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	<title>Clark Planetarium &#187; north star</title>
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		<title>The North Star (more than you ever wanted to know)</title>
		<link>http://www.clarkplanetarium.com/blog/the-north-star-more-than-you-ever-wanted-to-know</link>
		<comments>http://www.clarkplanetarium.com/blog/the-north-star-more-than-you-ever-wanted-to-know#comments</comments>
		<pubDate>Mon, 30 Mar 2009 16:14:19 +0000</pubDate>
		<dc:creator>Richard</dc:creator>
				<category><![CDATA[Astronomy Stuff]]></category>
		<category><![CDATA[astronomy]]></category>
		<category><![CDATA[north star]]></category>
		<category><![CDATA[polaris]]></category>
		<category><![CDATA[skywatch]]></category>

		<guid isPermaLink="false">http://www.clarkplanetarium.com/blog/?p=60</guid>
		<description><![CDATA[First of all, the North Star is not the brightest star in the sky&#8211;not even close. Its formal name is Polaris and at magnitude +2, it barely makes the top 50 brightest stars in the sky (#48, not including the Sun).
Secondly, Polaris is not the closest star to the Sun, being 430 light years away. Its [...]]]></description>
			<content:encoded><![CDATA[<p>First of all, the North Star is not the brightest star in the sky&#8211;not even close. Its formal name is Polaris and at magnitude +2, it barely makes the top 50 brightest stars in the sky (#48, not including the Sun).</p>
<p>Secondly, Polaris is not the closest star to the Sun, being 430 light years away.<span id="more-42"></span> Its relatively bright nature is due to its luminosity. Polaris is a yellow giant star 2500 times more luminous that the Sun, 6 times as massive as the Sun, and a diameter 45 times that of the Sun. If Polaris were put where the Sun is, its surface would be more than half the distance to Mercury.</p>
<p>Thirdly, Polaris is actually a triple star system. The two companion stars are very faint and very close making them extremely difficult to resolve by the backyard astronomer. Polaris is also a cepheid variable, with an imperceptible variability of 0.03 over its 4 day period.</p>
<p>Lastly, Polaris not exactly above Earth&#8217;s North Pole. At declination 89.18°, it is so close to the north celestial pole, that to the casual observer, it is the only star that doesn&#8217;t move over the course of an evening or from night to night. Polaris has been an important navigational star as its measured angle above a flat horizon approximates the observer&#8217;s latitude on the Earth. Of course, from the Equator south it is not visible. Because of the precessional wobble in the Earth&#8217;s rotational axis, Polaris will not always be the North Star. Around the year 2105, Polaris will be as close to the north celectial pole, 1/4° away, as it will ever get. After that it will move further away and eventually, there will be no &#8216;north star&#8217; in the sky.</p>
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