Why are the days getting shorter/longer?
Quick Answer: Days get shorter or longer because the Earth tilts on its axis as it orbits the Sun. This tilt changes how much sunlight each part of the planet receives, making daylight hours grow or shrink through the year.
The Earth’s axis is tilted about 23.5 degrees. This tilt means different parts of Earth lean toward or away from the Sun at different times. When your location tilts toward the Sun, you get longer days. When it tilts away, days get shorter.
This cycle causes the seasons and the changing day length. Near the equinoxes, day and night are nearly equal. Around the solstices, one hemisphere enjoys its longest day while the other has its shortest.