The Equation of Time

If you took a photo of the sun everyday at the same time for a year and overlayed the photos you'd find that the sun makes a figure eight-like pattern in the sky (i.e. if you observed the sun at noon everyday it will appear in a slightly different position each time that over the course of a year traces a figure-8 path). The phenomenon is known as an "analemma," and is the result of the earth and the sun's relative motions. Another way to explain it is that it is the difference between the actual position of the sun in the sky and the mean solar time measured by our clocks.

Solar time is time measured by earth's rotation relative to the sun, as explained by this Brittanica entry. Apparent solar time is measured by directly observing the position of the sun--as by a sundial. Mean solar time, kept by most clocks, is the time that would be measured by observation if the sun "traveled at a uniform apparent speed throughout the year rather than, as it actually does, at a slightly varying apparent speed that depends on the seasons." The difference between mean and apparent solar time is known as the "equation of time," derived from the medieval Latin aequātiō diērum, or "difference of days." (Back then the word equation referred to reconciliation.)

Anyways, the difference between mean and apparent solar time is related to two phenomena: First, the earth’s axis is tilted 23.5° relative to the plane of orbit (which causes the sun to appear higher or lower in our sky throughout the year) and second the earth moves through its orbit at slightly different speeds in different seasons. The result is captured in the spectacularly cool video below:

Of course, earth is not the only planet to have an analemma. Other celestial bodies have their own analemmas:

1. Mercury: a single point (because a day on Mercury takes exactly two years!)
2. Venus: an ellipse
3. Mars: teardrop
4. Jupiter: ellipse
5. Saturn: teardrop with a teeny-tiny loop at the end
6. Uranus: figure 8
7. Neptune: figure 8
8. Pluto: a very large figure 8 

New "Hell" Planet Discovered on the Edges of the Milky Way

Scientists have discovered a planet on the outer edges of our solar system where the oceans are made up of molten lava, it rains rocks and has supersonic winds. They gave it a catchy name: K2-141b. The news of the extreme planet was in many different places, but most intriguingly in...Travel + Leisure, because of course. If you were looking for a place to visit...who wouldn't want to explore a literal hell spot?

K2-141b is an Earth-sized exoplanet orbiting a dwarf-star--much cooler than our sun. K2-141b is so close to its own star, it completes a revolution in about a week. And because of that proximity it is gravitationally locked in place with two-thirds of the planet in perpetual daylight in 5,400F heat. While in the other third it is always night and freezing at -300F. 

K2-141b provides a glimpse of what Earth may have gone through billions of years ago, as all planets start off as molten worlds before rapidly cooling and solidifying. It also provides a window into our planet's own eventual future when the sun expands and consumes it. So yeah, this will happen...