Space Is Not Completely Empty
Even deep space contains particles, radiation, magnetic fields, and traces of matter spread across enormous distances.
Knowledge Base
Science
Space, nature, time, and discoveries that help explain how the world works.
One Species, Many Foods
Cabbage, broccoli, cauliflower, kale, Brussels sprouts, collard greens, Savoy cabbage, kohlrabi, and gai lan are all cultivars of the same plant species, Brassica oleracea. Over time, they were bred to emphasize different parts of the plant, such as leaves, stems, flower buds, or sprouts.
Seeing Into the Past
There is no single universal “now.” Because light takes time to travel, everything you see is actually a glimpse into the past. Even the person sitting across from you is seen as they were a tiny fraction of a second ago, while looking at the Sun means seeing it as it was about eight minutes earlier.
A Day on Venus Is Longer Than Its Year
Venus takes about 243 Earth days to complete one rotation but only about 225 Earth days to orbit the Sun. That means a day on Venus, measured by one full rotation, lasts longer than a Venusian year.
Three Hearts and Blue Blood
Octopuses and other cephalopods have three hearts: two move oxygen-depleted blood through the gills, while the third pumps oxygenated blood through the body. Their blood appears blue because it uses copper-based hemocyanin to carry oxygen rather than the iron-based hemoglobin found in human blood.