Today most scientists favor the capture theory of the Moon’s origin, since it would explain why the Moon still orbits in the ecliptic plane, as do other planets.

Venus can appear as a crescent through the telescope.

The most important greenhouse effect gas in our atmosphere is __________ .

Greenhouse gases in our atmosphere trap just enough heat to keep the earth’s oceans liquid.

The planet which shows us the widest range of surface temperatures between day and night is __________ .

While __________ gas is the main atmospheric component of both Mars and Venus, its density means it plays a far larger role in heating Venus.

The deepest depression found on the surface of Mars is the

A telescope design that uses a lens and no mirrors is a refractor.

The simplest telescope design is the prime focus reflector.

Grazing incidence optics are critical to focusing __________ .