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earth's orbit

bickerer

Critical Thinker
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Feb 8, 2008
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OK, so I'm apparently only 6 and have never taken a science course. I've been googling to no avail.
Why is June 22nd not also the hottest day of the year as well as the longest?? The hotter months in the northern hemisphere are July and August (in my neck of the woods anyway), when the earth is once again moving away from the sun in it's orbit...right?? Shouldn't the temperature start it's climb earlier, peaking ON the 22nd of June?? Or is the orbit such that the earth is still farther away in June and snuggled up closer to the sun in July and August?? Can anyone (like a 7 year old) help me on this?? Or provide me with an explanatory link or two??


Sincerely,
Too embarassed to sign my name
 
It takes a while for the heat to build up, and then to dissapate(sp?). During spring, the warming earth still has some ice to melt, and this ice (and cold water) keeps the heat from having its full effect. Then, during summer, there's no ice or cold water, so it gets hotter as the earth pulls away from the sun.
 
The earth, especially the oceans, have a nonzero heat capacity. That means it takes time to warm up. If the input heat is oscillating, the temperature won't oscillate exactly with the input heat, but will lag behind it, because it's still warming up even when you hit peak heat input. Same thing on the cooling side: it takes time to lose heat. Ocean temperature isn't so important in the day-night oscillations, which happen too quickly to transfer much heat from water to land, but it's VERY important in the summer/winter oscillations, since they happen slowly enough for large amounts of heat to be transferred back and forth.
 
Well, I don't think you're right about distance form the sun. The seasons are related more to the tilt of the earth on its axis than the Earth's proximity to the sun. I think, in fact, the earth is closer to the sun in January than it is in June.

As for why the longest day isn't also the hottest in the northern hemisphere - I'm not sure, but I'll bet it has something to do with more land mass in the northern hemisphere and land absorbing heat from the sun (as opposed to reflecting it away).
 
There are a lot of complicating factors as other posters have mentioned, but if I focus on the one factor you are looking at there is one thing to realize that is easy to overlook.

The longest day of the year is not when you'd expect the highest temperature. It's the day when you'd expect the greatest temprerature rise.

There are four points thoughout the year to be concerned with: The longest day of the year which you mentioned; Six months later the shortest day; in between those two there are two days of equal length.

That means there are six months of the year where day is longer than night and the longest day in the middle of that. However the entire six months all the way up to last day are days when you have more time to gain heat than lose it. These six moths are the heating months with the most heating happening in the middle. The other six months the nights are longer than the days and the shortest day is in the middle of those six months. And during these six months there is more time to lose heat at night than to gain it during the day. These six months are cooling months with the most cooling happening during the middle.

So, if the factor you are asking about was the only factor, the day of greatest temperature rise would be the longest day of the year, but the temperature would still continue to rise for three months after that because day is still longer than night. The day of greatest temperature drop would be the shortest day of the year, but the temperature would still continue to fall for three months after that because night is still longer than the day.

But the highest temperature would occur at the end of summer on the day where day and night are equal. That's the day that spot on Earth switches from warming to cooling. Same thing for the coldest day. It would occur at the end of winter on the day where day and night are equal. That's the day that spot on Earth switches from cooling to warming.
 
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What defines the temperature on a summer day is the amount of heat in a given, measured quantity of atmosphere. The heat doesn't just get there by magic; the sun has to radiate down on the earth until it strikes a surface that absorbs some of it, and then that surface warms up. It in turn begins warming air, by conducting heat directly into it, by allowing thus warmed air to expand and rise, and by radiating it back upwards as longer wavelength infrared radiation (known as heat conduction, convection and radiation). The latter effect, infrared radiation, may further warm the air if it is absorbed, as it is by the infamous "greenhouse gasses". These warm the air, whose temperature is then measured. The warmth of a particular parcel of air is affected by:
- the warmth left over in it from the day(s) before minus the lose of heat at night by radiation;
- how close it is to the conducting warm surface;
- how much it has risen due to bouyancy and how much it has mixed with the cooler air above and around it, and how cool that other air is;
- how much heat has radiated away from it as opposed to how much has been absorbed.
In all, a very complex result. Like anything else it takes time to thoroughly warm a parcel of air as great as the 30 mile deep atmosphere over a continent; it cannot happen instantaneously, and that time is reflected in the differential between the longest day of summer and consequent shortest night, and the day on which the temperature reacjhes a peak near the surface - typically 6 weeks or so.
 
