No, you haven't seen it with your own eyes. There's no need for argument from authority. There are several well reasoned arguments that the Earth is spherical (e.g., the shadow of the Earth is curved). It's proper to recite them.
Re:20 Reasons We Know the Earth Is Spherical
by Nadya on Thursday June 14, 2018 @03:22PM
(#17314563)
>There are several well reasoned arguments that the Earth is spherical (e.g., the shadow of the Earth is curved).
That argument would prove the Earth is round - but not necessarily that it is spherical. A flat, round disc would also produce a curved shadow.
To play devil's advocate - you would also need to prove that it is Earth's shadow on the moon and not the Sun's shadow. For an example, I made an HD image in paint [0].
> To play devil's advocate - you would also need to prove that it is Earth's shadow on the moon and not the Sun's shadow. For an example, I made an HD image in paint [0].
Very nice! A great demonstration of how difficult it is to be explicit about all our assumptions.
If you're an adult and the type of person who doubts the shape of the earth, I don't think anything a website says would convince you.