What is the approximate ratio of hydrogen and helium in the sun’s core based on its current age?

Measuring which physical property is most likely to produce the most precise results when trying to identify a substance

Three cards with holes are arranged in a straight line. a light is shined through the first card’s hole and travels through all three cards. what does this tell you about light rays? a) that light is reflected b) that light is refractive c) that light travels in a straight line d) that light does not travel in a straight line

Which type of fossil does this image depict?