arc tangent inférieur

CONT: Un peu au-dessus ou au-dessous de l'astre lumineux [soleil], à la distance de 22 degrés, on peut fréquemment voir des arcs supérieurs et inférieurs tangents au petit anneau.

CONT: The 22° halo is most common, but other halo forms are sometimes seen. The tangent arcs to the 22° halo can appear if the sun's declination is less than 32°. One is called the lower tangent arc to the 22° halo, and the other is the upper tangent arc to the 22° halo. The shape of these tangent haloes depends upon the sun's declination. If the sun is close to the horizon, the two upper arcs angle sharply away from the 22° halo. As the sun rises higher in the sky, the tangent arcs move toward the 22° halo. When the sun's declination reaches 32°above the horizon, the lower and upper tangent arcs make contact, and the resulting ring is called the circumscribed halo. It touches the 22° halo above and beneath the sun. When the sun is just above 32°the circumscribed halo resembles a double oval. As the sun rises higher it becomes increasingly circular and draws nearer to the 22° halo. When the sun's declination exceeds 70°, the circumscribed arc nearly coincides with the 22° halo.