The autumn begins about August.

秋天大致从八月开始。

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Frost's Descent, the 18th solar term of the year, is the last solar term of autumn, during which time the weather becomes much colder than before and frost begins to appear.

霜降是一年中的第18个节气，是秋天的最后一个节气，在此期间，天气比之前变得更凉，开始出现霜降。

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The school year begins in autumn.

秋季始业。

《新英汉大辞典》

Martin Johnson has said the World Cup countdown begins now as this is the last time England travel to the Southern Hemisphere before the tournament begins next autumn.

BBC: Injury-hit Wallabies look vulnerable

Construction on the Perth development begins in April and is scheduled for completion in the autumn.

BBC: Scheme to turn offices into social housing begins in Perth

Temperatures begin to cool, and eventually a new season begins and the leaves turn to shades of Autumn.

FORBES: Turning a New Leaf on Presentations