Oy! Oy! - Pardon my Norwegian

Some items raised in readers' letters, starting with a correction to our piece on Shipping Areas:

From the Rev John Williams, West Wittering, Chichester:

"A bight is not a smooth stretch of coastline: it's another word for bay. German Bight is the wide bay formed by the coastlines of Jutland, Schleswig-Holstein and Lower Saxony. Its name in German is "Deutsche Bucht", which very definitely means bay.

"And Utsire is not the Norwegian for island. That is "oy", connected linguistically with the English place-name suffix "-ey", as in Canvey, Selsey etc. Utsira is a small island off the West coast of Norway."

While grateful to accept that I can't tell my oy from my Utsire, I'm less convinced by bight. The Old English "byht" simply meant a bend, and a bight in a piece of string is any free curve. Chambers 21st Century Dictionary gives "a stretch of gently curving coastline" as one definition.

From KJ Teacher, East Finchley, London:

"For two or three weeks around the winter solstice the Sun both sets and rises each day at a later time. An equivalent situation occurs at the summer solstice, though here the period during which sunsets and sunrises move in the same direction is much shorter. I'd be fascinated to know why."

It's due to the difference between "Apparent Solar Time" (as read on a sundial) and "Mean Solar Time" (as seen on a clock). Because the Earth's orbit round the Sun is elliptical, and because of the tilt between the axis of the Earth's rotation and the plane of its solar orbit, the time from one sunrise to the next is not constant but varies from about 23 hours and 46 minutes to 24 hours and 16 minutes. Mean Solar time smooths out these differences. At their worst, sundials are 14 minutes slow in February and 16 minutes fast in November. The Sun's apparently both rising and setting later around the winter solstice is a symptom of the Earth's catching up with the clock. In summer, the discrepancy is not so wide, and the catching-up period does not take so long. If you want to set your sundial, do it round 15 April, 14 June, 1 September or 25 December - when Mean Solar Time and Apparent Solar Time coincide.

Steven Squires of Luton has sent us a photograph of an unusual rainbow: "... What puzzled me was the fact that the Sun was low in the sky and the curvature of the rainbow was away from the Sun rather than as a halo around it. The red of the rainbow was on the outer curve.

Red on the outer curve is a sign of a secondary rainbow, caused by a double reflection of the light inside each raindrop. These are very puzzling when you cannot see the primary rainbow. Even odder rainbows may be due to sunlight that is first reflected off the still surface of water, then refracted through raindrops.