Meaning of 相欠合 in Japanese

あの先生の講義はあくびが出る。
His lectures are terribly boring.

もちろん、実際に「はやぶさ」が太陽に近づいているわけではなく、図のように地球から見て太陽の反対側に位置するだけですが、このような現象を「合」と呼びます。
Of course "Hayabusa" is not actually closing in on the Sun, it is just positioned as in the figure so that, seen from the Earth, it is on the opposite side of the Sun; this is called 'conjunction'.