Pergunta estupida sobre o Sol
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Nthor
Banido
O que eu disse foi:
O que se explica pelo facto de o pólo norte terrestre não ser coincidente com o pólo norte solar é pelo eixo inclinado de rotação do nosso plneta, daí que no nosso inverno o hemisfério norte esteja a 152 milhões de km do Sol e o hemisfério sul a 147 milhões de km, de notar que a órbita da Terra não é um circulo perfeito mas antes elíptica o que ajuda a acentuar as diferenças entre as estações do ano.
Desculpem, mas não entendo qual é a duvida isto é matéria do 6º ano ou 8º (já não sei).
V?nia Morais
Banido
citação:Originalmente colocada por Nthor
A incidência dos raios solares justifica a variação da temperatura ao longo do ano, ou seja, devido à forma arredondada da Terra, os raios solares atingem a superfície terrestre com diferentes graus de inclinação.
Se projectarem a luz de uma lanterna na parede, na horizontal, verão um círculo perfeito circunscrito na mesma. Se agora experimentarem projectar a luz, à mesma distância, mas numa posição mais oblíqua, poderão constatar uma forma oval e de maiores dimensões. Então, concluímos que a energia dos raios solares quando é distribuída numa superfície menor (no caso do círculo - quando projecto a lanterna na horizontal)apresenta uma temperatura mais elevada; pois, quando os raios incidem sobre a Terra de um modo mais oblíquo a superfície a aquecer é maior e, assim sendo, há uma menor concentração da energia solar... Pelo menos é com este exemplo e de lanterna em punho que explico a variação da temperatura aos meus pequenitos... e dúvidas nunca persistem.
V?nia Morais
Banido
Liberal
New member
What causes the seasons?
Bad Astronomy: The seasons are caused by the change in the distance of the Earth to the Sun.
Good astronomy: The seasons are mostly due to the axial tilt of the Earth. The change in distance of the Earth to the Sun is a very minor player.
How it works: This is one of the most pernicious types of ideas: one that sounds reasonable, and so it propagates easily. Unfortunately, it's wrong. Well, not completely wrong; certainly the Earth's distance from the Sun has something to do with the temperature, but it is a relatively minor effect.
First, a sanity check: The Earth's orbit is an ellipse. The Earth reaches perihelion (the point in its orbit closest to the Sun) in January, and it reaches aphelion (farthest point from the Sun) some six months later. If that were all that governed weather, we'd have summer in January, and Winter in July! This may be true for our Southern Hemisphere friends, but not up in the North. Something else must be going on.
We can check our qualitative conclusion above with some (simple!) math. The math involved in calculating a planet's gross temperature has been known for a long time. Basically, the temperature depends only weakly on distance changes; the temperature goes as the inverse square root of the distance of the planet to the Sun. What does that mean? In other words, if you double the distance of a planet from the Sun, the temperature will drop by the square root of 2, or about 1.4. Doubling the Earth's distance from the Sun will drop the mean temperature by about 80 degrees Celsius (Careful here! You cannot use Celsius units for the actual calculation. You have to use the Kelvin scale, which has the same units as Celsius, but starts at 0. In other words, 0K = -273 C. If you take the square root of the temperature using Celsius you'll get the wrong answer! However, since the units are the same, an 80 degree drop is the same in both scales). Specifically, the Earth's average temperature is about 280 degrees Kelvin (10 Celsius). 280/1.4=200, or a drop of 80 degrees.
At perihelion (nearest point) the Earth/Sun distance is about 147,000,000 km, and at aphelion (farthest point) it's about 152,000,000 km. The change in temperature is then
square root( 152,000,000 / 147,000,000 ) =1.017
or just less than 2 percent. This turns out to be only 5 degrees Celsius, which is quite a bit less than the temperature change we see between winter and summer. Obviously, something else must be going on.
The largest contributor to the change in seasons is the tilt, or inclination, of the Earth's spin axis with respect to its orbital plane (the ecliptic). The usual explanation is as follows: take a flashlight and a piece of paper. Shine the light straight onto the paper, so you see an illuminated circle. All the light from the flashlight is in that circle. Now slowly tilt the paper, so the circle elongates into an ellipse. All the light is still in that ellipse, but the ellipse is spread out over more paper. The density of light drops. In other words, the amount of light per square centimeter drops (the number of square centimeters increases, however, so the total amount of light stays the same-- you expect that, as the light from the flashlight has not changed).
The same is true on the Earth. When the Sun is overhead, the light is falling straight on you, and so more light (and more heat) hit each square centimeter of the ground. When the Sun is low, the light gets more spread out over the surface of the Earth, and less heat (per square centimeter!) can be absorbed. Since the Earth's axis is tilted, the Sun is higher when you are on the part of the Earth where the axis points towards the Sun, and lower on the part of the Earth where the axis points away from the Sun.
For the Northern Hemisphere, the axis points most toward the Sun in June (specifically, around June 21), and away from the Sun on December 21. This corresponds to the Winter and Summer Solstices, or the midpoints of summer and winter. For the Southern Hemisphere, this is reversed.
There is more, too. In the summer, the Sun is higher, and therefore the days are longer. This gives the Sun more time to heat the Earth, so it gets hotter. In the winter, the sun is lower, and the days are short, giving the Sun less time to heat the Earth. This is a secondary effect.
The distance of the Earth to the Sun is a smaller effect yet, but it does exist! So the Southern Hemisphere gets slightly hotter summers and slightly colder winters than the North. But only by a couple of degrees, and only on average. Your mileage may vary!
http://www.badastronomy.com/bad/misc/seasons.html
Bad Astronomy: The seasons are caused by the change in the distance of the Earth to the Sun.
