Presentation on theme: "The Reason for the Seasons"— Presentation transcript:
1 The Reason for the Seasons School's Out!Brrrrrrrrrr!Leaves go down!
2 Here’s Mars… Where would you guess that it is COLDEST …you’re on Mars? right. Butwhy? Andhow did youknow?If you guessedhere……and here…
3 sunlight comes in from just one direction Half of Jupiter lit by theSunlight
4 It’s all about the angle at which the light hits the planet! Venus, lit by the SunLook at a ray of sunlighthitting the middle of theplanet.The ray hits this part ofthe planet directly at a 90 degree angle. It focuses the sun’s energy (heat)over a relatively small area.
5 But at the north & south pole? Here comes a second ray from the sun toward the south pole of Venus. Notice it hits Earth’s surface at a angle that is much less than 90 degrees.the direct ray of lightNotice how much LARGER an area the ray covers…this means it’s LESS concentrated (or more spread out).
6 So direct light heats planets up more than indirect light! Around the middle of the planet, the sun’s rays hit Earthdirectly, so the energy is more concentrated. There is more energy per unit area and the Earth heats up a relatively greater amount.But at the top and bottom of the planet, the light comesin at a less direct angle, meaning the energy is less concentrated. It is spread over a greater area and therefore does not warm the planet as much.
10 This helps, but it doesn’t explain the seasons! So far we only know why the hottest part of each planetis around the middle…the sunlight hits that part most directly.If that was all that happened, though, we WOULDN’T havedifferent seasons…just the same boring weather all year long.In Texas, it’d be about 90 degrees every day of the year with occasional rain. Not bad, but definitely BORING.
11 This is the key, so repeat after me… It’s…the…TILT
12 The Earth doesn’t sit perfectly straight up and down A “false” view ofEarth rotating on itsaxis.This just isn’t right!
15 Remember from earlier… …That the middle of the planet gets the most direct sunlight(heat).COLDmediumHOT
16 So one half of the Earth “tilts” toward the sun! What does the tilt do?Direct light = Summer!Indirect down here = Winter!Which hemisphere of Earth (Northern or Southern) is havingSummer & Winter in this diagram?
17 Scientists believe that the sun and the eight planets formed by chunks of rock and debris that self-accumulated through gravity. In other words, objects collided and clumped together, which increased their gravitational pull, which in turn drew more objects in, which made the object even more gravitationally powerful, and so on until the solar system looks like a sun and eight fairly neat planets with not much stray junk flying around.
18 Of course, occasionally these forming objects happen to attract something that's big enough to knock it off-kilter. That's what probably happened to the earth, after it was already large enough to start rotating. Actually, it probably took several substantial impacts to whack the earth into the position it's in today.
19 What does this mean for Texas? When our Northern Hemisphere tilts toward the Sun, weactually get nearly the most direct sunlight of anywhere on theplanet! No wonder we get over 100 degrees so often in July &August!
20 So…how do we get Winter here??? That happens when our (Northern) hemisphere tilts away fromthe sun.Summerdownhere!
21 And the final piece to the puzzle? So, the TILT is a big part of it, but something else mustcause us to tilt either away or toward the Sun at differenttimes during the year……and that last bit is something you’ve known for years!The Earth revolves aroundthe Sun!Watch the animation…payattention to the directionEarth’s axis points as itorbits the Sun.
22 So it’s a combination of the TILTed axis and our revolving around the sun! Yeah!!!
23 Complete the table4132A hemisphere is experiencing summer if it is tilted directly toward the sun.A hemisphere is experiencing winter if it is tilted directly away from the sun.
25 Misconceptions about the Seasons 1. We experience seasons because Earth is closer to the sun in the summer and farther in the winter.WRONGActually, the opposite is true. We are closer to the sun in the winter (91million miles away) than we are in the winter (94 million miles away).If this were true, wouldn’t Hawaii experience snow?
27 Why do we experience day and night? The Earth is…Rotating
28 Day versus NightWhen where you are is pointed toward the Sun, it is day. Then the Earth rotates you away from the Sun, and it is night.SunlightDaytimeNighttime
29 Day and Night as the Earth is rotating on its AXIS
30 Northern Hemisphere Summer Southern Hemisphere Winter Hemispheres experiencing summer receive MORE DIRECT RAYS from the sun than hemispheres experiencing winter. This direct light as its tilted towards the sun keeps the hemisphere ILLUMINATED for a greater amount of time during the day.
31 Length of Day in Hemispheres 4123#1 June Day lengthEngland (Northern Hemisphere) - 15 hours and 38 minutesAustralia (Southern Hemisphere) - 10 hours and 24 minutes
32 The Earth reaches 4 important points in its orbit 123Position 1: June SolsticeAbout June 21stTX tilted toward SunWe have our longest day, shortest nightBegins Summer
33 Three months later… Position 2: September Equinox About September 23rd 4123Position 2: September EquinoxAbout September 23rdTX tilt in between “toward” and “away”12 hrs day, 12 hrs nightBegins Fall
34 #23 Three months later… Position 3: December Solstice 4123Position 3: December SolsticeAbout December 22ndTX tilted away from SunShortest day, longest nightBegins Winter
35 Three months later… Position 4: Vernal Equinox About March 21st 3Position 4: Vernal EquinoxAbout March 21stTX tilt half way between “toward” and “away”12 hrs day, 12 hrs nightBegins Spring
36 So, In Summary…If somebody asked you, “Why do we have seasons on Earth?” youcould now answer with great confidence…Fact 1: Round planets heat up wherever they get direct sunlightand are cooler at the tops and bottoms.Fact 2: The Earth’s axis is TILTED 23.5o.Fact 3: As Earth revolves around the Sun, the tilt causes differentparts of it to receive more or less direct sunlight for a few months,causing the weather and daylight to change.