But not by much; the sun changes its diameter too, and shrinks and expands over time - just not by a whole lot relative to its overall size (the earth's orbit is changing slowly too, and so is the moon's).
Because all of them are in a state of elastic equilibrium, which depends on a number of influences, which change over time - if our star and the planets bound to it passes through a region of the galaxy that has significant background levels of hydrogen and other gases, it gets bigger (OMG Edit: the star, not the solar system), by absorbing some of the gas, and dust, or anything else in it's gravitational path. But not by very much.
Because all of them are in a state of elastic equilibrium, which depends on a number of influences, which change over time - if our star and the planets bound to it passes through a region of the galaxy that has significant background levels of hydrogen and other gases, it gets bigger (OMG Edit: the star, not the solar system), by absorbing some of the gas, and dust, or anything else in it's gravitational path. But not by very much.
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