Sound pressure levels: /2012/sound-meter


The Earth rotates at the equator at about 0.46 km/s = 460 m/s = 1700 km/h = 1000 mph.2 Multiply by cos(latitude) to get surface movement speed anywhere.

For example, Cambridge, Massachusetts is about 42°N and about 5 miles (8 km) east/west. The sun is overhead-and-directly-south 17 seconds later at the west end of Cambridge than the east end. The Connecticut River is about 75 miles (120 km) further west and experiences midday just over 4 minutes later.

Because some of my instruments aren't in metric

  1. synodic = length of time between one full moon and the next, based on the orbits of the moon about the earth and the earth/moon system about the sun; accurate to the number of significant figures I give for each figure

  2. to 2 significant figures; I use Earth's mean radius 6371 km = circumference 40030km because "The difference between a sphere and a reference ellipsoid for Earth is small, only about one part in 300." -