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For starters, cats’ visual fields are broader than ours, spanning roughly 200 degrees instead of 180 degrees, and their visual acuity isn’t as good. So, the things humans can sharply resolve at distances of 100-200 feet look blurry to cats, which can see these objects at distances of up to 20 feet. That might not sound so great, but there’s a trade-off: Because of the various photoreceptors parked in cats’ retinas, they kick our asses at seeing in dim light. Instead of the color-resolving, detail-loving cone cells that populate the center of human retinas, cats (and dogs) have many more rod cells, which excel in dim light and are responsible for night-vision capability. The rod cells also refresh more quickly, which lets cats pick up very rapid movements — like, for example, the quickly shifting path a marauding laser dot might trace. Lastly, cats see colors differently than we do, which is why the cat-versions of these images look less vibrant than the people-versions. Scientists used to think cats were dichromats — able to only see two colors — but they’re not, exactly. While feline photoreceptors are most sensitive to wavelengths in the blue-violet and greenish-yellow ranges, it appears they might be able to see a little bit of green as well. In other words, cats are mostly red-green color blind, as are many of us, with a little bit of green creeping in.

in timekeeping

3,600 seconds, now defined in terms of radiation emitted from atoms of the element cesium under specified conditions. The hour was formerly defined as the 24th part of a mean solar day—i.e., of the average period of rotation of the Earth relative to the Sun. The hour of sidereal time, 1/24 of the Earth’s rotation period relative to the stars, was about 10 seconds shorter than the hour of mean solar time.

In even earlier systems of timekeeping, an hour was 1/12 of a period of daylight or darkness—hence, variable in length with seasonal changes in the length of day and night. The custom of dividing the cycle of day and night into 24 periods seems to have originated with the ancient Egyptians.

The ocean is salty for several reasons, one of which is the groundwater from rain which trickles down into the ocean and picks up salt from the earth along its way! But this same water trickles down into lakes… so why aren't lakes salty?

The reason lake water usually isn't salty (or at least it's less salty than ocean water) is because the salty groundwater not only runs into the lakes, but also back out of it! Unlike the huge, vast ocean which already covers most of the Earth and therefore can't open up to any larger body of water, most lakes have outlets from which water leaves. This means that the salty groundwater has a chance to filter out and escape! (In the ocean, it has nowhere e

lse to go!)