My personal head canon. (Celestia and Luna)

This just for the sake of context for the rest of my blog post.

Celestia: Luna: Avg. Stallion: Avg. Mare:
Height (top of head)- 6ft. 0in. 5ft. 2in. 4ft. 3in. 4ft. 0in.
Weight - 200lbs. 185lbs. 155lbs. 140lbs.

Celestia and Luna's origins:
The three tribes were at an uneasy peace for years but far from unified. Celestia was born a Earth pony and Luna a Pegasus to a then exiled unicorn court scribe by the name of Faust. They never knew their father, and Faust later died of combination of malnutrition and sickness, when Luna was 7 and Celestia 10. They became street urchins for two years until both of them discovered their special talents and ascended to alicorns*, they were then sent to the unicorns in an attempt to unite the three tribes, the unicorn king in turn sent them to the Everfree to find the elements as a measure of proof (if they died they wouldn't be a problem and if they retrieved the elements he could use them to his own gain) the two went and got lost immediately but never gave up, eventually returning successful almost two years later.

*Faust was buried atop a hill under a tree just outside of town, Celestia and Luna had a habit of going to that hill and sitting under that tree together and watching the sun set and the moon rise every evening. One evening they started talking about how the unicorns raised and lowered the sun and moon, well they got it in their heads that if they closed their eyes and tried really hard they may be able to help a little bit, and lo n' behold when they opened their eyes they had new limbs and a set of cutie marks.