Two enemies wind up in Equestria due to a major mishap. Will they come to terms with this world? Most importantly, will they be able to put their old feud aside to survive?

After an argument with Luna, Celestia realizes that she is the only creature in Equestria who cannot sleep in. She enlists Twilight to help, and the two of them come up with a spell that will allow her to spend the night on a different world. Unfortunately, all their research failed to reveal that the world they sought was populated. Now, the Princess must decide whether to continue with contact, or destroy the only non-Equestrian witness to their existence.

Cover art is called "Sleeping Celestia" by Briskby

The star system Omega Centauri was just another oddity on a map to scientists in the not too distant future. However when they found the star was orbiting an earth-sized, earth-like planet instead of a black hole as its motion had suggested, a mission was scrambled to investigate this most unusual of celestial behaviors.

Hamstrung by politics, and nearly crippled before it began, the 'Lone Ranger' mission was reduced to just one crew member and left to his own devices.

These are the logs of Arrow 18 and its lone commander. This information is classified TOP SECRET by the Global Space Agency.

Do NOT tell the princess.

Celestia has a dangerous creature held in the deepest of Canterlot's high-security dungeons. It can create ponies (with full backgrounds and histories) with it's strange and often-times prophetic powers. The Princess does her best to keep it under wraps, but its only a matter of time before it's "creativity" will get out of control.

It is the year 2038, and the Earth is slowly being consumed by a space-borne monstrosity dubbed the Black Tide, which is using nanotechnology to remake the planet into something hideously alien.

Erin Olsen works for Project Harmonics, humanity's last-ditch effort to find a new world before the Tide can wipe them out. But when that world is found, and it turns out to be occupied, Erin will need to find the courage to face the unknown in order to save the inhabitants of both worlds.

(Many thanks to Easteu for the fantastic cover image for this story!)

Now with its own TV Tropes page

There is now a follow-up to this story: Sunflower - Side Projects
Sequel: Project Sunflower: Harmony