Saw this YouTube video of a amateur high altitude balloon launch. I have seen these things debated before regarding the horizon looking flat, or round, or whatever. There is much depending on the camera and lens and field of view, so I am making no claim either way on this.
What I find interesting about this is the view of the moon, and the sun rise.
The launch was from Santa Nella, CA at 6/21/2016 03:24:38 local time. According to timeanddate.com, on that date the sun rise would have been at 05:48 and the moon would have been one day past full.
In the video, the full moon can be seen before the sun rises. Being just past full, it is oriented in the opposite side of the sky from the sun (once it rises). Even though the moon is nearly as far from the sun as possible, we can clearly see that the sun is lighting the moon, but we can not see the sun. Just as expected on round Earth, not possible on flat Earth.
The sun rise is seen at 05:06 on the video. This is 41 minutes earlier than predicted by timeanddate.com. At a higher altitude the sun rise would be earlier, just as expected on round Earth, not possible on flat Earth.
The sun rises above the horizon. At altitude there is nothing to block the view to explain how the sun came above some imagined vanishing point.
This all makes sense on a round Earth. Video links are below.
Full video
https://www.youtube.com/watch?v=fxBid6YwoHsThe full video is over two hours long. Here are some shortcut links/
Example of view of moon, pre sun rise
https://www.youtube.com/watch?v=fxBid6YwoHs&t=1562sSun rise
https://www.youtube.com/watch?v=fxBid6YwoHs&t=6149sExample of view of moon, post sun rise
https://www.youtube.com/watch?v=fxBid6YwoHs&t=9351s