1. The core of the sun has a temperature of 15,000,000 °C.
  2. The surface of the sun has temperature around 5,000 °C.
  3. The sun is around 93 million miles (150 million km) away from earth.

My Question: With a surface of 5,000 °C, how does the sun provide heat for earth 93 million miles (150 million km) away?

  • $\begingroup$ I think its because of the greenhouse gas effect. $\endgroup$
    – Tardy
    May 2 at 21:35

2 Answers 2


It is a question of radiation emission - the temperature of the Sun's 'surface' is about 5500°C (according to NASA Earth Observatory), at that temperature, it emits radiation in the UV, visible and near infra red region - due to the fact that the hotter an object is, the smaller the wavelength radiation is emitted, as can be seen in the generalised image below (from NASA):

enter image description here

Note: the temperature of the Earth shown is an approximattion of its blackbody temperature, explained in the answer to the question What would be the temperature of earth if there was no atmosphere?.


enter image description here

Source: Wikipedia

Not all of this radiation reaches the top of Earth's atmosphere reaches the surface, a proportion is reflected off the atmosphere and some is absorbed by the atmosphere (as shown as the difference between the yellow and red in the diagram above) - but a good proportion reaches the Earth's surface.

But that is not the entire picture, we receive this 'shortwave' radiation from the Sun:

enter image description here

Which is also balanced by an equal amount of energy radiating into space as 'longwave' thermal infrared radiation:

enter image description here

(Both images from NASA Earth Observatory)

Which leads to a major point - we have an atmosphere and a natural 'greenhouse effect' due to the water vapour and carbon dioxide (and other components) that are seen in the above solar radiation spectrum diagram.

Some of the thermal infrared is absorbed by the atmosphere and re-radiated back to the surface. This radiation budget is shown below:

enter image description here

Source: NASA

Something to consider, looking at the value the NASA has for the incoming radiation reaching the Earth's surface - 168 Wm-2 - imagine that being a 168 watt light globes for every square metre - that value increases markedly when the re-radiated thermal infrared is taken into account.

Also, please view the YouTube clip How the Sun Heats the Earth which is a handy verbal and diagrammatic explanation of the content of this answer.


It is the warmth of the atmosphere that you feel on your skin. The atmosphere is warmed from the surface of the Earth. Visible light from the sun hits the surface of the Earth and some of it is absorbed, causing the Earth's surface to warm, which is re-radiated as infrared light and is then blanketed by our atmosphere. Without the atmosphere, the temperature of Earth's surface would be much colder and have a much more dramatic diurnal cycle.


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