how are we able to see planets that are 100’s of lightyears away? By continually increasing the magnification of a telescope? How do we know anything about the planets atmosphere if it’s that far away? For example, the Corot-7b, we are told it rains rocks there.
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The most common method is by watching the host star’s output for telltale signs of variation in it’s brightness and position. A star that wobbles a small fraction tells you that there is some other body’s gravity acting on it. This is done by watching a star’s spectral lines as they change because a star and it’s planet(s) will orbit a common center of mass. A star that moves away from you will have it’s spectral lines shift red, and then blue as it comes toward you.
Additionally if a star dims a small fraction on a periodic basis, then that means an orbital body has moved across it from our perspective.
The size and mass of a star is determined first by watching binary stars. If you determine the size of their orbits around each other and the period (speed) of their orbits, then you can calculate their respective mass as well. Once you know the mass of a pair of binary stars you can apply that knowledge to similar stars not in binary systems. (And the more binary systems you study, the larger the range of single stars you can size)
Once you know the size of the individual star, you can calculate the mass of the orbital body and it’s orbit by the parents star wobble and changes in luminosity.
What the planet is made up of can be seen in general terms from watching the transmission spectrum coming from the system, and the spectral lines will tell you what materials are present.
We’re not able to see them.
We see them block the light from their star.
Or we see their gravity tugging on their star.
We know about their atmosphere because when they block that star, some light pass through the atmosphere, which filters out some light but not others.
We don’t actually see them. When the plant passes in front of its star, it blocks some of the sunlight. We see the sunlight dim in a very predictable way. By doing some calculation we can figure out the size of the planet and how far it is from its star.
We can tell the chemistry of the atmosphere by looking at the light. By using a prism, we can tell what the Star is made of. And then, when the planet first starts to pass in front of the star some of this light passes through its atmosphere. By using a prism and comparing the changes in the light we can tell what the planets atmosphere is made of. Imagine looking at a flashlight at night, and then looking at it when there is smoke in front of it. It changes right?
A Prism is how we can see what something is made of
Simply put, you shine light through a prism and it reveals a spectrum of light waves. Based on the wave, you can determine the element present
ELI5 version:
You send 118 people into a muddy room, all with different shoes. No matter how far the muddy room is from you, you can tell who has been in the room because evereyone has different shoes, and there are different shoeprints in the room.
We cannot see them, we can see a spot of light of unknown size. That spot could get dimmer and brighter, we can measure that, and calculate the size of a planet passing it, or if it’s multiple planets, etc.
We can measure the star wobbling because it’s relative velocity to us changes and we see a color change from that, we can calculate if a planet is causing this.
And in some cases we can even measure light that came from a non-star and determine that it’s a planet. The plant is lit up by the star, and bounces off the planet to us, we get the light, but we can’t differentiate position of the planet from the star. What we can see is that the color of the planet is periodically added to the stars light and then not added, so we again see a change in color of the star, and we can determine that this is due to a planet, and the color of the planet (which we can use to tell if it has water on it or something)
We aren’t current capable of imaging planets *light years* away. The farthest planet scale objects we’ve imaged directly are within the Outer Kuiper Belt about 50 Astronomical Units (AU) away. 1 light year equals 63,241 AU. So the farthest planets we’ve directly imaged are on the order of 1/1,000th of a L.Y.
1 AU, in turn is roughly the Earth-Sun distance or 8.3 light-minutes.
We can detect extra-solar planets indirectly through several methods. The simplest is when a planet passes directly in front of a star, which slightly dims it in brightness, which can be measured with highly sensitive photometers. This can’t produce a clear image of the planet directly.
Increasing the magnification of a telescope by itself isn’t useful, because at a certain point [optical fringing effects become larger and stronger than the size of the object you want to image.](https://en.wikipedia.org/wiki/Angular_resolution) Thus, completely obscuring a planet in a haze optical noise around it’s parent star. This is an unavoidable physical consequence of the wave nature of light. This problem is made worse in the situation of trying to discern a very luminous object (a star) with a quite faint one near to it.
The size of these fringing effects are related to both the size of the primary mirror and the wavelength of light.
Increasing the effective size of the telescope apeture is the only real way around this problem. Simply using a larger mirror is one option.
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