[bezoar]

How fast the earth spins might depend on where on earth you are.

[roberth]

OK, then, 1,609 km/h at the equator.

[pipster]

The earth and all the other planets in the solar system are spinning because of the resultant angular momentum from their formation billions of years ago. As the clouds of dust and gas came together under gravity, the matter they contained was pulled in closer and closer until finally the planet we now live on was formed.
Just as when an ice skater spinning on the spot goes faster when they pull their arms in (try it on a swivel chair) this gas contraction increased the angular momentum that causes our days and nights to come round every 12 hours (at the equinox).

Like all systems, energy is lost over time (like a pendulum eventually comes to rest vertically) and so the rotation about our axis is decreasing. This will eventually increase the length of the day since more time will be spent in or out of sunlight at anytime.

Velocity of rotation of a point about an axis (in this case angular momentum) = 2xpixr/24hours
At the north pole where the distance to the centre of rotation could be close to zero, you will have zero angular momentum and it increases up to the equator.

IF the earth spinning around on its axis slows down enough, days will get longer and longer and eventually the length of a day might over take the length of the year, which I believe is what has happened to Mercury?

[Ultima]

The Earth wobbles on its axis wouldn't this effect the speed a tiny bit?

[roberth]

C'mon TNS. You should rename this topic "question of the fortnight".

[neilep]

As a kid, I used to think the wind was caused by the Earth spinning faster that day !!!!....

'Men are the same as women...just inside out !'

[Quantumcat]

Lol!! That's so cute! I remember thinking it was caused by convection before I learnt about pressure and stuff.

Am I dead? Am I alive? I'm both!

[NakedScientist (OP)]

Answer to HOW FAST IS THE EARTH SPINNING ? IS THE RATE CHANGING ?

The earth completes 1 revolution per day (24 hours). The distance that it effectively travels (at the equator) in completing 1 revolution is equal to the planet's circumference or girth.

You can calculate the circumference of a circle using the formula 2x pi x radius of the circle.

The radius of the earth is 3963 miles (6378 kilometres). The circumference is therefore 2 x 3963 x 3.141 (approx. value of pi) = 24900 miles (40,000 km)

The speed of the earth is therefore 24900 / 24 = about 1000 miles per hour (1600 km per hour).

The rate of rotation is indeed slowing down. About 65 million years ago, at the time of the dinosaurs, the earth span much more quickly meaning that a day was correspondingly shorter, lasting only about 16 hours.

It is worth bearing in mind, however, that the calculation above applies at the equator - the actual speed you would be travelling at varies according to where you stand on the planet surface - at the north pole, for instance, your speed would be zero. In the UK and north US your speed is closer to 700 - 900 miles per hour (1125-1450 kilometres per hour).

sorry this took a little while to come out - I've been a bit busy !

TNS

[NakedScientist (OP)]

Here's this week's QOTW :

"WHAT IS A SUNSPOT ? WHAT CAUSES THEM AND WHAT EFFECTS CAN THEY HAVE UPON EARTH ?"

TNS

[cuso4]

Astronomy is never my strong point. I'll have to do some research for this.

Angel

"The people who will succeed are those who see the invisible and do the impossible."

[CsManiacDan]

I'm pretty sure a sun spot is an area on the sun that's cooler than the rest of it, that's why it's darker, though why it's cooler i have know idea nor do I know whats causing it

I Love Caesium!!!

[neilep]

Yep...Im with you on that one Dan, I'm sure magnetism comes into the equation too somewhere along the line, as well as the eleven year cycle, where they pop up the most and last about a week or so. Not too sure what effects they have upon the earth apart from manifestations arising from magnetic disruptions ? perhaps electrical disruption and interference with satellite communications, and birds/sealife/animals that depend on the earths magnetic field for navigation.

Or is it just something that adolescent stars get as they go through puberty ? :-)

'Men are the same as women...just inside out !'

[Donnah]

I vaguely remember hearing something about sun spots and radioactivity.

[NakedScientist (OP)]

ANSWER TO LAST WEEK'S QOTW "WHAT ARE SUNSPOTS AND HOW DO THEY AFFECT THE EARTH ?"

Sunspots are dark spots, up to 50,000 miles in diameter, that move across the surface of the sun, expanding and contracting as they go. They usually last for several days, although very large ones can persist for several weeks.

A typical sunspot comprises a dark region called the umbra, surrounded by a lighter region known as the penumbra. They appear relatively dark because the surrounding surface of the Sun (called the photosphere) is about 5500 degrees C., while the umbra is a chillier 3480 degrees C.

