On this Friday, June 20th at 20:42 hours, a significant astronomical event will occur: the summer solstice. According to Julieta Fierro Gossman, a researcher at the Institute of Astronomy at UNAM, this phenomenon marks the longest day of the year in the Northern Hemisphere, with more hours of sunlight and the official start of summer.
Understanding the Name
The term “solstice” comes from Latin solstitium, meaning “Sun standstill”. This is because, at that moment, the Sun appears to halt its trajectory before reversing it. This apparent standstill occurs because the Sun reaches its highest point at noon, after which it begins to descend towards the Southern Hemisphere, marking the beginning of winter there.
Solar Rise and Fall
While we commonly learn that the Sun rises in the east and sets in the west, Fierro explains that this can vary slightly. In Mexico, for example, the solar rise can lean more towards the north or south depending on the time of year.
Moreover, the Earth’s orbit is elliptical, not circular, which causes the solar movement in the sky to form a figure-eight pattern known as analema. This happens because the Earth’s speed varies depending on its proximity to the Sun, as explained by Kepler’s laws.
This is why sometimes the northern hemisphere receives more sunlight, and other times the southern hemisphere does, causing the Sun to be overhead in Mexico during summer, more inclined towards the north, while in winter, it leans more towards the south.
The Solstice in Culture
Nordic countries are credited with inventing the four seasons of the year; due to Mexico’s proximity to the equator, these seasonal changes are not as pronounced as in other nations. For instance, in the United States, summers are extremely hot, and winters are very cold.
In Mexico, we differentiate more between the rainy and dry seasons; Mesoamerican calendars were organized around these cycles because the rains signaled the time for planting, while dry periods were dedicated to construction and trade.
Furthermore, the solstice is not just a reference point on Earth; other planets also experience seasonal changes. Uranus, for example, nearly lies on its side, causing its hemispheres to endure prolonged periods of day or night. Marte, with an axial tilt similar to Earth’s, also experiences seasons, though they last longer due to its more extensive orbit.
Key Questions and Answers
- What is the summer solstice? The summer solstice is the longest day of the year in the Northern Hemisphere, marking the official start of summer. It occurs when the Sun reaches its highest point at noon, after which it begins to descend.
- Why does the Earth’s orbit matter? The Earth’s elliptical orbit, rather than a perfect circle, causes the Sun to appear higher in the sky during summer and lower during winter in each hemisphere.
- How do other planets experience seasons? Planets like Uranus, which nearly lies on its side, and Mars, with a similar axial tilt to Earth, also experience seasons. However, due to their different orbital periods, these seasons can last much longer.
