When does the greatest percentage of Americans pull themselves away from their TV sets, computers and other indoor activities, and go outside after dark, and look up? Would you say when there is an eclipse? A meteor shower? Try July 4th fireworks!
One source says a five inch fireworks shell zips along at 126 miles per hour. Pretty fast!
As pretty as they are, who hasn’t grumbled when it takes a few seconds too long between firing off another rocket? Alas, we have come to expect everything fast. The adage, "good things come to those that wait" perhaps is more timely a message than ever.
Enjoying the heavens above takes some time and patience. The sky seems so static and unchanging- except of course when a meteor startles us. Although the stars and planets are actually hurtling through space at astonishing speed, due to the vast distances involved, things look quite steady to our eyes. All the stars move east to west as the Earth turns, but you don’t notice the motion at a glance.
The Earth travels in its orbit at 18.55 miles a second. That is not easy to imagine. In the time it takes you to read only a couple words of this column, the world- with you on it- has leaped over 18 miles. At the same time, Earth is being whisked along with the Sun and other planets in an enormous orbit around the galaxy- it takes an estimated 225 million years to go once around! The Sun and planets are moving at 135 miles a second. The velocity of the entire Milky Way Galaxy, relative to neighboring galaxies, has been estimated at 621 miles a second.
Physicists teach that the maximum possible speed is that of light, which exceeds 186,000 miles per second. Even at that fantastic rate, star light takes years to reach us; the Alpha Centauri star system is the closest to the Sun and the light reaches us in 4.3 years. Light from nearby galaxies takes millions of years. Sunlight is eight minutes old once it reaches your eyes. Stars are constantly on the move as they whisk around the Milky Way’s center, yet from hundreds or thousands of light years away, to detect their motion in respect to neighboring stars takes years, using telescope instrumentation.
One of the closest stars to the Sun also has an unusually high "proper motion"- that is, the speed it appears to take as it crosses the sky. Known as Barnard’s Star, this orange star is magnitude 9.5 and visible in a small telescope if you have a good finder star chart. The star is in the constellation Ophiuchus, a physician from Greek mythology, represented by a relatively large portion of sky prominent on summer evenings. Barnard’s Star is 6.1 light years distant, and crosses 10.3 "arc seconds" a year. A degree on the sky is approximately twice the width of the full Moon. Each degree is measured as 60 "arc minutes" and each of those minutes is subdivided by 60 "arc seconds." If you get a chance to see Jupiter in a telescope- the planet shines bright low in the southeast at the end of twilight- note that the planet is presently measured at 42 arc seconds across. So Barnard’s Star appears to move about one-fourth the apparent width of Jupiter, each year. American astronomer Edward Emerson Barnard discovered the star’s motion in 1916.
In about 180 years, Barnard’s Star will cross a half degree, the apparent width of the full Moon.
That amount of motion is detectable in a relatively small telescope at high power, by very carefully plotting the position of Barnard’s Star in respect to nearby stars. Comparing your dated sketches over a few years, you should be able to witness the motion of a star. This is one of many experiments you can do to enrich your experience under the stars, of you choose to do so.
Enjoy the fireworks, and remember the grand display that unfolds every clear night, so breathtakingly large and far that its apparent but deceptive slowness to our eyes underscores the majesty of it all.
Last quarter Moon is on July 6.
Keep looking up!
— Peter Becker is Managing Editor at The News Eagle in Hawley, PA. Notes are welcome at email@example.com. Please mention in what newspaper or web site you read this column.