The start of the astronomical summer in Spain will officially take place on Wednesday 21 June 2023, at 4:58 p.m. (in the peninsula and the Balearic Islands), according to calculations by the National Astronomical Observatory. The summer season will last 93 days and 16 hours, and will end on September 23, when autumn will arrive.
The beginning of summer in the northern hemisphere is defined by the instant when the Earth passes through the point in its orbit from which the sun presents its maximum northern declination. The day this happens, the sun reaches its highest elevation above the horizon at noon and describes the longest arc in the sky. As a result, it is the sunniest day of the year.
Furthermore, for several days the maximum height of the sun at noon appears to not change. Because of this, the beginning of summer is also called the summer solstice (from the Latin ‘solstitium’, that is, ‘quiet sun’). At that moment, winter begins in the southern hemisphere.
The National Astronomical Observatory points out in a report on the summer season that the beginning of summer can occur, at most, on three different calendar dates (June 20, 21 or 22), although during the 21st century it will only take place on June 20 or 21. The earliest start will occur in 2096 and the latest occurred in 2003.
The variations from one year to the next are due to the way in which the sequence of years according to the calendar fits (some are leap years, others are not) with the duration of each orbit of the Earth around the sun (known as a tropical year).
On July 6, the moment of maximum annual distance between the Earth and the Sun, called aphelion, will take place. When that happens, the distance between the planet and the star will be just over 152 million kilometres, that is, about five million kilometres more than at the moment of least distance (perihelion), which happened on January 4.
On the other hand, summer in the northern hemisphere is the longest season of the year, because the Earth’s orbit around the sun is not circular but elliptical and the summer period coincides with the time of year in which the Earth is farther from the Sun. When this happens, the Earth moves more slowly in its orbit (according to what is known as Kepler’s second law) and, therefore, it takes more time to reach the point where the next season begins, which is the autumn.
Although the day of the summer solstice corresponds to the day with the greatest number of hours of sunshine, the difference in hours between day and night depends on the latitude of the place. For Madrid, the day of the summer solstice will have 15 hours and 3 minutes of Sun, for the 9 hours and 17 minutes of sun that had the shortest day (winter solstice). The difference between the longest day and the shortest is, therefore, almost six hours of sunshine. This difference decreases the closer to the equator, while the difference is maximum at the terrestrial poles.
Summer nights, although short, are usually the warmest of the year. Therefore, they represent a good opportunity to explore the sky. In addition, in the summer it is common to travel to places like the countryside and the beach, which, having a dark sky, allow you to see the firmament better.
During this summer there will be no solar or lunar eclipse. The sky after sunset at the beginning of summer will have Venus and Mars as the only visible planets, but as the months progress, the former will get closer to the Sun and gradually disappear from the sky, giving way to a brief appearance. Mercury for a few weeks between July and August. We will have to wait until mid-August to see Saturn rise in the east at dusk.
The sky before sunrise, for its part, will begin the season with Jupiter and Saturn as visible planets, but the latter will disappear in late August in the brightness of dawn, while Venus will appear in the east. At the end of the summer, Mercury will begin to be seen.
In addition to the planets, it is easy to distinguish groups of bright stars in the sky. The most characteristic of summer is the triangle formed by Altair, in the constellation of the Eagle, Deneb, in the constellation of the Cygnus, and Vega, in the constellation of the Lyre. It is the so-called summer triangle and it is properly an asterism, since it combines stars from different constellations. To the south, the constellations of Scorpio, with the bright reddish star Antares, and Sagittarius, whose position roughly indicates the centre of the Milky Way, are typical of summer. This white band, which represents the combined brightness of the millions of stars that make up the galaxy, can be seen in all its splendour in summer crossing the sky from south to north, although a dark sky is needed to distinguish it clearly.
Other phenomena of astronomical interest this summer will be the Aquarid Delta meteor showers, whose maximum is expected around July 30, and the popular Perseids, whose maximum, around August 12, will coincide with the thin waning moon of in a way that will offer excellent conditions for observing shooting stars throughout the night. The full moons of the season will take place on July 3, August 1, and August 31.
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