Phases of the moon are a means for people to determine time and pilgrimage

 ۞ يَسْـَٔلُونَكَ عَنِ ٱلْأَهِلَّةِ ۖ قُلْ هِىَ مَوَٰقِيتُ لِلنَّاسِ وَٱلْحَجِّ ۗ وَلَيْسَ ٱلْبِرُّ بِأَن تَأْتُوا۟ ٱلْبُيُوتَ مِن ظُهُورِهَا وَلَـٰكِنَّ ٱلْبِرَّ مَنِ ٱتَّقَىٰ ۗ وَأْتُوا۟ ٱلْبُيُوتَ مِنْ أَبْوَٰبِهَا ۚ وَٱتَّقُوا۟ ٱللَّهَ لَعَلَّكُمْ تُفْلِحُونَ ١٨٩

They ask you (O Muhammad صلى الله عليه وسلم) about the new moons. Say: These are signs to mark fixed periods of time for mankind and for the pilgrimage. It is not Al-Birr (piety, righteousness) that you enter the houses from the back but Al-Birr (is the quality of the one) who fears Allah. So enter houses through their proper doors, and fear Allah that you may be successful.

Quran 2:189