# Astronomy Question help

1. Aug 30, 2004

### S. Dilly

Hello everyone.

Me and my fiance are takin Astronomy 101 this semester and we are having quite a hard time. We are absolutly stuck on this one question and the text book we are given is not helping one bit.

So as a last hope i did a google search on astronomy forums and this is where it lead us. So with out further ado, heres the question and ANY help at all would be great, i appriciate any help given in advance

:surprise:

What would the seasons be like if the Earths Axis were perpendicular to its orbit?

We think we may have the answer only becasue it seems quite easy, but we want to make sure...

thanks again.

2. Aug 30, 2004

### mathman

It seems there wouldn't be any seasons as we know them, since all days would have the same amount of daylight. The only seasonal temperature variation would be a small one due to the ellipsicity of the earth's orbit.

3. Aug 30, 2004

### turbo

This is a really good question. The reason we have the seasons we do is because of a couple of things, but the most important is that the Earth's axis is tilted with regard to it's orbit. At my modest latitude (VERY median, being almost exactly 45 degrees), the summer days are long and the winter days are short. The further north you go, the more exaggerated this difference becomes, until above the arctic circle, you can have whole days with the sun above the horizon and whole days with no sun visible above the horizon.

The Earth's orbit isn't exactly circular either, so the intensity of sun's radiation varies smoothly every year. Overall, though, it's the inclination of the Earth's axis that causes the seasons. Without the inclination, every day would have 12 hours of sunlight and 12 hours of darkness, and the only seasonal difference in temperature would be due to the varying distance between the Earth and the Sun due to the non-circular orbit. The farther you would go in latitude (North or South) from the equator, the colder the climate. I would like an Earth like this. I would move to the perpendicular Earth's equivalent of 45 degree September (except I would probably go nuts trying to deal with all the other 800 billion people who also moved there!).

4. Aug 30, 2004

### S. Dilly

I just wanted to Thank you Turbo-1. We came up with the same answer, But yours was alot more in depth and helped us understand it to its fullest extent.

Once again, we both appreciate all your help. :rofl:

5. Aug 30, 2004

### turbo

No problem. Remember that in the the real-life vs "perpendicular axis" scenarios a really major factor is "how direct is the sunlight"? If the sun is directly overhead, it can really cook you, but if its light comes to you through a LOT of atmosphere (closer to the horizon) its energy is reduced. It might be nice for us folks in higher latitudes to wish for more hours hours of sun every day during out long winters, but we have to realize that without the axial tilt, the summer sun will not warm us so much, because the sun will be closer to the horizon. Our latitude gives us a weaker heat source in the winter (for fewer hours per day) and a stronger heat source in the summer (for more hours per day).

6. Aug 30, 2004

### Integral

Staff Emeritus
Here is a nice visual on the difference the angle of the sun makes. Take a square piece of cardboard 1ft (~25cm) on each side. Poke a pencil through Normal (perpendicular to) the cardboard square. Now take the cardboard outside on a sunny day. Orient it so the pencil is pointing at the sun (make the pencils shadow disappear) and observe the size of the shadow on the ground. Perhaps you can get some rough measurements of the shadow, you will find that the area of the shadow is larger then the area of the cardboard. If you try this experiment at noon on various days of the year you will observer the size of the shadow change over the year.

Consider that the cardboard is always blocking the same area of light, but on the ground it is spread over a larger area, so the energy from the sun is spread 'thinner".

If the earth had no tilt you would measure the same area on the ground all year round, but the Northern Hemisphere further north you went the weaker the suns energy on surface of the earth gets. The same square foot of light must cover more ground. So one would expect the average temperature to depend strongly on your latitude.

Also since the sun would always take the same path though the sky day lengths would be uniform.

One interesting change would be that the ecliptic, the path the sun takes through the sky would correspond to the equator. So we would not have the same signs of the zodiac.