The dog-days start on this day and last until 11 August. The Romans reckoned these wee the hottest days of the year, and they probably were in Rome, but the British climate is less consistent.

According to the Romans, the dog-days were not just hot by chance. The brightest of the stars in Canis Major (the big dog) is Sirius. The Romans thought that, because Sirius is brightest star in the night sky, the earth received heat from it.

The period between July 3 and August 11 in the northern hemisphere, the dog-star Sirius rises with the sun, thus adding to the heat it gave out - to such extent that dogs are inclined to go mad. ( In the southern hemisphere they are usually between January and early March.)