Not sure about the border, but I like your use of negative space on to add dramatic impact. The wide aspect ratio works well and gives it a panoramic feel. The whisp of cloud prevents the image from becoming too stark.
Good concept and the wispy clouds are nice. It would be even better if there could be dimly lighted low mountains and a horizon to go with it. You might be tempted to artificially darken the bright crescent to keep it from being too overwhelming. The idea of this image is great.