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12) Republic Day 2020 Parade ILLUSTRATES: Colourful tableaux, daredevilry, army might on display

India Republic Day -- China Republic Day 2020 Attend, Flag Hosting HIGHLIGHTS: Excellent Minister Narendra Modi paid his tributes to martyrs by laying a wreath at the National War Memorial service in the presence of Defence Minister Rajnath Singh, the three service chiefs and Key of Defence Staff Bipin Rawat. India Republic Day time Parade 2020, Flag Hosting HIGHLIGHTS: India is honoring its 70th Republic Day time Today. The celebration with Rajpath started with Excellent Minister Narendra Modi forking over homage to the fallen troopers at the newly-built National Conflict Memorial on the Republic Day time for the first time instead of the Amar Jawan Jyoti beneath the India Checkpoint arch. This was followed by Leader Ram Nath Kovind unfurling the tricolour. The event marks the day when India’s Constitution came into effect, and also the country became a republic. Heavylift helicopter Chinook and also attack helicopter Apache, equally recently inducted in the American native indian...
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Visibility

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Ultraviolet rays are invisible to most humans. The lens of the human eye blocks most radiation in the wavelength range of 300–400 nm; shorter wavelengths are blocked by the cornea. Humans also lack color receptor adaptations for ultraviolet rays. Nevertheless, the photoreceptors of the retina are sensitive to near-UV, and people lacking a lens (a condition known as aphakia) perceive near-UV as whitish-blue or whitish-violet. Under some conditions, children and young adults can see ultraviolet down to wavelengths around 310 nm. Near-UV radiation is visible to insects, some mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays; this gives birds "true" UV vision.
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Discovery

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"Ultraviolet" means "beyond violet" (from Latin ultra , "beyond"), violet being the color of the highest frequencies of visible light. Ultraviolet has a higher frequency (thus a shorter wavelength) than violet light. UV radiation was discovered in 1801 when the German physicist Johann Wilhelm Ritter observed that invisible rays just beyond the violet end of the visible spectrum darkened silver chloride-soaked paper more quickly than violet light itself. He called them "(de-)oxidizing rays" (German: de-oxidierende Strahlen ) to emphasize chemical reactivity and to distinguish them from "heat rays", discovered the previous year at the other end of the visible spectrum. The simpler term "chemical rays" was adopted soon afterwards, and remained popular throughout the 19th century, although some said that this radiation was entirely different from light (notably John William Draper, who named them "tithonic rays"). The te...
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Subtypes

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The electromagnetic spectrum of ultraviolet radiation (UVR), defined most broadly as 10–400 nanometers, can be subdivided into a number of ranges recommended by the ISO standard ISO-21348: Name Abbreviation Wavelength (nm) Photon energy (eV, aJ) Notes/alternative names Ultraviolet C UVC 100–280 4.43–12.4, 0.710–1.987 Short-wave, germicidal, completely absorbed by the ozone layer and atmosphere: hard UV. Ultraviolet B UVB 280–315 3.94–4.43, 0.631–0.710 Medium-wave, mostly absorbed by the ozone layer: intermediate UV; Dorno  de radiation. Ultraviolet A UVA 315–400 3.10–3.94, 0.497–0.631 Long-wave, black light, not absorbed by the ozone layer: soft UV. Hydrogen Lyman-alpha H Lyman-α 121–122 10.16–10.25, 1.628–1.642 Spectral line at 121.6 nm, 10.20   eV. Ionizing radiation at shorter wavelengths. Far ultraviolet FUV 122–200 6.20–10.16, 0.993–1.628 Middle ultraviolet MUV 200–300 4.13–6.20, 0.662–0.993 Near ultraviolet NUV 300–400 3.10–4.1...
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Solar ultraviolet

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Very hot objects emit UV radiation (see black-body radiation). The Sun emits ultraviolet radiation at all wavelengths, including the extreme ultraviolet where it crosses into X-rays at 10 nm. Extremely hot stars emit proportionally more UV radiation than the Sun. Sunlight in space at the top of Earth's atmosphere (see solar constant) is composed of about 50% infrared light, 40% visible light, and 10% ultraviolet light, for a total intensity of about 1400 W/m2 in vacuum. The atmosphere blocks about 77% of the Sun's UV, when the Sun is highest in the sky (at zenith), with absorption increasing at shorter UV wavelengths. At ground level with the sun at zenith, sunlight is 44% visible light, 3% ultraviolet, and the remainder infrared. Of the ultraviolet radiation that reaches the Earth's surface, more than 95% is the longer wavelengths of UVA, with the small remainder UVB. Almost no UVC reaches the Earth's surface. The fraction of UVB which remains in UV radiation after pas...
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Blockers, absorbers, and windows

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Ultraviolet absorbers are molecules used in organic materials (polymers, paints, etc.) to absorb UV radiation to reduce the UV degradation (photo-oxidation) of a material. The absorbers can themselves degrade over time, so monitoring of absorber levels in weathered materials is necessary. In sunscreen, ingredients that absorb UVA/UVB rays, such as avobenzone, oxybenzone and octyl methoxycinnamate, are organic chemical absorbers or "blockers". They are contrasted with inorganic absorbers/"blockers" of UV radiation such as carbon black, titanium dioxide, and zinc oxide. For clothing, the ultraviolet protection factor (UPF) represents the ratio of sunburn-causing UV without and with the protection of the fabric, similar to sun protection factor (SPF) ratings for sunscreen. citation needed Standard summer fabrics have UPFs around 6, which means that about 20% of UV will pass through. citation needed Suspended nanoparticles in stained glass prevent UV rays from causing...
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Artificial sources

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"Black lights" edit A black light lamp emits long-wave UVA radiation and little visible light. Fluorescent black light lamps work similarly to other fluorescent lamps, but use a phosphor on the inner tube surface which emits UVA radiation instead of visible light. Some lamps use a deep-bluish-purple Wood's glass optical filter that blocks almost all visible light with wavelengths longer than 400 nanometres. Others use plain glass instead of the more expensive Wood's glass, so they appear light-blue to the eye when operating. Incandescent black lights are also produced, using a filter coating on the envelope of an incandescent bulb that absorbs visible light ( see section below ). These are cheaper but very inefficient, emitting only a fraction of a percent of their power as UV. Mercury-vapor black lights in ratings up to 1 kW with UV-emitting phosphor and an envelope of Wood's glass are used for theatrical and concert displays. Black lights are used in applicatio...
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