# Eli5 The sun converts about 4 million metric tons of its mass into energy every second. Does this mean that it’s mass reduces significantly over the span of, say, ten years?

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4 million tons a second is a lot of mass to be lost given enough time. Considering the fact that the sun is over four billion years old, does this mean that the sun was physically bigger when it formed?

What about a couple of hundred years ago? Or a few years ago? Could the suns loss of mass imply that it’s shrinking over time?

In: Physics

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What is “significant” when talking about the reducing mass of the sun? On one hand 4 million tons a second seems significant to us, but the sun is really massive.

Over the course of a year it loses 174 trillion tons of mass. But over the next 5 billion years it will lose 0.034% of its total mass. So yes, it is technically becoming less massive over time, but not to any amount significant to its scale.

Actually, counter to your intuition, it’s growing. The sun is mostly only held together by gravity, so as it’s mass decreases, it’s density decreases, and the sun grows. While we have a hard time visualizing 4 million tons, for an object the size of the sun, that is so little as to hardly be worth mentioning. The sun is on the order of 1.989*10^30 kg, so it would take roughly 1.577*10^13 years for the sun to completely consume itself, given a constant rate of consumption. The best estimate of the age of the entire universe is 1.38*10^10 years, roughly 1/1000th of our time frame. As such, for the sun to significantly change in size requires an incredibly long time scale.
Disclaimer: I am a sleep deprived, drunk mechanical engineering student doing some VERY back-of-napkin calculations, for the purposed of conceptualization, so my numbers may be a couple orders of magnitude out of whack, but the point still stands.

4 million tons is alot.
But the sun weighs 1.989 x 10^27 tonnes.
or
1.9 thousand million billion billion tonnes.
So it’s got a lot of mass to lose.

With questions like this I like to write it out.

The sun loses 4,000,000,000kg of mass per second.

Or 174,000,000,000,000,000kg a year.

But it has a mass of 1,989,000,000,000,000,000,000,000,000,000kg