10 curiosities about the winter skies that begin on Friday
Winter in the northern hemisphere (and summer in the south) begins on December 22 at 4 hours 27 minutes on the peninsula and in the Balearic Islands (3h 27m in the Canary Islands). At this time, if there are no clouds, it is when the skies are most transparent. We indicate 10 astronomical curiosities about the day of the solstice and the coldest months of the year.
1. short days. On the day of the solstice, this year December 22, the longest northern night takes place. On that day, in Madrid the night will last 14 hours and 43 minutes, while there will only be 9 hours and 17 minutes of sunlight.
2. Tropic of Capricorn. On the winter solstice, the Earth's North Pole is farther from the Sun than the South Pole.. Seen from Earth, the Sun is at noon in the “Tropic of Capricorn”, its southernmost possible position.. After the solstice, the midday Sun appears a little further north each day, that is, a little higher if we look at it from the northern hemisphere.
The Earth at the solstice
3. still sun. The days before and after the 22nd, the maximum height of the Sun in the sky at noon does not change much in the sky. That's where the word “solstice” comes from, which means 'Static Sun'.
4. North Pole. At the North Pole, the night that began on the autumn equinox (September 23) reaches its midpoint, with another three months of night remaining until spring arrives.
5. Close to the Sun. The paradoxical circumstance occurs that winter in the northern hemisphere arrives when the Earth, in its elliptical movement around the Sun, is as close as possible to the sun.. The closest point, called perihelion, will be reached on January 3, 2024, when the Earth is at a slightly greater distance of 147 million kilometers from the Sun, that is, five million kilometers closer than in the position of aphelion per which we will spend on July 5, 2024.
Perihelion and aphelion
6. morning stars. During the sunrises at the beginning of this winter we will have Venus as a brilliant morning star. Mercury will make an appearance in January. In March, Mars will begin to be visible very low on the horizon, remaining the only morning star at the end of the season, when Venus will no longer be observable.
7. evening stars. At dusk these days we can see Saturn and Jupiter. As winter progresses, Saturn will approach the Sun and will no longer be visible in mid-February.. But Mercury will begin to be visible in the sunsets starting March 10, so the season will end with Jupiter and Mercury as evening stars.
8. Quadrantids. The most important meteor shower of the winter is the Quadrantids, which will have its maximum on the night of January 3 to 4, during the last quarter (the new moon will be on the 11th).. That is why the best time to observe the meteors will be the first part of the night, when the Moon has not yet risen and the radiant (in the constellation of Boyero) is rising above the northeastern horizon.
9. Sin eclipses. During this winter there will be no eclipse, neither of the sun nor the moon.
10. The shortest season. This winter will last 88 days and 23 hours. It will end on March 20, 2024 with the arrival of spring. Winter is always the shortest of the four seasons. This is due to Kepler's Second Law: the line that joins the Earth to the Sun sweeps equal areas in equal times. As the Earth is now in its closest positions to the Sun, it is moving with maximum speed in its orbit, which translates into the shorter duration of winter 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.