What is the exosphere?
It refers to the outermost boundary of the Earth’s atmosphere, where it blends into the emptiness of space. By conversation, it is nominally taken to be at an altitude of 1000 km above the mean sea level.
The density of the atmosphere at the exosphere is one thousand trillionth that at the mean sea level.
What is geodesy?
Geodesy refers to the study of the shape and gravitational field of the Earth based upon data collected from artificial satellites.
What is meant by the geoidal shape of the Erath?
The geoidal shape of the Erath is the one established from data obtained from geodesy. The Earth is an oblate spheroid or a geoid with mean polar radius of 6356.779 km and equatorial radius of 6378.164 km. the Equator itself is basically elliptical and differs from the circular shape by a maximum of about 100 meters.
What is the tropical year?
The tropical year refers to the cycle in which the seasons repeat themselves. The length of the tropical year is 365.2422 mean solar days.
For comparison, the sidereal year is 365.2564 mean solar days and the calendar years is taken as 365 days and corrected by one extra day in every four years to avoid fractional days. Hence the calendar year is virtually the same as the topical year for practical purpose.