Our lives literally revolve around cycles: series of events that are repeated regularly in the same order. There are hundreds of different types of cycles in our world and in the universe. Some are natural, such as the change of the seasons, annual animal migrations or the circadian rhythms that govern our sleep patterns. Others are human-produced, like growing and harvesting crops, musical rhythms or economic cycles.

Cycles also play key roles in Earth’s short-term weather and long-term climate. A century ago, Serbian scientist Milutin Milankovitch hypothesized the long-term, collective effects of changes in Earth’s position relative to the Sun are a strong driver of Earth’s long-term climate, and are responsible for triggering the beginning and end of glaciation periods (Ice Ages).

In this video we will have a look at these #Milankovitch cycles:

Our tiny little Sun and solar system is about 28,000 light years away from the galactic center, moving above and below the galactic plane during its orbit at around 828,000 km per hour or about 230 km per second. Our Solar system takes about 226 million years to complete one orbit around Milky way center in a clock wise direction. However Earth revolves in a counterclockwise direction around the Sun. Let us zoom in on our little Earth and learn more about its motions.

The shape of Earth's orbit is known as Eccentricity. As Earth moves around the sun, the orbital eccentricity changes slightly over a period of 100,000 years. Earth's orbital speed averages about 107,208 km/h or 66,616 mph, and one complete orbit takes 365.256 days, during this time Earth will travel around 940 million km or 584 million miles. During this orbit, Earth is farthest from Sun on around 3rd of July and closest to sun on around 3rd of January.

As we move around the sun, we experience Longest day in Northern hemisphere on 21st June, we call this Summer Solstice. Winter Solstice comes on 21st of December with Longest night. Around 21st March and 23rd September, the length of day and night will be around the same. We call this Vernal Equinox and Autumnal Equinox.

We experience this 4 seasons because the Earth's Axis is tilted by about 23.4° with respect to the Earth's orbital plane around the sun. The Axial tilt, which is also known as Obliquity, oscillates between 22.1° and 24.5° on a 41000-year cycle and this tilt is currently decreasing.

You see, presently the North Celestial pole is directed towards Polaris or the present North Star, but by about 13,000 AD our North star is going to be Vega, as our rotational axis points toward it. The direction to which Earth's axis of rotation is pointed, rotates in circular motion and a complete cycle takes about 26,000 years. This is called Axial Precession or wobble.

How will it effect our seasons? Well for starters, it is going to hot summer days during Christmas time as all our understanding about equinoxes and Solstices will simply reverse. But hey don't worry, it will be very slow and progressive change and we may not even notice it, if we humans are still around by then.

Lets recap. The earth rotates once every 23 hours, 56 minutes and 4 seconds, the surface of the earth at the equator moves at a speed of 460 meters per second or roughly 1,000 miles per hour and one complete orbit takes 365.256 days. Mainly there are three periodic motions in Earth's orbit, also known as Milankovitch cycles. These motions contribute to variations in Earth's climate. Changes in Eccentricity, cycles in 100,000 years, Axial Precession happens in 26,000 year cycle and changes in obliquity takes 41,000 years to complete one cycle. These numbers may seem huge in terms of human life cycle, but compared to universal time scale they are just a blink of an eye.

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