Explore the fascinating science behind the changing length of days throughout the year, from the tilt of the Earth’s axis to the impact of the moon’s gravitational pull. Discover how this natural phenomenon leads to the seasonal variations in daylight, and how it relates to the upcoming switch to daylight saving time. Axial tilt and precession play key roles in this captivating natural cycle.
The Tilt That Randomizes Everything
The Earth is tilted along an axis of 23.44 degrees off the normal (this is relative to how it orbits the Sun). So, picture the Earth as a ball on a stick that goes around like you hold and spin a frisbee. Were the stick not tilted, daylight and darkness would be equal in length, all year long. This tilt ends up being the reason we have seasons and why daylight days differ in length.
The Northern Hemisphere is titled towards the Sun during summer months resulting in longer days and exposure to sunlight. When Southern Hemisphere feels winter (short days and less daylight) Six months later the opposite happens when Earth’s tilt makes it the other way around with the Southern Hemisphere tilted to face towards the sun. The summer solstice and winter solstice are when the top (or bottom) end of the stick is aimed directly at the sun, respectively shocking days of the year for your hemisphere.
Day and Night at equal lengths
The time in between the solstices is known as an equinox and that was the latest here, where the axis of Earth is “side-on” to the sun resulting in roughly even lengths of day and night. It then crossed the imaginary line in the sky that marks when the sun is directly over the equator.
In the Southern Hemisphere, the September equinox marks the first day of spring when days start getting longer. That’s when clocks move back an hour in some parts of the world (like Australia, where daylight savings time does not last year-round and we get An Extra Hour of Evening Sunlight). Of course, it’s crucial to understand that altering our clocks is not the adjustment of the total length of a day. All daylight saving does is change when that daylight happens, giving you more light at night-time instead of the morning.
A CELESTIAL DANCE THAT IS ALWAYS SHIFTING
All the time, Earth is shifting on its tilt and how its oriented. The tilt angle varies between 22.1 and 24.5 degrees over a period of 41,000 years in a series of tilted circles, or wobbles, produced by precession the axis itself makes. The incremental shift in the position of our planet over millennia that tamper with the length of our days, which are currently almost exactly 24 hours long.
In the long run, gravitational interactions between Earth and its satellite are to blame, as they gradually lengthen our days by about 2.3 milliseconds over the course of a century or so. A day was only 19 hours long on Earth billions of years ago! We lose an hour of sleep during the switch-over to daylight time but we can then also take comfort in the fact that our days are longer than ever — at least a little bit longer than they were for our ancient ancestors.
