Spring gets its official start Tuesday in the Northern Hemisphere. This year's vernal equinox arrives on Tuesday. But what does that mean? The Earth's axis is tilted at an angle as it travels around the sun. On the equinox, the Earth's orbit lines up so both hemispheres get the same amount of sunlight. This means day and night last about the same amount of time, and marks the start of a new season. Solstices are the opposite. They happen when the Earth is tilted most strongly toward or away from the sun, so day and night are very different lengths.
