And how do we know their sizes and distances?
In: Physics
1) stars are sun’s because definition. Our Sun is a star. A big ball of hydrogen gas that’s undergoing fusion
2) when we observe a star that has a periodic dimming, that’s a sign there’s a planet that’s orbiting the star at the plane that intersects our line of sight with the star.
3) by observation and using math. The earth moves about our Sun and every 6 months, the position of the Earth is farthest away from its position 6 months ago. By measuring the difference in location in the view and knowing the distance of Earth orbit about the sun, you can calculate angle difference and the distance using trigonometry.
If a planet passes in front of a star it causes the light from the star to bend slightly around it. This process is called lensing, and it makes the star look like it’s wobbling slightly every time the planet moves between it and us. By measuring how much the light bends you can work out how large the intervening object is. Distance is measured using parallax; how much the position of a star in the sky varies during the Earth’s orbit around our sun. The more a star seems to move, the nearer it is.
The size of stars is measured by looking at their brightness (how much light they emit) as well as their composition which we can find by analysing the different energy levels (called frequencies) in the emitted light. The relationship between all these things tell us what stage of life the star is in and how much stuff is in it, and hence how big it is.
The main way of detecting planets is to watch the star over time. When the star pulls planets towards it, the planets also pull the star. Because the planets weigh so little compared to the sun it’s not a huge effect. But it’s there, and minute, cyclical wiggle is a good way of detecting exoplanets.
As for size and distance, that’s a little more technical. But in general distance can be understood by its brightness and the redshift of the star. If you need a more powerful telescope to see it, and if it’s more redshifted, it’s likely farther away.
Astronomers don’t just look at objects. They measure their energy outputs, their spectrographic data, their distance and movement, etc. Everything about stars lines up with observations we’ve made about our own sun.
So either those stars are very similar structures to our sun, or someone is playing a *fantastic* trick on us.
Stars are literally defined as suns. A star is a stellar object, a ball of plasma that emits light as a result of nuclear fusion.
Not all stars have planets. The ones where we can determine that they do, we can by seeing that planet pass in front of them (i.e. between us and the star) we can see that by the tiny change in luminosity as the planet passes in front of the star. This is why we could only detect gas giants like Jupiter for the longest time, because these things are big and caused a relatively large change in luminosity. With better and better detectors, we’re now capable of seeing even the rather small change an earth-like planet passing in front of a star causes.
By the speed such planets pass in front of the star, we can determine the distance the planet has from its star. The closer a planet is to a star, the faster it orbits around the star and the faster it passes in front of it.
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