| North Hemisphere | Period | South Hemisphere | Period |
| Spring | March 1-May 31 | Spring | Sept. 1-Nov. 30 |
| Summer | Jun. 1-Aug. 31 | Summer | Dec. 1-Feb. 28 |
| Fall | Sept. 1-Nov. 30 | Fall | March 1-May 30 |
| Winter | Dec. 1-Feb. 28 | Winter | Jun. 1-Aug. 31 |