- The best time to travel is in the autumn.
- The best time to travel is in autumn.
Which sentence is correct?
This is a great question!
Although both phrases are technically correct in the example you have given, the second is preferable. Native speakers in the UK, US and Australia generally exclude the "the". For instance, "the best time to travel is in autumn" would be more common, especially among educated speakers.
Therefore, if you are learning English and would prefer a simple rule, your best option would be to exclude the "the" in front of a season name.
In general, the difference between including and excluding the article is mainly one of poetic effect, and that will depend on the specific examples.
Sometimes the inclusion of "a" or "the" in front of a season will add emphasis and make the sentence sound more interesting. However, it takes years of reading good literature and poetry to sense the difference.
Therefore, the safest option - to ensure that your sentences always sound correct - is to exclude the article.
Note # - The words "the" and "a" are called "articles".