row, or make up your own pattern.

To hear your whistle-stick, go outside or find a large open area where you can swing the stick without breaking anything. Hold tightly onto the loose end of the string and whirl the paddle around in front of you or over your head.

What happens: You hear an unusual whistling sound over and over again.

Why? As you whirl the paddle around, the air passes through the holes in it at a higher speed than the air going around the paddle. When this happens, the paddle whistles.

What next: Different numbers and sizes of holes make different whistle sounds. You might want to make several whistle-sticks— some with only a few small holes to catch the air and others with larger or a lot of holes. Then you can compare the whistle sounds that each one makes.

What you will needWooden paint stirrer or

small paddleHammer

Large-size nailLong piece of string

The Wonderful Whistle-Stick

Be careful NOT to do this

experiment where people are passing by.