![]() ![]() Seasons are caused by the fact that the Earth is tilted on its axis by 23.5°. This fact may sound counter to what we know about seasons in the Northern Hemisphere, but actually, the difference is not significant in terms of climate and is NOT the reason why we have seasons. The aphelion, or the point at which the Earth is about 1.6 million miles farther away from the sun, occurs during the first week of July. During the first week in January, the Earth is about 1.6 million miles closer to the sun. This means that the distance between the Earth and Sun, which is 93 million miles on average, varies throughout the year. We all know that the Earth makes a complete revolution around the sun once every 365 days, following an orbit that is elliptical in shape. ![]() Naval Observatory. An alternative text link is found here. In the Northern Hemisphere, it occurs when the sun is directly over the Tropic of Capricorn, which is located at 23.5° south of the equator and runs through Australia, Chile, southern Brazil, and northern South Africa.įor a complete listing of the dates of the winter and summer solstices and spring and fall equinoxes through 2025, check out this site from the U.S. The winter solstice marks the shortest day and longest night of the year. For every place north of the Tropic of Cancer, the sun is at its highest point in the sky and this is the longest day of the year. The summer solstice occurs when the sun is directly over the Tropic of Cancer, which is located at 23.5° latitude North and runs through Mexico, the Bahamas, Egypt, Saudi Arabia, India, and southern China. Therefore, on the day of the summer solstice, the sun appears at its highest elevation with a noontime position that changes very little for several days before and after the summer solstice. The summer solstice occurs at the moment the earth's tilt toward/from the sun is at a maximum. Therefore, on the equinox and for several days before and after the equinox, the length of day will range from about 12 hours and six and one-half minutes at the equator, to 12 hours and 8 minutes at 30 degrees latitude, to 12 hours and 16 minutes at 60 degrees latitude. Additionally, the days become a little longer at the higher latitudes (those at a distance from the equator) because it takes the sun longer to rise and set. The "nearly" equal hours of day and night are due to refraction of sunlight or a bending of the light's rays that causes the sun to appear above the horizon when the actual position of the sun is below the horizon. At the equator, the sun is directly overhead at noon on these two equinoxes. The word equinox is derived from two Latin words - aequus (equal) and nox (night). These events are referred to as Equinoxes. Therefore, the larger a planet’s orbit, the longer the planet takes to complete it.There are only two times of the year when the Earth's axis is tilted neither toward nor away from the sun, resulting in a "nearly" equal amount of daylight and darkness at all latitudes. Kepler’s Third Law Compares the Motion of Objects in Orbits of Different SizesĪ planet farther from the Sun not only has a longer path than a closer planet, but it also travels slower, since the Sun’s gravitational pull on it is weaker. The farther it is from the Sun, the weaker the Sun’s gravitational pull, and the slower it moves in its orbit. The closer a planet is to the Sun, the stronger the Sun’s gravitational pull on it, and the faster the planet moves. Kepler’s Second Law Describes the Way an Object’s Speed Varies along Its OrbitĪ planet’s orbital speed changes, depending on how far it is from the Sun. The distance from one focus to any point on the ellipse and then back to the second focus is always the same. A focus is one of the two internal points that help determine the shape of an ellipse. The Sun (or the center of the planet) occupies one focus of the ellipse. The orbit of a planet around the Sun (or of a satellite around a planet) is not a perfect circle. Kepler’s First Law Describes the Shape of an Orbit ![]()
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