Halakhah zu Schemot 23:21

We find that the light of the sun and of all the stars is eternal, of itself it does not increase nor decrease. However, the light appears to increase or decrease depending on whether the object being viewed is far or near. Also, the light varies due to changes in the atmosphere at the beginning or the middle of the day. Only the moon has a renewal of its light.¹ Ibn Ezra believes that the sun, all planets and all stars, generate their own light, and only the moon reflects light of another body (the sun). Therefore, the Hebrew term for month, “hodesh,” can truly apply only to a lunar month.² In Hebrew, a month is called “hodesh,” which is derived from the root “hidesh” meaning “renew.” Since only the moon has a renewal of its light, “hodesh” can only refer to a lunar month. We examine when such a month begins.