Witness Earth's equal day and night: European Space Agency shares equinox's satellite image

European Space Agency shares a satellite image showcasing the Autumn equinox, marking the division of day and night on Earth's surface.

The European Space Agency (ESA) shared a satellite image on Saturday, showcasing a clear division of day and night on Earth's surface, representing the autumn equinox.

During an equinox, day and night are approximately equal in length all across the globe. (EUMETSAT)

Taking to X (formerly Twitter), ESA posted the picture with the caption: "Winter is coming. Day and night are split in half today, as the Sun crossed the celestial equator in the sky at 07:50 BST (12:20 pm as per Indian time), marking the autumn equinox in the Northern Hemisphere."

What is the equinox and why is the image significant?

An equinox, which translates to "equal night" in Latin, is an astronomical event that occurs twice a year when the centre of the Sun aligns directly above Earth's equator.

During an equinox, day and night are approximately equal in length all across the globe.

For the rest of the year, the Sun's illumination varies between the Northern and Southern Hemispheres. This is a result of Earth's 23.5 degrees axial tilt relative to its orbit around the Sun. Due to this, the Sun shines more directly on one hemisphere than the other. However, during the spring and autumn equinoxes, the Sun's light is evenly distributed to both the northern and southern regions.

On which other dates are day and night of equal length?

• The Spring Equinox (Vernal Equinox) takes place around March 20th or 21st in the Northern Hemisphere and around September 22nd or 23rd in the Southern Hemisphere. In the Northern Hemisphere, it marks the commencement of spring, while in the Southern Hemisphere, it signifies the start of autumn.

• The Autumn Equinox (Fall Equinox) occurs approximately on September 22nd or 23rd in the Northern Hemisphere and around March 20th or 21st in the Southern Hemisphere. In the Northern Hemisphere, the autumn equinox denotes the beginning of fall, whereas in the Southern Hemisphere, it heralds the arrival of spring.

For the rest of the year, day and night length is unequal depending on the geographical location. As you move closer to the poles, the variation in day length becomes more pronounced.

Near the equator, day and night lengths remain relatively consistent throughout the year.

Conversely, at higher latitudes, particularly during the summer and winter solstices, more significant disparities in day and night duration are experienced.