Sun and the Poles
The discussion here is from a question that was raised in the yahoogroup
http://groups.yahoo.com/groups/Astronomy_Activities_2009/
Q. I understand that Sun is bigger than Earth by 100 times. In that case why North pole is not getting proper sunlight ?
Question From Prudhviraj studing in Avalon Heights International School, Navi Mumbai in Std IV
Answer from From Sagnik Chakrabarty, of Amateur Astronomers Association, Delhi,
Hey Prudhvi,
The Sun is 100 times bigger than the earth, but it is about 150,000,000 km away
from earth! So, it appears quite small to us. Now, the axis about which earth
rotates is not straight. it is tilted by about 23.4 degrees. That is why all
globes you see are also tilted, not straight. So, at one point of the year, one
of the poles is nearer to the sun and another is farther. This is the reason why
both the poles don't see the Sun for months in end. It is the same reason why we
have different seasons. When the northern hemisphere (the upper half of the
globe) is farther from the sun we have winter and the north pole gets no
Sunlight. At that time, the southern hemisphere (the other half of the globe),
which is closer to the sun has summer season and the south pole gets sunlight. 6
months later, when the earth is in the opposite point on the orbit, the
situation changes. North pole gets sunlight and south pole is dark. If you have
problems understanding the concept, I suggest you do an experiment. Draw a big
circle on the floor and place a candle in the center. This is your Sun. Now,
take a globe and place it at a point on the circle so that one half of the globe
is towards the candle and the other is away. This is the earth. The circle is
the orbit of earth. Make sure that the height of the candle is about half the
height of the globe. So now, the candle's flame will shine directly on the
globe's equator. You will notice that the candle shines brighter on the nearer
side of the globe. Now move the globe to a point on the circle, exactly opposite
to the one before. Make sure that the direction of the axis is not changed. You
will see that the other half of the globe gets more light now. Hope I have been
able to help you. Keep wondering how things happen and keep asking questions
buddy!!
Further Discussion by N. Rathnasree, Nehru Planetarium, New Delhi.
Actually the relative closer distance to the Sun, that comes
about due to the fact that one of the hemispheres is tilted towards the Sun,
does not effect the amount of sunlight - Earth's orbit is hardly elliptical
enough for this.
The reason one gets less of sunlight in regions of the Earth that are away from
the latitudes where the Sun is perpendicular at that time, is that the
inclination makes sunrays at other latitudes fall in an oblique manner - the
same amount of sunlight gets spread over a larger area - this is the only reason
why we have seasons. The relative nearness arising either from the ellipticity
of the orbit or the inclination and one hemisphere tilting towards or away from
the Sun does not matter. For Mars, it does though and I will post later about
that.
And, Prudhvi, the Sun would never shine perpendicularly on the poles - I think
one would need some relevant figures to be drawn to give a better idea. Here is
a page (to be uploaded) on our website that might help get this concept
clarified.
(This is a topic that has not been discussed and calrified fully as yet, please do join the group http://groups.yahoo.com/groups/Astronomy_Activities_2009/ and add your inputs)