# How big does a LEO object need to be to be clearly visible from the ground? [duplicate]

Pretty simple question I just don’t know the math for. If I want my space station/megastructure that’s orbiting 2000-ish km above Earth to seem roughly as large as the Moon to an observer on the ground, how large would it need to be? My blind best guess is more than ten kilometers long/wide, but I’d like to know exactly how big an object would need to be in order to partially obscure the Moon by at least 50%.

• Your title asks the object to be clearly visible, then your question asks first as large as the Moon and then 50% of the Moon. Can you make up your mind and ask just for one thing? – L.Dutch Dec 18 '18 at 6:16
• It's not exactly the same question, but the same math can be applied; just substitute your own values. Hint: the angle subtended by Earth's moon, as viewed from Earth, ranges from 0.49 to 0.55 degrees. – user Dec 18 '18 at 8:16
• The questions title seems like a duplicate, but OP is actually asking for size to partially obscure the moon, not size visible from earth as in 'duplicate' – bukwyrm Dec 18 '18 at 8:16
• @bukwyrm OP specifies an orbital altitude and an apparent size. The math involved is thus the same; all that's needed is to apply it slightly differently. Whether an object partially or completely obscores another is a function of many things besides merely the two objects' apparent size, not least the angle at which they are observed. – user Dec 18 '18 at 8:18
• I don't think this question is a duplicate at all. As the other query says, the ISS is "visible ... but its features cannot be distinguished". IOW, it is not "clearly visible". Z.Schr., I think if you clarified your query by defining what you mean by "clearly visible", and added a link to the other query, it could be reopened as a distinct but related question. – elemtilas Dec 18 '18 at 18:16