Urban areas get really hot, especially at night, which can be bad for our health. Scientists are studying how cities trap heat and how this affects different parts of the city. They are using satellite data to create models that show where it's hottest at night in Barcelona. They found that areas with more buildings and less greenery are hotter at night, while less dense areas with more plants are cooler. This research helps us understand how urban areas can stay cooler at night to improve our comfort and health.