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Hamlet
2003-Sep-30, 07:17 PM
I had to pass this along. My 6 year old nephew came home from school last week with the following bit of information. He told his parents that "from now until springtime there would be more darktime than lighttime." When his parents asked how he knew this, he answered that his teacher had taught them that "as the earth moves around the sun it is sometimes tilted toward the sun and sometimes away from it. When it's tilted toward the sun we get more day than night and when it's tilted away we get more night than day."

The teacher didn't go into how the Northern and Southern hemispheres see this effect at different times of the year, but I thought it was pretty good that she was able to teach the concept so that my nephew was able to explain it to his parents later. For the record, his parents didn't know the change in day length was caused by the change in Earth's axial tilt.

Anyway, this story made my week and I wanted to share this little bit of good astronomy with the group. Being the proud uncle that I am, I also wanted to brag about my nephew. :D

fingolfen
2003-Sep-30, 07:21 PM
Anyway, this story made my week and I wanted to share this little bit of good astronomy with the group. Being the proud uncle that I am, I also wanted to brag about my nephew. :D

(snipped to conserve bandwidth)

Awesome on both counts (your bright nephew and the fact he was taught good science at an early age in a way he can understand it!) =D>

gethen
2003-Sep-30, 07:25 PM
Good for your nephew and hurray for a talented teacher.
On a similar note, my new son-in-law was busily cutting out large circles of cardboard last night, and folding them in half. When I asked what he was doing, he said that it was for the world history class in which he's student teaching. They're studying the Age of Exploration and he's having them make rudimentary astrolabs. He wants them to try to determine their latitude (roughly) at home at night so that they can get an idea of what kind of knowledge had to be developed for all that exploration to get started. I'd even like to give it a try.

Betenoire
2003-Oct-01, 02:21 PM
Rock on teach! And your nephew speaks well for your genetic stock:-D

Hamlet
2003-Oct-01, 02:59 PM
Thanks for the nice replies everyone!

RichField
2003-Oct-02, 07:41 PM
The teacher didn't go into how the Northern and Southern hemispheres see this effect at different times of the year, but I thought it was pretty good that she was able to teach the concept so that my nephew was able to explain it to his parents later. For the record, his parents didn't know the change in day length was caused by the change in Earth's axial tilt.

There's a fine point there that escaped me for longer than it should have. For some time I took this to mean that there was a yearly wobble in the Earth's axis. I think it was originally learned as changes in axial tilt but never mentioned relative to what.

For short time scales, the axial tilt doesn't change relative to the plane of the orbit, but because of the tilt, the angle between the axis and a line from the Earth to the Sun changes. If it wobbled like I once thought, we'd have many different pole stars throughout the year.

AGN Fuel
2003-Oct-02, 11:59 PM
There's a fine point there that escaped me for longer than it should have. For some time I took this to mean that there was a yearly wobble in the Earth's axis. I think it was originally learned as changes in axial tilt but never mentioned relative to what.

For short time scales, the axial tilt doesn't change relative to the plane of the orbit, but because of the tilt, the angle between the axis and a line from the Earth to the Sun changes. If it wobbled like I once thought, we'd have many different pole stars throughout the year.

This is correct. However, the Earth's rotational axis itself does precess slowly - once every ~26,000 years (a bit like the axis of a toy gyroscope that is slowing down). Our rotational axis will not always point toward Polaris! :(

Because of this, any co-ordinates given using Right Acsension/Declination should strictly also include the 'epoch' for which these co-ordinates apply, as they do drift slowly over time. The epochs are usually quoted in 50 year intervals (e.g. we currently use epoch 2000).

Hamlet
2003-Oct-03, 01:29 PM
The teacher didn't go into how the Northern and Southern hemispheres see this effect at different times of the year, but I thought it was pretty good that she was able to teach the concept so that my nephew was able to explain it to his parents later. For the record, his parents didn't know the change in day length was caused by the change in Earth's axial tilt.

There's a fine point there that escaped me for longer than it should have. For some time I took this to mean that there was a yearly wobble in the Earth's axis. I think it was originally learned as changes in axial tilt but never mentioned relative to what.

For short time scales, the axial tilt doesn't change relative to the plane of the orbit, but because of the tilt, the angle between the axis and a line from the Earth to the Sun changes. If it wobbled like I once thought, we'd have many different pole stars throughout the year.

This had me going for a while too when I was younger. I finally did an experiment using an unshaded light bulb, a volleyball, and a dark room. I simulated the Earth orbiting the Sun making sure to keep the "North Pole" aimed at the same point in space. It then became obvious what was going on and I felt kind of silly I hadn't worked it out beforehand.