Exploring how solstices and equinoxes can be shown using satellite imagery.
01 August 2022
20 June 2013
Today (20 June 2011) is the solstice, the longest day in the Northern Hemisphere and the shortest in the Southern Hemisphere.
The date of the summer solstice depends on the shift of the calendar, in the Northern Hemisphere it can be any time between 20 June and 22 June.
For a period of some days around the solstice it is possible for our geostationary satellites to see what is known as the ‘midnight Sun’. Because of the position of the Sun, the sunlight is reflected off the Northern polar region and is seen by our Meteosat Second Generation satellites, as shown in Figure 1 (right).
At the same time as the summer solstice heralds the astronomical start of summer in the Northern Hemisphere, the winter solstice heralds the start of winter in the Southern Hemisphere.
This changing of the seasons takes place because the plane of Earth’s equator is tilted 23.5 degrees to our orbit around the Sun.
Figure 2 (right), shows the change in the Sun's illumination of the Earth due to the position of the Earth relative to the Sun.
The March and September equinoxes mark the times in the year when day and night are of equal length across the globe.
The December solstice marks the shortest winter day in the Northern Hemisphere and the longest summer day in the Southern Hemisphere.
The line that separates the portions of the Earth experiencing daylight from the portion experiencing darkness is known as the 'terminator line'.
Other solstice cases
Cancer solstice 2020
The Cancer solstice, with the Sun directly over the Tropic of Cancer, took place in 2020 on 20 June at 21:43 UTC.
Annular solar eclipse on solstice
During the 2020 June solstice the shadow of the Moon, travelling from west to east, appeared in the images of three geostationary satellites.
June solstice 2019
The June solstice is the Summer Solstice in the Northern Hemisphere and the Winter Solstice in the Southern Hemisphere. It took place at 15:54 UTC on 21 June.
December solstice near the southern polar circle
December solstice occurred in 2018 at 22:23 UTC on 21 December and could be 'seen' in satellite imagery.
Other equinox cases
Sunglint during March equinox
Satellite imagery during the Spring Equinox (Autumn in Southern Hemisphere) captured very obvious sunglint near the Equator.
Atmosphere mirroring around the equator
In a few days the Sun is going to equally shine in both hemispheres when the equinox takes place at exactly 10:29 UTC on 20 March.
Sunglint during September equinox
In 2016, 22 September was the autumnal equinox in the Northern Hemisphere and the vernal equinox in the Southern Hemisphere.