Illustrated below and nicknamed the "Sun's Signature" by astronomers, the solar analemma is a more subtle aspect of the Sun's skypath. And so, the Sun can only ever be seen "directly overhead" between the Tropic of Cancer and the Tropic of Capricorn! You can easily confirm this with the "tiltable-Earth" tool further below. At the eastern and west- ern horizon the Sun rises and sets at an angle that is the complement of your latitude! Also, as it arcs across the sky, it can never climb higher than the complement of your latitude plus 23.44° (Earth's tilt relative to its orbit). The geometry of the rotating spherical Earth determines how the solar spiral is perceived. Taken together, spring and summer in the Northern Hemisphere are over a week longer than spring and summer in the Southern Hemisphere! The solar spiral's northern half has 7½ more coils than its southern half! This means that spring and summer in the Northern Hemisphere are each a few days longer than spring and summer in the Southern Hemisphere! In addition, the Sun makes 183½ coils while moving south, yet only 181¾ coils while moving north! However, because these three fac- tors are slightly "out of synch" with each other, the spiral that they produce is not quite symmetrical. These are Earth's spin on its axis, its motion in its elliptical orbit, and its varying tilt (relative to the Sun)-the last of these making the Sun appear above each hemisphere for six months at a time. Though we speak of "the Sun's motions", three motions of Earth are actually responsible for the solar skypath. The solar spiral's northern half has 7½ more coils than its southern half! The solar position on the spiral depends on the time of year and-as the Sun on average completes a full coil every 24 hours-the time of day.įrom an equinox to a solstice the Sun's spiral has about as many "coils" as a child's "Slinky" toy! How much of the solar spiral is visible, and the angle that its coils make with the eastern and western horizon, depend on an observer's latitude. In fact, the Sun's north or south motion is always less than one solar diameter per day. Then it winds north, back to where it began this journey, its combined westward and north-south motions having traced a spiral of 365¼ "coils" (close to half winding south, the balance winding north!) The separation between any two adjacent coils is greatest at the equinoxes, least at the solstices, but it is never very great. the Sun moves "due west" through our skies at only two instants each year!-at the Solstices!Ĭharting the solar skypath starting at the June solstice, the Sun is over the Tropic of Cancer and winds south for half the year until it is over the Tropic of Capricorn (at the December solstice). K E E P S A F E !It is never safe to look directly at the real Sun with the naked eye! Moreover, viewing it through a telescope, binoculars, camera or similar device without adequate safeguards-even for an instant -can cause permanent blindness! NEVER DO IT! Even during Solar Eclipses, when you'll surely be tempted! To learn how to safely "observe" the real Sun, consult the professionals at your local planetarium or observatory.Ī bit like a child's Slinky toy, to us here on Earth the path that the Sun appears to take through our skies in the course of a year is actually a "very shallow spiral"! Of course, on a daily basis the Sun always appears to traverse the sky predominantly westward, but in a year's time it also appears to move-though far more slowly and subtly- southward for six months then northward for six months, actually creating "a reciprocating spiral!" In fact.
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