Final answer:
The acute angle formed by the line of sight of an object above an observer and the horizontal line is known as the angle of elevation. This concept is part of trigonometry and is important for determining distances and heights in relation to the observer's position.
Step-by-step explanation:
If an object being sighted is above the observer, the acute angle formed by the line of sight and the horizontal line is an angle of elevation.
This concept is part of trigonometry, which is a branch of mathematics that deals with the relationships between the sides and angles of triangles. The angle of elevation is used when we calculate the height of an object or a distance from an observer, based on the angle up from the horizontal. When using a sextant, as described in LibreTexts™, one would measure the angle of elevation to get a precise reading of the angle between the observed object and the horizon.
In relation to objects perceived by the eye, the angle subtended by an object, such as one above the observer, affects the perceived size of the object. As described in Figure 2.36, the larger the angle, the larger the image appears on the retina. This is why an object at a higher angle of elevation might appear larger if closer to the viewer.