> Surely the close the blocking object is to the sun the better how close could we get a parasole?
Moving an object closer to the sun will enlarge its penumbra, but this does not mean that it will block more light. Because its apparent size relative to the sun will also get smaller.
For example, mercury and the moon are roughtly the same size. Yet a Mercury transit will not block much light; it looks like a small dot moving across the sun[1]. While a solar eclipse caused by the moon will block a lot of light.[2]
That doesn't mean that a space sunshade is completely infeasible. But you do need something very large, e.g. a 1000km diameter object (or cloud of smaller objects) placed at the L1 Lagrange point. It would probably cost at least trillions of dollars[3].
Moving an object closer to the sun will enlarge its penumbra, but this does not mean that it will block more light. Because its apparent size relative to the sun will also get smaller.
For example, mercury and the moon are roughtly the same size. Yet a Mercury transit will not block much light; it looks like a small dot moving across the sun[1]. While a solar eclipse caused by the moon will block a lot of light.[2]
That doesn't mean that a space sunshade is completely infeasible. But you do need something very large, e.g. a 1000km diameter object (or cloud of smaller objects) placed at the L1 Lagrange point. It would probably cost at least trillions of dollars[3].
[1] https://en.wikipedia.org/wiki/Transit_of_Mercury
[2] https://i.stack.imgur.com/5E5fZ.png
[3] https://www.sciencedirect.com/science/article/pii/S009457652...