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What is the brightest star (by absolute magnitude) that we can see by naked eye?
Accepted answer
5 votes

Mu Sagittarii is a star system, not a single star. If that can be included, then Eta Carinae should be included, and it has an absolute magnitude of -12.0. It's a star system about 7,500 light-years ...

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Is it possible to use Hubble Telescope to observe Earth in the past?
4 votes

Not without some hypothetical faster-than-light travel. Hubble is seeing distant galaxies as they were in the past because they're so far away that the light from those galaxies takes a very long ...

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Why are radio telescopes shaped so differently than optical telescopes?
3 votes

Radio telescopes are shaped differently primarily because we can't see microwaves or radio waves. Optical telescopes are designed so that there is a focal point where you can look and see the image. ...

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