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
