Hotter still is the core. In the sun this is thought to be 10 - 20 million degrees. These temperatures are due to the pressure caused by gravity trying to compress the star. It has to be this temperature for fusion of hydrogen to take place. Once fusion starts in a young star this adds to the temperature to ensure that fusion continues.
Weather in Lisbon in September. The average maximum daytime temperature in Lisbon in September is a warm 27Â°C (81Â°F) with low heat & humidity. There are usually 9 hours of bright sunshine each day, which represents 68% of the 12 hours of daylight. The average sea temperature in and around Lisbon in September is 19Â°C (66Â°F). Expect 26mm (1.0 inches) of rainfall across the whole of September with 6 days with some rain falling. Maximum UV levels will be high (6 UV index) at midday when the skies are clear.
Spring is an agreeable time in Lisbon with average temperatures by May creeping up to the 17Â°C mark with daily highs reaching 21Â°C and above. Sea temperatures creep up about a degree a month too and by May reach 17Â°C.ach average 5mm of rain at most. September sees a little more rain â about 20-25mm; still very dry compared to the rest of the months of the year. Autumn is another good time to visit Lisbon, with very pleasant temperatures most of the time.