rna is a user on mastodon.cosmicanimal.jp. You can follow them or interact with them if you have an account anywhere in the fediverse.
If you don't, you can sign up here.
望遠鏡による眼視観測でどこまで暗い天体が見えるかという話。http://www.geocities.jp/okita_tenmon/discussion/limitmag.html
難しすぎる…！
