Winter

[solbjerg]

Inspired by the snow and cold I am experiencing at the moment I set up this little diagram J

http://forums.iobit.com/attachment.php?attachmentid=6465&stc=1&d=1291979425

(kepler's law - area swept out per time unit is the same)

(arrows are speed vectors)

(to make it a bit more "true" we will have to see A as the position of the Earth in the summer on the southern hemisphere)

The diagram is for educational purposes and doesn’t show the actual location of the relative position of Earth and Sun.

http://forums.iobit.com/attachment.php?attachmentid=6477&stc=1&d=1292062751

This screenshot I made depicts a more true picture.

Circumference: diameter*pi = 939.336.203 km (I used 299 Mill. km)

1 year = 31.557.600 seconds (I used 365,25 days)

Velocity: 939.336.203/31.557.600 = 29,77 km/s → 30 km per second

 

In reality the ellipse is rather close to a circle, the difference for winter and summer is only 5 mill. km out of a mean distance of almost 150 mill. km. In the northern hemisphere we are actually closest to the sun in the winter, but the North Pole is leaning away from the sun in the winter and we therefore receive less energy per square meter in the winter. (about 7% less generally – depends on the latitude too (which is why we have a winter – above the arctic circle we/they do not see the sun for a period in the winter in the northern hemisphere)

Where I live the angle to the sun at midday is 12° at its lowest in the winter

In summer 57° at its highest,

That means sin(rad(12))/sin(rad(57)) = 0,247906 → 25% of the energy from the sun in the summer.

At the same time the lenght of the day drops from 17,5 hours in summer to 7 hours in winter

7*100/17,5 = 40% of the daylight in the summer.

That tells us that we only recieve about 10% of the energy in winter compared to summer.

Fortunately the loss of heat emanating also drops about 20%, so that the net amount of energy in winter is about 30% of what it is in summer from where I stand.

Cheers

solbjerg

p.s. ♫ And that's what I learned in school today ♫ :-)

[solbjerg]

I added a bit of information to the post :-)

 

Inspired by the snow and cold I am experiencing at the moment I set up this little diagram J

http://forums.iobit.com/attachment.php?attachmentid=6465&stc=1&d=1291979425

(kepler's law - area swept out per time unit is the same)

(arrows are speed vectors)

(to make it a bit more "true" we will have to see A as the position of the Earth in the summer on the southern hemisphere)

The diagram is for educational purposes and doesn’t show the actual location of the relative position of Earth and Sun.

http://forums.iobit.com/attachment.php?attachmentid=6477&stc=1&d=1292062751

This screenshot I made depicts a more true picture.

Circumference: diameter*pi = 939.336.203 km (I used 299 Mill. km)

1 year = 31.557.600 seconds (I used 365,25 days)

Velocity: 939.336.203/31.557.600 = 29,77 km/s → 30 km per second

 

In reality the ellipse is rather close to a circle, the difference for winter and summer is only 5 mill. km out of a mean distance of almost 150 mill. km. In the northern hemisphere we are actually closest to the sun in the winter, but the North Pole is leaning away from the sun in the winter and we therefore receive less energy per square meter in the winter. (about 7% less generally – depends on the latitude too (which is why we have a winter – above the arctic circle we/they do not see the sun for a period in the winter in the northern hemisphere)

Where I live the angle to the sun at midday is 12° at its lowest in the winter

In summer 57° at its highest,

That means sin(rad(12))/sin(rad(57)) = 0,247906 → 25% of the energy from the sun in the summer.

At the same time the lenght of the day drops from 17,5 hours in summer to 7 hours in winter

7*100/17,5 = 40% of the daylight in the summer.

That tells us that we only recieve about 10% of the energy in winter compared to summer.

Fortunately the loss of heat emanating also drops about 20%, so that the net amount of energy in winter is about 30% of what it is in summer from where I stand.

Cheers

solbjerg

p.s. ♫ And that's what I learned in school today ♫ :-)

[wozofoz]

I feel the Earth move

 

After reading this I was interested to know if the Earth was getting closer or further away from the Sun. A search found this wonderful website Ask an Astronomer at Cornell University where I found an answer (which I could basically understand) to the question Is the distance from the Earth to the Sun changing?

 

There is an effect which is making us move very slowly away from the Sun. That is the tidal interaction between the Sun and the Earth. This slows down the rotation of the Sun, and pushes the Earth farther away from the Sun. You can read about tides, as they relate to the Earth-Moon system here. The principle for the Sun-Earth system should be the same. But how big of an effect is this? It turns out that the yearly increase in the distance between the Earth and the Sun from this effect is only about one micrometer (a millionth of a meter, or a ten thousandth of a centimeter). So this is a *very* tiny effect.

 

There is another effect which is also small, but somewhat bigger than the tidal effect. The Sun is powered by nuclear fusion, which means the Sun is continuously transforming a small part of its mass into energy. As the mass of the Sun goes down, our orbit gets proportionally bigger. However, over the entire main sequence lifetime of the Sun (about 10 billion years), the Sun will only lose about 0.1% of its mass, which means that the Earth should move out by just ~150,000 km (small compared to the total Earth-Sun distance of ~150,000,000 km). If we assume that the Sun's rate of nuclear fusion today is the same as the average rate over those 10 billion years (a bold assumption, but it should give us a rough idea of the answer), then we're moving away from the Sun at the rate of ~1.5 cm (less than an inch) a year. I probably don't even need to mention that this is so small that we don't have to worry about freezing.

 

"I probably don't even need to mention that this is so small that we don't have to worry about freezing."

Glad to read that :smile:

 

All the best, woz of oz

[solbjerg]

Great woz!

Yes the distance to the center of the sun will slowly be changing, but did it say anything about the distance to the surface of the sun?

As the hydrogen is getting used up the sun will start fusing helium thereby creating a higher temperature and this will expand the volume of the sun - bringing its surface nearer to us - eventually the earth will be just inside the surface of the sun, before the sun collapses and becomes a red dwarf I think.

Bleak prospects - but it won't happen in our time - nor in the era of mankind I suspect. :-)

Cheers

solbjerg

p.s. the tidal action of the moon will slowly make the earth's rotation slow down creating a year with fewer but longer days.

p.p.s. Isaac Asimov in 1979 wrote a book called "A choice of catastrophes" explaining much of what we have discussed here + a lot more in easy to understand form. I recommend it.

 

 

After reading this I was interested to know if the Earth was getting closer or further away from the Sun. A search found this wonderful website Ask an Astronomer at Cornell University where I found an answer (which I could basically understand) to the question Is the distance from the Earth to the Sun changing?

 

 

 

"I probably don't even need to mention that this is so small that we don't have to worry about freezing."

Glad to read that :smile:

 

All the best, woz of oz