Here's an answer that didnt come out of a butt. When you see the sun on the horizon does it not look bigger also? When the sun sets it is at its furthest visible distance from you but appears larger also. That is because there is a lot more of earth's atmosphere between you and the sun which magnifies it at the same time as it filters its radiance. So, the atmosphere tones down the sun's fiery magnitude during sunset and sunrise. If I'm wrong shoot me.

Here's what I found on the subject. The following is an excerpt from: http://mintaka.sdsu.edu/GF/vision/Galileo.html "In fact, in the article “Eye protective techniques for bright light,” published in Ophthalmology 90, 937-944 (1983), David H. Sliney wrote: When the sun is low in the sky it is yellow or orange indicating that the hazardous blue light has been scattered out of the direct path of sunlight, and the sun may be fixated for many minutes without risk. It's worth going through the numbers for this situation, because there is a very large and rapid change in the brightness of the Sun near sunset. For example, the smallest possible atmospheric extinction coefficient at sea level in blue light is about 1/4 stellar magnitude per airmass (the airmass at the zenith is taken to be unity.) When the Sun is 5° above the horizon, the airmass is about 10, so the blue light is reduced by at least 2.5 magnitudes, or a factor of 10. This would ordinarily not permit a threshold lesion to develop in 100 seconds; if we suppose the damage depends only on the total exposure, then 1000 seconds would be required, assuming the brightness remained constant. But, at low latitudes, the Sun sets 20 minutes or only 1200 seconds after reaching an altitude of 5° — and during this time, its brightness is rapidly decreasing. This suggests that, at low latitudes, staring at the Sun for the full 20 minutes before sunset might be marginally enough to produce a threshold photochemical retinal lesion in an average eye. As there is evidently some variation in sensitivity, not all eyes would necessarily be safe at this point. AND: "D. Sliney and H. Wolbarsht Safety with Lasers and Other Optical Sources (Plenum, New York, 1980) On pp. 205-206, they say: As sunset approaches, the relative fraction of blue light in this direct solar spectrum dramatically decreases as the sun nears the horizon. … [O]nce the total irradiance falls below 3 mW/cm2 (corresponding to an elevation angle of less than 5° at sunset in relatively clear weather), most people find it reasonably comfortable to look at a sunset which lasts for less than 10 minutes. … [They then go through a detailed calculation that need not be repeated here.] This would also explain why an individual who drives toward the sun at low elevation angles as he goes to and from work does not receive a retinal injury. "

We have man made polution that filters out the light and give us wonderfull colors.

The simple answer is "due to the angle of the viewer from the sun". The atmosphere greatly reduces the amount of light the viewer sees. However, staring at the sun is not necessarily permanently damaging. Take Sir Isaac Newton. To test a question about colours, he stared at the sun with one eye until all the colours changed. As a result he had to shut himself up in the dark for several days before he could rid himself of the spots now floating before his eyes. Thomas Harriot, who discovered sunspots independently, once observed the Sun near noon, and reported that “My sight was after dim for an houre.” John Greaves reported afterimages looking like “a company of crows” for “some days” after making solar observations directly through a telescope. G. Lowe also wrote: "As there appears to be prevalent a belief that looking at the sun with the naked eye would be injurious … , for some years I have experimented with the sun by looking at it with the naked eye … . On one occasion, on the 21st of June at 12 o'clock noon, I looked steadily at the sun for 15 minutes, changing from one eye to the other at intervals of about 30 seconds, and beyond making my eyes run there was no inconvenient effect. This was done while I was living in Atlanta, Ga., where the sun is fairly strong on the date given. As this took place 12 years ago, and, as at the age of 68 my sight is very good, I am sure that no one need fear trying similar experiments." So, it's rare to hear of anyone suffering eye damage from just looking at the Sun under normal conditions. I would add that I would still not recommend trying this one yourself.

A somewhat less technical answer is that the nitrogen in our atmosphere tends to scatter the higher energy, blue, wavelengths of light. The more atmosphere the light has to pass through, the more blue light that is scattered. So, by the time the sun is approaching the horizon, it is passing through so much atmosphere that most of the blue light is scattered out of the Sun's light. (BTW, this scattered blue light is why the daytime sky is blue.) Thus, the setting Sun is not as bright and is much more red in color. The red color is also important because red light is not as energetic as blue light so it would take a longer exposure to the red light to do damage than it would to the same amount of blue light.