March and September are the months when the Sun changes its declination at the fastest rate of the year. If that sounds technical, it merely means that the Sun’s apparent distance from the North Star is decreasing rapidly. It’s moving north in our sky. Needless to say, that’s good news for us who live in the northern part of the planet, for it means that the Sun is rapidly becoming more nearly overhead.
The change in its arc is now so obvious that one can construct simple observational experiments to chart the transformation. The most obvious is that it’s higher in the sky, and this is most striking from 11 a.m. to 3 p.m. when the Sun is in the south. At 1 p.m. it’s due south and highest – currently standing halfway up the heavens. At this altitude, solar rays are now well more than half their full summertime strength – enough to tan or burn us if we exposed our skin for 90 minutes. Thanks to the still-cold air, only skiers and snowboarders tend to do this in March; their red faces provide proof of how they’ve spent their day.
The ever-later sunsets are obvious, too, with daylight now advancing by three minutes per day. The only reason some meteorologists report “two minutes more sun” one day but “four minutes” the next is because they use tables that round off to the minute. In reality, the daily variation is negligible right now, and hovers right around three minutes.
Days and nights are also very nearly equal, with sunrise and sunset occurring just about 12 hours apart. This happens with our clocks reading 7 a.m. and 7 p.m., and will exactly coincide during the middle of next week.
Less apparent to the casual nature-lover is the speedy disappearance of the constellations and stars of winter, the rapid slide of Orion and his friends into the western twilight. It’s an exaggerated consequence of the daily four-minutes-earlier that the stars rise and set throughout the year.
In a way, we get cheated. In the fall, the slow disappearance of the stars’ slide into the west is partially canceled out by the ever-later sunsets, so that when darkness falls each night, the constellations appear nearly the same. Thus, Andromeda, Cygnus and Pegasus linger with us for many months.
Now, the reverse occurs. As Orion marches westward, the ever-earlier twilight advances to meet it, so that the winter stars seem to vanish quickly. Each evening as twilight ends, Orion has visibly jumped closer to the west, nearer to being swallowed into the twilight, with only dazzling Venus heading the other way and rising ever-higher in the west.
In a nutshell, it’s a time of rapid change, on Earth and in the heavens. Don’t think our friends in the forest and beneath the diminishing snowpack aren’t noticing, too.
Want to know more? To read Bob’s previous “Night Sky” columns, visit our Almanac Weekly website at HudsonValleyAlmanacWeekly.com.