Sunspots are surrounded by an intense magnetic field over 2,500 times stronger than Earth's, which is much higher than anywhere else on the Sun. This powerful magnetic field slows down the flow of hot gases from the Sun's interior to the surface, which is why sunspots are relatively cooler than the rest of the sun's surface. They usually occur in pairs which have their magnetic fields pointing in opposite directions

People have been watching sun spots since Galileo Galilei first described them in the early 1600s, and we probably knew about them even before that. There are reports of ancient peoples noticing the sun's blemished appearence, particularly on cloudy days and during dust storms.

But thanks to Galileo's work we now know that the sun follows an 11 year cycle - the Solar Cycle - during which the number of sunspots steadily increases to a maximum, then decreases again at the end of the cycle. Towards the maximum the sunspots occur closer to the equator of the Sun. Plotting the area covered by sunspots at a given latitude versus time produces an interesting butterfly shaped distribution of unknown significance.

Some studies have suggested that the average ocean temperature increases and decreases, world-wide, by 0.5 degrees C in phase with the sun spot cycle, but the mechanism is not understood.

So how do sunspots affect the earth ?

This is not known for certain. During periods of maximum sunspot activity scientists have recorded a very slight increase in the energy output from the sun, and ultraviolet (UV) radiation increases dramatically which can affect our atmosphere. Also, a period known as known as the Maunder Minimum, during which there were very few sunspots, coincided with a number of long winters and severe cold temperatures (called the Little Ice Age) in Western Europe.

Furthermore, sunspots are also associated with phenomena called CME - Coronal Mass Ejections or solar flares. These stellar convulsions produce as much energy as a billion megatons of TNT and occur near to sunspots on the dividing line between the pair of oppositely directed magnetic fields. Solar plasma interacting with the strong magnetic field is ejected away from the sun's surface and out into space forming the flare which bathe the earth in cosmic radiation leading to an increase in geomagnetic storms which can affect satellites, power grids and radio transmissions. They also produce a more pleasant side effect - the beautiful northern and southern lights - where the charged particles interact with the earth's magnetic field...

Some sunspots :

[NakedScientist (OP)]

Here is this week's question of the week :

"CAN YOU EXPLAIN 'WIND CHILL FACTOR'" ?

TNS

[Quantumcat]

I think so. Wind chill factor is when lots of bits of moisture in the air go past your skin fast, taking heat as they go. Or maybe it's not moisture it's air. Oh well, doesn't matter. That's why you're cold when you get out of the bath too, because the water becomes a thin layer and the abundant heat in your skin goes into the water and it evaporates. All the heat moving out of you makes you feel cold. Also why fans that push air around make you lose heat and feel cooler.

Am I dead? Am I alive? I'm both!

[BlooGoo]

I think I have to agree with Quantumcat, but I'm not sure if it's moisture in the air, or air molecules themselves, that cause the decrease in temperature, because (I think) it's possible to have a windchill when there's very little moisture in the air.

Just my 2 cents.

[tweener]

Moisture in the air (aka relative humidity) affects the wind chill factor by making the air capable of holding more heat for a given volume.  At the boundary between skin and air, there is a layer of still air that warms up and serves to insulate the skin from losing more heat.  When wind moves the air, this layer is thinned and cooled, thus increasing the rate  of heat loss.  The faster the wind blows the faster the heat is lost, thus the wind chill temp. is lower.  The higher the relative humidity, the more efficiently the air removes heat from the skin, and the lower the wind chill temp.

Sounds good anyway.

----
John - The Eternal Pessimist.

[NakedScientist (OP)]

ANSWER TO LAST WEEK'S QOTW "CAN YOU EXPLAIN 'WIND CHILL FACTOR'"

You have all pretty much hit the nail on the head. Heat leaves our bodies, which are much warmer than the surroundings, by following a thermal gradient (hot to cold). The cooler the surroundings relative to body temperature, the steeper the gradient and hence the greater the rate of heat loss.

When you stand in still air, heat leaving your body warms the air around you so that it acts like a layer of insulation. This effectively reduces the thermal gradient, slowing down heat loss. But when you are out in a high wind the air around your body is continuously being replaced with fresh cold air. Under these circumstances the thermal gradient becomes much steeper and you lose heat much more rapidly, at a rate equivalent to the surrounding temperature being much colder than it really is. Hence the term "wind chill factor".

TNS

[NakedScientist (OP)]

This week's QOTW is much more challenging and might require a bit of research on your part, but has a satisfying answer. Have a go at :

"WHY ARE THERE 7 DAYS IN A WEEK, AND WHY DOES THE WEEK BEGIN ON A MONDAY ?"

Happy hunting

TNS