How does this happen? Long ago, people believed many weird things about the Sun and how it traveled across the sky. The ancient Greeks believed that the Sun rode across the sky in a chariot drawn by four white horses driven by the god Heleius! These days, we know that the Sun appears to move across the sky because the Earth rotates on its axis.
So how does the turning of the Earth lead to the Sun's motion across the sky? It is easy to see this if you shine a bright light on the side of a globe in a darkened room. In order to understand the motion of the sun and Earth they must imagine a different point of reference. This can make ideas in this area very challenging for students to grasp. The views held by students about the shape of the Earth are varied and often unique to the individual. Even though students can often articulate that the Earth is a sphere, upon further investigation they often believe in fact that the Earth is how they perceive it, flat.
Some children view the Earth as round or circular as opposed to spherical see diagram 1 below. Another common view is of the Earth as flat and that it and the air form a sphere see diagram 2 below.
Students can often represent the Earth as a sphere or circle on the plane of the paper but they still perceive the person on the top of the sphere as the upright person see diagram 3 below.
These views are also evident in and related to the focus idea Forces without contact. The Earth is one of several planets that orbit the sun, and the moon orbits the Earth. The Earth is essentially a sphere and the sun is a nearby star which is an unimaginably large ball of gas that radiates light and heat as products of nuclear reactions.
For example, the June solstice is the point in the Earth's orbit where the North Pole faces the sun. In the Northern Hemisphere, the June solstice is the longest day of the year. In the Southern Hemisphere, the June solstice is the shortest day of the year.
Your place on the Earth relative to the equator also affects the number of daylight hours you get in a solar day. For example, during summer in the Northern Hemisphere, daylight hours increase the farther north you go; at this time, the Arctic gets very little nighttime darkness.
In the winter, daytime is shorter the farther north you go. The seasonal changes in daylight hours are small near the equator and more extreme close to the poles.
Serm Murmson is a writer, thinker, musician and many other things. He has a bachelor's degree in anthropology from the University of Chicago. Mercury's day and night cycle is more complex. Mercury rotates one-and-a-half times during each orbit around the Sun. Because of this, Mercury's day — from sunrise to sunrise — is Earth days long.
The larger planets spin much faster. Jupiter rotates once every 10 hours, Saturn spins once every 11 hours, and Neptune completes a rotation in 16 hours. Pluto, at the farthest reaches of our solar system, spins on its axis once every 6. Pluto is so distant from the center of our solar system that our Sun would look like a very bright star in its sky!
Why does Earth's day length change during the year? Every location on Earth experiences an average of 12 hours of light per day but the actual number of hours of daylight on any particular day of the year varies from place to place. Locations around Earth's equator only receive about 12 hours of light each day. In contrast, the north pole receives 24 hours of daylight for a few months in the summer and total darkness for months in the winter.
These two annual times of light and dark are separated by a long sunrise and a long sunset. Earth rotates on its axis; this causes us to experience day and night.
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