Sure, I’m kind of naive. I know it has to do with the axis of the earth and its rotation around the sun, but i need more specifics.
thanks
Sure, I’m kind of naive. I know it has to do with the axis of the earth and its rotation around the sun, but i need more specifics.
thanks
Take a mounted globe and a flashlight into a dim room, and shine the flashlight on the globe. Now rotate it slowly. About half the time a given point on the surface will be lighted by the flashlight, and about half not.
Now, hold the flashlight above the Tropic of Cancer (the line paralleling the Equator a smidgen south of the south tip of Florida). Repeat the rotation process, and notice how long the flashlight illuminates a given point – say your home town.
Find the Tropic of Capricorn, which parallels the Equator exactly as far south of it as the Tropic of Cancer is north of it. Hold the flashlight above it, and repeat the experiment again, noticing how long it illuminates the same point.
Assuming you’re in the Northern Hemisphere, you should see the point illuminated somewhat more than half the time with the flashlight at Cancer and somewhat less than half with it at Capricorn. (Exactly the reverse in the Southern Hemisphere.)
Here’s the point – the Earth’s axis holds a steady bearing on (more or less) Polaris as it moves around the Sun. Since it’s tilted 23 degrees from the plane of the Ecliptic – which is the plane of Earth’s orbit, the Sun’s apparent position moves north and south over the course of a year, being directly over the Equator at the Equinoxes, directly over the Tropic of Cancer at the June (Summer in the Northern Hemisphere) Solstice, and directly over Capricorn at the December (Winter/NH) Solstice.
Therefore, any point north of the tropics will experience a shorter day in the winter months and a longer day in the summer months. (The same thing is true for points south of the tropics, but the seasons are six months out of phase with the north.)
The further north (or south, in the Southern Hemisphere) you go, the greater this disparity becomes. Thursday’s paper, which happens to be handy, says that sunrise was at 7:08 and sunset at 5:01 here in North Carolina. In northern New York state where I grew up, it’s more like 7:30 and 4:30 respectively.
Some of our Aussie and Kiwi members may want to post what’s going on there – it’s approaching the longest day of the year for them. And you’ll find that folks around Sydney will probably show a 14 or 15 hour daytime, but won’t have quite as much daylight as those around Melbourne or Adelaide, with someone from South Island, NZ, showing an even longer day.
Poly was more genteel.
The sun doesn’t “rise”, the lazy sod! It sits back and waits for you and me to rotate on our axis and view it.
You, being on one side of the Earth, get to see it a one instant. I, being in the US, on the opposite of the globe, get to view it as the Earth spins. I get to see it after you. Or vice versa. I’m never sure which way that goes.
What’s The Deal With The Tilt of The Earth?, an animated answer
Just going to add a bit to sunrise sunset questions rather than start a new thread, since it is probably all related.
#1 question—
When is sunrise? When the tip of the ‘top’ of the sun starts to show over the horizon? When it is halfway showing? When can see the whole circle of the sun?
(Ditto basically same question for sunset.)
#2 question.-----
I live in Florida. We have a very short twilight. ===sun goes down and within 1/2 hour it is pitch dark.
Spent a couple weeks in Paris one summer. Very surprised at super lengthy twilights. Sun would go down at maybe 8:30—and twilight lasted for 3 more hours.
Why is that?
Maybe this is the most concise definition:
What that def doesn’t say is the observer must be at sea-level as well.
As for question #2, a few sketches have convinced me of the following: The length of twilight is dependent on how long the sun spends “just below” the horizon; the faster the sun gets below the horizon, the shorter the period of twilight will be. If you were standing on the equator, the sun would cross the horizon at a 90-degree angle; as you go farther & farther north, the path of the sun crosses the horizon at a shallower angle. Since the speed of the sun across the sky is constant no matter where you are, this means that northerly latitudes will have more twilight: since the sun is moving at an angle, it doesn’t get below the horizon as quickly. If you’ve got a mathematical bent, the length of twilight is roughly proportional to 1/sin(latitude), which means that the twilight in Paris (lat. 49 N) is roughly 72% longer than the twilight in Miami (lat. 26 N.)
(I think that my sketches also show that twilight is longer in the summer & winter than it is in the spring & fall, but that may not actually be true. Anybody know for sure?)
Oh, and nitpick: the sea-level horizon is, by definition, the horizon observed by someone at sea level. Someone on a mountaintop could figure out where the sea-level horizon was (it would be a little above their “natural” horizon) and compensate for that in their observations. But this is probably overly picky.
I got to thinking about this. I live on the Western shore of Lake Michigan, which is nominally 576 feet above sea level. Standing on the beach, I can get a clear, unobstructed (unless there is a ship in the way) view of the horizon. But would sunrise at 576 feet for such an observer be at a different time than if the lake & observer were at true sea level?
I guess you could use trig and compute times based on an earth 576 feet greater in radius than sea level, but for all practical purposes, the sun’s rays arrive at the earth parallel, so the sunrise time difference would be extremely small.
Just for kicks, I am going to try a test the next day that is clear on the horizon. Standing on my patio, about 15 feet above lake level, the exact instant the sun pops over the horizon, I will run down to the water’s edge (takes about 10 seconds). I wonder if the sun will disappear, then reappear when I am lower?
One more thought about differences in sunrise/sunset times. Not only is the latitude of a location a factor, but so is the longitude. Typical time zones are 1 hour apart. Ths sun doesn’t come up at the same time in the extreme western and eastern edges of any time zone, in fact the difference would be close to one hour.
Example: sunrise in Minneapolis, MN today is 7:37AM CST. For Green Bay, WI it is 7:14. Green Bay and Minneapolis are at about N44° lat, but approximately 250 miles east-west of each other.
Interesting thought: if we didn’t have time zones, sunrise/sunset for all locations at identical latitudes would have identical times in one 24-hour period, wouldn’t they?
(Don’t forget, if you click on those links any day other than 12/07/2003, since the data is dynamically generated for “today,” you may get different numbers!)