The sun is surrounded by planets that may have moons orbiting them.
Our solar system includes Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto is considered a dwarf planet.
Planets have different numbers of moons. Gas giants have the most.
Astronomy is the study of the universe beyond Earth.
Ancient civilizations studied the movements of the sun and the moon.
Earth's Movement in Space
Earth rotates or spins on its axis causing night and day. The side facing the sun experiences day, while the side away experiences night.
Earth completes a rotation every 24 hours.
Earth's axis is tilted, causing seasons. The part tilted towards the sun is in summer; the part tilted away is in winter.
Earth revolves around the sun. A year is defined by the time it takes Earth to make a complete revolution: 365.25 days.
The path Earth follows in its revolution is called its orbit, which is shaped like an ellipse.
Moon's Movement
The moon rotates on its axis once every 27.3 Earth days.
The Moon revolves around the Earth in about 27.3 Earth days.
The same side of the moon always faces Earth.
The phases of the moon are caused by the relative positions of the moon, Earth, and Sun.
The moon reflects light from the sun, and half of the moon is always lit by the sun.
Phases of the Moon (Lunar Cycle)
The lunar cycle begins with the new moon, which is not visible.
Waxing Crescent: About one quarter of the moon is visible.
First Quarter: Half of the moon is visible.
Waxing Gibbous: Three quarters of the moon is visible.
Full Moon: The entire surface of the moon is reflecting sunlight.
Waning Gibbous: The part of the moon we observe decreases.
Third Quarter: Mirror image of the first quarter.
Waning Crescent: A sliver on the left side of an otherwise dark moon.
Eclipses
An eclipse occurs when the moon's shadow covers part of the earth or when the earth's shadow covers part of the moon.
Solar Eclipse: A new moon blocks the view of the sun.
A total solar eclipse occurs when the moon completely covers the sun's disk.
Lunar Eclipse: The Earth is directly between the moon and the sun.
A total lunar eclipse occurs when the Earth's shadow completely covers the moon, causing it to look red.
A partial lunar eclipse occurs when only a portion of the moon enters Earth's shadow.
Tides
Earth's tides are caused by the gravity of the moon and the sun.
High tides occur in areas with more pull from either the sun or the moon.
Low tides occur in areas with less pull from the sun or the moon.
Spring Tides: During full and new moons, the sun, Earth, and moon are almost in perfect alignment, creating very high tides.
Neap Tides: During the first and third quarter phases of the moon, the sun and the moon are at right angles, creating lower high tides and higher low tides.