September 25th, 2007

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This is probably important only if you are a werewolf

In a geeky discussion in a chat, the conversation turned computing the phases of the Moon, I wondered if the POM calculator in emacs needed the observer's lat/lon numbers.

someone: Phases of the moon don't depend noticeably on lat/long - the moon is far enough away compared to the diameter of the earth that to all intents and purposes you see the same hemisphere of the moon no matter where you are on earth. I think they're ususually just calculated wrt the centre of the earth. http://aa.usno.navy.mil/faq/docs/moon_phases.php says "For practical purposes, phases of the Moon and the percent of the Moon illuminated are independent of the location on the Earth from where the Moon is observed."
mra: (looks up numbers, does trig)
mra: the sin of the max angle of view is (12750km / 2) / (384403km / 2)
mra: so the max angle of divergence from plumb is 0.0331743996 radians
mra: which is .005282547 of the full circle, 3.46 hours of the lunar orbit
mra: so the apparent phase can be 3.5 hours early or late, depending on where you are standing on the earth
mra: when something is computing the time of the phase to the closest minute, it looks like your lat/long is significant


Did I get my math right?
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Dear Lazyweb. vCard IM addresses, as done by Apple and Microsoft.

The vCard standard does not currently have a standard way to express IM address (ICQ, AIM, YM, MSN, XMPP, etc). There are assorted discussions and proposals, but nothing solid. So I am reduced to looking at where the rubber meets the road.

How does Microsoft Outlook and the Apple Macintosh OSX contact manager do it?

If y'all export your personal vCard or interesting addresses from your own contact list, especially if you have IM addresses in them, and email them to me at me@mark.atwood.name, so I can pick them apart, I'd appreciate it.


Update: I was just sent a link to RFC4770, "vCard Extensions for Instant Messaging". Cool! Of course, do Apple and Microsoft actually honor it?