Understanding Sunrise and Sunset: A Deep Dive into the Analemma
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Chapter 1: The Nature of Daylight
Although a day on Earth is consistently 24 hours, the amount of sunlight we receive varies significantly throughout the year. The summer solstice is recognized as the day with the most extended daylight; however, it is not when we experience the earliest sunrise or the latest sunset. This discrepancy invites curiosity, as illustrated by a question from Patreon supporter Ben Turner, who asks:
"While we know solstices mark the longest and shortest days, when do the earliest and latest sunrises and sunsets occur? Does this vary by latitude?"
The answer is complex and varies by location. Let's delve into the science behind it.
Section 1.1: The Analemma Explained
The analemma represents the Sun's position over the year if you photograph it daily from the same spot at the same time. This unique shape, resembling a figure-8, varies depending on your hemisphere and the time of day.
For example, if captured at noon, the analemma appears vertical. However, if photographed at different times, it tilts either counterclockwise in the morning or clockwise in the afternoon. The summer solstice is located at one end of the analemma, while the winter solstice is at the opposite end.
Subsection 1.1.1: Factors Influencing the Analemma
The shape of the analemma is influenced by two main factors: the tilt of Earth’s axis (23.5 degrees) and its elliptical orbit around the Sun. If Earth were not tilted and orbited in a perfect circle, the Sun would appear to follow the same trajectory daily.
As the planet rotates, it takes 23 hours and 56 minutes to complete a full turn, with an additional 4 minutes needed to "catch up" due to its orbit around the Sun. This extra time accounts for our 24-hour day.
Section 1.2: Understanding Sunrise and Sunset Variations
When we account for these influences, the Sun's path changes throughout the year. The difference in the Sun's apparent position between the June and December solstices is significant, with a total angular change of 47 degrees due to axial tilt.
The elliptical nature of Earth's orbit further complicates this. When Earth is farthest from the Sun (aphelion), it moves more slowly, while it speeds up when closest (perihelion). This creates noticeable shifts in sunrise and sunset times, which depend on latitude.
Chapter 2: Latitude-Dependent Patterns
As you approach the solstices, variations in sunrise and sunset times manifest distinctly across different latitudes. In the northern hemisphere, for example, the earliest sunrise occurs days before the solstice, with the timing influenced by how far north you are.
Conversely, the latest sunsets shift after the June solstice, with similar latitude-dependent variations. Close to the Arctic Circle, the latest sunsets happen shortly after the solstice, while areas around the Tropic of Cancer experience these later sunsets near the Fourth of July.
The unique interplay of Earth’s axial tilt and elliptical orbit means that what we experience during the June solstice does not perfectly mirror the December solstice. The larger shifts in time around the December solstice indicate that sunrise and sunset times change more dramatically during this period.
In summary, understanding the relationship between Earth's axial tilt and its elliptical orbit provides insight into the intriguing patterns of sunrise and sunset throughout the year. As we continue to observe these celestial events, we can appreciate the dynamic nature of our planet's movement.
Send your questions to Ask Ethan at startswithabang at gmail dot com!
Starts With A Bang is featured on Forbes and Medium, thanks to our Patreon supporters. Ethan has written two books, "Beyond The Galaxy" and "Treknology: The Science of Star Trek from Tricorders to Warp Drive."