Polaris is the Closest, Brightest Cepheid Variable. Very Recently, Something Changed.

View from within the Polaris triple star system; artist's rendering. The North Star is labeled Polaris A. Credit: NASA/ESA/HST, G. Bacon (STScI)

When you look up in the night sky and find your way to the North Star, you are looking at Polaris. Not only is it the brightest star in the Ursa Minor constellation (the Little Dipper), but its position relative to the north celestial pole (less than 1° away) makes it useful for orienteering and navigation. Since the age of modern astronomy, scientists have understood that the star is a binary system consisting of an F-type yellow supergiant (Polaris Aa) and a smaller main-sequence yellow dwarf (Polaris B). Further observations revealed that Polaris Aa is a classic Cepheid variable, a stellar class that pulses regularly.

For most of the 20th century, records indicate that the pulsation period has been increasing while the pulsation amplitude has been declining. But recently, this changed as the pulsation period started getting shorter while the amplitude of the velocity variations stopped increasing. According to a new study by Guillermo Torres, an astronomer with the Harvard & Smithsonian Center for Astrophysics (CfA), these behaviors could be attributed to long-term changes related to the binary nature of the system, where the two stars get closer to each other, and the secondary perturbs the atmosphere of the primary.

Continue reading “Polaris is the Closest, Brightest Cepheid Variable. Very Recently, Something Changed.”

Astrophoto: Polaris and Circumpolar Rotation in 30 Minutes

This recent image from astrophotographer John Chumack shows the Earth’s natural rotation in just 30 minutes of exposure time. Polaris, the North Star, is the stationary point over a Sequoia tree in Warrenton, Virginia, USA. “The rotational speed of the Earth at the equator is about 1,038 miles per hour,” John writes. “At mid-latitudes, the speed of the Earth’s rotation decreases to 700 – 900 miles per hour. You can notice star trails “rotation” in your photographs even in as little as 1 minute exposures. I notice star trailing in about 30 seconds with a 17mm wide angle lens. But the longer you leave the shutter open the more trailing and the more dramatic the effect!”

John used a Canon Rebel Xsi, ISO 400, .17mm Lens at F4.

See more of his work at his website, Galactic Images.

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