• Question: is the sun geting bigger or smaller

    Asked by jally to Nazim, Karen on 19 Mar 2012.
    • Photo: Karen Masters

      Karen Masters answered on 19 Mar 2012:

      Ah you did ask it off line. Great. 🙂 The answer is both, depending on what you mean as I said in the chat.

      So the Sun is very slowly loosing mass though solar wind etc, and also every time it converts two hydrogen atoms to helium it looses a tiny bit of mass (which is what creates the huge amount of energy). And it is burning hydrogen in this way very very fast – fortunately it has enough of it to keep doing it for another 5 billion years!

      But it is also very slowly expanding (growing in radius). We can tell this because it’s very slowly getting brighter – and the brightness of a star depends on it’s temperature (brighter=hotter) and it’s radius (brighter=larger). It’s doing this because it’s loosing mass – so the gravity pulling down on the surface of the Sun to keep it there is very slowly getting weaker. Not much will change until the Sun runs out of hydrogen though, so it’ll just keep very slowly expanding for the next 5 billion years.

    • Photo: Nazim Bharmal

      Nazim Bharmal answered on 19 Mar 2012:

      At the minute, it is slowly expanding as the nuclear reactions in the core use up the hydrogen (converting it to helium). But when that hydrogen runs out, it will dramatically grow bigger for a few million years before finally shrinking into a much smaller star called a white dwarf where it will stay for billions of years longer before finally cooling down and fading away.

      But nothing drastic will happen for about 4.5 billion years.