PHYS 1000 Lecture Notes - Lecture 6: List Of Transformers Planets, Tidal Locking, Solar Wind
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We often find it helpful to compare mercury and the moon, because of their similarities. The orbits of venus and mercury show that these planets never appear far from the sun. Mars could appear to traverse the entire sky. The terrestrial planets have similar densities and roughly similar sizes, but their rotation periods, surface temperatures, and atmospheric pressures vary widely. The easiest way to measure rotation rates is to identify a prominent feature on the object and see how long it takes to move 360 degrees. Mercury can be difficult to image from earth; rotation rates can be measured by radar. Mercury was long thought to be tidally locked to the sun; measurements in 1965 showed this to be false. Mer(cid:272)ur(cid:455)"s da(cid:455) a(cid:374)d (cid:455)ear are i(cid:374) a (cid:1007):(cid:1006) reso(cid:374)a(cid:374)(cid:272)e; mer(cid:272)ur(cid:455) rotates three ti(cid:373)es (cid:449)hile going around the sun twice. Be(cid:272)ause of mer(cid:272)ur(cid:455)"s e(cid:272)(cid:272)e(cid:374)tri(cid:272) or(cid:271)it it (cid:272)a(cid:374)(cid:374)ot get a pre(cid:272)isel(cid:455) s(cid:455)(cid:374)(cid:272)hro(cid:374)ous rotatio(cid:374).