Accuracy

Sun Times has been thoroughly tested in its basic calculation of sunrise and sunset times against many other reputable sources. The calculation of sunrise and sunset is of course prone to underlying error in the latitude and longitude of the locations in Sun Times. Although sunrise and sunset is presented to the nearest second, varying local conditions mean that actual observed sunrise or sunset will normally take place within a few minutes of the times presented. Most astronomical functions in Sun Times, and the calculation of the elevation and bearing of the sun in the sky are also accurate for most practical purposes. One notable exception in the astronomical calculations is for the circumstances of solar eclipses. Sun Times does not employ the high-precision algorithms required for practical accuracy here, ie a hundred miles off-track makes a big difference in the appearance of a total solar eclipse. Times for prayers and other solar-based significant times of day are also accurate and checked, although the basis for the calculations can often be slightly more complex than allowed for in Sun Times.

The most time-consuming task in Sun Times is in managing the data on which it is based. Location data includes population, latitude, longitude, region and time zone data (with daylight saving rules) for over 10,000 places. Gross errors in locations have hopefully been avoided, but there will be some errors in precise latitude and longitude (which is somewhat arbitrary anyway for larger cities). Again, there has been thorough checking of time zone data, which include several time zones in addition to the time zones provided in Microsoft Windows. Notable potential problems with time zones are where the simple time zone rule structure in Sun Times is incompatible with the actual time zone rules used, eg Middle-Eastern countries operating rules based on their lunar calendars (eg Jordan, Israel). In a handful of cases I've resorted to guessing time zone assignment, eg for remote un-populated islands which have no formal time zone. City names, regions and time zones will also change occasionally, often with wide-ranging impact such as the North American daylight saving changes in 2007. The calculation of the population of larger cities is a subjective process with considerable disagreement in different sources, eg the treatment of Tokyo-Osaka as a single city, or deciding which towns near London should be counted within the population of London. Sun Times has made some simple general assumptions about how close in distance places need to be in order to be considered part of that city. Care has been taken to avoid double-counting of population. It should also be noted that the official populations for many cities are under-estimates - where people live in areas of lower-quality housing that is not officially recognised, are living temporarily in a city as refugees, or live as de facto long-term residents without official recognition.

Climate data has been gathered from a number of sources and processed to remove obvious errors based on consistency. It should be noted that there is often no simple authoritative historical record for many cities - weather stations move, nearby forests are cleared, buildings are erected and weather recording equipment is changed over the years. One potential source of error is in the matching of Sun Times locations to nearby weather stations. Sometimes, the closest weather station in distance will (wrongly) have an elevation substantially different to the actual city. Again, I have tried to avoid these types of errors. Climate observations from 2000 onwards have also been processed to eliminate measurements that differ too much from climate averages. In this process, I will have (correctly) removed erroneous climate reports and (wrongly) removed a handful of real extreme climate measurements. One visual way to check for large climate errors in Sun Times is in the climate maps, where nearby locations have very different colours. Any such cases in Sun Times should be down to differences in elevation for temperature measurements rather than errors in the data.

The flight data presented in Sun Times is based on a number of airline timetables and other sources. I've tried to correct obvious duplication and other errors in these sources of information. One-hour errors in departure and arrival times are relatively frequent for a couple of weeks around the time that daylight saving adjustments are applied. It should of course be noted that airlines often choose not to fly timetabled flights with low loadings and sometimes fly extra flights which are not timetabled, which Sun Times cannot take account of. Sun Times also has sophisticated procedures to establish which flights are actually codeshare flights operated by another airline that is already included in Sun Times. Sun Times therefore avoids showing duplicate flights by assigning codeshare flights to the actual operating airline (if that airline is included in Sun Times). Airline timetables can sometimes contradict each other in details for the same codeshared flight, so again, best guess methods often have to be used in processing the large number of flights. I have found relatively good agreement between the flight details presented in Sun Times and scheduled departure and arrival boards from airport websites. The major difference is that Sun Times omits data for many (especially budget) airlines.