Lunar eclipses can only happen when the Moon is opposite the Sun in the sky, a monthly occurrence we know as a full Moon. But lunar eclipses do not occur every month because the Moon's orbit is tilted five degrees from Earth's orbit around the Sun. Without the tilt, lunar eclipses would occur every month.
When a biologist counts the number of zebras in a population each year and notices an increase in the zebra population, this would be an example "of <span>observation"</span>