I think you ought to be able to piece it together from that onslaught. For tomorrow's quiz, tell us what the effect of having a ocean beach has on that hottest day of the year. Dismissed!
 
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I love all of you...................... thanks so very much. Durn it but sometimes I wishes I wuz smarter.:D
 
Season driver

bickerer said:
Or is the orbit such that the earth is still farther away in June and snuggled up closer to the sun in July and August??
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madurobob said:
Well, I don't think you're right about distance form the sun. The seasons are related more to the tilt of the earth on its axis than the Earth's proximity to the sun. I think, in fact, the earth is closer to the sun in January than it is in June.
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I want to follow up on madurobob's comment. On average, the closest Earth gets to the sun is about 147,090,000 km (91,400,000 miles; perihelion) and the farthest it ever gets from the sun is about 152,100,000 km (94,510,000 miles; aphelion). I say "on average" because Earth's orbit, like all the other orbits in the solar system, is not exactly constant, just almost constant. Each year Earth takes a slightly different orbit around the sun, because of the gravitational tugging of all the other planets (but mostly Jupiter, which by itself is "most of the other planets"). The difference between those two numbers is a bit more that 3%, say about 3.3%. That's hardly enough to be the driving force behind the annual change in seasons. The real power behind the driving of the seasons has already been pointed out by others. It is a combination of a more efficient heating because of the higher sun angle and more abundant heating due to longer days.

I also note that madurobob is correct that perihelion occurs in January, and aphelion occurs in July. Since Earth's orbit is not constant neither are the dates of perihelion and aphelion. But see the Earth's Seasons webpage, courtesy of the data Services department of the U.S. Naval Observatory. In 2009, perihelion occurred on January 4 at 15:00 UT, and aphelion will occur on July 4 at 02:00 UT (times approximate). So Earth is actually closest to the sun in winter and farthest from the sun in summer.

But of course that's winter & summer in the northern hemisphere only. Remember that the seasons are reversed for our friends south of the equator, and that by itself should be a clue that distance from the sun is not the season driver.
 
Think of it this way. The Northern Hemisphere will warm as long as there is more heat coming in then going out. It will cool for as long as there is more heat going out then coming in.

Because the earth holds a lot of heat the outgoing energy doesn’t fluctuate nearly as much as incoming energy but over the course of a full year their average needs to be pretty close. (global warming notwithstanding)

June 22 is the time most energy is coming in, so it’s when you get the greatest warming but the NH still receives a more energy then the yearly average until mid September. If outgoing energy were absolutely constant, you would actually expect the NH to warm until incoming energy dropped below the yearly average incoming energy. Since outgoing energy is in part a function of current temperature this peak occurs a little sooner.
 
bickerer said:
I love all of you...................... thanks so very much. Durn it but sometimes I wishes I wuz smarter.:D
Click to expand...

The fact that you're asking the question at all puts you above the average IMHO.
:)
 
This is also the same reason that it is warmer at 5pm than it is at noon. Tides also "lag" the movement of the moon.
 
portlandatheist said:
This is also the same reason that it is warmer at 5pm than it is at noon. Tides also "lag" the movement of the moon.
Click to expand...

If I don't turn the AC on in my house, the peak temperature will be about 8 PM on a sunny day due to fast heating of the attic by the sun but very slow transmission of that heat to the rest of the house.
 
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