POLARIS: THE NORTH STAR……FOR NOW.
Photo By: Noel Carboni. CLICK photo for full size and see below for all related links.
This week I feel like focusing on STARS! I will keep it short and sweet, probably focus on about five or so then move on. Let’s start at the top, or more appropriately, the north at Polaris the “North Star”.
Cataloged as HD 8890 or SAO 308 Polaris is known the world over as the North Star and there are some things you should know about our famous guide star. Though it is the brightest star in the constellation Ursa Minor or the asterism of the Little Dipper it’s not even close to being the brightest star in the night sky. In fact at an apparent magnitude of around 2 it’s tough to even see in light pollutes skies. Its remarkable how often that I hear that misconception and I’m honestly not sure where it came from as it’s the 46th brightest star in the night sky. You don’t want to follow the brightest stars in the sky if you intend to move northerly.
Another great feature about Polaris is that it’s a three star system that comprises of Polaris A, and the much smaller Polaris Ab & Polaris B; a fact that was discovered by William Herschel in 1780. Polaris is also a Population 1 Cepheid Variable star, in fact its been noted that it is 2.5 times brighter now than when it was originally discovered by Ptolemy which is actually a pretty large change.
Polaris may be our North Star for now but with Earth’s axial precession (Due to torque; spin a top or gyroscope, it’s the same force) at 23.5 degrees and taking approximately 26,000 years to conclude, Polaris’s days as our North Star are numbered nor has it always been the North Star. The night sky shifts about one degree per 75 years-ish so your grandchildren, though the night sky will still be there (Unless light pollution ruins it for everyone) it will however be shifted significantly from what we view it as today.
Going back to 3000BC, the star Thuban in the constellation Draco was the North Star. In the future, as the celestial pole migrates in the direction of Cygnus and Lyra; Deneb will be within 5 degrees of the North Pole in 10,000AD and Vega will reach about the same distance from the North Pole in about 14,000AD.
As I said, in about 26,000 years (Around 27,800AD) Polaris will again become the North Star but aside from axial precession the stars themselves display proper motion as everything in the universe is constantly moving. At that time Polaris will be further from the pole than it is today. It’s also worth noting that 23,600BC in its previous life as the North Star it was closer to the pole than it is today.
Finally, I should remind you how to find Polaris by using the Big Dipper as a pointer. The two end stars in the “cup” of the Big Dipper asterism; Merak and Dubhe, point you right to Polaris, the first star in the handle of the Little Dipper asterism. Don’t plan on seeing much without black skies because none of the stars in the Little Dipper are very noticeable.
NAME: Polaris, North Star, Ursae Minoris, Alpha Ursae Minoria, HD8890, SAO308 etc etc…..
WHAT IS IT?: A 3-star system acting as the northern most star to within 1 degree. It is also a Population-1 Cepheid Variable star and the nearest Cepheid Variable to the Sun.
HOW FAR AWAY IS IT?: About 323 light years distant. It was until recently believed to be a more distant 434 light years distant but new data shows the closer measurement to be true.
HOW BIG IS IT?: About 30 solar masses and about 4000 times the brightness of the Sun.
APPARENT MAGNITUDE: About +2.
WHERE IS IT? (General): Constellation Ursa Minor or the asterism of the Little Dipper.
WHERE IS IT? (Exact RA/DEC J2000): RA 02h 31m 49.09s / DEC +89° 15′ 50.8″.
EarthSky article on Polaris: http://earthsky.org/brightest-stars/polaris-the-present-day-north-star
Wikipedia page on Polaris: http://en.wikipedia.org/wiki/Polaris
SPACE .COM article on Polaris: http://www.space.com/15567-north-star-polaris.html
NASA Polaris page: http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question64.html