How big would the sun be from the surface of Mercury and from the surface of Neptune? From the planet Neptune, the sun would look only slightly brighter than all of the other stars in the sky. You would be able to look at it directly without doing any damage to your eyes. From the surface of Mercury, the sun would appear three times larger than it does from Earth.
Neptune takes 164.8 years to orbit the sun once and is an average of 4.5 billion km away from it. Despite the great distance, light from the sun still reaches Neptune in 4 hours.
Mercury takes 87.97 Earth days to orbit the sun and is an average of 52 million km away from it. It takes light 3.2 minutes to reach the planet’s surface.
Neptune is the coldest planet in the solar system and has a temperature of -218℃ at the top of its atmosphere. It also has the highest windspeeds of any planet: 2,400 km/h! The highest windspeed ever recorded on Earth was 371 km/h. If we had Neptune windspeeds on Earth, we would either have to live underground or we would all be blown to the moon. Because Neptune is so far away from the sun, it only receives about one thousandth of the sunlight that we get here on Earth. This is still enough energy to warm up the planet’s atmosphere. The South Pole of the planet is far hotter than the rest of the planet. The planet takes 165 Earth years to make an orbit, so the South Pole is towards the sun for half of that time and the North Pole for the other half. This heats up one part of the planet and causes the incredibly fast winds.
Mercury is so close to the sun that it is basically baked. However, because it has no atmosphere, it is only hot in direct sunlight. The side facing the sun reaches 427˚C, and the side away from the sun falls to -172˚C. The fact that the planet is only hot in direct sunlight means that there is probably ice on the planet, hidden in deep craters.
Interestingly, Neptune was not discovered until 60 years after Uranus, and it was discovered through mathematical calculations, rather than being spotted. In 1821, Alexis Bouvard made astronomical predictions for the path of Uranus. However, he discovered that Uranus was not following the predictions, but was deviating. He guessed that another, unknown planet, was gravitationally affecting Uranus and pulling it off its predicted orbit.
Urbain Le Verrier made the same calculations and persuaded Johann Gottfried Galle at the Berlin Observatory to help him search. They found it on 23rd September 1846. It was exactly where Le Verrier had calculated it would be. Neptune was finally visited by Voyager 2 in 1989.
Mercury was discovered in about the 14th century BC. Unlike Neptune, Mercury is visible with the naked eye. The people at the time thought it was a star. It wasn’t until the Greeks that people became aware that planets and stars are different. Galileo was the first person to view the planet through a telescope in 1610.
Neptune is a very blue planet because the methane in its upper atmosphere absorbs the red sunlight and reflects the blue. Both Neptune and Uranus have methane in their atmosphere, but this produces a blue-green color in Uranus but a blue color in Neptune. Neptune must have an unknown component that makes it so much bluer. It is possible that the color is produced because the gases on Neptune move faster than on Uranus, meaning it absorbs light more efficiently. There is a planned probe mission from the Chinese Space Agency, but this isn’t until 2038, so it will be a long time before astronomers can analyze the atmosphere.
So, if you were able to stand on Neptune and look up at the sky, you would only just be able to distinguish the sun from any of the others stars. If you stood on Mercury and looked up at the sky, you would be dazzled by a sun that is three times larger than the sun we can see here on Earth. Then about one second later you would combust. And that is what I learned today.
Sources
https://en.wikipedia.org/wiki/Neptune
https://calgary.rasc.ca/sun_and_transits.htm