# Effects of a Change of Direction of the Rotation of the Earth?

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## Summary:

What if the Earth rotated about its axis in a N-S direction instead of doing so in an E-W direction.

## Main Question or Discussion Point

Summary: What if the Earth rotated about its axis in a N-S direction instead of doing so in an E-W direction.

Hi,
Just curious:
What would be the effects/consequences if the Earth rotated about its axis in a North-South ( or South-North) direction instead of an East-West one as it currently does, and at the same rate, i.e., with a period of around 24hrs( while keeping the same rotation about the sun unchanged)s? I can only think of sunlight being spread constantly in horizontal sections instead of vertical ones. I assume the present EW rotation has to see with the effect of other planets' gravity and otherwise. Any other condequences? I have just a basic undergrad understanding of Physics , Earth sciences.

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russ_watters
Mentor
Substantially more severe seasons.

Gold Member
Substantially more severe seasons.
Could you please elaborate? Cant see a connection.

russ_watters
Mentor
Could you please elaborate? Cant see a connection.
You want the axis still fixed relative to the stars, right? So on Jun 21 it points toward the sun and Dec 21 it points away from the sun? That moves the arctic/Antarctic circles to the equator an means from 1 day to 6 months of sunlight during summer (depending on latitude) and vice versa for winter. In Philadelphia when the sun would rise one day in May (estimate) it would then next set in August. That would make for a hot summer.

Janus
Staff Emeritus
Gold Member
As already mentioned, greater variance in seasons would be a result.

In the diagram below the top image is what things are like in the present. The rotational axis is the the arrow passing the green sphere ( Earth) as it orbits the Sun, The Earth is shown at opposite sides of its orbit around the Sun. Winter is on the left, summer on the right.

The bottom image is what would happen if you tip the rotational axis by 90 degrees, During summer, the region near one pole would have the Sun almost directly overhead. The equivalent of our present Arctic and Antarctic circles would extend all the way down to what we now consider the Tropics.
At present, the regions between the Tropics (~23 degrees North-South of the Equator) and the above mentioned circles are known as the Temperate Zones. On an Earth with such a severe axial tilt, there would be no temperate zones by this definition.

For practical purpose Uranus is like that. It takes 84 years for Uranus to complete one rotation around the Sun, where as its axis has a near parallel tilt for 97.77 degress with its ecliptic. So, the effect is 42 years summer and 42 years winter on most of the places.

So, extending that to our Earth, we would have 6month of summer and winter. Now, we could find 6months summer/winter only on the two Poles. But, if the axial tilt is 90 degree, there would be 6 months of summer and winter in most of the places.

256bits
Gold Member
If that was my earth, I would want to live nearer the equator than the poles, where it alternates from being barbequed to freeze dried. At least nearer the equator the summers might not be too hot nor the winters too cold, of course referring sunlight hours only, and not weather patterns of which I know not.

On the poles you get a 6 month night with and a six month day, with at midsummer a 24-hour insolation more than 2x as big as what you now get in the tropics.
On the equator however, you get 2 summers and two winters each year. When it is summer on the north or south pole the sun is just at the horizon at the equator, and the insolation per square meter is essentially 0 at these times. At 21 March or September, you will get a normal day on the equator, just the same as you get now, with the sun directly overhead at noon.
There's actually a point between the equator and the poles where the summer insolation is the same at 21 march, 21 june, and 21 september, so you get a really long summer, with the same average insolation for a six month stretch. For a few months you get a 24 hour day, but the sun will be so low in the sky that it won't be hotter than at the start of spring/autumn.
In the winter there will still be a few months of darkness.

I did not get how you have 2 summers/winters each year on the equator. On each day except both solstice, there would be 12 hours day/night on the equator. On the day of solstice, the Sun would be rotating around you through the horizon.

On the poles you get a 6 month night with and a six month day, with at midsummer a 24-hour insolation more than 2x as big as what you now get in the tropics.
On the equator however, you get 2 summers and two winters each year. When it is summer on the north or south pole the sun is just at the horizon at the equator, and the insolation per square meter is essentially 0 at these times. At 21 March or September, you will get a normal day on the equator, just the same as you get now, with the sun directly overhead at noon.
There's actually a point between the equator and the poles where the summer insolation is the same at 21 march, 21 june, and 21 september, so you get a really long summer, with the same average insolation for a six month stretch. For a few months you get a 24 hour day, but the sun will be so low in the sky that it won't be hotter than at the start of spring/autumn.
In the winter there will still be a few months of darkness.

I did not get how you have 2 summers/winters each year on the equator. On each day except both solstice, there would be 12 hours day/night on the equator. On the day of solstice, the Sun would be rotating around you through the horizon.
At both the summer and winter solstices the sun will be on the horizon all day. How many watts per square meter do you think that is? Just a tiny bit, if the sun was a point source it would be 0.
At N days from the solstice you have 12 hour days, but the maximum altitude of the sun above the horizon would be N*360/365 degrees. If N is small averagge insolation will be smaller than P*sin(360N/365)/2 where P is solar power with the sun directly overhead. For small N this will be much lower than the average solar power over the entire surface of the earth of P/4.

Gold Member
Sorry, don't get the ref. No clue what it is.

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mfb
Mentor
@willem2: The equatorial regions (defined based on the new axis) will still have 12 hours of day and 12 hours of night all the time. Twice per year the Sun is quite high in the sky (directly overhead at the equinoxes), twice per year it is only up to 23.5 degrees up in the sky. In between you get something in between.
This is very similar to the equatorial regions now already, just the minimal angle is much lower now.

DEvens