It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Thank you.
Some features of ATS will be disabled while you continue to use an ad-blocker.
originally posted by: DigginFoTroof
So I'm trying to make sure I'm thinking correctly about how shadows work as the seasons change vs how they change throughout the day. From what I understand if you put a stick vertically (plumb) & perpendicular in the ground like for a sun dial and then trace the end point of the shadow, the only difference will be the length of the shadow or the size of the arc. The arc will always be facing the same direction but each "ray" will vary in length between the solstices - in the summer they should be shorter thus longer in the winter. We should be able to guess the relative time of year based on the length of the shadow, if it is long enough or you have very accurate measurement device.
So if you go out at the same time every day throughout the year, the shadow from the stick/pole/sundial should always be in the same place but vary in length (excluding issues with daylight savings).
So there is no way that the shadow from stick (like described above) could be off 30-35 degrees at the same exact time of day, from one to another, isn't that correct?
originally posted by: chr0naut
a reply to: DigginFoTroof
No, the Earth has a tilt in its axis of 23 degrees (seasonal changes) and also precesses axially (i.e: it has a wobbly oscillation around its axis), as well as rotating and spinning.
The sundial is only approximately the same and only on human time frames.
The relative angles at particular times will change due to precessional oscillation with a period of 25,772 years.
This is further complicated by additional variances such as nutation (like precession but caused by gravitational interaction with other bodies like the Sun and Moon) and polar motion (caused by ocean and atmospheric currents and as the molten spinning core of the Earth lags behind crustal movement).
originally posted by: Krakatoa
originally posted by: chr0naut
a reply to: DigginFoTroof
No, the Earth has a tilt in its axis of 23 degrees (seasonal changes) and also precesses axially (i.e: it has a wobbly oscillation around its axis), as well as rotating and spinning.
The sundial is only approximately the same and only on human time frames.
The relative angles at particular times will change due to precessional oscillation with a period of 25,772 years.
This is further complicated by additional variances such as nutation (like precession but caused by gravitational interaction with other bodies like the Sun and Moon) and polar motion (caused by ocean and atmospheric currents and as the molten spinning core of the Earth lags behind crustal movement).
Also, didn't the recent plate slip causing the tsunami in Indonesia alter the Earth axis tilt (or did it change the rotation rate)? That would also change the data recorded after that date....wouldn't it?
We should be able to guess the relative time of year based on the length of the shadow, if it is long enough or you have very accurate measurement device.
originally posted by: hombero
a reply to: DigginFoTroof
r u serious? think about a tilting planet going around a glowing sphere and that's how shadows behave throughout the seasons.
originally posted by: Krakatoa
originally posted by: DigginFoTroof
So I'm trying to make sure I'm thinking correctly about how shadows work as the seasons change vs how they change throughout the day. From what I understand if you put a stick vertically (plumb) & perpendicular in the ground like for a sun dial and then trace the end point of the shadow, the only difference will be the length of the shadow or the size of the arc. The arc will always be facing the same direction but each "ray" will vary in length between the solstices - in the summer they should be shorter thus longer in the winter. We should be able to guess the relative time of year based on the length of the shadow, if it is long enough or you have very accurate measurement device.
So if you go out at the same time every day throughout the year, the shadow from the stick/pole/sundial should always be in the same place but vary in length (excluding issues with daylight savings).
So there is no way that the shadow from stick (like described above) could be off 30-35 degrees at the same exact time of day, from one to another, isn't that correct?
It would be if there was no tilt to the Earth's axis. The Earth is tilted on it's axis approx 23 degrees. That tilt results in those lines being separate from the previous lines as the Earth revolves around the sun throughout the year (that is what causes the seasons too).
So, the lines will differ in both length and relative position to each other each day.
ETA: After re-reading your OP, I may have misunderstood your question. Here is a link that describes, what I think, you are asking.
Astronomy with a Stick