Although the Vietnamese calendar is the same as our Gregorian calendar, some Vietnamese holidays are based on the lunar calendar. The exact dates are different every year, depending on the position of the moon. Tet Nguyen Dan (usually abbreviated to Tet) is celebrated in January/February and is the Vietnamese New Year, the biggest annual celebration. The Tet celebrations are officially three days long, but many Vietnamese have the week off. Festivities such as processions, dragon dances, fireworks and flower parades are organised, but in the main it is a family celebration and is not targeted at tourists. The Vietnamese travel throughout the country to visit family members and eat festive meals, such as we do at Christmas. They buy new clothes for new beginnings, houses are thoroughly cleaned and the graves of their ancestors are spruced up. Most shops and many restaurants are closed during Tet. Trung Nguyen is the day of wandering souls (July/August), where gifts are offered to spirits forgotten or neglected by their surviving relatives. Tet Thrung Thu is the mid-autumn festival, held at the end of September, when ‘moon cakes’ are sold everywhere and children with beautifully shaped lanterns walk through the streets. This festival is becoming less important in the cities and towns, but is still a very strong tradition in the countryside. Dates of fixed national holidays are 1 January (the New (Gregorian) Year), 3 February (the day of the founding of the Vietnamese Communist Party in 1930), 30 April (the day of the liberation of Saigon in 1975), 1 May (Labour Day), 19 May (the birthday of political leader Ho Chi Minh), 2 September (National Day, the celebration of independence in 1945) and 25 December (Christmas).