It happens every year. The seasonal westward drift of the stars is temporarily put on hold when we “spring forward” an hour on the second Sunday in March.
With daylight saving time or DST we gain an hour of evening daylight and lose an hour of early morning light. After a long winter, who doesn’t welcome more light at the dinner hour?
A one-hour later sunset naturally means an additional hour for night to begin. Yesterday, twilight ended and true night began around 7:45 p.m. Darkness descends tonight around 8:45 p.m. Since we’ll have to wait that extra hour for stars to come up in the east, the time change has the effect of retarding every star’s rising by an hour.
For instance, last night around 8:30 p.m. I watched brilliant Sirius twinkle west of due south. When the clock glows 8:30 p.m. tonight, Sirius will sparkle east of due south. The same holds true for Orion and the other winter stars. Compared to last night at the same clock time, the winter constellations will be higher up in the sky. Meanwhile, the spring constellations of Leo, Virgo and Bootes, which have been steadily gaining ground in the east, will be shoved back an hour.
While it’s not a great hardship, it does mean that to see the cool spring stuff, we have to go out an hour later compared to a night ago. I’ve been watching Mars finally make its way into the evening sky. To observe it now means getting out at midnight instead of 11. Oh well.
All will take care of itself in due time. We’ll come to accept the change, just as our bodies will finally figure out to do with the hour we lost. And since the westward drift of stars with the seasons never stops, come late-April, Sirius and friends will be memories and bright Arcturus and Mars will gleam in the southern sky.
As Earth travels in its orbit around the sun at 18.5 miles per second, we peer into a different direction in space as the weeks and months pass. Think of going for a ride on one of those merry-go-round horses at a carnival. As the merry-go-round turns, we look out to see a different part of the fairground as the seconds pass. After one spin, the view repeats until the ride is over.
If you substitute the Earth for the horse and our orbit for the merry-go-round, the very same thing happens during a year’s stargazing with the view repeating once every year. During Earth’s “little spin” around the sun, we see the stars and constellations drift from east to west across the sky as we pass them by.
This isn’t the same as the nightly rising and setting of stars – that’s due to Earth’s rotation. Every star you see makes a complete circle around the sky in 24 hours. The much more leisurely seasonal drift is superimposed on that pattern and reveals itself to sky watchers who spend time regularly under the stars.
Cosmos trailer on Fox-TV. The series will air at 8 p.m. Central Time Sundays starting tonight
A final note. The new 13-part “Cosmos” TV series, hosted by astrophysicist and astronomy popularizer extraordinaire Neil deGrasse Tyson, starts tonight on Fox-TV at 8 p.m. CDT (Central time) and 9 p.m. Monday nights on the National Geographic Channel. Don’t miss it!