S1, E4: Earth is painted with stunning colors. By understanding how those colors are created and what they mean, we can look out into the Universe and look for other planets just as vibrant and colorful as our own. The colors we see are created by the way the light energy from the Sun interacts with whatever it strikes. The signature color of our planet is the blue of its oceans but the unique way water interacts with sunlight to create this color, also explains why, each year, thousands of humpback whales congregate in the waters off the Dominican Republic. Earth is swathed in another color, the color of life itself: the green of the pigment chlorophyll, which absorbs some of the color energy of light, and reflects others back out into our eyes. Plants have evolved to harvest the light energy of the Sun using color. But life has also evolved to sense and use color. In Papua New Guinea just as the spectacular Birds of Paradise use color to attract a mate, the richly colored feathers are highly prized by the local human males, for much the same reason. Earth has colored itself richly and as humans we see beauty in the colors it displays. None more so than in the Northern Lights of the Arctic Circle. Like all colors, the green and purple of the night sky is a code, it has meaning. Each color is the result of atmospheric gases energized by the solar wind blasting out from the Sun. Green is created by the oxygen of the air we breathe, purple by nitrogen. Each element has its own unique color signature. With this knowledge we have started to explore the furthest corners of the Universe as alien photons bring the color signatures of far distant stars and planets to Earth.