In Western church tradition, Michaelmas, or the Feast of Saint Michael and All Angels, is celebrated on September 29th ~
 

In Christian angelology, the Archangel Michael is the greatest of all the Archangels and is honored for defeating Satan in the war in heaven. He is one of the principal angelic warriors, seen as a protector against the dark of night, and the administrator of cosmic intelligence.
 
Michaelmas has also delineated time and seasons for secular purposes, as well, particularly in Britain and Ireland as one of the quarter days.

Source: Wikipedia

Father, today we remember Your special emissaries, the angels who are testified to in the Bible as one of the means by which Your will was communicated. Thank You for preserving these messages in Scripture. Help us to remember our role as modern messengers in delivering the Good News to unbelievers. We look forward to the day when we sing with the angels to Your glory. Amen
 

Related:
St. Michael and All Angels ~ Traditional Christianity still recognizes and celebrates Michaelmas each September