Spring is the season after winter and before summer. Days become longer and weather gets warmer in the temperate zone because the Earth tilts relative to its orbital plane around the Sun. In many parts of the world it rains for hours. This helps the plants grow and flowers bloom. Often people with hay fever suffer more, because some plant pollens are allergens. Many animals have their breeding seasons in spring. At the start of spring, people suffering from seasonal affective disorder will feel better. The vernal equinox in springtime makes days and nights equally long in the temperate zone. Holidays celebrated in spring include Passover and Easter.