why do you have to be so beautiful
Why are LiverpoolÁs sunsets so beautiful? ItÁs one of the few things that can stop everyone in the city in its tracks. The first sign is a ripple of pink and orange across the sky. Then the colour will deepen and broaden. When Liverpool knows itÁs in for a good sunset, the home time commute can wait. Instead, people stand, watch and enjoy. When the Labour Conference came to Liverpool in late summer, early autumn, the Instagram and Twitter feeds of the countryÁs top politicos were filled less with snaps of politicians, but instead the view across the waterfront as the sky turned red and orange. Liverpool Wavertree MP, Luciana Berger, took a snap of the
across the River Mersey. Indeed, search Google images and youÁll find plenty of pictures of the Liverpool skyline drenched in the rich light of a sunset. And itÁs nothing new, watercolour artists have long travelled to the city to capture the colour of its skies. So why does Liverpool get such beautiful sunsets? Are we unique? When sound recordist Chris Watson was recording the birdsong at LiverpoolÁs Alder Hey Hospital for his work, ÁWildsong at DawnÁ project bringing birdsong into the hospital he mentioned that because of where the city sits, its longitude and latitude, it has a long birdsong. Could that be one of the reasons why we have such long and rich sunsets? Not quite, says Emma Sharples from the Met Office. ÁWe actually get quite a few places asking us if thereÁs a meteorological reason why they, in particular have beautiful sunsetsÁ. Oh. OK. But there might be, she says, something about where we are that means enjoying the sunset in Liverpool is better than anywhere else. ÁLiverpool looks westward and because of the River Mersey you have uninterrupted views as the sun sets. ThereÁs a huge expanse as the river runs into the Irish Sea and the colour in the sky is reflected in the waterÁ. Ah, so if weÁre at the waterfront, we feel as though weÁre getting two for the price of one, as the sunset is replicated on the waves. WeÁre surrounded by the light.
And, in front of the river, you get the full effect. Perch Rock lighthouse at New Brighton near Liverpool, UK. At sunset. There could, also, says Emma, be something about the way the city is built. ÁSunsets are most noticeable in Spring and around early autumn. The sunÁs angle at this time of year might mean that we notice it moreÁ. Also, if we think of the time of the sunset at those periods of the year weÁre travelling home from work so if weÁre all sitting on a bus are we more likely to suddenly look up and notice the sunset. WeÁre on the streets, rather than at our desks, so weÁre going to take more notice of the sunset than we might have done already. ThereÁs also the question of how Liverpool is built. LiverpoolÁs grid structure is very particular. ThereÁs two things you notice as you walk through Liverpool city centre. Firstly the streets are very straight, especially around Ropewalks. These streets, designed to support the merchants trading along the city are straight because they allowed for ropes to be straightened. The cityÁs streets run down to the river, as well. So everything in the city is pointed towards the Mersey as its source of life. If the sunset is at its most magnificent along the waterfront, then the cityÁs streets are pointed directly towards the show. Those straight streets allow for a focus, and as the light starts to scatter, the pink and orange light spills along those streets, almost magnifying the experience. LiverpoolÁs streets are also lined with tall buildings, red brick warehouses, glass, perfect materials for reflecting and absorbing that colourful light. So the streets take what the sky is producing and provide the perfect stage for it. So LiverpoolÁs geographical location, being on the river looking westward means weÁre better placed than most to see the sunset. And because the city is built looking towards the sunset, when itÁs good weÁre all pointed towards it. With that kind of a stage itÁs worth taking note of the time of todayÁs sunset (3. 57pm, 1 December 2016) and get your eyes pointed to the sky.
In the case of both light and water, a wave is either strengthened or weakened (the interference phenomenon) when it encounters another wave. If two waves with identical waveform and movement come into contact and their crests are superposed (in phase), the crests heights will double. Similarly, superposing each of the troughs creates a trough with twice the depth of the original. When two waves of the same amplitude but 180 phase difference are superposed, the crests of one wave coincide with of the troughs of the other neutralizing the highs and lows and creating a zero amplitude. In the case of light waves, if one crest overlaps another, you will see brighter light. The reverse is true with darker light, which occurs when one trough coincides with a crest. What happens when several waves heading in the same direction overlap? As with waves of water, overlapping strengthens and weakens waves of light, creating new patterns. We call this phenomenon interference. Soap bubbles glimmer because light waves reflected from the back and front surfaces of the bubble interfere with one another, thus concentrating the light. When all the necessary conditions are in place, the light waves create beautiful figures as pictured. Dr. Thomas Young (1773-1829), an English physicist, confirmed through tests that light waves cause interference. Dr. Young used a screen to confirm the interference pattern consisting of bright fringes and dark fringes that resulted when light from one source was split into two light waves with the same wavelength, which were then made to overlap. Interfering in phase causes brightness, while interfering out of phase causes darkness. Two waves interfering with one another are called coherent. Waves that do not interfere in this way are incoherent. Dr. Young used light from the same source, so he was able to reproduce a coherent state. With a soap bubble, there is interference between countless light waves, but the person creating the soap bubble may see the bubbles in an incoherent state, with no color at all.
Incidentally, lasers emit coherent light. Coated lens surfaces and greasy water surfaces show us the colors of rainbows. This is because of light interference. Lens coating, using a thin, transparent film, is designed to decrease reflections while increasing transparent light. This film is designed by calculating the appropriate thickness and refractive index to ensure that light of a specific wavelength (the design wavelength) reflected from the surface of the film and light reflected from the border between the film and the glass interfere and neutralize one another. However, it is not always possible to guarantee zero-percent reflection of light with wavelengths different from the design wavelength. The eye therefore perceives these light waves as purplish reds and blues. Although the physical conditions are different, the colors you can see on a thin film of oil floating on a surface of water are also the result of mutually interfering light waves. Holography uses light to create what seems like a three-dimensional image of an object. You often find some wonderful examples at art exhibitions and museums. Holography takes advantage of the diffraction and interference of light. There are several ways to create holograms, but the most common is using the laser, which generates coherent light. Holograms are created by dividing a laser beam in two using a beam splitter, illuminating an object with one of the divided beams, and simultaneously illuminating a dry photographic plate with the light reflected from the object (diffracted light) and the light from the second divided beam (reference light) at an angle. The diffracted and reference light interfere with one another to make an interference pattern. The recorded pattern is the hologram. When the hologram is illuminated using a laser at the same angle as the reference light, the pattern diffracts the laser light, reproducing the image. As shown in the image below, some kinds of hologram reproduce the actual image and the virtual image.
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