In the year 2448 from Creation (1313 BCE), Tammuz 16 was the 40th day following the Giving of the Torah at Mount Sinai, and the people of Israel wrongly expected Moses' return from the mountain (he would actually return on the following day). When their leader failed to return, they demanded from Aaron: "Make us a god that shall go before us". Hur (Moses' nephew, the son of Miriam and Caleb) tried to stop them and was killed by the mob. Aaron fashioned a calf of molten gold.
Links:
The Making of the Golden Calf (text of Exodus 32 with Rashi's commentary)
An anthology of Midrashim and Commentaries on the making of the Calf
The Day Before (on the deeper significance of Tammuz 16, from the teachings of the Lubavitcher Rebbe)
More on the Golden calf
See also "Today in Jewish History" for tomorrow, Tammuz 17.
In the Temple in Jerusalem was a seven-branched menorah.
That is us, the Jewish people.
Each of us is a flame. One flame burns softly. Another burns with a roar. Until seven branches are filled with millions of distinct, unique flames.
All are drawn upwards, all yearning to reunite with their Beloved above.
And that is the work of Aaron the Kohen, the priest of kindness and love:
That every soul should burn its own flame, and not a single one should remain dark or dim.