If I could get a temperature reading, for, say, every 100 square miles of earth, and then average them out, would it be about the same every day? (I’m assuming we would measure the temp above bodies of water as well as on land.)
From WIKIanswers:
"The average temperature of Earth’s surface has varied between 13.8 and 14.6 degrees Celsius (56.8 and 58.3 degrees Fahrenheit) during the period from 1950 to 1999.
In the year 1999, the average global temperature was approximately 14.4 degrees Celsius (57.9 degrees Fahrenheit). "
I would guess that the average temperature would be slightly greater in the Northern hemisphere’s Winter months, because the Earth is slightly closer to the Sun at that time.
That’s a year-to-year figure, though, not a day-to-day.
I suspect that there will be a variation through the year, since the Earth’s land mass is disproportionately concentrated in the Northern Hemisphere. So July, when a lot of sunlight is falling on land, will be different from January, when a lot of sunlight is falling on water. So I would expect that July would be warmer overall (since water is more reflective than land).
Another factor, which would mitigate this, is that the Earth isn’t always the same distance from the Sun. We’re closest some time in January, so if the surface of the Earth were uniform, then the average temperature would be warmest in January.