The Great Eight

there is a time-lapse picture of the path the sun takes in the sky, which resembles the number eight.

Photo by Dennis di Cicco. © Sky & Telescope. Used with permission.

What's this, a new constellation? Spaceships flying in formation? A secret message from the number 8? It's actually an analemma, the figure our sun traces in the sky over the course of 12 months. This patient photographer snapped the sun at the same time every week for a solid year.

The photographer lives in Massachusetts, a state that has definite seasons, and the analemma shows you why it does. Can you guess where the sun was in mid-summer? It was at the top of the 8. Because the sun is higher in the sky and stays in the sky longer, the Earth becomes warmer. At mid-winter, the sun is at the bottom of the 8 and stays above the horizon only briefly, which is why people in Massachusetts have to put up with the cold (and daylight savings time).

Of course, the sun itself doesn't move (at least not this way). It appears to move in our sky because the Earth moves in relation to it. But you can see why ancient people who studied the sky used to be confused about this. Oh yes, one more thing. If you wake up one morning and see this out your window, check your pulse—you've been standing there for a year!

Activity

  1. What is an analemma?
    [anno: An analemma is the pattern or figure made by the Sun as it passes through the sky throughout the year.]
  2. In this photograph, when the Sun is near the top of the analemma, is the Southern Hemisphere tilted towards the Sun or away from the Sun? Write a few sentences to explain your answer.
    [anno: When the Sun is near the top of the analemma, the Southern Hemisphere is tilted away from the Sun. Massachusetts is in the Northern Hemisphere. When the Sun is at the top of the analemma in this photograph, it means that it is summer in the Northern Hemisphere. Since it is summer in the Northern Hemisphere, it means the Northern Hemisphere is tilted towards the Sun, and the Southern Hemisphere is tilted away from the Sun.]
  3. What would an analemma look like if it was photographed from a town near the Equator? Explain your answer.
    [anno: The analemma would not show as much variation in height distance because the Equator is not affected as much as the Northern and Southern Hemispheres are by Earth's tilting towards and away from the Sun.]