Weather Blog

Does the sun look smaller now? It should...

Does the sun look smaller now? It should...

Not that you're supposed to be looking at the sun anyway, but if you were, and if by some miracle you were able to get a clear day and see the sun in December to compare, you would notice that the sun is smaller right now -- about 5 percent smaller.

But not to worry -- it's like this every July.

The Earth's orbit around the sun isn't a perfect circle -- it's more of an ellipse. Around the Fourth of July, the Earth is at its farthest point from the sun -- called the "aphelion". This year, that occurred at 9 p.m. PDT on July 4th and we are now 3.1 million miles farther from the sun than we will be on "perihelion" -- the closest point which will occur next year on Jan. 1.

The next question you might ask is -- does that mean our summers are cooler than those in the Southern Hemisphere, since they are closer to the sun in their summer?

The logic is sound, but it's not the case. The Earth does receive 7 percent more energy from the sun in January than July, but most of the Earth's land is concentrated in the Northern Hemisphere. Land does a much better job than ocean of absorbing and releasing the sun's energy -- i.e., ground heats up faster and more easily than water.

So even though we are getting less of the sun's energy now, we have more land in the Northern Hemisphere summer to heat up.  Add it all up, and Earth is about 4 degrees warmer in July than January, even though there's less sun energy shining on us.

(Note that the Earth's tilt on its axis is way more influential to the seasons and global temperature than the minor change in the distance from the sun.)

Another stumper: the Earth's orbit speed is slightly slower this time of year as when the Earth is farthest away from the sun. That means virtually speaking, our summer ends up being about 3 days longer than the Southern Hemisphere summer/Northern Hemisphere winter.

Of course, around here, you might be hard pressed to convince people that summer is three days longer than winter.

For more information, check out this great article from NASA.

And to find out exactly when it will be aphelion or perihelion here. Just remember that is on UTC time which is +7 from PDT in the summer and +8 from PST in the winter.