Blue Dot Computer, v1.0 Readme file Robert Beezer, July 1996 (beezer@ups.edu, http://buzzard.ups.edu) Your Blue Dot is the time-weighted average of your location on the Earth. This spreadsheet will help you calculate it. Usage: 1. Place your date of birth in cell B12. Use the dd-mmm-yy format, for example 07-Feb-45. 2. In A13, type the name of a place that you have moved away from, and in the adjoining cell in column B13, type the date of this move. Continue in this fashion down columns A and B, in chronological order. Thus, the place entered in A13 would be your birthplace. The last name in column A will be where you currently reside, and the corresponding date will be today's date (even though you may not be moving today, pretend as if you were). 3. For each of these locations, enter the latitude and longitude along the corresponding line, using degrees, minutes, and seconds along with compass directions. If you don't want to bother with minutes and seconds, just enter 0 for these. You might want to use greater accuracy for places where you have lived a long time, and lesser accuracy for places where you have lived only for a short time. The degree of precision is up to you - for example, will you enter places you went on short vacations? Latitudes and longitudes can be found easily on the WWW using one of the sites listed below. 4. Your Blue Dot will appear in the rectangle D7..J8. You can figure out where this location is by visiting the on-line map generator listed below. To update your Blue Dot simply change the last date in the B column to today's date. Internet Resources: Geographic Name Server telnet://martini.eecs.umich.edu:3000 Telnet to this server, and enter a US place name. You will get back a latitude and longitude, among other things. Geographic Name Server/Xerox Map Gateway http://wings2.buffalo.edu/cgi-bin/gazetteer A crude, but easy-to-use interface to the server listed above. USGS Mapping Information: GNIS Data Base http://www-nmd.usgs.gov/www/gnis/gnisform.html The definitive US Government database of US place names. This also lists "features", such as mountains and bays, so if you are not near a city, this might be your best bet. Its easy to get a map back that confirms the place you have requested. Online Map Creation http://www.aquarius.geomar.de/omc/ Once you have your Blue Dot computed, visit this site, where you can enter the boundaries of a region (with latitudes and longitudes) and receive back a map of the area. Technical Details: It seemed inappropriate to me to compute one's Blue Dot by simply averaging latitudes and longitudes. Consider the person who lives just on either side of the International Date Line for roughly equal amounts of time - the longitude of their Blue Dot should be near the Date Line, but instead it could end up near 0 degrees longitude, depending on how East versus West longitudes are handled. Clearly this is inappropriate. Here's how I handled this. Every location on the Earth is converted to a point in Cartesian coordinates on a sphere of radius 1. This is done by first converting to spherical coordinates (consult any serious calculus text for more on this conversion). These points are then averaged, with time-weighting. The result is a point somewhere in the interior of the sphere. This point is projected outward from the center of the sphere, onto its surface. This point is converted to spherical coordinates and then to a latitude and longitude. Spreadsheet Design: Columns K through R have been shrunk down to 0 width. Row 7 contains the averaged values, while the other rows deal with the corresponding place in column A. Here are the contents of the columns: K: Phi for spherical coordinates, in radians. L: Theta for spherical coordinates, in radians. M, N, O: Cartesian coordinates (x, y, z, respectively). P, Q, R: Coordinate-time products (x, y, z, respectively). Only rows 13-112 and cell B12 should be used for data entry. Terms of Use: This spreadsheet is emailware. In other words, if you enjoy using it, send me some email and tell me where your Blue Dot is! I am not a practiced spreadsheet designer, so it will not surprise me in the least if there are not some bugs in this, or things that could be done more efficiently. Please let me know if you uncover either instance. Thanks!