Throughout the course of the year, most places on Earth goes through four noticeable seasons: summer, autumn (fall), winter and spring, each lasting for about 3 months. The seasons experienced by the northern and southern hemisphere always differ by six months – when it is summer in the northern hemisphere, it is winter in the southern hemisphere, and so on. Seasons are a direct consequence of the Earth’s tilted rotation axis, which makes an angle of about 23.5 degrees to a line drawn perpendicular to the plane of the ecliptic. The direction of the Earth’s axis stays nearly fixed throughout one orbit, so that at different parts of the orbit one hemisphere ‘leans’ towards the Sun (summer), while the other ‘leans’ away (winter). Six months later, the Earth is leaning in the opposite direction.
The Earth’s tilt causes the Southern Hemisphere (SH) to lean towards the Sun during SH summer. Meanwhile, it is winter in the Northern Hemisphere (NH) which leans away from the Sun. Six months later, the situation is reversed. For locations north or south of the equator, the main feature accompanying each season is a change in temperature caused by the varying amount of sunlight that falls on each hemisphere of the Earth throughout its annual orbit. The hemisphere tilted towards the Sun will experience longer hours of sunlight, and more direct sunlight.
left: Winter in the Northern Hemisphere – the amount of sunlight falling on the Northern Hemisphere is much less than than… right: …the amount of sunlight falling on the Southern Hemisphere during Southern Hemisphere summer. As the Sun is higher in the sky during summer, the sunlight reaching the surface is more concentrated. In winter, the Sun is lower in the sky, and sunlight is spread out over a larger area. During spring and autumn, both hemispheres receive about the same amount of sunlight.
At the equator, the temperature variation is much smaller throughout the year, and it is common to consider just two seasons: dry and wet (or monsoon). For observers right at the north pole and the south pole, there are only two seasons – an almost six-month long winter night followed by an almost six-month long summer day! Within the Arctic circle and the Antarctic Circle (latitudes 66.5 degrees north and south), there will be at least one polar day (24 hours of continuous daylight, sometime called the ‘midnight sun’) and one polar night (24 continuous hours of darkness). The date of the start of the seasons is often chosen to start on the dates of the solstices (summer and winter) and equinoxes (autumn and spring). Alternatively, the start of a new season may be associated with the first day of the month (December, March, June and September) in which a solstice or equinox occurs. The Earth’s changing distance from the Sun due to the Earth’s elliptical orbit is sometimes thought to cause the seasons. This is incorrect! The Earth’s distance from the Sun varies by about 3% from closest (perihelion distance = 147.09 million km) to furthest approach (aphelion distance = 152.10 million km). This small change in distance cannot account for the temperature differences between summer and winter, and cannot explain how it can be winter in one hemisphere and summer in the other hemisphere. Many people believe that Earth is closer to the Sun in the summer and that is why it is hotter. And, likewise, they think Earth is farthest from the Sun in the winter. Although this idea makes sense, it is incorrect. It is true that Earth's orbit is not a perfect circle. It is a bit lop-sided. During part of the year, Earth is closer to the Sun than at other times. However, in the Northern Hemisphere, we are having winter when Earth is closest to the Sun and summer when it is farthest away! Compared with how far away the Sun is, this change in Earth's distance throughout the year does not make much difference to our weather. There is a different reason for Earth's seasons. Earth's axis is an imaginary pole going right through the center of Earth from "top" to "bottom." Earth spins around this pole, making one complete turn each day. That is why we have day and night, and why every part of Earth's surface gets some of each. Earth has seasons because its axis doesn't stand up straight. But what caused Earth to tilt?Long, long ago, when Earth was young, it is thought that something big hit Earth and knocked it off-kilter. So instead of rotating with its axis straight up and down, it leans over a bit. By the way, that big thing that hit Earth is called Theia. It also blasted a big hole in the surface. That big hit sent a huge amount of dust and rubble into orbit. Most scientists think that that rubble, in time, became our Moon. As Earth orbits the Sun, its tilted axis always points in the same direction. So, throughout the year, different parts of Earth get the Sun’s direct rays. Sometimes it is the North Pole tilting toward the Sun (around June) and sometimes it is the South Pole tilting toward the Sun (around December). It is summer in June in the Northern Hemisphere because the Sun's rays hit that part of Earth more directly than at any other time of the year. It is winter in December in the Northern Hemisphere, because that is when it is the South Pole's turn to be tilted toward the Sun. Earth's lopsided orbitEarth's perihelion (point closest to Sun) = 91,400,000 miles from Sun Earth's aphelion (point farthest from Sun) = 94,500,000 miles from Sun While that is a difference of over 3 million miles, relative to the entire distance, it isn’t much. And, believe it or not, aphelion (when Earth is farthest from the Sun) occurs in July, and perihelion (when we are closest) occurs in January. For those of us who live in the Northern Hemisphere where it's summer in July and winter in January, that seems backwards, doesn't it? That just goes to prove that Earth's distance from the Sun is not the cause of the seasons. Related Resources for Educators Seasons (Educator Guide to go with Seasons Spotlite video)
Get the answer to your homework problem. Try Numerade free for 7 days
Question 10 1 pts Select the feature(s) of planet Earth that are responsible for causing the seasons in temperate regions. Earth is tilted on it' s rotational axis and this remains fixed over the course of the year at 23.59 The region of the Earth most directly facing (he sun receives more solar energy per Iand area than those areas not directly facing the sun Thc Earth has an symmetrical orbit around the sun which brings the Earth closer to (he sun for part of the vear The Earth s tilt on its rotational Jxis shifts over the course of the vear Because of Earth's tilt; one hemisphere is closer to the sun during part ot the vear while the other hemispherc Is furthcr away from the sun
20 Questions | Total Attempts: 283
|
Which of the following best describes the tilt of the Earth when it is summer in the hemisphere?
Postagens relacionadas
direito autoral © 2024 estudarpara Inc.
