hulk

Find a tennis ball. Drop it. Then find a bowling ball, and drop that. Notice how they both fall towards the centre of the Earth, and at the same rate? That's gravity, and she's a harsh mistress.

The Earth is indeed round, as can be seen in photographic evidence here and due to the fact that if you climb a large hill, you cannot see yourself. The sun, if you'll care to look at it (with the proper protection, of course) is also round. As well as round, it's a big fiery ball of cosmic death, many times greater than the Earth. Next time there's a solar eclipse, note how the moon (which is small and close, and has been landed on) overshadows the sun. Hence, due to simple reality, the Sun's mass would be far greater than that of our little watery home.

To put it simply, Earth is falling towards the sun. As there's no air resistance or outside forces, and because we're not headed directly towards it (throw a ball horizontally, it still is pulled towards the ground in an arc) we continue falling.

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"'There's a tendency among the press to attribute the creation of a game to a single person,' says Warren Spector, creator of Thief and Deus Ex."
-- From an IGN game review.