Recently I’ve run across several people offhandedly offering disclaimers that they’ve never personally checked that the earth is round. I’ve never thought to check either, but a moment’s reflection reveals that I’ve traveled far enough, both north-south and east-west that the curvature is obvious.
Time zones are a measure of the curvature of the earth. When I travel from New York to California, I know that noon has changed, trusting only my wristwatch. In fact, it was pretty clear to my circadian rhythm. Or just make a phone call to someone you trust on the other coast. Most of the time I don’t discuss sunlight on such calls, but it has come up.
I’ve traveled shorter distances north-south. I’ve been to Glasgow, which is 15 degrees north of NYC. If I went in the spring, there’s probably little to notice, but I went near the solstice, when it was obvious that the nights were much shorter. Similarly, if you go south 15 degrees to Miami, I’m told that the winter and summer day lengths are obviously moderated.
Accurate clocks and instant communication give us a big advantage over the ancients, but the north-south method is largely unchanged.
Added: East-West travel produces a linear effect. North-South travel produces non-linear effects, which can be easy to notice. If I were measuring the height of the sun at noon, that would be linear in the latitude. 15 degrees might be enough to measure without instruments, if I chose to think about it. But the length of the night is not linear. Summer solstice night heads to zero not at the north pole, but just at the arctic circle. So summer solstice in Glasgow was obviously shorter than any night I had previously experienced, maybe cut in half. Whereas summer solstice in Miami is shorter than summer solstice in New York, but just an ordinary length day from other times of the year. Maybe if I had thought to ask the question I could have told the difference without a clock, but I didn’t think about it, whereas the night in Scotland was striking and a topic of conversation. If someone from Miami comes to New York for the solstice, he will experience the shortest night of his life, which might be obvious, but it won’t as dramatic as half the length he’s used to. I knew a guy who moved from Miami to New York and he noticed it, but I think it was about the experience of life, not a single night. There is another non-linear effect as you head to the tropics, which is the solstice shadows at noon shorten to zero. That might be obvious to some people, but it’s not the kind of thing I pay attention to.
Recently I’ve run across several people offhandedly offering disclaimers that they’ve never personally checked that the earth is round. I’ve never thought to check either, but a moment’s reflection reveals that I’ve traveled far enough, both north-south and east-west that the curvature is obvious.
Time zones are a measure of the curvature of the earth. When I travel from New York to California, I know that noon has changed, trusting only my wristwatch. In fact, it was pretty clear to my circadian rhythm. Or just make a phone call to someone you trust on the other coast. Most of the time I don’t discuss sunlight on such calls, but it has come up.
I’ve traveled shorter distances north-south. I’ve been to Glasgow, which is 15 degrees north of NYC. If I went in the spring, there’s probably little to notice, but I went near the solstice, when it was obvious that the nights were much shorter. Similarly, if you go south 15 degrees to Miami, I’m told that the winter and summer day lengths are obviously moderated.
Accurate clocks and instant communication give us a big advantage over the ancients, but the north-south method is largely unchanged.
Added: East-West travel produces a linear effect. North-South travel produces non-linear effects, which can be easy to notice. If I were measuring the height of the sun at noon, that would be linear in the latitude. 15 degrees might be enough to measure without instruments, if I chose to think about it. But the length of the night is not linear. Summer solstice night heads to zero not at the north pole, but just at the arctic circle. So summer solstice in Glasgow was obviously shorter than any night I had previously experienced, maybe cut in half. Whereas summer solstice in Miami is shorter than summer solstice in New York, but just an ordinary length day from other times of the year. Maybe if I had thought to ask the question I could have told the difference without a clock, but I didn’t think about it, whereas the night in Scotland was striking and a topic of conversation. If someone from Miami comes to New York for the solstice, he will experience the shortest night of his life, which might be obvious, but it won’t as dramatic as half the length he’s used to. I knew a guy who moved from Miami to New York and he noticed it, but I think it was about the experience of life, not a single night. There is another non-linear effect as you head to the tropics, which is the solstice shadows at noon shorten to zero. That might be obvious to some people, but it’s not the kind of thing I pay attention to.