Good astronomy: The seasons are mostly due to the axial tilt of the Earth. The change in distance of the Earth to the Sun is a very minor player.
How it works: This is one of the most pernicious types of ideas: one that sounds reasonable, and so it propagates easily. Unfortunately, it's wrong. Well, not completely wrong; certainly the Earth's distance from the Sun has something to do with the temperature, but it is a relatively minor effect.
First, a sanity check: The Earth's orbit is an ellipse. The Earth reaches perihelion (the point in its orbit closest to the Sun) in January, and it reaches aphelion (farthest point from the Sun) some six months later. If that were all that governed weather, we'd have summer in January, and Winter in July! This may be true for our Southern Hemisphere friends, but not up in the North. Something else must be going on.
We can check our qualitative conclusion above with some (simple!) math. The math involved in calculating a planet's gross temperature has been known for a long time. Basically, the temperature depends only weakly on distance changes; the temperature goes as the inverse square root of the distance of the planet to the Sun. What does that mean? In other words, if you double the distance of a planet from the Sun, the temperature will drop by the square root of 2, or about 1.4. Doubling the Earth's distance from the Sun will drop the mean temperature by about 80 degrees Celsius (Careful here! You cannot use Celsius units for the actual calculation. You have to use the Kelvin scale, which has the same units as Celsius, but starts at 0. In other words, 0K = -273 C. If you take the square root of the temperature using Celsius you'll get the wrong answer! However, since the units are the same, an 80 degree drop is the same in both scales). Specifically, the Earth's average temperature is about 280 degrees Kelvin (10 Celsius). 280/1.4=200, or a drop of 80 degrees.
At perihelion (nearest point) the Earth/Sun distance is about 147,000,000 km, and at aphelion (farthest point) it's about 152,000,000 km. The change in temperature is then
square root( 152,000,000 / 147,000,000 ) =1.017
or just less than 2 percent. This turns out to be only 5 degrees Celsius, which is quite a bit less than the temperature change we see between winter and summer. Obviously, something else must be going on.
The largest contributor to the change in seasons is the tilt, or inclination, of the Earth's spin axis with respect to its orbital plane (the ecliptic). The usual explanation is as follows: take a flashlight and a piece of paper. Shine the light straight onto the paper, so you see an illuminated circle. All the light from the flashlight is in that circle. Now slowly tilt the paper, so the circle elongates into an ellipse. All the light is still in that ellipse, but the ellipse is spread out over more paper. The density of light drops. In other words, the amount of light per square centimeter drops (the number of square centimeters increases, however, so the total amount of light stays the same-- you expect that, as the light from the flashlight has not changed).
The same is true on the Earth. When the Sun is overhead, the light is falling straight on you, and so more light (and more heat) hit each square centimeter of the ground. When the Sun is low, the light gets more spread out over the surface of the Earth, and less heat (per square centimeter!) can be absorbed. Since the Earth's axis is tilted, the Sun is higher when you are on the part of the Earth where the axis points towards the Sun, and lower on the part of the Earth where the axis points away from the Sun.
For the Northern Hemisphere, the axis points most toward the Sun in June (specifically, around June 21), and away from the Sun on December 21. This corresponds to the Winter and Summer Solstices, or the midpoints of summer and winter. For the Southern Hemisphere, this is reversed.
There is more, too. In the summer, the Sun is higher, and therefore the days are longer. This gives the Sun more time to heat the Earth, so it gets hotter. In the winter, the sun is lower, and the days are short, giving the Sun less time to heat the Earth. This is a secondary effect.
The distance of the Earth to the Sun is a smaller effect yet, but it does exist! So the Southern Hemisphere gets slightly hotter summers and slightly colder winters than the North. But only by a couple of degrees, and only on average. Your mileage may vary!
http://www.badastronomy.com/bad/misc/seasons.html
Nthor
Banido
Imaginem um pião a rodar, nunca está no mesmo sitio, o mesmo acontece com o Sol, esta movimento do Sol é acompanhado por todos os planetas e corpos do sistema solar, mas este movimento (do Sol) é um movimento lateral e não para cima e para baixo como foi referido, e como é acompanhado por todos os corpos do sistems solar pode ser comparado a uma valsa elegantemente dançada, isto tudo a uma escala irrelevante para nós e para a forma como a Terra recebe os raios solares.citação:Originalmente colocada por Noé
citação:Originalmente colocada por Nuno_Cabral
citação:Originalmente colocada por 16v
O Sol não mexe ...
Nem um centímetro.
Nem um milimetro[]
Toda a galáxia mexe...
Como diz o Noé toda a galáxia se move, quase como um sistema mecânico de um relógio (é uma péssima analogia mas serve para explicar o conceito) em que o movimento do buraco negro no centro da galáxia ao rodar (o tal exemplo do pião) "arrasta" consigo toda a galáxia.
Nthor
A terra está no Inverno em Portugal e no Verão no Brasil, ao mesmo tempo.
Não é possível teres o hemisfério Norte no Inverno e o Sul no Verão com a "parte de cima-Norte a 152 milhões de km do SOL e a parte de baixo-Sul a 147 milhões de km do SOL com uma terra com 12 mil Km de diâmetro.
Concordas???
Einstein
New member
Se te referes à distancia da Terra ao Sol, no Verão o Sol está mais longe, devido a forma elíptica da arbitra Terrestre em torno do Sol