Is the Earth out of tilt?
Jul 2, 2011 16:30:38 GMT -5
Post by abeowitz on Jul 2, 2011 16:30:38 GMT -5
In this youtube video, the creator suggests the Sun is rising too early for the South Pole.
However, if he had done a little homework, he would have learned that this station is NOT at the South pole, but at the edge of the Antarctic continent.
And this link shows that it's perfectly normal for that location to get Sun that time of year:
www.die.net/earth/
Then there was this article last year:
Is the Earth tilted too much? or too little?
Well, we can find out for ourselves!
The Equinoxes.
Twice a year, around Sept 22nd and March 20th, the Earth's North Pole is perpendicular to the solar system plane. This means the day and nights are equal in time.
This day will vary from year to year, as the Earth's wobble does vary, and our calendars are off. (Which is why we add a leap day every 4 years.) Reference: www.timeanddate.com/calendar/september-equinox.html
What's neat about the Equinox, is that at Solar Noon (When the sun is the highest above you), the angle of a shadow is equal to your Latitude.
If you're on the equator, (point C) you'll have no shadow angle, because the sun is directly above you.
If you're at the North Pole, (point A) your shadow will have no end.
If you're in between, (point B) your shadow angle equals your latitude.
The Solstice
(I need to make a graphic for this.)
On the Winter Solstice, the Northern hemisphere is tilted away from the sun about 23.5°.
On the Summer Solstice, the Northern hemisphere is tilted towards the sun about 23.5°.
But since we want to know what the Earth's tilt should be right now, we need to do a little math.
Current Tilt
According to www.timeanddate.com/calendar/seasons.html there are 94 days between June 21st and Sept 23rd 2011.
Today (July 2nd) is 83 days till Sept 23rd.
Let's calculate how much tilt the Earth should have right now. The Max tilt of the Earth is 23.44 degrees. en.wikipedia.org/wiki/Solstice
83/94 = 0.883 (Meaning we should be at 88% of the full tilt today.)
23.44° x 0.833 = 20.7°
Our summer shadows are shorter, so we subtract this number from my Latitude:
47.75° - 20.7° = 27°
That's the shadow angle we should expect to see.
The Experiment
I've tied a string to the end of a broomstick on a stepladder here. The string has washers at the bottom to ensure a perpendicular shadow. (Or you could use a pole, if it is perfectly vertical. --use a level.)
I then put a board on the ground and ensured it was level. (If it's not level, your shadow lengths will be off.)
I added some washers higher up so I could measure this shadow as it moves across the board.
I'm marking off the shadow curve every few minutes. The green line is an estimate where the shadows will fall.
The blue line is our triangle. The bottom short leg points approximately North.
The shortest shadow will give us the angle we need. But we can't trust the clock due to daylight savings and wide time zones. The shortest shadow will also point true North, so no compass needed.
To get an estimate on when to measure the shadow, put your location in here:
www.srrb.noaa.gov/highlights/sunrise/sunrise.html
Mine was 1:13pm local time. And in fact, my shortest shadows were at 1:10pm and 1:20pm. So, this seems right on.
Interpolating between the two points, I got about 21".
Since my washers were 46.3" above the board, I should get 21"!!!
46.3" x sin(27°) = 21"
Conclusion
The Earth is about the right tilt, as far as I can tell. If it is off, it is off by an amount that only precise measurements can tell.
As for Greenland, it could be less ice, or it could be their calendars are off, and next year is a leap year. Equinoxes and seasonal tilts do vary slightly each year. But in short, this is much adieu about nothing.
Don't believe the crap they put up on Youtube about the Sun being in the wrong place. (Or the moon for that matter.) With a little science, we can verify it ourselves.
If you have any questions, or if you want to post your own findings, please add on to this thread!
However, if he had done a little homework, he would have learned that this station is NOT at the South pole, but at the edge of the Antarctic continent.
