If for example 2 people are using computers and one replaces his 2x in a 3 year period and the other only does once, market-share dynamics dictate that one demographic has 75% market share while the other has only 25%
I agree with the sentiment but shouldn't that be 67% and 33%? Three computers were sold.
I stand corrected on the summer/winterdesignation. I had assumed that astronomers would have just picked one
Ah, I didn't even think of astronomers, I was just thinking of normal language, Dec+South=Summer. So I was accidentally right about any official astronomy definitions!
It turns out that I was mistaken. You are correct.
Thanks. I only figured it out one day when I noticed that the sun was setting directly at the end of Bourke St, Melbourne, Australia, which goes about 30 degrees south of west. That confused me because at the time I thought that the sun should always be northish, so I worked out why.
I'll have to do that next time I get south of the equator in December:-)
;)
Of course you can see the same effect pretty much anywhere I think (swapping North/South), unless you're at extreme latitudes.
Actually it does. Yeah, ok I said "equinox" when I meant "solstice" but apart from that I was right.
First, in NZ (which is what the thread is about), Dec 21 is the *summer* solstice, not the winter.
Second, at 37 degrees south, in the summer the sun rises south of east *and* sets south of west. This is most extreme at the solstice where it rises about 30 degrees south of east, and *also* sets about 30 degrees *south* of west.
Similarly, at a similar latitude in the northern hemisphere (eg San Francisco), at the local summer solstice (eg June 20 or similar, depending on the year) the sun would rise around 30 degrees *north* of east, and set 30 degrees *north* of west.
Third, I don't care about the camera, but I assume your "140 to 280 degrees" is a typo. Anyway, I was just correcting someone who said that in NZ the sun is always to the north. But yes, with a normal camera, even though the sun *isn't* always north in NZ (despite what someone claimed), if you point the camera south the sun is likely to be outside the field of view. So it is "outside" the camera, but not necessarily "behind" the camera.
Anyway, how can the sun be slightly south at sunrise/sunset in Auckland (or many other places)?
Well, it is a common misconception that because the sun is always directly above the tropics (between around 23 degrees north or south of the equator),
it is believed that it therefore always appears to the north at locations further south (and vice versa in the northern hemisphere).
However, this is false. The apparent paradox is explained by the fact that for a given location the sun's "direction" (azimuth) is on the great circle joining the viewer's location to the point that the sun is above (in the tropics).
So, for example, during summer in Auckland the sun is above a point further north (in the tropics)
but the great circle to this point may start off going somewhat south from Auckland (eg heading 120 or heading 240), especially at sunrise and sunset, hence in summer the sun rises and sets south of east/west respectively.
Calculate it yourself:
Sun calculator
I'm sure you can find a better one at NASA or wherever.
Or if you don't believe that, go outside and have a look!:)
For example, in Auckland on Dec 21 (the summer equinox) the sun rises around heading 120 degrees (30 degrees south of east) and sets around 240 degrees (30 degrees south of west).
[Hi, yeah. I was the AC. It's a little confusing, i only just got an accout]
It happens because rotational inertia is not a scalar (a single number), it is a tensor.
For a rigid body rotating with no external
torque, the angular momentum is constant (as seen by a fixed observer), but there are a whole set of
"legal" angular velocities, ie that satisfy the
"angular momentum = angular velocity * inertia tensor" equation.
The instantaneous solution, ie current angular velocity, changes over time because the angular momentum is fixed in world space, but the inertia
tensor is fixed in body space.
It's kind of like this: the angular velocity defines how the object rotates, the object rotates
a little around that axis, which has changes the relationship between the inertia tensor and the world-space moment vector, which gives a *new* angular velocity. Of course, it's a continuous process, not a discrete one.
The result of this is that a torque-free rigid
body rotating (eg in deep space) in general *does*
have a continually changing instantaneous axis of rotation.
See a physics book or search for "body-cone space-cone angular momentum rigid body" or something like that.
Slashdot Mirror
I agree with the sentiment but shouldn't that be 67% and 33%? Three computers were sold.
Ah, I didn't even think of astronomers, I was just thinking of normal language, Dec+South=Summer. So I was accidentally right about any official astronomy definitions!
It turns out that I was mistaken. You are correct.
Thanks. I only figured it out one day when I noticed that the sun was setting directly at the end of Bourke St, Melbourne, Australia, which goes about 30 degrees south of west. That confused me because at the time I thought that the sun should always be northish, so I worked out why.
I'll have to do that next time I get south of the equator in December :-)
First, in NZ (which is what the thread is about), Dec 21 is the *summer* solstice, not the winter.
Second, at 37 degrees south, in the summer the sun rises south of east *and* sets south of west. This is most extreme at the solstice where it rises about 30 degrees south of east, and *also* sets about 30 degrees *south* of west.
Similarly, at a similar latitude in the northern hemisphere (eg San Francisco), at the local summer solstice (eg June 20 or similar, depending on the year) the sun would rise around 30 degrees *north* of east, and set 30 degrees *north* of west.
Third, I don't care about the camera, but I assume your "140 to 280 degrees" is a typo. Anyway, I was just correcting someone who said that in NZ the sun is always to the north. But yes, with a normal camera, even though the sun *isn't* always north in NZ (despite what someone claimed), if you point the camera south the sun is likely to be outside the field of view. So it is "outside" the camera, but not necessarily "behind" the camera.
Anyway, how can the sun be slightly south at sunrise/sunset in Auckland (or many other places)? Well, it is a common misconception that because the sun is always directly above the tropics (between around 23 degrees north or south of the equator), it is believed that it therefore always appears to the north at locations further south (and vice versa in the northern hemisphere).
However, this is false. The apparent paradox is explained by the fact that for a given location the sun's "direction" (azimuth) is on the great circle joining the viewer's location to the point that the sun is above (in the tropics).
So, for example, during summer in Auckland the sun is above a point further north (in the tropics) but the great circle to this point may start off going somewhat south from Auckland (eg heading 120 or heading 240), especially at sunrise and sunset, hence in summer the sun rises and sets south of east/west respectively. Calculate it yourself: Sun calculator
I'm sure you can find a better one at NASA or wherever.
Or if you don't believe that, go outside and have a look! :)
For example, in Auckland on Dec 21 (the summer equinox) the sun rises around heading 120 degrees (30 degrees south of east) and sets around 240 degrees (30 degrees south of west).
>Sun is always in the North
Except when it's not.
In summer in NZ the sun rises south of east, and sets south of west.
It happens because rotational inertia is not a scalar (a single number), it is a tensor.
For a rigid body rotating with no external torque, the angular momentum is constant (as seen by a fixed observer), but there are a whole set of "legal" angular velocities, ie that satisfy the "angular momentum = angular velocity * inertia tensor" equation.
The instantaneous solution, ie current angular velocity, changes over time because the angular momentum is fixed in world space, but the inertia tensor is fixed in body space.
It's kind of like this: the angular velocity defines how the object rotates, the object rotates a little around that axis, which has changes the relationship between the inertia tensor and the world-space moment vector, which gives a *new* angular velocity. Of course, it's a continuous process, not a discrete one.
The result of this is that a torque-free rigid body rotating (eg in deep space) in general *does* have a continually changing instantaneous axis of rotation.
See a physics book or search for "body-cone space-cone angular momentum rigid body" or something like that.