SHARON SHANKS | The Cosmos Equinox heralds official start of spring

Despite what the weather says outside, spring officially arrives at 8:28 a.m. on Tuesday. That's the day when the length of day and night are the same -- the time of equinox, or equal night.
It takes our part of the world quite a while to warm up. It has spent the past six months cooling down, and will need several more weeks before the ground starts to thaw. But longer days and more sunshine are coming -- and so are warming weather, spring flowers, greening grass, and tiny leaves.
Tipped axis: Because our planet is tipped about 23.5 degrees on its axis of rotation, we spend six months leaning toward the sun and six months leaning away. The time of the equinoxes in March and September are really just midpoints. We're neither leaning toward nor away.
The Earth revolves around the sun in a path called the ecliptic, or the ecliptic plane. All the solar system's planets travel in the same nearly flat plane (with the exception of Pluto, which is tipped out of the plane).
It also rotates (spins on its axis) in another plane, this one called the equatorial plane or the celestial equator, the imaginary projection of the Earth's equator into space.
The sun's path through the sky is determined by where we are on the ecliptic and the equatorial planes. On the date of the equinoxes, the sun's path on the ecliptic intersects with the celestial equator.
The other two midpoints are the summer and winter solstices, when the sun's apparent path on the ecliptic takes it the farthest north (summer) and south (winter) of the equatorial plane.
Ready for winter: Of course, when the northern hemisphere is tipped toward the sun, the southern hemisphere is tipped away. Tuesday is also the first day of fall for the southern hemisphere, and people there will be gearing up for the colder weather to come.
It's all quite confusing, but we really don't need the movement of the Earth in its orbit or the intersections of planes to tell us it's spring. The air is beginning to smell like spring, the tulips are starting to break the ground, and buds are appearing on the trees. These are the best signs of spring.
Some anniversaries to remember: Humankind's foray into space was still a dream 75 years ago when Dr. Robert Goddard launched the first rocket fueled by liquid. The date was March 16, 1926; the place was Auburn, Mass. Goddard's 10-foot, 10-pound rocket flew just over 40 feet into the air. It used a mixture of gasoline and liquid oxygen; today's mighty engines use liquid oxygen and liquid hydrogen as the fuel and oxidizer to send millions of pounds into orbit -- and to the moon.
Although the start of the space age is often attributed to the launch of the Russian satellite Sputnik in 1957, the true start of our conquest of space came when Goddard mixed liquid fuels together to power his little rocket. Until that time, other fuels couldn't provide the amount of thrust needed to break us very far away from Earth's surface.
March 13 is also a date to remember when thinking about Pluto. It was Percival Lowell's birthday -- and the date that the announcement of the discovery of Pluto was made to the world via the International Astronomical Union.
Percival Lowell was born on March 13, 1955, in Boston. This businessman and traveler became obsessed with Mars and the idea that intelligent beings inhabited the planet. Giovanni Schiaparelli had reported in 1977 that he observed canali on the red planet. The word means channels in Italian; in English it was unfortunately translated into canals. Running water can cut channels and they can also form naturally. Canals, however, seems to imply something built by intelligent hands, not nature.
He founded the Lowell Observatory near Flagstaff, Ariz., to study Mars, and spent a decade observing and charting the canals on Mars.
Beyond Neptune: The Lowell Observatory was also the workplace for a young astronomer hired by Lowell to search for a planet beyond Neptune. The astronomer was Clyde Tombaugh, and on Feb. 18, 1930, he discovered a tiny speck on photographic plates that had moved against the backdrop of stars -- a speck that would later be named Pluto and become, although somewhat controversially, our ninth planet.
Lowell died in 1916 and missed the excitement of the discovery. It was fitting that the announcement of the discovery to the world was delayed until his birthday -- and that Pluto's first two letters are "pl," for Percival Lowell.
March 13 is also the 220th anniversary of the discovery of the planet Uranus. Amateur astronomer and musician William Herschel spotted the planet on that night in the year 1781, noticing that this star-like object was moving a tiny bit from night to night.
Found with telescope: Uranus was the first planet to be discovered by using a telescope. Until that night, humans knew of only five planets in the heavens (Mercury, Venus, Mars, Jupiter, and Saturn) and the one planet upon which they lived. Each is easily visible by the unaided eye. Uranus, Neptune, and Pluto, however, are so far away that it takes telescopes to see them.
Herschel originally named the new planet Georgium sidus (George's star) in honor of King George III, his patron. Its name was changed later to Uranus, an ancient Roman god of agriculture, to keep the names in the planets consistent.
Herschel continued to use Georgium sidus his entire life. Today's astronomers (and middle school teachers) probably would prefer that Georgium sidus was still in use -- Uranus is one of the most mispronounced words in astronomy (ranking close behind Halley's Comet).