The Honbasho is an official professional sumo tournament. There are six held each year.
The system is established in 1958. Only honbasho results matter in determining promotion and relegation for rikishi (sumo wrestlers).
Tournaments in general may be called basho.
This is like “main” or “real” tournament. They last for 15 days. Sumo wrestlers ranked in the top two divisions (makuuchi and jūryō) wrestle once each day, while those of the lower divisions wrestle seven times, approximately once every alternate day.
|January||Hatsu (Opening) Basho||Tokyo||Ryōgoku Kokugikan||1st or 2nd Sunday|
|March||Haru (Spring) Basho||Osaka||Osaka Prefectural Gymnasium||2nd Sunday|
|May||Natsu (Summer) Basho||Tokyo||Ryōgoku Kokugikan||2nd Sunday|
|July||Nagoya Basho||Nagoya||Aichi Prefectural Gymnasium||1st or 2nd Sunday|
|September||Aki (Autumn/Fall) Basho||Tokyo||Ryōgoku Kokugikan||2nd Sunday|
|November||Kyūshū Basho||Fukuoka||Fukuoka Kokusai Center||2nd Sunday|
Source: Wikipedia, Japan Times, You Tube.