abeles@mhuxm.UUCP (abeles) (02/11/85)
I wish to make a correction to the time I calculated in the original article for the minimum time of orbit of the earth. It is about 66 minutes, not 125 seconds. The relevant paragraphs should have read as follows; the basic idea (minus extraneous comments) is not affected. In addition, I should add that the north-south orbit which could prevent the halachic problem of constant (i.e., about hourly) sunrises and sunsets is very specific in that it would have to be almost exactly perpendicular to the line between the sun and the earth. In that orbit, the sun would cease to set and rise at all and (presumably in line with Teitz arguments) the astronaut would never have to daven at all. Also, Shabbos would never come. Forget about chagim! One additional question I have is whether Teitz feels that the returning astronaut (from just such a voyage) would have Shabbos at the same time as others on earth or would count seven sunsets from the previous erev Shabbos for his Shabbos. In that case he might easily end up having Shabbos on another day of the week, in our eternally earthly calendar. Teitz? -------------------------------------------------------------------------- If a person were to keep local time in space, a day (where the term day means the period of time from one sunrise or sunset to another) could be as little as 66 minutes. This would arise because in a low orbit where the pull of gravity is strong a manned satellite would have to go at a speed of about 6300 meters/sec to counteract the pull of gravity. (The acceleration of gravity is about 10 meters/sec/sec at the earth's surface. Centrifugal acceleration is the square of the velocity [6300 ^ 2 = 40000000 meters^2/sec^2] divided by the radius which is about the radius of the earth [4000 km], or again about 10 meters/sec/sec. This 10 meters/sec/sec balances the pull of gravity and allows the orbit to exist.) If this spaceship goes at a speed of about 6300 meters/sec, it would take only about 66 minutes to go around the world. This must be adjusted slightly to allow the orbit to take place above most of the atmosphere, but it would still only be about an hour at such heights.