Answer to Question 1
Occasionally you can see the Moon darken and turn copper-red in a lunar eclipse. A lunar eclipse occurs at full moon when the Moon moves through the shadow of Earth. Because the Moon shines only by reflected sunlight, you see the Moon gradually darken as it enters the shadow. If you were on the Moon and in the umbra of Earth's shadow, you would see no portion of the Sun. If you moved into the penumbra, however, you would be in partial shadow and would see part of the Sun peeking around the edge of Earth so the sunlight would be dimmed but not extinguished. In a lunar eclipse, it is the Moon that is being hidden in the Earth's shadow and Earth that is in the way of the sunlight.
Answer to Question 2
From planet Earth, you can see a phenomenon that is not visible from most planets. It happens that the Sun is 400 times larger than our Moon and, on the average, 390 times farther away, so the Sun and Moon have nearly equal apparent diameters. Thus, the Moon is just about the right size to cover the bright disk of the Sun and cause a solar eclipse. In a solar eclipse, it is the Sun that is being hidden (eclipsed) and the Moon that is in the way.
Frequency distribution curve: interpatient variability in drug response.
Schematic diagram showing polyclonal response by B cells against linear epitopes.
The yellow, blue, and green sections of the Emergency Response Guidebook (ERG). The yellow section ...
J or U dose-response curve
Reflex Response
An example of a cell-mediated immune response targeting virus-infected cells.