I love astronomy stuff, not an expert at all, but have always been so fascinated by it. I am totally baffled by how we seem to claim that we can approximate how long the sun has been around. Like the margin of error for a number like that is crazy…. totally incomprehensible to me. Say that we are 25% off, that means we are over 1 billion years off. So, how do people confidently claim that the sun is 4.6 billion years, rather than 3 billion or 10 billion?
In: 1140
Astronomers can see stars similar to ours in various stages of life. By comparing stuff like size, luminosity, and frequency distribution of the light emitted from these stars to our own, they can know by the of our sun what stage of its life it is in and thus the approximate age of it.
Several ways helped narrow it down.
The suns gravity and the way it affects the planets orbits allows scientists to calculate its mass.
Rock samples from the earth, moon and asteroids have been dated. Assuming we formed around the same time from the same material.
The suns spectrum shows us its metal composition.
Here is an overview of methods for dating the sun, including how age limits were set:
http://solar-center.stanford.edu/FAQ/Qage.html#:~:text=Dating%20the%20Sun%20is%20an,dating%20of%20the%20oldest%20meteorites.
Our Sun and all of the objects in its solar system were formed at roughly the same time in astronomical terms (a few hundred thousand to a few millions of years). So all of the matter is about the same age.
Moreover, the matter clumps differently at different distances from the Sun’s gravitational center. Objects closest to the Sun (such Mercury, Venus, and Earth) are quite dense, while the objects farther out are much less dense (such as Jupiter, Saturn, Neptune, and Uranus). Even though these objects have different amounts of elements (with the heaviest elements being found in greater proportion closer to the sun), all of those elements are about the same age.
So what is their age? In the case of elements that have a radioactive half-life, we can calculate how much decay has taken place. Isotopes of these elements have different rates of decay. For instance, carbon-14 decays quite rapidly (thousands of years) so it doesn’t surprise that most of this has all decayed. Carbon-12, in constrast, is stable and it doesn’t surprise us that it’s all still here. How much of each isotope is left can be used to calculate how long it’s been here.
One important element to look at is lead (Pb). Lead is formed when uranium decays, so the ratio of Pb-207 to Pb-206 changes because U-235 decays to Pb-207 and U-238 decays to Pb-206. By comparing these, we can figure out how they have been hanging around, and the number comes to about 4.54 billion years.
We can check our math by comparing really old stuff like meteorites. We know how old they are by how much of each kind of lead isotope they have. The oldest ones seem to be about 4.568 billion years old if we do that. So this might be the higher possible age of the solar system and the Sun.
We can also check our math with rocks from the Moon, which hasn’t had the same biological and geological action as rocks on Earth. If we calculate based on those rocks, we get an age 4.51 billion years, which is probably the lower possible age of the solar system.
That’s really a pretty tight range on astronomical scales, so we can be quite confident the actual age is within that narrow range. However, we can do even better than that.
Remember we compared the proportion of isotopes U-238 to U-235 and assumed that this proportion was about the same through the solar system. However, in places where curium (which has a very short half-life) we find a little more U-235 than we expected. That’s because curium also decays to U-235. This helps us be even more confident of our estimation of the age of the Sun. We sometimes want to account for the Sun being formed slightly earlier than the planets, so we add a little extra and use a age of 4.6 billion years.
Oversimplified TL;DR: We can calculate how old the Sun is quite precisely by looking at how old the different rocks are.
The solar system formed 4.5 billion years ago. We know this from radiometric dating of the oldest rocks. We assume the sun ignited at about the same time.
We don’t even know when (or how) the pyramids were built, which was likely only a few thousand years ago. So to answer your question, educated guesses by scientists (but they could be very wrong and truly do not know for sure).
Dr becky on youtube does a video about the sun. And helps explains some things. https://youtu.be/IMogF5W7Pbw
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I understand this is eli5 but what youre asking is covered in high school physics and you keep doubting the responses youre getting. nuclear and astrophysics allows scientists to accurately date stellar objects.
well, ill tell you…. i dont know. I think its weird how the Sun is 4.6 and the earth is 4.5 and then boom earths moon came less than a few hundred millions years later , and a milions not much when dealing with billions …. my dumb ass thought for years that the moon didnt come along until the earth was already 2 billion years old or something
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