Praise be to Allah.
Shaykh Muhammad ibn ‘Uthaymeen (may Allaah have mercy on him) said:
The believer’s responsibility with regard to reports of the unseen is to accept and submit to them, and not to ask how or why. This is the foundation on which out ‘aqeedah must be built, because this is a matter that is beyond your comprehension. So you have to accept it and submit and say, “We believe. We believe that the sun will be brought close to mankind on the Day of Resurrection until it is one mile away from them. Asking any futher questions about that is a kind of innovation (bid’ah). Hence when Imam Maalik (may Allaah have mercy on him) was asked how Allaah rose above the Throne, he said, “Asking about this is bid’ah.” Similarly it is bid’ah to ask about all other matters of the unseen; man's attitude towards them should be to accept and submit.
The answer to the second part of the question, about the sun being brought close to mankind on the Day of Resurrection:
We say that bodies will not be resurrected on the Day of Resurrection in the form in which they were in this world, with their shortcoming and inability to bear that; rather they will be resurrected whole and complete. Hence the people will stand on the Day of Resurrection for a day which is equivalent to fifty thousand years, neither eating nor drinking. This is something which would be impossible in this world. Then the sun will be brought close to them and their bodies will be given the ability to bear its being brought close, as we have mentioned above that they will be able to stand for fifty thousand years without needing food or drink. So their bodies on the Day of Resurrection will be different from their bodies in this world.