Galileo's telescope brought about revolutionary changes in astronomy. A comparable leap in our ability to observe the universe took place as a result of the Hubble Space Telescope. The space telescope can see stars and galaxies whose brightness is of the faintest objects now observable using ground-based telescopes. Use the fact that the brightness of a point source, such as a star, varies inversely as the square of its distance from an observer to show that the space telescope can see about seven times farther than a ground-based telescope.

The planet Mercury is closer to the Sun than the Earth is, so it can sometimes come between Earth and Sun. That's called a transit. A transit is like a failed solar eclipse: In a solar eclipse, the Moon gets between Earth and Sun and blocks all sunlight. In a transit, Mercury blocks only a small fraction of the Sun's light because Mercury isn't close enough to us to completely block our view of the Sun.     We want to calculate by how much the Sun will be dimmed when such a transit occurs, because that's important to know for satellites which are powered by solar panels (shown hovering around the Earth in the image above). Without Mercury in the way, the radiation intensity that hits the top of the Earth's atmosphere from the Sun is 1,360.8 W/m2  (W stands for Watt, measuring energy transferred per second).  The fraction of this intensity that is blocked by Mercury during a transit is equal to the ratio between the cross-sectional area of Mercury (as seen from Earth) and the…

The radius of the earth is 6400 Km and the height of a person is 1.7m, how high can you stand to see how far the horizon is from you (going back in degrees after the arc)

You record the spectrum of a distant star using a telescope on the ground on Earth. Upon analysing the spectrum, you discover absorption lines spaced at intervals typical of oxygen atoms. Which of the following are possible interpretations of this evidence? Select all that apply. The width of the spectral lines gives the diameter of the star The star is likely orbited by habitable planets with breathable atmospheres. The height of the spectral lines above the star's general blackbody spectral curve tells us how much oxygen is in the star The atmosphere of Earth contains oxygen The red or blueshift of the set of lines can tell us the speed of the star's motion toward or away from us