A key aspect of telescopes is their angular resolution. Here we discuss what makes up the concept of angular resolution and seeing. This is part of my intro Astronomy class taught at Willam Paterson University and CUNY Hunter. • Telescope’s Resolving Power: The ability of a telescope to discern details of an object, related to its resolution capacity. • Angular Size: How big an object appears to be, dependent on its actual size and distance from the observer. • Tangent and Circles: The tangent of an angle in a circle is a segment of the radius. The adjacent side is the base of the radius, the opposite side is the segment from the base to the circle, and the hypotenuse is the radius itself. • Trigonometry and Right Angles: Trigonometry, which deals with angles and circles, involves right angles. In the context of a circle, the right angle is formed between the opposite and adjacent sides. • Radian Definition: A radian is defined as the angle subtended at the center of a circle by an arc whose length is equal to the radius of the circle. • Small Angle Approximation: When angles are very small (measured in arcseconds or arcminutes), the angle in radians can be approximated by the physical size of the object divided by the distance to the object. • Angular Size and Physical Size: The angular size of an object, when very small, can be used to calculate its physical size if the distance to the object is known. • Tangent Approximation: For very small angles measured in radians, the tangent of the angle is approximately equal to the angle itself. • Angular Size Definition: Angular size is how big an object appears to be, influenced by its actual size and distance from the observer. • Telescope Resolving Power: The ability of a telescope to distinguish between two closely spaced objects, such as separating a star from a planet or resolving details within a gas cloud. • Resolving Power of Telescopes: The importance of resolving power in telescopes, which is limited by diffraction of light. • Diffraction and Image Clarity: Explanation of how diffraction, even at the telescope’s aperture, can blur images of distant objects. • Resolution and Detail: Higher resolution allows for clearer images and the ability to distinguish finer details in astronomical objects. • Diffraction Limit: The diffraction of light waves as they pass through an aperture limits the resolution of all telescopes. • Diffraction Pattern: A circular aperture creates a diffraction pattern with a bright central peak and surrounding rings, impacting the clarity of observed objects. • Airy Discs and Telescope Resolution: Airy discs, named after Sir George Airy, are diffraction patterns formed by light entering a telescope’s circular aperture. Overall, the segment emphasizes clear definitions, underlying geometry, and practical observing guidance so viewers can connect the concept to the real sky.