Judaism uses a lunar calendar. The source of this is Genesis 1:5, “And there was evening and there was morning, one day.” This is why every new day begins in the evening, and all Jewish holidays start at sunset.
During the time of the Sanhedrin (Rabbinic tribunal in the days of the Romans), Rosh Hashanah began when the crescent new moon was sighted. It was customary for the rabbis to study the sky every night. In the 4th Century CE, Hillel II, the Nasi or leader of the Sanhedrin, calculated the Jewish calendar. After the Sanhedrin was disbanded, Hillel’s calendar was used to determine the dates of the Jewish holidays.
Galileo Galilei is credited with being the first person to observe the moon through a telescope and to record what he saw. He was an Italian astronomer in the late 1500s. He built his own telescopes and recorded his observations of the moon by painting the moon as he observed it every night. Galileo drew the moon with a pen. He then dipped a brush in brown ink and painted. This technique is called wash. He focused on light and shadow to show what phase the moon was in. You may track the moon by recreating Galileo Galilei’s lunar journal. You can see his drawing in the Museo Galileo.
Hand-held telescope (optional)
Observe the moon every evening at the same time. Record the date and time in your sketchbook.
Draw a circle with the pencil. Paint the shadows you see with the watercolors.
Record the shape of the moon, the date, and time.
At the end of thirty days, flip through your notebook and observe the changes. Rosh Hashanah falls on the new moon. This is the first crescent of the moon that can be seen in the west after the sun sets.