Can anyone explain why does our earth rotate around the sun & spin in a slanting axis & not straight?
The Earth (and all the planets) formed by the collision and merging of hundreds of thousands of smaller objects (planetesimals) – as the last ones collided with the forming planet their momentum (energy of motion) were enough to tilt the rotational axis and alter the orbital plane. All the planets in our solar system have their axes tilted by some amount, and all the planets orbit the sun angled to some degree from the ecliptic.