Chapter 1 Section 1 Earth in Space

What causes day and night? Earth’s rotation on its axis causes day and night

Why are there 24 hours in a day? It takes Earth about 24 hours to rotate once on its axis--each 24 hour cycle of day and night is called a day

How long does it take the Earth to travel around the sun? It takes about a year for the Earth to travel around the sun.

Why do the sun and moon seem to move each day? The sun and moon seem to move each day mainly because Earth is rotating on its axis.

How did the Egyptians develop one of the first calendars? Egyptian astronomers counted the number of days between each first appearance of the star Sirius which was 365 days.

Why is there a “leap year” on Earth? Because Earth’s orbit around the sun takes about 365 1/4 days. So we take 3 years of 365 days and a 4th year of 366 days to make up the difference.

Why is it warmer near the equator than near the poles? At the equator, sunlight hits the Earth’s surface directly.

Why does the Earth have seasons? Earth has seasons because its axis is tilted as it moves around the sun

Why does the Northern Hemisphere have summer in and why is it warmer in June? Because the north end of the axis is tilted toward the sun and the combination of direct rays from the sun and more hours of sunlight heats the surface more than any other time of year.

Why is the Southern Hemisphere colder in June? The combination of indirect rays and fewer hours of sunlight heats the Earth’s surface less and causes the Southern Hemisphere to be cold.

When does the winter solstice occur in the Northern Hemisphere? When the noon sun is overhead at 23.5 degrees South--it is the shortest day of the year

When does the winter solstice occur in the Southern Hemisphere? Around June 21st when the noon sun is overhead at 23.5 degrees North in the Northern Hemisphere.

Why do the solstices occur? Because of the tilt of the Earth’s axis. On noon two days of the year, the sun is overhead at either 23.5 degrees south or 23.5 degrees north.

When do equinoxes occur? Halfway between the solstices, the sun is directly overhead at the equator which means that there is an equal amount of day and night.

How do seasonal changes affect living things? During warmer days, plants can grow and animals and insects will feed more. During the fall and winter, plants will stop growing and animals will go into a dormant state or go to warmer climates.