UV index 2 or low.įorecast Forecast issued: 5:00 AM MDT Monday 10 October 2022 Detailed ForecastForecast issued: 5:00 AM MDT Monday 10 October 2022 Becoming a mix of sun and cloud in the afternoon. Wind northwest 40 km/h gusting to 70 diminishing to 20 gusting to 40 near midnight. Risk of a thunderstorm early this evening. Showers ending this evening then clearing. Wind becoming west 20 km/h gusting to 40 near noon then northwest 40 gusting to 60. Risk of a thunderstorm late this afternoon. …and the Sun will continue to rise and set, every day.Increasing cloudiness. The solution? Perhaps smart forecasts can work to account for local atmospheric conditions, delivering to observers a better sunrise and sunset prediction. I think the really fascinating story here, though, is the fact that the science surrounding this basic facet of astronomy is something that really anyone could have done, had they simply thought to do it. Also, for now, our time is set to astronomical time, though there has been calls to move away from this standard and abolish the deletion and insertion of leap seconds starting in 2023. Navy has resumed teaching cadets old-school celestial navigation, in the event a cyber attack blinds GPS capability. Why does it matter? Wilson notes that one minute of error measuring sunrise at sea using celestial navigation can lead to up to 15 nautical miles of error. Wilson found that using the current 34′ standard, we can’t predict the actual sunrise time to better than within 2 minutes. Moreover, modeling the complex effect of the weather in the troposphere didn’t make the discrepancy go away. Sunrise over Jimena de la Frontera, Spain. Viewing sunrise over water seemed to magnify the effect, though taking into account the observer’s altitude did dampen down the discrepancy. Wilson found that while sunrise and sunset varied by season, wintertime predictions tended to run late, while summer predictions ran early. The site, which Wilson then fed into three separate refraction Most of these (about 600) came along with weather data for Records of 514 sunsets and 251 sunrises from 30 separate geographic Yet, simply using a standard value assumes the true conditions at these disparately different sites are the same. Air behaves very differently, say, on a still January morning over the Great Lakes versus a hot dusty July morning off the west coast of Africa. However, this value is an approximation, and does not account for local meteorological conditions. Wilson notes in the study that this value is cited as far back as 1865, and its use may go all the way back to that 17 th century master of optics, Isaac Newton. Most standard sunrise calculations assume a refraction angle of 34′ arcminutes, a little larger than the apparent diameter of the Sun. Of course, your actual horizon is probably cluttered with foreground objects that the Sun needs to clear, unless you live on a remote mountaintop or are lucky enough to observe sunrise and sunset from the beach. Most calculations assume local sunrise and sunset time as when the center of the Sun’s disk clears the horizon. This size also changes very slightly from perihelion in January to aphelion in July, as the Sun seems to grow then shrink from a value of 31.6′ 32.7′ arc minutes. Also, like the Moon, the Sun’s apparent diameter is about half a degree across, meaning you could line the local horizon with 720 Suns end to end, or 180 Suns from horizon to zenith. Along with the Moon, the Sun is one of the few celestial objects that is large and close enough to appear as more than a point of light to the naked eye. Air bends light, meaning we see the Sun slightly offset from its true position on the horizon due to the atmosphere. If we lived on an airless word, the calculated and observed moment of sunrise would be easy… but as air-breathing mammals, we’d have other problems to contend with.
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