I haven't put much thought in to that but not because I'm not interested, I'm fully interested in the topic, but because I have no way of verifying for myself one way or another and really no other prominent flat earther does, either

I guess we would need an expedition to Antarctica to get near the foundations of the firmament, assuming a firmament is there. Can't go to Antarctica without prior approval, unfortunately, and it is guarded by military.

We're only allowed to go to a few pre-determined locations in Antarctica and I could go on about things that should give pause about Antarctica but I stick with the simple stuff I can experiment for myself

https://www.bitchute.com/video/EGZzu883JtdN/

Here's a longer video about shenanigans re Antarctica's supposed 24 hour sun during their summer

I can’t verify that for myself so I don’t bother talking about that when I’m posting FE stuff

When I'm talking FE with someone for the first time, I start with the formula for calculating curvature:

Earthcurvature.com

Do you live near a large body of water? You COULD do it over land but I would then recommend you test in a few places to almost entirely rule out the possibility that all of your large parcels of land happened to coincidentally be perfectly flat, however unlikely that may be

Bring binoculars if you have them

On a clear day and assuming your vision is 20/20 you should be able to see at least 20/25 kms without any issue

Bring the binos to go further and really leave yourself little room for doubt

You want to do this over water because we know water finds and maintains its level

No one denies this obvious truth about water maintaining its level

What you want to do is scan across the water or up the coastline to the most distant landmark/building you can spot

Pay attention to what you’re seeing. Notice how you’re seeing not only 100% of the distant landmark but also even the ground/shoreline running up to it

Hit google maps on a pc and right click your starting point, measure distance from here, and then right click again at your distant landmark(s)

It will give you an accurate distance and then you go to earthcurvature.com to enter in the distance and calculate how much curve there should be

20kms is about 95ft of drop

25kms is about 150ft of drop

But you’re looking at 100% of the distant landmark

Why isn’t it blocked by the earth itself?

We have examples much further than this but I don’t like linking YouTube videos when it’s much better to go out and do for yourself so that your own eyes can show you the Truth

Mentioning that we have navy vessels than can target an enemy ship 100 miles away by pointing a laser at them

At 100 miles there should be like 6,600ft of drop

Lighthouses impossibly in view, etc

Try it out, sometime!