Space-Physics What is Rotation? A rotation is a circular movement of an object around a centre of rotation. If three-dimensional objects like the earth, moon and other planets always rotate around an imaginary line, it is called a rotation axis. If the axis passes through the body’s centre of mass, the body is said to rotate upon itself or spin. What is Revolution? Revolution is often used as a synonym for rotation. However, in many fields like astronomy and its related subjects, revolution is referred to as an orbital revolution. It is used when one body moves around another, while rotation means moving around the axis. For example, the Moon revolves around the Earth, and the Earth revolves around the Sun. Rotation of the Earth Earth rotates on its axis from west to east, and the Sun and the Moon appear to move from east to west across the sky. The spinning of the Earth around its axis is called ‘rotation’. The axis has an angle of 23 1/2º and is perpendicular to the plane of Earth’s orbit. This means the Earth is tilted on its axis, and because of this tilt, the northern and southern hemispheres lean in a direction away from the Sun. The rotation of the Earth divides it into a lit-up half and a dark half, which gives rise to day and night. The direction of the Earth’s rotation depends on the direction of viewing. When viewed looking down from the North Pole, Earth spins counterclockwise. On the contrary, when viewed looking down from the south pole, the earth spins in the clockwise direction. Importance of Earth Rotation Some of the importance of the rotation of the Earth are listed below: The Earth’s rotation creates the diurnal cycle of lightness and darkness, temperature and humidity changes. The Earth’s rotation causes tides in the oceans and seas. Revolution of the Earth The movement of the Earth around the Sun in a fixed path is called a revolution. The Earth revolves from west to east, i.e., in the anticlockwise direction. The one revolution of the Earth around the Sun takes around one year or precisely 365.242 days. The revolution speed of the earth is 30 km/s-1. Importance of Revolution Revolution causes seasons. Revolution creates perihelion and aphelion. Perihelion occurs when the Earth is closest to the Sun. Aphelion occurs when the Earth is far from the Sun. Revolution has a direct influence on the varied length of day and night time. The duration of days and nights are the same at the equator. This is known as the equinox. The duration of days and nights vary in the Northern and Southern hemispheres. This is known as solstices. Change of day and night Earth rotating on its axis is the reason behind days and nights every 24 hours. If the earth does not rotate day/night cycle would be nonexistent. As the earth is tilted 22½° on its axis this causes the difference of longer and shorter days. When the difference is largest we call it solstice. When days and nights are equal we call it equinox. What is an equinox? An equinox is defined as the time when the sun crosses the celestial equator such that the length of the day and night are equal. Every year has two equinoxes. Also, the length of nights at latitudes L degree north and L degree south are equal. The Solstices The solstices are the positions of the Earth's orbit that mark the longest and shortest days of the year. The winter solstice in the Northern Hemisphere is the shortest day, after which daylight hours grow longer. The summer solstice in the Northern Hemisphere falls on the longest day, after which daylight hours become shorter. The solstices can also be named for the month in which they occur. 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. The Seasons The timing of the seasons is opposite for each hemisphere. This is because when the north pole is tilted toward the sun, the northern hemisphere faces the sun at a greater angle than the southern hemisphere. Therefore the northern hemisphere gets warmer. This represents the summer months for the northern hemisphere and winter for the southern hemisphere. As the Earth continues its orbit, the south pole eventually is tilted toward the sun, reversing the seasons in each hemisphere. Altitude & Latitude First, altitude describes how high a certain point is located above sea level. It mainly affects the climate in regions situated at high altitudes by making them cooler as the air pressure and temperature decreases. An example of a highaltitude region is the Himalayas, with an altitude of nearly 9000 meters, and fall in temperature from 0.2 to 1.2 degree Celsius every 100 meters. These regions are typically characterized by high amounts of precipitation, strong winds and low levels of oxygen due to the lower air pressure. Altitude does affect climate, but primarily the local climate of a specific location; it does not contribute to affecting the entire planet’s climate. This thus downplays its significance in contributing to the Earth’s climate. The further away a location is from the equator, the less sunlight it receives to heat the atmosphere because the sun’s rays are dispersed over a larger area of land as you move away from the equator due to the curvature of the Earth. As a result, places nearer to the equator such as the Sahara Desert tend to be hotter with a mean temperature of 30-40 degrees Celsius, as opposed to the polar regions with an average temperature of 0 to -40 degrees Celsius.
