Looking Up: Watch the sky turn around Polaris
Like a turning wheel, the great celestial dome rotates over our heads every day and night. In fact it rotates under our feet too but there’s a planet forever blocking our view (the one you’re standing on, the Earth).
Only the astronauts have had a sense of the starry scape in the form of a great sphere, with oneself floating in the middle. Trying to fathom the cosmos, mankind has gradually gained some sense of perspective, with an understanding that is only liable to be outdated as time and debate goes on.
At one time the Earth was seen as the center of the Universe with the Sun, Moon and planets revolving around us, and the starry firmament beyond.
As we hopefully heard as school kids, the stars rise in the east and set in the west, and that goes too for the Sun- our home star, and the reason they appear to move is the Earth is turning the opposite way.
An imagined line through the South and North Poles, the 'axis of rotation' points at the sky at both ends. Around that point on the celestial sphere, all the constellations appear to spin around, once every 24 hours.
The next clear night, (assuming you are in the northern hemisphere) look north towards the North Star, otherwise known as Polaris, or if you want to be different, Alpha Ursae Minoris.
There’s nothing magic about Polaris. It is not the brightest star in the heavens. Polaris is famous for it is both fairly bright and very close to the point on the sky around which the sky seems to turn (the North Celestial Pole- NCP). It is only 3/4 of a degree from that point, not quite 1-/2 times the disc of the Moon.This makes Polaris appear practically motionless.
To find Polaris, first find the familiar Big Dipper, which on April evenings stands high up with the bowl appearing to be upside down and the handle to the right. The front two stars of the bowl point almost exactly straight down (from this angle) to Polaris.
Depending on your latitude, a whole region of the north sky is 'circumpolar'- the stars therein never set, but constantly encircle the NCP and remain visible, as long as you have no hills or other obstructions blocking the view.
From the North Pole, the entire sky is circumpolar since the NCP- and Polaris are right overhead.
Polaris has not always been considered the North Star. The axis of the Earth has an extremely slow wobble, inscribing an imaginary circle on the sky once around in about 26,000 years. The NCP keeps moving and as the millennia go by, a different naked eye star is seen close to the NCP and is honored as the 'North Star.'
In a telescope of any size, it is interesting to train it on Polaris and just leave it there for a while. If you point it anywhere else on the sky, the stars seem to move fairly quickly past your eyepiece field of view. The apparent motion west to east becomes magnified. Looking at Polaris, however, it seems to hardly move in comparison. Higher magnification, by the way, may show you that Polaris is a double star, with a faint stellar companion right next to it.
Polaris is about 2nd magnitude in brightness, and is between 346 and 433 light years away. The star is at the end of the handle of the Little Dipper, also called the Little Bear. Most of the stars of the Little Dipper are dim and require a dark, moonless night to see them well. On April evenings the handle of the little Dipper extends straight to the right, and the bowl stars aim up towards the Big Dipper. One star in the Little Dipper’s bowl is fairly bright, at 2nd magnitude; Kochab. It appears reddish in binoculars. Kochab is known to have at least one planet.
New Moon is on April 15.
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.