Mid-Autumn Festival revellers' view of the biggest full moon of the year last night was obscured by cloud and pollution. Yet even without the cloud, Hong Kong's dirty atmosphere could affect the brightness of the moon, astronomers said. Dust particles trapped city light and emitted a background glow that cut light coming from stars and the moon, Hong Kong Astronomical Society honorary secretary Ng Hung-cheung said. 'People always ask me why the moon looks so yellowish these days and I think that has something to do with its light being dimmed by atmospheric pollution,' he said. The moon often appeared an orange-red colour because the earth's atmosphere refracted the red bands and dispersed the blue bands of the sunlight being reflected from the moon. Yesterday's air-pollution index was between 57 and 62, indicating moderate air quality - below the unhealthy level of 100. The full eclipse of the moon occurred between 2.15 am and 3.18 am this morning. At 11.22 pm the moon's orbit came closest to the earth this year at 356,965 kilometres. The average distance between the two bodies is about 400,000 kilometres. Hong Kong Observatory scientific officer Lee Shuk-ming said the weather should be generally sunny today, allowing better moon-gazing. The next total lunar eclipse will be on July 16, 2000. The last total eclipse was on June 4, 1993 and the last one that fell on the Mid-Autumn Festival was in 1978. A lunar eclipse occurs when the earth passes between the moon and the sun, throwing its shadow on the moon.