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Earth and the Moon


The third planet from the Sun is the planet Earth. It is the largest terrestrial planet in the solar system. Earth has only one satellite, which is the Moon.

Earth rotates around the Sun on an axis of rotation that is tilted by 23.5 degrees to the axis of its orbit, causing Earth to have seasons. The tilt makes days longer and the midday Sun higher in the sky in the summer than winter. It is a common misconception that seasons are caused by the varying distance from Earth to the Sun; however the truth is that the distance only varies slightly.


How was the Moon formed?

A leading hypothesis suggests that the Moon was formed when an object about the side of Mars collided with the young Earth. The debris was eventually pulled together by Earth’s gravity to form the Moon.


What will be the temperature of the future Earth when the Sun becomes a white dwarf?

In approximately 4.5 billion years from now, the Sun will become a white dwarf and this change will have a drastic effect on the Earth’s temperature. The current temperature of the Earth is about 285 K (12 °C) but it will drop to 90 K (-183 °C) when the Sun becomes a white dwarf. Unfortunately, this is the temperature at which oxygen becomes liquid. Oxygen will rain down on Earth’s surface and the atmosphere will only be composed of nitrogen. There will still be air to breathe but it will not contain oxygen, which most living things require.


Solar time:

1 Earth day = 24 Earth hours

Sidereal day:

1 Earth day = 23 Earth hours 56 minutes

Orbital period:

1 Earth year = 365 Earth days


Click here for this planet's panel in the model

For an image of Earth's eastern hemisphere like the western hemisphere image seen on the panel, click here

Click here for images of Earth and the Moon at their right relative size and separation

Click here for the Wikipedia entry on Earth and the Moon