It wouldn’t be a matter of difficulty, teleportation was second nature to an alicorn such as herself. Even the several hundred thousand kilometers she assumed it would take to reach the ships wouldn't be an issue, she did come down from the moon after all.
No the problems were the risk and the fact that it was totally out of her nature to even think up such an idea, Celestia would probably do it, but nobody expect Luna to be so brash, but well these were strange times and strange things were of course going to happen.
She couldn’t directly go to one of the ships, she was not sure of how far they were, she might end up in space and while she could protect herself from the vacuum she would still be helpless and adrift.
Her best bet was to go to the moon, she had gone many times before and knew the terrain like the back of her hoof. Also it would be a lot closer to the ships, from there she would be able make a better decision on what to do next.
It was the middle of the night and the castle (excluding the guards) was asleep. She decided to leave a note instead of waking everypony, she planned to be back before sunrise, but just in case. Still she was excited as a filly sneaking out of the house to hang out with friends. She focused her mind on the moon and with a quick pop she vanished from Canterlot Castle.
She instantly materialized in the northern region of the of the Equestria facing hemisphere of the moon. Instantly an invisible protective bubble formed around her the kept and replenished an atmosphere for her.
She looked around to get her bearings, she was in one of the many rock fields that covered the moon, boulders of all shapes and sizes were scattered about, thrown up by meteor impacts thousands of years ago. She began to walk up to a nearby rise. She looked up to find Equestria and then she saw them.
Massive was an understatement, they were huge! They sat up there like great lumbering sea monsters. Easily larger than all of Canterlot Castle, and there were nearly a hundred of them. Dozens of tiny ships buzzed around and between each one like flies. She could see clearly the details of each ship even though they were same. She could she lights that must of been windows into the ships, large doorways or gates that open and closed for the smaller ships to go in and out of. She saw the massive metal shield on each of the ships connected to the front of each ship on what looked like massive springs and pistons and the strangely shaped funnels on the rear emitting a strange blue glow that must of been the engine.
As she walked she considered her next plan of action. She figured her best bet to get onto one of the ships would be to teleport inside one of the gates that the smaller ships went into, they were large open areas and she wouldn’t risk teleporting into a wall or one of the creatures inside, which would be a bad thing. Of course she would use an invisibility spell to avoid detection.
Now the problem was which one? While trying to decide a small beam of light hit her in the eye, it didn’t hurt but it did scare her. It was coming from one of the ships, they found her, oh crap. Then several small beams began to appear on her from other ships, double crap. She ran behind a boulder in an attempt to hide. She knew it was pointless, they knew where she was now, she should teleport away to another part of the moon or back home, but despite the fear her curiosity overpowered it. She wanted to see what they would do.
As she peeked her head above the boulder a gate on the closest ship opened and 6 strange craft flew out. Unlike the other tiny ships which were boxy and plain, these were fast and graceful ships akin to falcons or eagles. After them came out a large lumbering craft that slowly followed the 6 other ships.
The falcon like ships quickly reached the rock field and slowed to a near hover. They began searching for Luna. She wanted to hide under the boulder, she didn’t know what they would do with her if they actually captured her. She kept her teleportation spell on tap just in case.
One of the ships slowly came over the boulder and Luna, as it passed it slowly spun around to face her but still kept moving until there was several hundred meters between them, then it just watched her. The other 5 joined it and kept a distance between themselves and her. They were beautiful craft which looked like styled falcons that were flying, or facing her backwards, towards the rear of each one was the small blue glow of what must of been a smaller version of the engines of the bigger ships.
Her fear crept up but she committed herself to being stoic and stamped it away, she stood up and face the first craft the found her. She didn’t know what to do, she couldn’t speak since sound waves didn’t not carry in a vacuum, she didn’t know how of even if these creatures raised a limb in greeting. Even though Equestria was her planet as was the Moon she still had a nagging feeling that she had intruded upon them. Her best option she felt she had was to just stand there and see what they would do next, and be ready to make a hasty retreat.
She almost forgot about the large lumbering craft until one of the falcon like craft moved to make room for it. This craft was even stranger, it had a very fat grub like apperence with 4 engines on either side of it. It came towards her and the rotated around and lowered itself to the ground, kicking up plumes of dust doing so. Soon the engines powered down and it just sat there.
Luna became annoyed with this behavior of just sitting there. However she knew better, they were not expecting this and they like her were trying to figure out what to do next. It started to feel like a stand off when all of a sudden the craft made its move.
