galileo galilei proposed elliptical orbit of the planets around sun.
galileo galilei proposed elliptical orbit of the planets around sun.
who proposed elliptical orbit of the planets around sun?
galileo galilei
until the work of johannes kepler (1571–1630), a german astronomer, it was believed, or assumed, that planets traveled in circular orbits around the sun. when kepler studied danish astronomer tycho brahe's careful observations of mars's position in the sky on many nights, kepler realized that mars's orbit could not be a circle. after considerable analysis, kepler discovered that mars's orbit was an ellipse, with the sun occupying one of the elliptical orbit's two focal points. this, in turn, led to kepler's discovery that all planets orbit the sun in elliptical orbits, with the sun at one of the two focal points. this became the first of kepler's three laws of planetary motion.
orbit of mars
for interplanetary travel, a spacecraft can use its engines to leave earth's orbit. it is not explicitly necessary as the initial boost given by the rocket, gravity slingshot, monopropellant/bipropellent attitude control propulsion system are enough for the exploration of the solar system (see new horizons). once it has done so, it must somehow make its way to its destination. current interplanetary spacecraft do this with a series of short-term trajectory adjustments. in between these adjustments, the spacecraft simply moves along its trajectory with a constant velocity. the most fuel-efficient means to move from one circular orbit to another is with a hohmann transfer orbit: the spacecraft begins in a roughly circular orbit around the sun. a short period of thrust in the direction of motion accelerates or decelerates the spacecraft into an elliptical orbit around the sun which is tangential to its previous orbit and also to the orbit of its destination. the spacecraft falls freely along this elliptical orbit until it reaches its destination, where another short period of thrust accelerates or decelerates it to match the orbit of its destination. special methods such as aerobraking or aerocapture are sometimes used for this final orbital adjustment.
spacecraft propulsion