And this link shows that it's perfectly normal for that location to get Sun that time of year:
www.die.net/earth/
Then there was this article last year:
www.dailymail.co.uk/sciencetech/article-1346936/The-sun-rises-days-early-Greenland-sparking-fears-climate-change-accelerating.html
The sun over Greenland has risen two days early, baffling scientists and sparking fears that Arctic icecaps are melting faster than previously thought.
Experts say the sun should have risen over the Arctic nation's most westerly town, Ilulissat, yesterday, ending a month-and-a-half of winter darkness.
But for the first time in history light began creeping over the horizon at around 1pm on Tuesday - 48 hours ahead of the usual date of 13 January.
The mysterious sunrise has confused scientists, although it is believed the most likely explanation is that it is down to the lower height of melting icecaps allowing the sun's light to penetrate through earlier.
Is the Earth tilted too much? or too little?
Well, we can find out for ourselves!
The Equinoxes.
Twice a year, around Sept 22nd and March 20th, the Earth's North Pole is perpendicular to the solar system plane. This means the day and nights are equal in time.
This day will vary from year to year, as the Earth's wobble does vary, and our calendars are off. (Which is why we add a leap day every 4 years.) Reference: www.timeanddate.com/calendar/september-equinox.html
What's neat about the Equinox, is that at Solar Noon (When the sun is the highest above you), the angle of a shadow is equal to your Latitude.
If you're on the equator, (point C) you'll have no shadow angle, because the sun is directly above you.
If you're at the North Pole, (point A) your shadow will have no end.
If you're in between, (point B) your shadow angle equals your latitude.
The Solstice
(I need to make a graphic for this.)
On the Winter Solstice, the Northern hemisphere is tilted away from the sun about 23.5°.
On the Summer Solstice, the Northern hemisphere is tilted towards the sun about 23.5°.
But since we want to know what the Earth's tilt should be right now, we need to do a little math.
Current Tilt
According to www.timeanddate.com/calendar/seasons.html there are 94 days between June 21st and Sept 23rd 2011.
Today (July 2nd) is 83 days till Sept 23rd.
Let's calculate how much tilt the Earth should have right now. The Max tilt of the Earth is 23.44 degrees. en.wikipedia.org/wiki/Solstice
83/94 = 0.883 (Meaning we should be at 88% of the full tilt today.)
23.44° x 0.833 = 20.7°
Our summer shadows are shorter, so we subtract this number from my Latitude:
47.75° - 20.7° = 27°
That's the shadow angle we should expect to see.
The Experiment
I've tied a string to the end of a broomstick on a stepladder here. The string has washers at the bottom to ensure a perpendicular shadow. (Or you could use a pole, if it is perfectly vertical. --use a level.)
I then put a board on the ground and ensured it was level. (If it's not level, your shadow lengths will be off.)
I added some washers higher up so I could measure this shadow as it moves across the board.
I'm marking off the shadow curve every few minutes. The green line is an estimate where the shadows will fall.
The blue line is our triangle. The bottom short leg points approximately North.
The shortest shadow will give us the angle we need. But we can't trust the clock due to daylight savings and wide time zones. The shortest shadow will also point true North, so no compass needed.
To get an estimate on when to measure the shadow, put your location in here:
www.srrb.noaa.gov/highlights/sunrise/sunrise.html
Mine was 1:13pm local time. And in fact, my shortest shadows were at 1:10pm and 1:20pm. So, this seems right on.
Interpolating between the two points, I got about 21".
Since my washers were 46.3" above the board, I should get 21"!!!
46.3" x sin(27°) = 21"
Conclusion
The Earth is about the right tilt, as far as I can tell. If it is off, it is off by an amount that only precise measurements can tell.
As for Greenland, it could be less ice, or it could be their calendars are off, and next year is a leap year. Equinoxes and seasonal tilts do vary slightly each year. But in short, this is much adieu about nothing.
Don't believe the crap they put up on Youtube about the Sun being in the wrong place. (Or the moon for that matter.) With a little science, we can verify it ourselves.
If you have any questions, or if you want to post your own findings, please add on to this thread!
