Question:Your obstetrician just pegged your likely due date as Dec. 25. Pretty neat! You wonder, though, about the likelihood of your little bundle of joy actually arriving right along with Santa.
Answer: The due date represents the date Baby will be born if your pregnancy lasts the "mean length for all pregnancies," either 266-268 days or 280, depending on how it's calculated, say Jeffrey Bennett and William Briggs in "Using and Understanding Mathematics." Actual lengths of pregnancies turn out to be nearly normally distributed about the due date (the mean), with a standard deviation of 15-16 days. Going by the 68-95-99.7 rule, this means 68 percent of all births will occur on the due date plus or minus 15 days; 95 percent within two standard deviations, or on the due date plus or minus 30 days; and 99.7 percent within 45 days (3 standard deviations).
Thus, for those with a projected due date of Dec. 25, about 68 percent will deliver between Dec. 10 (15 days early) and Jan. 9 (15 days late). If you assume a bell-shaped (normal) curve and divide up the 68 percent over the 30-day interval, then the chances of a direct hit on Dec. 25 compute to 2.5 percent, or about 1 in 40. So, sorry, for your baby it's a bit of a long-shot for a Merry Christmas and happy birthday to be wrapped up into one.
Question:Why do retailers put Christmas decorations on display as early as September, long before the "official" Friday after Thanksgiving? Are we likely to see a year-round "holiday season" soon?
Answer: No to the second question because Santa's bag can contain only so many items regardless of promotional activity, says Robert Frank in "The Economic Naturalist." But it's a BIG bag, with the holiday season accounting for some 40 percent of annual retail sales volume and almost 65 percent of annual retail profits. Still, gifts bought from one store won't be purchased from another, so to ignore the potential sales from a head-starting September and October could be costly to individual competing retailers. But this reasoning will only go so far, which means September is about the earliest seasonal startup we're likely to see.
Question:He was perhaps the most famous observer of snowflakes of all times, having been given a microscope by his mother at the age of 15 and a camera from his dad, leading to the first successful snowflake micrograph ever. After almost 50 years of chasing them down at an average rate of 70-75 per storm, he published a book of his photos and drawings. Alas, in that same year, two days before Christmas 1931, he contracted pneumonia following a six-mile hike in a particularly severe snowstorm and died, surrounded by specimens of his beloved obsession. Who was this "Snowflake Man"?
Answer: Wilson Alwyn Bentley, of Jericho, Vt., whose book "Snow Crystals" featured fully half of his 5,381 photographs and gave birth to the belief that no two snowflakes are ever identical. This has been challenged but is almost certainly correct, says Roger Highfield in "The Physics of Christmas."
Send STRANGE questions to brothers Bill and Rich at strangetrue@compuserve.com, coauthors of "Can a Guy Get Pregnant? Scientific Answers to Everyday (and Not-So- Everyday) Questions," from Pi Press.