Calculate the fraction of the total emitted sunlight that reaches Earth. (Hint: Imagine a sphere around the Sun the size of Earth’s orbit (area = 4πa2), then calculate the fraction of that area taken up by the disk of Earth (area = πr2planet). Earth's reflectivity is 29%).

The two stars in a certain binary star system move in circular orbits. the first star, alpha, has an orbital speed of 36 km/s. the second star, beta, has an orbital speed of 12 km/s. the orbital period is 137 d. a) what is the mass of the star alpha? b) what is the mass of the star beta?

What is the role of lenses in microscopy?

Debris produced by mining is called