The Sun can help you tell time with shadows. A sundial, or shadow clock, has something that sticks up from a flat surface, casting a shadow in the sunlight. During the day, the shadow moves. By watching the shadows, you can mark off hours and keep track of the time.
Why can't you tell time with a sundial at night?
Make a Sundial
1.Take a notebook-sized piece of cardboard.
2. Stick a 4-Inch pencil Into a small ball of clay.
3. Press the clay near one end of the cardboard as shown in the picture.
4. Take your cardboard outside early on a sunny morning. Lay it on a flat surface away from any possible shade.
5. Use a compass, an instrument for finding directions, to make sure the side of cardboard with the pencil Is to the north.
6. Every hour trace the pencil's shadow on the cardboard. Write the time next to the point.
7. At day's end, connect the points of the shadows Into a curve.
8. What time was the line the shortest? Why?_
The shadows moved on your sundial. When we look in the sky, the Sun seems to move. We say that the Sun rises in the east and the Sun sets, or goes down, in the west. Sometimes this can be confusing. It seems the Sun moves, and we stand still. Actually, the Sun stays in one place and Earth rotates like a top. It takes 24 hours for Earth to rotate one time. We call this amount of time one day.
The Sun also helps us to tell time In another way. The time it takes for a planet like our Earth to travel around the Sun is called a year. It takes 365 and 1 days for Earth to travel around the Sun once. The extra 1 days add up to one full day every four years. That year is called a leap year
How many days are In a leap year?
A light-year is the distance that light travels In one year. Light travels at 186,282 miles per second. That's equal to about seven and a half times around the Earth in one second! In one year, light travels almost 6 trillion miles—or 6.000,000.000 miles!
Astronomers measure distances in space by light-years because most things in space are so faraway. Proximo Centauri, the nearest star to Earth after the Sun. is more than four light-years away.
I. Which is bigger, a billion or a trillion?_
2. What is an astronomer?
3. What instruments do astronomers use to study space?
1. Why is it important for scientists to continue investigating space?_
5. Why is the Sun important to life on Earth?
6. What does the expression "Today's computers are light-years ahead of the first computers" mean?_
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