It cracked open, well the end of it facing Luna did. A split opened horizontally in the middle of the craft and the upper part lifted itself into the craft, while the lower part came down to the ground and turned into a ramp. She could not see inside. But that wasn’t the interesting part.
From the opening came 2 rows of bipedal creatures, some of whom quickly ran to nearby boulders while others stayed out in the open. They were taking up defensive positions against her. They looked to be clad head to toe in heavy grey armor, she could not make out any flesh which was just as well since there was no atmosphere. In their forelimbs they carried a large cannon or gun of a kind Luna had never seen before it was large enough to have to be carried with both limbs, she figured they must be soldiers. Other than that their heads were at the top of their bodies and they lacked tails, though they may be hidden under their armor.
About 20 of these soldiers filed out of the craft. After them out came 2 other creatures, these two were smaller and not as well armored as the soldiers, their armor was mostly white and had various symbols on them. Them seemed to be carrying equipment that looks like small guns that were bulkier and less threatening than what the soldiers had in what she now could see were hands, similar to have dragons and griffins hand, allowing them to easily manipulate them.
They approached Luna cautiously, when they came rather close Luna started to step back and they stopped. They look to be communicating with each other somehow, as they looked at each other and gave expressions with their hands. One pointed at it’s chest and then pointed at Luna, they seemed to come to an agreement. The one doing all the pointing then stepped foward with the strange little gun pointed at her, it wasn’t aiming in fact it was just casually holding it and looking at some kind of screen on the top. It started to push at the screen and various lights came on at the end facing Luna. Then a beam of light came out of it right at Luna’s face.
Luna reacted instantly, firing a magical beam at the creature. It flew back and skidded to stop on the ground quite a distance away. It’s companion ran back towards it. Immediately the soldiers moved to block those 2 from Luna’s line of sight, pointing their weapons at her and manipulating them, she looked around and saw all the other soldiers doing the same. Her looked up to the falcon like craft hovering around her and saw very large cannons appearing from under their skins. This was not going well at it.
Before anything more could happen she teleported with a pop, leaving the creatures and the moon behind. She found herself back on her balcony panting and sweating and still generally terrified at what just happened. It was still dark outside, if she was lucky she could get cleaned up and retrieve the note before anypony noticed. She made her way inside, she needed time to figure out what happened, and whether or not to tell anypony. She didn’t know if she made the situation worse or what..”Where did you go?”
Luna froze, out of the darkness came Celestia with a look of contained anger.
“Luna, where did you go? And do you look like such a mess?”
“I.. um.. I can explain!” Luna said with shocked guilt.
Celestia cocked an eyebrow and sat down at the foot of Luna's bed.
“Please do, we have all night.”
“Well.. um.. that new telescope I had built was great, but it didn’t help me get any closer to finding out why they are here.”
Luna proceeded to tell Celestia of everything that happened on the Moon. The massive ships, the falcon craft, the large craft filled with soldiers, the 2 creatures, her getting hit with light and attack back and her retreat back to Equestria.
Celestia was gazing out at the stars and ships by then. She turn to Luna and stared her straight in the eyes.
“I can’t make you do anything, you are of royalty and I cannot give you orders, but I want you to promise me something.”
“What is it, Sister?”
Celestia stared even more intently, Luna felt tiny.
“Promise me that for the duration of the alien’s visit here, you will not return to the moon.”
Luna looked shocked, the moon was her domain.
Celestia went on “It obvious they can easily spot anypony who is on the moon, and with what happened up there I do not feel it would be safe for you or anypony to go up there. We don’t know if you just hurt or killed that creature, and we don’t know how they will respond.”
“Luna please promise me that you will not go back there.”
Celestia looked at Luna almost pleadingly. Luna lowered her head and said “I promise.”
Celestia went over to her sister and began to nuzzle her.
“Thank you, if something happened to you while you were up there... I don’t want to lose you again.”
Luna noticed that Celestia was weeping. They stayed like that for a couple minutes until Celestia broke contact.
“Well then, it looks like I have a busy day today. I will need to let everypony know about what happened and that we should keep our observations and patrols at alert in case the ships decide to do something.”
As Celestia left Luna turned to see that it was already dawn. She also realized how exhausted and tired she was. She went to her washroom, and cleaned the dust and filth from the moon off of her, and staggered into bed and fell into a deep sleep.