You are currently viewing The summer solstice in an astronomical key
Nicolas de Stal, The Sun, summer 1953

Summer is here, the longest of the four seasons. The solstice takes place at dawn on Monday, June 21. We tell you everything you need to know about the longest day of the year and about the celestial phenomena that will take place during the summer period.

Ten keys

1) Start. Summer in the Northern Hemisphere (and winter in the South) begin on June 21 at 5:32 a.m. peninsular time (4:32 a.m. in the Canary Islands).

2) The longest day. On the day of the summer solstice, the shortest boreal night takes place. On that day, in Madrid the night will last 8 hours and 57 minutes, while there will be 15 hours and 3 minutes of sunlight. Oddly enough, the longest day of the year is not the day the Sun rises earlier, nor is it the day the Sun sets later. This is because the Earth’s orbit is an ellipse and the axis of this ellipse is not related to the inclination of the Earth’s axis that defines the seasons. The earliest sunrise in 2021 occurred on June 14, while the latest sunset will occur on June 27.

3) Tropic of Cancer. At the summer solstice, the North Pole of the Earth is closer to the Sun than the South Pole. Seen from Earth, the Sun is at noon at the “Tropic of Cancer”, its northernmost possible position.

4) Afelio. The paradoxical circumstance occurs that the summer of the Northern Hemisphere arrives when the Earth, in its elliptical movement around the Sun, is as far away as possible from the sun king. The farthest point, called aphelion, will be reached on July 5, 2019, when the Earth is about 152 million kilometers from the Sun, that is, 5 million kilometers further than at the perihelion position we are passing through. last January 2.

5) Still sun. The days before and after day 21 the maximum height of the Sun at noon does not change much in the sky. This is where the word solstice comes from, which means ‘Static Sun’ or ‘Still Sun’.

6) Polo without night. At the North Pole, the nightless period that began on March 20 now reaches its midpoint, with another three months of sunlight left until fall arrives and a six-month period of night begins.

7) A supermoon and a blue moon. This summer it will have four full moons, including a supermoon and a blue moon. The first full moon of the season, called the ‘strawberry moon’ will happen on June 24 with our satellite in its closest possible position to the Earth (perigee), it is what is sometimes called ‘supermoon’. The other full moons will be on July 23, August 22 and September 20. When a season has four full moons, the Anglo-Saxons call the third of them ‘blue moon’, blue moon (the second full moon of a month that has two is also called ‘blue moon’). So the full moon on August 22 will be a ‘blue moon’, but naturally this has nothing to do with the color of the Moon.

8) Planets in sight. During early summer sunrises, Jupiter and Saturn will be visible. Both giant planets will be present for almost all of the nights in August and will remain in the evenings at the end of the season. Venus will act as the evening star and Mars will also be visible in the evening towards the end of August.

9) Tears of Saint Lawrence. This is a good year to observe the Perseids, the most important meteor shower of the summer. This is due to the fact that the maximum activity of the rain, on August 12, will take place with the crescent moon that sets at midnight, leaving most of the night very dark. The observation conditions will be similar for the Acurid Delta that have their maximum on July 30, during the first quarter, although on this date it will be the first part of the night that will not have a moon.

10) 93 days and 15 hours. Summer will last 93 days and 15 hours. End on September 22, 2021 with the arrival of autumn. In fact, summer is always the longest season of the four. This is due to Kepler’s Second Law: the line connecting the Earth to the Sun sweeps out equal areas in equal times. Because the Earth is now in its farthest positions from the Sun, it is moving at a slower speed, which translates into the longest duration of summer compared to the other three seasons.


Rafael Bachiller is director of the National Astronomical Observatory (National Geographic Institute) and academic of the Royal Academy of Doctors of Spain .

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