baxman2 asked,

Why isn't the date of the summer solitice, and the date of the farest distance of Earth from the Sun, not the same?

Because in the Earth's distant past, a large planetiod hit the Earth and caused it to tilt on its axis. That being a random event, one would not expect to find any relationship between the shape of the Earth's orbit and the tilt of its axis. People usually notice the relationship because the hottest time of the year (in the north-centric view of the Earth's hemisphere) does not correspond with its closest distance to the Sun. Northern hemisphere high temperatures correspond to the Earth's farest orbital distance from the Sun. Both the distance from the Sun (aphelion greatest; perihelion smallest) and the 23 1/2 degree tilt of the Earth's axis to the ecliptic effect the relative intensity of the seasons in both the southern and northern hemispheres. But, the climate effect of the tilt of Earth's orbital axis (that ranges other 47 degrees in a year) is many times greater than that of climate changes induced by the changes in distance of the Earth from the Sun (152,097,701km vs. 147,098,074km or about a 3 percent distance range). Surface temperatures in Utah can range over a 40 degrees C - associated with the tilt of the Earth. Even if you could measure changes in surface temperature associated with changes in the Earth's distance from the Sun, they might amount to just a few degrees C - nothing that you would notice while walking around outside. As others have pointed out, the northern hemisphere can be in the depths of a hot summer even though the Earth is at its farest orbital distance from the Sun; conversely, the southern hemisphere can be in the depths of winter when the Sun is nearer the Sun. Currently in the northern hemisphere, the closest distance of the Sun does not correspond to summer and the farest distance does not correspond to winter. Earth is near its greatest distance (aphelion) from the Sun at the summer solistice. The Earth is at it's closet approach (perihelion) at the winter solstice, when the North Pole points away from the Sun. So, the temperature changes of the two effects - tilt and distance - are not cumulative. Currently, they tend to cancel each other out. (Looking at today's SLC weather, they are not seem to be cancelling each other out enough!) Over the next 10,000 years, this situation will reverse - the closest distance to the Sun will correspond to summer and the farthest distance from the Sun will correspond to winter. See illustration at: http://upload.wikimedia.org/wikipedia/en/4/4e/Precession_and_seasons.jpg - from http://en.wikipedia.org/wiki/Precession#Precession_of_the_equinoxes The correspondence of these cycles of distance and tilt are called "Milankovitch cycles". http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/Images/orbital_... from - http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/milankovitch_3.... Wikipedia. Milankovitch_cycles. << http://en.wikipedia.org/wiki/Milankovitch_cycles accessed 11/2004 >> (online encyclopedia) The climate effect of Milankovitch cycles have been associated with changes in the layers of ocean bed sediments. I am not sure what the indicators are, but I am assume that they involve the number of fossilized plankton and the depth of the sediment layers. - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net