yeah! loved the www.thumb.com site. Very busy indeed. I saw Thumb Wars on TV, VERY funny.
About the term, "rule of thumb", does anybody know where it comes from? I have heard (but not verified) that it came way back long ago from England (? or elsewhere), and it was because a man could beat his wife, but only if the stick he used was no bigger around than his thumb... So unfortunately this term may have had a bad past... :o( ----- Original Message ----- From: Jeff Adkins <[EMAIL PROTECTED]> To: Steve Lelievre <[EMAIL PROTECTED]> Cc: Sundial mailing list <[email protected]> Sent: Sunday, January 23, 2000 8:02 PM Subject: Re: Rules of thumb > Here's a few more rules of thumb. > > Jeff Adkins > > > Holding your hand at a 90 degree angle, wrist bent up, fingers splayed apart, > at arm's length, the distance from your thumb to the tip of your small finger > is about 20 degrees. > > The width of a closed fist is about 10 degrees. > > The width of the middle and index finger, held upright at arm's length and > separated as much as possible into a "V" or "Peace" sign (shows my age and > geographic location, eh) is about 5 degrees. > > The width of your index finger's nail is about a degree (roughly twice as wide > as the moon). > > Since larger people have longer arms and larger hands, the proportions will > stay roughly the same no matter how large you are. > > The sun moves roughly 1 degree every 4 minutes, since the sun is 1/2 degree > wide, sunsets from first contact to total sunset take 2 minutes+ a bit > depending on the angle of incidence. > > There are 360 degrees in a circle because there are 365 days in a year. 90 > degrees is a right angle because there are roughly 90 degrees in a season. > There are 12 months (moonths?) because the moon goes around the earth 12 times > + some leftover days in a year; the leftover days are why the months aren't all > 28 days long. There are 24 hours in a day -- which is conveniently related to > 12 and divides evenly into 360 (15 degrees per hour) which, interestingly, is > not too different from the number of degrees them moon moves against the > background stars in a day. > > The number of seconds in a year is roughly pi x 10 to the seventh power. > > > The lit side of the moon always towards the sun. The cusps of a crescent moon > always point away from the sun. > > Since the sun is not a point source of light, but is an extended object, if you > were a small (elf-size) person observing the sun from behind your sundial's > gnomon, the dark part of the shadow would be where the sun is completely > covered up; the fuzzy part would be where the sun is partially covered up. > Since the sun is about half a degree wide, the fuzzy part of the sundial > shadows is about half a degree wide (as measured from the gnomon). This ignores > several optical effects of little significance compared to the > light-moves-in-a-straight-line-and-never-bends model. I think. > > On an equinox day at noon, the distance from the sun to zenith is roughly equal > to your latitude. > > The moon is 30 times as far from the center of the earth as the earth is wide; > or, roughly, the moon is 60 times farther from the center of the earth than you > are. > > The sun is roughly 400 times bigger than the moon in diameter, but it is also > roughly 400 times farther away; that's why our solar eclipses are so nice. > > Each solar day is about 4 minutes longer than a sidereal day; so over the > course of 365 solar days you gain 360 x 4 (roughly) minutes = surprise(!) 24 > hours. > > How's that? > > Speaking of thumbs, those of you on the other side of the pond may never have > seen this wierd little site: www.thumb.com. This is a very busy, but very > silly site unrelated to sundials. > > Jeff Adkins > > Steve Lelievre wrote: > > > I'm relatively new to dialing, and indeed this is my first post to the > > mailing list (but I've lurked here for a few months). I'm also a great > > enthusiast for using "rules of thumb" in everyday life, but so far I've not > > found many cases where I can put the two together. I'm hoping that this > > posting will lead to a discussion about rules of thumb which bear on > > sundials / sun naviagation / sky navigation. > > > > Here are a few examples of the kind of thing I mean: > > > > - Point the hour hand of your watch in the direction of the sun. Divide the > > angle between the hour hand and the 12 o'clock position. This shows you > > where North/South are. > > > > - Put a stick in the ground. Use a pebble to mark where the tip of the > > shadow is. Wait a few minutes, now make a line from the pebble to the new > > position of the shadow tip. This is an East-West line. > > > > Of course, these two are not accurate - rules of thumb often aren't - but > > I'm hoping a few gems will turn up. Anybody got any, good or bad? Especially > > ones for telling the time. > > > > Steve > > -- > =-=-=-=-=-=-=-=-=-=-=-=-= > [EMAIL PROTECTED] > Jeff Adkins > Location: 38.00 N, 121.81 W > CA, USA, Earth, Sol III > >
