Highlights of the Season: January-March 2021

Located very near Mars in the evening sky is the distant planet Uranus, the first planet whose discovery was made only with a telescope in 1781. When William Herschel spotted it, he wasn't quite sure what he was looking at. It wasn't the sharp pinpoint that a star would appear as, and at first he thought it was a comet. However, it didn't move the way a comet was expected to, and after further observations and consultation with other astronomers, he concluded that he'd discovered a new planet.

A German-born British subject, he wanted to honor King George III by naming the new object Georgium Sidus, or George's Star. Other astronomers objected, arguing that doing so broke with the established tradition of naming planets after deities of ancient myth. Hence, it was named after Ouranos, the Greek personification of the sky, anglicized to Uranus—still not perfectly kosher, since the other planets in the sky are named after Roman figures. Following that tradition, the planet should have been named Caelum, who was Ouranos' Roman counterpart. Still, astronomers like to joke that in any case, the planets would otherwise have been known as Mercury, Venus, Earth, Mars, Jupiter, Saturn...and George.

Yes, Mars does have seasons, one of which, spring, begins on February 7. The Red Planet's axis of rotation is slightly tilted, like Earth's, and maintains its orientation to the stars as the planet orbits the Sun. This results in a similar cycle of seasons to ours, lasting about twice as long (because Mars is farther from the Sun) and subjecting it to temperatures that average minus 80 degrees Fahrenheit but ranging from about minus 200 to 70 degrees Fahrenheit through the year.

With a 40 percent variation in solar energy between Mars' closest and farthest points from the Sun, seasonal windstorms are created that kick up the fine dust particles on the planet's surface. Every few Martian years, these can merge into giant, global dust storms that envelop the entire planet.

For roughly the last half-century, someone sends a spacecraft to Mars about every two years, when Earth and Mars are closest to each other, making such a trip more feasible. In February, a small fleet of three spacecraft is expected to arrive at the Red Planet, all having launched last July. Two of the vehicles are slated to land, while the third remains in orbit.

The first to arrive on the 9th is the Emirates Mars Mission, the first interplanetary effort from the United Arab Emirates. The orbiter, dubbed Hope, will study the planet's meteorology from above. NASA's Mars 2020 mission arrives on the 18th, featuring the Curiosity-like Perseverance rover and the Ingenuity experimental drone-copter. Finally, China's Tianwen-1 ("Questions to Heaven") mission is an ambitious orbiter/lander/rover combination that will join the party sometime between the 11th-24th, and will perform soil analysis and search for biomarkers.

As we switch to Daylight Time on March 14, the science- and math-inclined among us also celebrate the irrational number pi (or 3.14…), which can be used to calculate—among other things—the circumference of a circle whose diameter is known.

To wit: We learn in school that Earth is about 93 million miles from the Sun. That's the radius of our planet's orbit, making the diameter 186 million miles. If you multiply the diameter of a circle by pi (3.14), you get its circumference, in this case about 584 million miles. So what? That's the distance Earth travels in a year, or every 365.25 days. That breaks down to roughly 1.6 million miles a day—or 66.6 thousand miles per hour (or about Mach 86). That's how fast you're moving through space at this moment, and if you want to break that down further, it works out to about 1100 miles per minute...or 18.5 miles per second. So the next time someone calls you a slowpoke, feel free to set them straight...then share a slice of pie.

The March equinox arrives on March 20 at 1:37 am, when the Sun crosses the celestial equator, as seen from Earth. The planet's axis of rotation is perpendicular to the plane of its orbit and tilted neither toward nor away from the Sun. Traditionally, this is observed as the vernal equinox, or beginning of spring, in the Northern Hemisphere and the autumnal equinox, or beginning of fall, south of the equator.

To avoid confusion between the hemispheres, the month in which it occurs is often used for clarity. However, that doesn't mean people can't still be confused about it—here are a few misconceptions about the equinox:

• Day and night are equal in length
  In this usage, "day" is when the Sun is visible above the horizon, but it's not exactly half of one rotation of the planet, or 12 hours. The "equal length" idea is theoretical, based on the Sun being a mathematical point in the sky, when it actually has a measurable angular diameter. Whether "rise" and "set" are defined as the center or the top of the Sun's disk intersecting the horizon makes a difference of a couple of minutes. In addition, refraction of light by our atmosphere causes mirages of the Sun's limb to appear before sunrise and to linger after sunrise, further lengthening the actual period when the Sun is observable by several minutes.
   
• The Sun casts no shadows at noon
  Unless the sky is overcast, the Sun always casts shadows. This myth refers to observers on the equator, where the Sun is directly overhead at noon on the equinox and casts the smallest shadows possible. But it still casts shadows. Light does that.
   
• Eggs balance on their ends
  Eggs (or brooms) can be stood on their ends on any day of the year, if you have the patience to keep working at it. There's no unusual gravitational equilibrium that occurs to make it easier on the equinox. Gravity just doesn't work that way.