Possible Clues:

• Device to measure angles to a celestial body
• Pie slice, typically
• 45 degrees of a circle
• Circle division
• Circle with constant tangent that's origin for one of its segments
• Navigator's bit of kit to turn brown within 31 days
• Circle eighth
• Soak up sun in autumn month -- it's 45 degrees
• One eighth
• One eighth of a circle