A Little Bit About the Universe

NB 39 (lined paper) In your notes, draw a representation of the Earth, Moon and Sun showing how they are arranged relative to each other. If you are not sure, just do the best you can. You can use about half the page.

1 astronomical unit An astronomical unit is the average distance between the Earth and the sun or 149,597,870,700m or 93 million miles. 1 astronomical unit

Seasons are caused by the tilt of the Earth’s axis, NOT by the distance from the Sun. Sumer occurs in the Northern hemisphere because the Earth is at a point in its orbit where the North Pole is tilted toward the Sun. Winter occurs when Earth is in its opposite position, where the North Pole is tilted away from the Sun. Notice that the seasons in the Northern hemisphere are opposite the seasons in the southern hemisphere. This is because when the North Pole is tilted toward the Sun, the South has to be tilted away from the Sun.

The phases of the moon are caused by the changing position of the moon relative to the Earth and the Sun. in this diagram, the Sun is off to the right so the right sides of the Earth and moon are lit up. Look at each moon position. Depending on where the moon is, it will look different to someone standing on the Earth. When the moon is between the Earth and the Sun, we cannot see the side of the moon that is lit. Look at the moon position “first quarter”. To someone on Earth, it would look like half of the moon is lit. A full moon is when the Earth is between the moon and Sun, but does not block the Sun’s light. To us, it looks like the entire moon is lit.

The Sun is a star. It is the ONLY star in the Solar System. Stars are very, very hot balls of gases and plasma. The constant nuclear reactions within stars release heat and light. Stars are the ONLY objects in the universe that give off their own light.

The sun with its family of planets goes around the center of the galaxy at 150 miles per second, completing an orbit in 225 million years. This interval is called a cosmic year. The solar system is inclined relative to the plane of the galaxy. Sun and orbits exaggerated for clarity.

The bright spots in the background of the galaxy are not individual stars, but other galaxies, which are clusters of billions of stars.

Distances across galaxies and between galaxies are much, much greater than distances between planets within the solar system. Those distances are measured in units called light-years. One light-year is the distance light can travel in one year. One light year = 9,460,730,472,580,800 m =5.88 trillion miles = 63,241 AU (astronomical units)