Added to this that a tunnel would have to be about 50 km long and that the removal of earth would require a fleet of trucks etc it is liable to detection.
Trimming lead times on sunspot detection would allow for better forecasts of space weather—bursts of radiation and charged particles from the sun that can cause real problems on and around Earth.
黑子探测可用于预报空间天气---即源于太阳的辐射爆发和带电粒子等引起的各种空间活动现象。
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But as detection methods improved, astronomers began to find planets closer in size to Earth and planetary systems that contain nearly as many planets as our solar system.