der Januar
January
The first month of the year in the Gregorian calendar.
Im Januar ist es in Deutschland oft sehr kalt.
In January, it is often very cold in Germany.

January
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January
The first month of the year in the Gregorian calendar.
Im Januar ist es in Deutschland oft sehr kalt.
In January, it is often very cold in Germany.

To express that something happens in the month of January, German uses the preposition 'im' (in dem). The article 'der' is then no longer needed.
Im Januar hat meine Schwester Geburtstag.
My sister has her birthday in January.
To name a specific part of the month, you can put 'Anfang' (beginning), 'Mitte' (middle), or 'Ende' (end) directly before 'Januar' (January), without any preposition. The word 'Januar' is not declined in this case.
Die Ergebnisse werden Mitte Januar bekannt gegeben.
The results will be announced in mid-January.
In Austria and parts of southern Germany, the word 'der Jänner' is also very common instead of 'Januar' (January). Both words mean exactly the same thing.
In Österreich beginnen die Semesterferien oft erst im Jänner.
In Austria, the semester break often doesn't begin until January.
January
'der Januar' and 'der Jänner' mean the same month, namely the first month of the year. The difference is mainly in regional usage. In Germany, people almost always say 'Januar'. 'Jänner' is common mainly in Austria and South Tyrol. Learners may confuse the words because they really do refer to the same time of year. If you are speaking generally or in Germany, 'Januar' is the more natural form; in Austria, 'Jänner' sounds completely normal.

Im Januar beginnt mein neuer Deutschkurs.
My new German course begins in January.
Mein Bruder aus Wien kommt im Jänner zu Besuch.
My brother from Vienna is coming to visit in January.