Why isn't there an eclipse every month?

Because the Moon's orbit is tilted. If the Moon circled Earth in exactly the same flat plane that Earth circles the Sun, there would be an eclipse at every new moon. Instead its orbit is tilted by about 5 degrees, so the Moon's shadow usually misses Earth. At new and full moon the Moon usually lies north or south of a straight line through Earth and the Sun, so it passes above or below the shadows.

The orbits cross at two points called nodes. A solar eclipse can occur only when a new moon happens close to one of them, and the same goes for a lunar eclipse at full moon. New moons fall near the nodes at two times of the year, about six months apart, which are called eclipse seasons. Because each eclipse season brings at least one, every year has at least two solar eclipses, and at most five.

The two kinds are different experiences. A solar eclipse happens when the Moon passes between Earth and the Sun, and its shadow touches only a small part of Earth. Total solar eclipses occur somewhere on Earth about every 18 months, but only once every 360 to 410 years at any given place. A lunar eclipse is the Moon passing through Earth's shadow, and anyone on the night side of Earth can see it, often for an hour or longer.

During a total lunar eclipse the Moon often turns orange or red. Sunlight reaching it first passes through Earth's atmosphere, which scatters out the blue and violet light.