CHAPTER 1.1 – EARTH IN SPACE

I. HOW EARTH MOVES Definition of Astronomy: The study of the moon, stars, and other objects in space. Definition of Astronomy: The study of the moon, stars, and other objects in space. The Earth move in space in two ways: The Earth move in space in two ways: 1) it rotates on its axis once every 24 hours and1) it rotates on its axis once every 24 hours and 2) it makes one revolution around the sun once every 365 days.2) it makes one revolution around the sun once every 365 days.

A. ROTATION Definition of Axis: the imaginary line that passes through the Earth’s center to the North and South poles. Definition of Axis: the imaginary line that passes through the Earth’s center to the North and South poles. - Definition of Rotation: spinning of the Earth on its axis - Definition of Rotation: spinning of the Earth on its axis - The Earth’s rotation causes day and night to appear. - The Earth’s rotation causes day and night to appear.

The rotation is in an eastward direction. Hence, it appears as if the sun rises in the East and sets in the West. The rotation is in an eastward direction. Hence, it appears as if the sun rises in the East and sets in the West. - It takes a full 24 hours for the Earth to make one rotation on its axis. - It takes a full 24 hours for the Earth to make one rotation on its axis. - When it is daylight on one side of the Earth, it is nighttime on the other side of the Earth. - When it is daylight on one side of the Earth, it is nighttime on the other side of the Earth.

Earth Rotating Eastward on its Axis

B. REVOLUTION As the Earth rotates on its axis, it is also revolving around the sun as well in its orbit. As the Earth rotates on its axis, it is also revolving around the sun as well in its orbit. Definition of Revolution: the movement of one object around another object. Definition of Revolution: the movement of one object around another object. One complete revolution around the sun is called a year. One complete revolution around the sun is called a year.

The Earth follows a path or orbit around the sun while making its revolution. The orbit is the shape of an ellipse or a slightly elongated circle. The Earth follows a path or orbit around the sun while making its revolution. The orbit is the shape of an ellipse or a slightly elongated circle.

C. CALENDARS Definition of Calendar: a system of organizing time that defines the beginning, length, and division of a year. Definition of Calendar: a system of organizing time that defines the beginning, length, and division of a year. The calendar is based on the Earth’s revolution around the sun. The calendar is based on the Earth’s revolution around the sun. The Egyptians were one of the first people to create a calendar based upon the first appearance of the star Sirius in the sky. It took 365 days for Sirius to appear. The Egyptians were one of the first people to create a calendar based upon the first appearance of the star Sirius in the sky. It took 365 days for Sirius to appear.

To divide the year into smaller parts was usually based upon the moon cycles. The time from one full moon to another full moon was 29.5 days. This was equal to a year of 354 days. To divide the year into smaller parts was usually based upon the moon cycles. The time from one full moon to another full moon was 29.5 days. This was equal to a year of 354 days. The Romans used the Egyptian calendar but found that the Earth revolves around the sun days. To keep everything even, the Romans added the ‘leap year’. Every four years, February is given an extra day – the 29th day. The Romans used the Egyptian calendar but found that the Earth revolves around the sun days. To keep everything even, the Romans added the ‘leap year’. Every four years, February is given an extra day – the 29th day. The Roman calendar was off by 11 minutes a year. In 1582, Pope Gregory XIII dropped 10 days from the calendar to even the days out. This is still the calendar we use today. The Roman calendar was off by 11 minutes a year. In 1582, Pope Gregory XIII dropped 10 days from the calendar to even the days out. This is still the calendar we use today.

II. THE SEASONS ON EARTH Most places on Earth have four distinct seasons: spring, summer, fall, and winter. Most places on Earth have four distinct seasons: spring, summer, fall, and winter.

A. HOW SUNLIGHT HITS EARTH The sunlight hits the Earth most directly at the equator and then spread out its light from there. The sunlight hits the Earth most directly at the equator and then spread out its light from there. That is why the warmest places on the Earth are located on and near the equator. That is why the warmest places on the Earth are located on and near the equator.

B. EARTH’S TILTED AXIS The Earth has seasons because its axis is tilted as it revolves around the sun. The Earth has seasons because its axis is tilted as it revolves around the sun. The Earth is always tilted at an angle of 23.5 degrees on its axis from vertical. The Earth is always tilted at an angle of 23.5 degrees on its axis from vertical. As the Earth revolves around the sun, the north end of the axis is pointed away from the sun for part of the year and pointed toward the sun for part of the year. As the Earth revolves around the sun, the north end of the axis is pointed away from the sun for part of the year and pointed toward the sun for part of the year.

The change of seasons is caused by the Earth’s position in its orbit as it revolves around the sun. It is not caused by the Earth changing its distance from the sun. The change of seasons is caused by the Earth’s position in its orbit as it revolves around the sun. It is not caused by the Earth changing its distance from the sun.

C. EARTH IN JUNE The north end of the Earth’s axis is titled toward the sun. The north end of the Earth’s axis is titled toward the sun. In the Northern Hemisphere, there are more hours of daylight than night. Also, there are more direct sun rays which make the Northern Hemisphere very warm. In the Northern Hemisphere, there are more hours of daylight than night. Also, there are more direct sun rays which make the Northern Hemisphere very warm. - All of this is the opposite for those areas in the Southern Hemisphere. - All of this is the opposite for those areas in the Southern Hemisphere.

D. EARTH IN DECEMBER In December, the Southern Hemisphere receives more direct sunlight. In December, the Southern Hemisphere receives more direct sunlight. As a result, it is warmer and there are more hours of daylight than night. As a result, it is warmer and there are more hours of daylight than night. This is the opposite for the Northern Hemisphere. This is the opposite for the Northern Hemisphere.

E. SOLSTICES - Definition of Solstice: the two days of the year when the sun is farthest north or south of the equator. - Definition of Solstice: the two days of the year when the sun is farthest north or south of the equator. In the Northern Hemisphere, the sun is the farthest north of the equator around June 21. This is known as the summer solstice. This is also the longest day of sunlight in a year. In the Northern Hemisphere, the sun is the farthest north of the equator around June 21. This is known as the summer solstice. This is also the longest day of sunlight in a year. - Around December 21, the sun is the farthest south of the equator. This is known as the winter solstice. This is the shortest day of sunlight in a year. - Around December 21, the sun is the farthest south of the equator. This is known as the winter solstice. This is the shortest day of sunlight in a year.

F. EQUINOXES Halfway between each solstice, there are equinoxes. These occur twice year when the sun is directly above the equator. Halfway between each solstice, there are equinoxes. These occur twice year when the sun is directly above the equator. Equinox means “equal night”. During an equinox, there are 12 hours of daylight and 12 hours of nighttime. Equinox means “equal night”. During an equinox, there are 12 hours of daylight and 12 hours of nighttime. The Vernal Equinox is around March 21 to start spring in the Northern Hemisphere. The Vernal Equinox is around March 21 to start spring in the Northern Hemisphere. The Autumnal Equinox is around September 22 to start fall in the Northern Hemisphere. The Autumnal Equinox is around September 22 to start fall in the Northern Hemisphere.