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.
Why is Torah compared to light? Because it tells us the place of each thing.
Because, in truth, there is no need to change the world. Everything is here.
Each thing has a place, and in that place it is good. Altogether, it is very good, a beautiful world. All that’s needed is a little light.
What is light? Light doesn't add anything or take away. It only reveals the meaning and purpose of all that it shines upon.
Think of your own home. In the dark, there is no way to know what belongs in your closet and what belongs in the laundry, what is ready for use and what is in need of repair. Instead, that which could be washed or repaired is rejected and despised, and your most valuable possessions may become the greatest hazards.
Switch on one little light and a dangerous place becomes a home. With every light you add, you become suddenly wealthier and more blessed.
So too, this world is meant to be G-d’s home. Torah is light. Shine it bright and heal the world.