Lets change is up a bit, what are your feelings on the banishment, I have given my below but I want to see what everyone else feelings and thoughts on it. Do you feel Celestia was in the wrong, Luna was in the wrong? Do you think Celestia was horrible for banishing her sister in the moon when she became Nightmare Moon?
During what would be called the Time of Troubles an entity by the name of Discord brought about unrest and disharmony after having gained control of Equestria, one that tore apart the bonds that had been formed by ponies of the land. He caused confusion and even manipulated the ponies to start fighting with each other. It is said he did all this because he found it funny; it caused him to laugh to see that under his care everything could unravel by the seams.
Two sisters, unlike any other race of pony who had the qualities of all three, rose up against Discord... yet these sisters realized they would not be able to figh him without aid. The sisters went in search of an ancient power said to only be able to be controlled by the bonds of friendship... the Elements of Harmony.
Celestia and Luna, with the Elements of Harmony, faced Discord... yet Discord had a plan, as he would do so over a thousand years later with six young mares, where he worked to turn the sisters against each other to play upon weakness of their hearts. He failed to turn them against each other, yet it would seem that he may have managed to plant seeds of doubt in the heart of the youngest. That though he was bound in stone he would help bring about his goal of turning the sisters against each other. Some time passed, and the chaos was replaced with order and harmony. Life returned to the land as did it's beauty. Each of the sisters took on a duty; the oldest Celestia took on the duty of the day while the youngest Luna took on the duties of the night. There was peace, and ponies lived in happiness... yet all was not well.
The seeds had been planted by Discord, they just needed to grow and with the older sister Princess Celestia growing so busy with her royal duties as well as the fact that ponies played during the day while sleeping during the night... the youngest sister Princess Luna begin to feel alone. Unhappiness grew in Princess Luna's heart which she hide from her dear sister who seemed so busy, unhappiness grew into jealousy and anger. Luna begin to believe that her sister and her subjects did not care about her, that they thought she was weaker than her sister. What happened at this time is unknown but it would seem that perhaps Princess Luna looked for a way of making herself more powerful, of finding a way for the ponies of Equestria to have to see her night, that some dark magic or power overcame her. By the time Princess Celestia realized what was going on it was too late, and she found that she had lost her sister... that in her place was a mare of darkness calling herself Nightmare Moon.
Princess Celestia tried to bring her sister back, to take her from the dark shell she saw her in but she failed and because she was either not strong enough to, or was unable to bring herself to do so, defeat Nightmare Moon. She went to the only power she know that could help her... the Elements of Harmony. Yet they did not work the way they should, as the bonds Celestia had shared with her sister was broken... yet impressively she was still able to get them to work partly and with the Elements of Harmony she was able to banish Nightmare Moon to the moon itself. To save Equestria from endless darkness and the suffering that would come from it, she gave up her only friend and beloved sister. Such sacrifice cost much and became of the loss of her sister Princess Celestia had need to take on burden of the responsibilities of both the day and the night until she could find the one that would be able to bring back her sister.
Towards the end of one thousand years Princess Celestia found her sister's savior through that of a little filly by the name of Twilight Sparkle... one whose talent was magic itself. She took this filly as her student so that she could be prepared for the part she would play in Equestria's history, and it would seem Celestia and her student became very close. Yet by this time the young filly had grown into a young mare.
Through perhaps the help of her mentor Celestia, Twilight learned of the legend of Nightmare Moon and that it was the time she would be released. Twilight sent word of her findings to Celestia... but much to her surprise and frustration Celestia seemed to ignore the mare's pleas for action and sent her to Ponyville to make friends instead. She did not realize this would actually lead her to saving Equestria from the very threat she so worried about. Twilight and five other ponies journeyed together, discovering the joys of a growing friendship and not only found the Elements of Harmony but unlocked
With the power of friendship they defeated their evil foe... yet in the place of the frightening and dark Nightmare Moon... was that of a scared and confused alicorn. The sister and other half of Celestia had been recovered and all because of the heroes of Equestria. At long last the sisters where together again and their joy was full. Luna after this time studied up on what she had missed in 1000 years as well as worked to make amends for her actions, feeling great guilt for almost causing ponies so much harm. She would even be pleased to realize that in the time she was gone ponies had more and more come to enjoy the night and be a part of it, to come to love the night as she did.