The longest leg in every ledger against daylight, month by month

Every driving ledger on this site has one day that decides which months it is for. Set that day's minutes on the move against the daylight at its midpoint, allow an hour, and the answer falls out: the South Coast, North and Norway ledgers fit in every month but December; the two Ring Road loops, the Westfjords loop and Lapland fail January as well, the Ring Road by six minutes; the Highlands and ferry ledgers fail November too. The table is computed, not observed, and the method is stated so it can be re-run.

#The method

For each journey, the longest day is the ledger row with the most minutes on the move, driving plus ferry. Its midpoint is the mean of the coordinates on this site's stop pages for the day's ends, or for a there-and-back day the far point's coordinates. Daylight is sunrise to sunset at a zenith of 90.833° by the NOAA solar equations, declination taken at 12:00 UTC on the 15th of each month of 2027. A month "fits" when daylight is at least the day's minutes plus 60. Stops come out of that margin: a day with three long stops needs more than an hour over, and the figure to carry is the one in the "need" column plus whatever you intend to look at.

#The table

April to September are above 14 hours at every midpoint and are left out of the columns; they fit everything. The Greenland add-on and the Copenhagen or Oslo stopover have no driving rows and no longest leg. The Icelandic midpoints differ from the Reykjavík table on this site by minutes in spring and autumn and by more than an hour in December, where every degree of latitude counts; a few minutes also come from taking the declination at noon.

#Reading the rows

The Ring Road's longest day fits November with an hour and nine minutes over, which is the margin and little more, and misses January by six minutes; the 330 km rule post on this site, which also counts stops, puts the same day below the line in November, and both are right about what they measure. If the day is driven with one stop and lunch in the car, it fits; if it is driven the way the ledger describes it, with Hvammstangi and a look at the coast, it does not.

The Westfjords day is the one with a ferry in it: 180 minutes of road and the 130-minute Baldur crossing, and the ferry's winter timetable, not daylight, is what actually fixes the day between September and May. Daylight simply confirms that October is the last month with a clear hour over; 15 November clears the margin by a single minute.

The Highlands day fails November by an hour and three-quarters, which is academic, because the F-roads it uses close in September; its real window is the June-to-September one the ledger states, and the daylight column only says that the day would fit in February if the road were open, which it is not.

Lapland on 15 December is 0:00 by this definition: at the midpoint between Levi and Kilpisjärvi, 68.4° N, the sun does not reach the 90.833° zenith on that date. Civil twilight gives a few hours of grey the formula does not count, and the ledger's February start date is chosen with that in mind. November fits by two minutes, which in practice is not fitting. In June and July the same formula returns 24:00 for the North ledger's midpoint and for Lapland: the sun does not set.

Norway's day has the most daylight in every winter column because Geiranger is at 62° N, seven degrees south of Akureyri; it is the ferry suspension on that road, covered elsewhere on this site, that constrains the day, not the light.

#Sources

• NOAA Global Monitoring Laboratory, solar calculator equations: https://gml.noaa.gov/grad/solcalc/calcdetails.html
• Coordinates from this site's stop pages (Akureyri, Borgarnes, Skaftafell, Stykkishólmur, Brjánslækur, Ásbyrgi, Mývatn, Askja, Reykjavík, Levi, Kilpisjärvi, Flåm, Geiranger), checked 1 November 2026.
• The nine ledgers linked above; minutes from their ledger rows, checked 1 November 2026.
• Computed here on 1 November 2026 for the 15th of each month of 2027.