Weather Blog

Hypothetically speaking, the sun looks larger now

Hypothetically speaking, the sun looks larger now
Not that we've seen the sun in the past month to notice (and you're not supposed to be looking at the sun anyway) but if it were out, it would appear about 5% larger than it does in July.

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

The Earth's orbit around the sun isn't a perfect circle -- it's more of an ellipse. Around Jan. 4th, the Earth is at its closest point to the sun -- called the "perihelion". We are now 3.1 million miles closer to the sun than we will be around the 4th of July, when we're at "aphelion". (No correlation on whether the smaller sun is the responsible for the fact that July 4 is statistically the wettest day of July. That's just Seattle working its ironic weather magic.) The next question you might ask is -- does that mean our summers are cooler then the southern Hemisphere, since they are closer to the sun in their summer? And our winters are warmer since the sun is closer?

The logic is sound, but in actuality, it turns that it's not the case.

The Earth does receive 7% 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.

Thus, even though we get less of the sun's energy in the summer, we have more land in the Northern Hemisphere summer to where the sun's energy heats up more. So much so that the Earth is actually, on a whole, about 4 degrees warmer in July than January, even though there's less energy.

(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 trick -- 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 at this link

And to find out exactly when it will be aphelion or perihelion, check out this link

Just be sure to subtract 7 hours for winter (PST) and 8 hours for summer (PDT) as these times shown are for GMT.

P.S. As another aside, Jan. 4 is about the coldest day of the year and now the average temperatures start their climb again toward summer.