Similar to a compass heading, but expressed in 360 degrees with North at 0°. In Suntime there are eight headings: N, NE, E, SE, S, SW, W, and NW.Īzimuth: The direction of objects in the sky can also be measured as an angle from due North. If you want to see a more comprehensive example of this, check out this repository in Github.Heading (or Direction): The compass direction of an object in the sky. This means that our time of 17:09 was still considered day, but only just. Night <- c(strftime(sunlight.times$night, format=”%H:%M”), strftime(sunlight.times$dawn, format=”%H:%M”)) Note that this also accounts for daylight savings!įrom this we can calculate dawn, day, dusk, and night periods to determine in which our time of 17:09 falls:ĭawn <- c(strftime(sunlight.times$dawn, format=”%H:%M”), strftime(sunlight.times$sunrise, format=”%H:%M”))ĭay <- c(strftime(sunlight.times$sunrise, format=”%H:%M”), strftime(sunlight.times$sunset, format=”%H:%M”))ĭusk <- c(strftime(sunlight.times$sunset, format=”%H:%M”), strftime(sunlight.times$night, format=”%H:%M”)) Sunlight.times <- getSunlightTimes(date=as.Date(datetime), lat=coords, lon=coords, tz=timezone) Now it’s as easy as invoking the getSunlightTimes function in the suncalc package to get the sunlight transition periods: Now, we need to get the date itself into the right format:ĭatetime <- strptime(paste(date.char, ” “, hr24,”:”, mn60, sep=””), format=”%d-%m-%Y %H:%M”) Mn60 <- substr(time24, 3, 4) # carves off the minutes Hr24 <- substr(time24, 1, 2) # carves off the hour Time24 <- sprintf(“%04d”, time.num) # makes sure there are four digits I need to get this into a time format, so I use sprintf to do this: I often come across times in databases that are entered as 24-hour numerics for example, 06:02 (morning) is entered as 602 (i.e., the leading zero is dropped). Timezone <- tz_lookup_coords(coords, coords, method = “accurate”)Ĭombine the date and time into a single date-time POSIX object:Ī little trick first. Obviously, this time could not be dawn, but it could conceivably be day, dusk, or even night.įigure out what time zone relates to these coordinates: Let’s say you have a location (we’ll use my home city of Adelaide at latitude = -34.945989, longitude = 138.533281 this is the airport), a date (we’ll say 16 July 1972 just for the hell of it), and a time (17:09). R comes to the rescue here with two cool packages: suncalc gives you these transitions for any given latitude/longitude coordinate, and lutz gives you the time zone for coordinate. Sounds difficult, but, there’s a function for that! So, after all that malarkey, now we need a way of determining when those transition periods occur on any given day in any given location. We can therefore define four major periods of relative light availability per 24-hour period: night (between the start of astronomical dusk and end of astronomical dawn), dawn (between the end of nautical twilight and sunrise), day(between sunrise and sunset), and dusk (between sunset and the onset of astronomical twilight). It’s still ‘dark’ in astronomical twilight, but light starts to be discernible at the start of nautical twilight. These latter refer to when the sun is 18º, 12º, and 6º below the horizon, respectively. ‘Twilight’ is the period between night and sunrise/ sunset (the latter being when the sun first appears/disappears above/below the horizon), further broken down into three periods: astronomical twilight, nautical twilight, and civil twilight. ‘Night’ is defined as the time between astronomical dusk and astronomical dawn, which are when the sun is 18º below the horizon. What matters instead - from a biological/phenological perspective - is the period of day in terms of available light.įortunately, there are some clear definitions of relative light availability we can use. Yes, we could just do a histogram of the time bins (say, every 2 hours), but this ignores a very important phenomenon - 17:00 in July in Hobart isn’t directly comparable to 17:00 in January in Darwin (and so on). The specifics of the ‘incidents’ isn’t important here - suffice it to say they were biological in nature, and we wanted to see if they were clustered around any particular times of the day. Without giving away too many details, we had a long list of incidents spread right across Australia, covering all periods of the year and going back to the early 20th Century.
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