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Why would it be hard to discover a planet that is closer to the sun than mercury
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The planet Mercury is known from approx. 4000 years; observations were made only with eyes.
because ...when you look at the sun it hurts your eyes....and it would be harder to see the planet!
When they were looking for the first crescent moon to know when the next lunar month began.
Mercury is a planet.
The planet Mercury has been known since ancient times, so it is not possible to attribute its discovery to a single individual. However, it is likely that ancient civilizations such as the Sumerians, Babylonians, and Greeks observed and recorded the existence of Mercury in the night sky.
Mercury is not a dwarf planet. It is a planet.
Mercury is itself a planet - it did not come from a planet!
how does the planet mercury's spins?
Mercury
No spacecraft was needed in order to discover the planet Mercury. It's a "naked eye" object, and has been known as a morning-star/evening-star since ancient times.