Comments on: Ep. 170: Coordinate Systems http://www.astronomycast.com/astronomy/ep-170-coordinate-systems/ Take a weekly facts-based journey through the cosmos with Astronomy Cast. Sun, 11 Jul 2010 12:05:12 +0000 http://wordpress.org/?v=2.9.2 hourly 1 By: Stephen Krisocki http://www.astronomycast.com/astronomy/ep-170-coordinate-systems/comment-page-1/#comment-5464 Stephen Krisocki Wed, 10 Feb 2010 04:16:29 +0000 http://www.astronomycast.com/?p=1109#comment-5464 In my last post, the question marks should be the Greek letter pi, meaning 3.14159265. Fraser and Pamela, I hereby challenge you to allow the posting of Greek symbols in the comment section of Astronomy Cast! In my last post, the question marks should be the Greek letter pi, meaning 3.14159265. Fraser and Pamela, I hereby challenge you to allow the posting of Greek symbols in the comment section of Astronomy Cast!

]]> By: Stephen Krisocki http://www.astronomycast.com/astronomy/ep-170-coordinate-systems/comment-page-1/#comment-5463 Stephen Krisocki Wed, 10 Feb 2010 04:12:15 +0000 http://www.astronomycast.com/?p=1109#comment-5463 I spelled "Ares" wrong, sorry about that. "Mars was at its closest approach a few years ago, it was 3 arc seconds across." WRONG again, Pamela. The real figure was 25.1 arc seconds for the August 27-28, 2003 opposition of Mars. Even distant Uranus is always bigger than an apparent 3 arc seconds, with a range of 3.4 to 4.1 arc seconds. At maximum distance, Mars can appear about 3.5 arc seconds across. It's easy to calculate apparent angular sizes. Take the diameter of a planet(or star, or moon, satellite or airplane or any other DISTANT body), divide it by its distance, then multiply by 206,264. You will get the angular size in arc seconds. Try it! I dare you! To get the angular size of a distant object in degrees, use (diameter/distance)*57.296. The last number equals the value of 1 radian expressed in degrees. A radian is the angular value of a circle divided by 2?. The circumference of a circle = 2?r. 3600 arc seconds make up one degree. Also, to see the point of the vernal equinox directly overhead on the first day of autumn, the observer would have to be standing on the Equator. I spelled "Ares" wrong, sorry about that. "Mars was at its closest approach a few years ago, it was 3 arc seconds across." WRONG again, Pamela. The real figure was 25.1 arc seconds for the August 27-28, 2003 opposition of Mars. Even distant Uranus is always bigger than an apparent 3 arc seconds, with a range of 3.4 to 4.1 arc seconds. At maximum distance, Mars can appear about 3.5 arc seconds across. It's easy to calculate apparent angular sizes. Take the diameter of a planet(or star, or moon, satellite or airplane or any other DISTANT body), divide it by its distance, then multiply by 206,264. You will get the angular size in arc seconds. Try it! I dare you! To get the angular size of a distant object in degrees, use (diameter/distance)*57.296. The last number equals the value of 1 radian expressed in degrees. A radian is the angular value of a circle divided by 2?. The circumference of a circle = 2?r. 3600 arc seconds make up one degree. Also, to see the point of the vernal equinox directly overhead on the first day of autumn, the observer would have to be standing on the Equator.

]]> By: Jo http://www.astronomycast.com/astronomy/ep-170-coordinate-systems/comment-page-1/#comment-5462 Jo Tue, 09 Feb 2010 19:33:32 +0000 http://www.astronomycast.com/?p=1109#comment-5462 Strike that. Strike that.

]]> By: Jo http://www.astronomycast.com/astronomy/ep-170-coordinate-systems/comment-page-1/#comment-5461 Jo Tue, 09 Feb 2010 19:32:46 +0000 http://www.astronomycast.com/?p=1109#comment-5461 Please bring back the embedded player. Please bring back the embedded player.

]]> By: Stephen Krisocki http://www.astronomycast.com/astronomy/ep-170-coordinate-systems/comment-page-1/#comment-5460 Stephen Krisocki Mon, 08 Feb 2010 17:09:25 +0000 http://www.astronomycast.com/?p=1109#comment-5460 The Vernal Equinox does NOT currently begin at "the first point of Aries" as was stated in this podcast. Astrologers use this term today to mark the zero point of the signs of the Zodiac, preserving a fixed celestial coordinate system free from precession. About 2000 years ago, the precession of the equinoxes shifted the first point of Aries into the constellation of Pisces. Although it's in Pisces, it can still be called the "first point of Aries". Around the year 2600 AD, the Vernal Equinox point will drift into the constellation of Aquarius. Then the Age of Pisces will give way to the Age of Aquarius. See http://www.glyphweb.com/esky/concepts/firstpointofaries.html The Vernal Equinox does NOT currently begin at "the first point of Aries" as was stated in this podcast. Astrologers use this term today to mark the zero point of the signs of the Zodiac, preserving a fixed celestial coordinate system free from precession. About
2000 years ago, the precession of the equinoxes shifted the first point of Aries into the constellation of Pisces. Although it's in Pisces, it can still be called the "first point of Aries". Around the year 2600 AD, the Vernal Equinox point will drift into the constellation of Aquarius. Then the Age of Pisces will give way to the Age of Aquarius. See
http://www.glyphweb.com/esky/concepts/firstpointofaries.html

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