sentences:  The shape of an upper tangent arc varies with the elevation of the Sun; while the Sun is low (less than 29–32°) it appears as an arc over the observed Sun forming a sharp angle.As the Sun is seen to rise above the Earth's horizon, the curved wings of the arc lower towards the 22° halo while gradually becoming longer.As the Sun rises over 29–32°, the upper tangent arc unites with the lower tangent arc to form the circumscribed halo.