atmospheric scienceheatsuntemperature
I've heard that if a space shuttle enters the atmosphere from a bad angle its surface will become so hot that it will be hotter than the surface of the Sun.
How can that be? It seems to an uneducated mind that Sun is really really hot, how could something seemingly minor such as a wrong angle of entrance to the earth's atmosphere could end up generating a heat hotter than the Sun?
There is a nice article about this on the Scientific American web site. The simple answer is that we don't know why the corona is so hot though there are a few well established and plausible suggestions.
Some introduction:
The coronal temperature is not just a bit higher than the Sun's surface, it's getting on for a thousand times hotter - a few million kelvin as opposed to around $5,700$ K at the surface of the Sun. But what we mean by this is the atoms/ions in the corona have very high velocities. The corona is pretty tenuous. The pressure in the corona is around a million times lower than the pressure at the Earth's surface, so the corona is pretty close to a vacuum. Rather than thinking of the corona as a hot gas we should think of it as a region in which a low density of atoms/ions have been accelerated to high velocities. The question is then what is doing the accelerating?
An obvious suggestion is that the Sun's magnetic field is responsible for transferring energy to the corona. The magnetic field is subject to various forms of turbulence and since the ions in the corona interact strongly with the magnetic field it is quite plausible that turbulence in the field is accelerating the ions.
The other suggestion is that turbulence at the surface generates sound waves, in effect the sort of shock waves created by explosions on Earth, and it's these shock waves that transfer energy to the particles in the corona.
But right now we don't have the experimental data to tell which, if either, of these mechanisms is correct.
In general, the sun's light (particularly the UV that causes sunburn) has to pass through a lot more atmosphere (or a greater amount of air mass) in the morning and evening to get to a vertical surface than it does when it is at zenith to a horizontal surface.
An example is shown in the generalised image below (all graphs are obviously generalised):
The caption from the source (The Daily Cycle of Sunlight: Part 1) is (the relevant statements are in bold):
When the sun is close to the horizon, its rays pass through a thicker slice of the atmosphere, which warms the color of sunlight (orange arrow). During the middle portion of the day, the sun’s rays pass through a thinner slice of the at-mosphere (white arrow). We define noon sunlight as being neutral white—neither warm nor cool.
As such, the solar radiation is absorbed and scattered more in the atmosphere in the morning or evening. The net effect can be shown on the following diagram:
Source: It's Coldest After Dawn
In terms of sunburn, the erthemal dose rate (related to UV radiation) follows the same pattern, as seen below:
Image source: NOAA, where the define erythemal dose rate as
indicates the instantaneous amount of skin damaging UV radiation.
Best Answer
As for the question of whether anything can be hotter than the sun. The Sun is composed of plasma, an energetic phase of matter in which electrons get ripped off of atoms, and electrons and ions coexist in something that might best be described as an ionized gas.
According to this wiki page, the so-called Z machine has achieved temperatures on the order of $10^9\,\mathrm K$ (billions of Kelvin) which is even hotter than the Sun's core which is apparently at around $10^7\,\mathrm K$ according to the physical characteristics listed here.
Thanks to user Gugg who points out that apparently Brookhaven is recognized as having achieved the hottest man-made temperature on the order of $10^{12}\,\mathrm K$. See the link he provides down below.