Earth and Solar System – Ibex Aviation Academy

Solar System

Kepler propounded three laws regarding planetary motion
Kepler’s first law states that the orbit of each planet is an ellipse with the Sun at one of the foci
Kepler’s second law states that the line joining the planet to the Sun sweeps equal areas in equal time
Kepler’s third law states that the square of the sidereal period of a planet is proportional to the cube of its mean distance from the Sun

Kepler’s first law states, earth revolves around the sun in an elliptical orbit
Elliptical orbit implies earth will come close to sun and move away periodically
Perihelion is the point on ellipse where earth is closest to sun
Perihelion falls on 4 January each year
Earth is 91.5 million statute miles from the sun at its perihelion

Elliptical orbit implies earth will come close to sun and move away periodically
Aphelion is the point on ellipse where earth is farthest from sun
Aphelion falls on 3 July each year
Earth is 94.6 million statute miles from the sun at its aphelion

Speed of movement of earth is fastest near perihelion and slowest near the aphelion
Kepler’s second law implies the radius vector sweeps equal areas in equal time
Therefore, the speed of movement of earth has to reduce when earth is farther away from the sun

Plane of the ecliptic is the orbital plane of all major planets including earth around the sun
Plane of equinoctial can be also be called as the equatorial plane or the plane of equator
Spin axis of earth is tilted by 23 ½ degrees to perpendicular
Therefore, the planes of Ecliptic and Equinoctial make an angle of 23 ½ degrees
This is called Obliquity of the ecliptic and is the main reason for changing seasons

Declination of the Sun is the angle subtended between plane of equinoctial to plane of sun’s position
Declination is the celestial equivalent of latitude for any celestial body like sun
In other words, it is the angle that the sun is above or below the equator
Sun’s declination varies from 23.5 degrees north to 23.5 degrees south over a one year period

Sun is at its maximum northerly or southerly declination at its solstices
Solstice literally translated means sun standing still
Maximum difference in duration of day and night is seen during solstices
Minimum day to day variation of sun’s position happens at solstices
Winter solstice is seen on 21 Jan every year when the Sun’s declination is at 23 ½ south
Summer solstice is seen on 22 Jun each year when the Sun’s declination is 23 ½ north

Equinox means equal night that occurs when the sun is overhead the equator
Duration of days and night are equal during equinoxes
Declination of the sun is zero meaning sun at equinoctial plane
Maximum day to day variation of sun’s position happens at equinoxes
Vernal equinox happens on 21 March each year during transit of the sun from southern to northern hemisphere
Autumnal equinox is seen on 23 December every year during transit of the sun from northern to southern hemisphere

Daylight time as well as seasons are dependent on the Declination of the sun and Latitude of observer
Hours of day light are caused due to annual change of declination due to the tilt of earth’s spin axis
Whole days of continuous daylight and darkness are found at high latitudes
Sun may not rise or set above 66 ½ deg North and South latitudes
Minimum daily variation in daylight is seen near solstices
Maximum daily variation of daylight is seen equinoxes