Sunrise and sunset

Reverend said:
Do they each occur at the exact same time in the mornings and nights?

Is this a trick question? Of course they do not occur at the same exact time. Of course, you could say that sunrise "defines" morning and sunset "defines" night and hence they always occur relatively in the same position, but that would not be a convention definition.

The ultimate example is sunrise/sunset at the artic circle latitudes in winter vs summer.
 
Reverend said:
Do they each occur at the exact same time in the mornings and nights?
Well, if you mean, "Is the day symmetric about noon?" then the answer is no, it isn't. Part comes from the discreetized time zones. Part from daylight savings time.
 
Well they're symmetrical about local noon (in the formal definition of noon) to within a minute or so.

Time zones and daylight savings time are conventions which influence where the hands on your watch point, but don't have much influence on the Earth's rotation nor it's motion about the Sun!
 
Well, unless you live right next to a mountain range, where the mountain range runs north-south, and lies entirely to one side of your house :) But if we're talking about areas that are mostly flat, sure :)
 
You mean the Earth isn't flat!!! :oops: Seriously though I think this is all semantics -- the common-use meaning of sunrise/sunset obviously relate to when the Sun appears above or disappears below the apparent horizon.

A more formal definition might be based on the zenith distance of the Sun, which doesn't take account of local terrain.

Anyway, refraction in the Earth's atmosphere screws this all up!
 
What is this "sun" thing y'all are talking about? Does it have something to do with that mysterious "outside" thing all the kids talk about? :-|
 
digitalwanderer said:
What is this "sun" thing y'all are talking about? Does it have something to do with that mysterious "outside" thing all the kids talk about? :-|

Kids? I know only old people who talk about that misterious "outside". All the kids I know haven't seen it yet.

And sun is a british paper with tits on page 3, which is about all the useful content it has ;)
 
Reverend said:
Do they each occur at the exact same time in the mornings and nights?
Only if you live on the equator ;)

Everywhere else experiences longer days in the summer and shorter days in the winter. That precludes the sun from rising and setting at the same time each day.
 
OpenGL guy said:
Only if you live on the equator ;)

Everywhere else experiences longer days in the summer and shorter days in the winter. That precludes the sun from rising and setting at the same time each day.
Well, actually, everywhere experiences longer days at some times, shorter at others. It's only during the equinoxes that the length of day and night are the same, and even then, if you're in an area that is extremely flat, the refraction of the light through the atmosphere extends the day very slightly.
 
Chalnoth said:
Well, actually, everywhere experiences longer days at some times, shorter at others. It's only during the equinoxes that the length of day and night are the same, and even then, if you're in an area that is extremely flat, the refraction of the light through the atmosphere extends the day very slightly.
I'm pretty certain the equator has the same length of day every day of the year. Here's some info for you, http://en.wikipedia.org/wiki/Equator. Note the passage:
wikipedia said:
Places near the equator experience the quickest rates of sunrise and sunset in the world, taking minutes. Such places also have a relatively constant amount of day/night time on every day throughout the year compared with more northerly or southerly places.
 
Chalnoth said:
Keyword: relatively.
Note that it also says locations "near" the equator. If you were exactly on the equator, the day would be the same length every day, discounting weather conditions of course.

It's ok to admit you're wrong, you know.
 
Oh, God, don't know what I was thinking. But you don't have to be an ass about it :p

Anyway, if you want to convince me quicker, you'd be better-off appealing to a logical description, not worrying about outside sources.

Yes, at the equator, the length of the day is independent of the time of year. A simple argument is that in the northern hemisphere, the day is longer than night between the March equinox and the September equinox six months later. In the southern hemisphere, it's shorter during the same period. Since the length of the day cannot possibly be discontinuous, at some point inbetween the length must be constant.

Granted, the above assumes that the Earth is rotating with zero wobble, which is not absolutely true. So there will be some small variations, but these won't be related to the yearly cycle the rest of the world experiences.
 
Chalnoth said:
Oh, God, don't know what I was thinking. But you don't have to be an ass about it :p
If you can be arrogant, why can't I?
Anyway, if you want to convince me quicker, you'd be better-off appealing to a logical description, not worrying about outside sources.
If you won't take my word for it, why wouldn't I point out other sources?
Yes, at the equator, the length of the day is independent of the time of year. A simple argument is that in the northern hemisphere, the day is longer than night between the March equinox and the September equinox six months later. In the southern hemisphere, it's shorter during the same period. Since the length of the day cannot possibly be discontinuous, at some point inbetween the length must be constant.
That argument is not very good as you don't know that the place where equality happens is the same place for each day.
Granted, the above assumes that the Earth is rotating with zero wobble, which is not absolutely true. So there will be some small variations, but these won't be related to the yearly cycle the rest of the world experiences.
Whew, I'm glad you finally agreed, at least up to 6 decimal places :rolleyes:
 
Addis Ababa (Somalia capital city).

Daily prayer times are the same all year round from what a friend told me. The prayer times are calculated using the sun and the zenith is also measured and recorded.

Edit: thought I would clarify, Islamic daily prayer times.

Edit2: so it isn't Addis Ababa either. Oops.
 
Last edited by a moderator:
Back
Top