Did you sleep through Winter? Or, at least, the Winter Solstice? It happened at 5:44 our time this morning. The sunsets have actually gotten later already, but the sunrise won’t get earlier for a few weeks. The reason is below, from the United States Naval Observatory. For sky watchers: the site also updates a feature called “The Sky This Week,” to help you scan the heavens with a little more certainty. Click here if you wanna skip the explanation:)
Day and night are not exactly of equal length at the time of the March and September equinoxes. The dates on which day and night are each 12 hours occur a few days before and after the equinoxes. The specific dates of this occurrence are different for different latitudes. On the day of an equinox, the geometric center of the Sun’s disk crosses the equator, and this point is above the horizon for 12 hours everywhere on the Earth. However, the Sun is not simply a geometric point. Sunrise is defined as the instant when the leading edge of the Sun’s disk becomes visible on the horizon, whereas sunset is the instant when the trailing edge of the disk disappears below the horizon. These are the moments of first and last direct sunlight. At these times the center of the disk is below the horizon. Furthermore, atmospheric refraction causes the Sun’s disk to appear higher in the sky than it would if the Earth had no atmosphere. Thus, in the morning the upper edge of the disk is visible for several minutes before the geometric edge of the disk reaches the horizon. Similarly, in the evening the upper edge of the disk disappears several minutes after the geometric disk has passed below the horizon. The times of sunrise and sunset in almanacs are calculated for the normal atmospheric refraction of 34 minutes of arc and a semidiameter of 16 minutes of arc for the disk. Therefore, at the tabulated time the geometric center of the Sun is actually 50 minutes of arc below a regular and unobstructed horizon for an observer on the surface of the Earth in a level region. For observers within a couple of degrees of the equator, the period from sunrise to sunset is always several minutes longer than the night. At higher latitudes in the northern hemisphere, the date of equal day and night occurs before the March equinox. Daytime continues to be longer than nighttime until after the September equinox. In the southern hemisphere, the dates of equal day and night occur before the September equinox and after the March equinox. In the northern hemisphere, at latitude 5 degrees the dates of equal day and night occur about February 25 and October 15; at latitude 40 degrees they occur about March 17 and September 26. On the dates of the equinoxes, the day is about 7 minutes longer than the night at latitudes up to about 25 degrees, increasing to 10 minutes or more at latitude 50 degrees.PAUL’S PREVIOUS PREDICTION Yesterday’s high was 36 in Indy. My forecast was 32. INDY ALMANAC The average high today is 37 and the average low is 23. Records are 67 and -21. The sun rises at 8:03am and sets at 5:24pm. INDY SEVEN DAY FORECAST Today: Partly cloudy. High 38. Tonight: Partly cloudy. Low 27. Thursday: Partly to mostly cloudy, with flurries possible. High 35. Thursday Night: Partly cloudy. Low 21. Friday: Partly sunny. High 38. Friday Night: Chance of rain, maybe mixed with some snow. Low 32. Saturday: Cloudy. Slight shower chance. High 40. Christmas Eve: Chance of showers. Low 34. Christmas Day: Showers likely. High 50. Sunday Night: Chance of showers. Low 50. Monday: Showers likely, mainly in the morning. Breezy. (Maybe some thunder?) High 53. Monday Night: Partly cloudy. Low 29. Tuesday: Mostly sunny. High 38. ]]>
Never miss me! Subscribe for free. My Huge Radar has real-time weather tracking, current temperatures, and severe weather watches and warnings. Get detailed Indiana conditions by clicking here. Click here to see my central Indiana 7-Day Forecast. Follow these links to get my forecasts for Lafayette, Muncie, Hendricks County, and Hamilton County. Need a second opinion? Click here for central Indiana National Weather Service forecasts. (Some charts via WeatherBELL.)