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	<title>David Pratten &#187; Solar Calculations</title>
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	<link>http://www.davidpratten.com</link>
	<description>Interests, Ideas and Observations</description>
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		<title>SVG Visualisations</title>
		<link>http://www.davidpratten.com/2006/04/29/svg-visualisations/</link>
		<comments>http://www.davidpratten.com/2006/04/29/svg-visualisations/#comments</comments>
		<pubDate>Sat, 29 Apr 2006 09:26:00 +0000</pubDate>
		<dc:creator>david</dc:creator>
				<category><![CDATA[Eye Candy]]></category>
		<category><![CDATA[Solar Calculations]]></category>

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		<description><![CDATA[A few years ago I created this solar Equation of Time visualisation using a visual basic macro and DeltaCAD: That was at a time before SVG was supported by any major browser. Today the situation is quite different and it is time to revisit the creation of Visualisations for the web. Is it possible to create a SVG visualisation that is contructed as part of page creation by a PHP script? After many visits to google, I finally found the keys here: In order to use PHP in conjunction with SVG you have to do two additions in your webservers config-file. We will describe the Apache case, because it is the most-popular webserver. We assume that PHP is already installed and working correctly. First you need to add the type &#8220;psvg&#8221; to your mime-type file so that the relevant line reads like image/svg+xml svg svgz psvg. The mime-types are usually either located at /etc/mime.types or /etc/httpd/mime.types. Secondly you have to add an additional SVG-handler in the apache config-file, so that your relevant line reads like: AddType application/x-httpd-php .php .php4 .phtml .psvg, assuming you call your php-generated svg-files .psvg. Stirring stuff! Actually with my bluehost.com control panel adding the mime type [...]]]></description>
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		<title>Leap Seconds</title>
		<link>http://www.davidpratten.com/2006/04/22/leap-seconds/</link>
		<comments>http://www.davidpratten.com/2006/04/22/leap-seconds/#comments</comments>
		<pubDate>Sat, 22 Apr 2006 19:10:47 +0000</pubDate>
		<dc:creator>david</dc:creator>
				<category><![CDATA[Solar Calculations]]></category>

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		<description><![CDATA[Some of you will be aware that the rotation of the earth is not at a completely uniform speed. In fact, due to the action of the tides and other forces, the earth is slowing down. (Dr. Richard Sauder has written an interesting summary here. ) The international time standard UTC is linked to the earth&#8217;s rotation and this means that UTC occasionally has leap seconds added to it to account for the slowing. The last leap second was added just last January. Why do I care about this? The solar calculation software that I have written depends for it&#8217;s high accuracy calculations on what is called dynamical time &#8211; time that is determined by an atomic clock, not subject to the vagaries of the earth&#8217;s spinning. The Sun API, as the software is called, must convert backwards and forwards between common UTC time and Dynamical Time. The last time that I updated the conversion tables was in 2002 and I was curious if they were still valid. The International Earth Rotation &#038; Reference System Service has provided this handy summary of the history of the gap between time based on the earth&#8217;s rotation and the time kept by atomic [...]]]></description>
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