Transcript Document
SPH4UI 10 Rainbow Questions 1. 2. 3. 4. Is the inside red? Radius in degrees? Width in degrees? Comparison of light intensity inside outside. 5. Time or Day 6. Direction 7. If 2, where is the second bow? 8. If 2, Is the inside red? 9. If 2, Radius of Second? 10. Are rainbows polarized? SPH4UI Blue light more readily “scattered” by air molecules called Rayleigh Scattering; strong function of wavelength blue light in sky has been diverted from some other path with some blue light missing, sun looks yellow/orange/red 2 SPH4UI 3 SPH4UI WHY IS THE SKY BLUE ? INCOMING SOLAR RADIATION NITROGEN MOLECULE SPH4UI WHY IS THE SKY BLUE ? SCATTERING OF BLUE LIGHT SPH4UI Blue Haze & Selective Scatter Plants exude terpenes that react with ozone and can also selectively scatter blue wavelengths, creating a blue haze. Mountains allow for enough viewing distance to create this needed scatter. SPH4UI Atmospheric Dust & Rays Dust and salts are large enough to cause geometric scattering, and change blue skies into hazy white skies. Concentrated dust or salts beneath clouds can create white crepuscular rays of sunlight. SPH4UI Is the night sky blue too? • You bet! Just too dim to perceive – time exposure at night under moonlight shows this You can find blue from scattering in other circumstances as well: water, glaciers, astrophysical reflection nebulae… 8 SPH4UI Red at Sunrise and Sunset Low on the horizon, the sun's light passes through nearly 12 times more atmospheric gas and aerosol, which has scattered out most short (blue) wavelengths. Longer oranges and reds then comprise the sunlight, which reflects from clouds and water. SPH4UI 10 SPH4UI The Rainbow 11 SPH4UI Water Droplet 12 SPH4UI Rainbow Colours 51 54 13 SPH4UI The Angle’s 14 SPH4UI The Angle If sun is higher than 42 degrees, then alas no rainbow (it is below the horizon). rainbow 42 15 SPH4UI Rainbows come in pairs… Secondary rainbow has two reflections. Red now appears lower than blue in the sky. Area between rainbows often seen to be darker than elsewhere. Beautiful double rainbow in Zion National Park. The primary is brighter, and the color sequence is reversed from that seen in fainter secondary. Note: rainbow can exist in foreground. 16 SPH4UI 17 SPH4UI Primary 18 SPH4UI Secondary 19 SPH4UI Then we have Two 20 SPH4UI Questions • Which general direction will a rainbow be found in the evening? Look East • Why don’t you see rainbows during the middle of the day? 45 degrees up from your toes is still at the ground. 21 SPH4UI The halo, and sun-dogs • 22° halo around sun due to hexagonal ice crystals – often more noticeable around moon at night (less glare) • Sun-dogs (parhelia) join halo, level with sun – from horizontally situated ice crystals • akin to leaves falling in stable horizontal orientation – colored due to refractive dispersion through ice crystal 22 SPH4UI 23 SPH4UI Are Rainbows Polarized? Any light that is reflected is polarized in the plane. Therefore rainbows are somewhat polarized, about 96%. 24 SPH4UI Sun-dog geometry 25 SPH4UI Glorys and Heiligenschein (shadow-hiding) • A circular rainbow about the anti-solar direction is called a glory – Sometimes 2–3 colored rings – often see shadow in middle – water droplet phenomenon • The anti-solar point may also get bright due to shadow-hiding – called heiligenschein – often see from airplane over textured terrain – no, the person in the photo is not an angel 26 SPH4UI Cool Rainbow Effects The pot of Gold? Primary, Secondary, and Reflected Rainbow Supernumerary Reflected Primary and Reflected Rainbow 27 SPH4UI Rainbow at Night 28