赤気 is read as せっき (sekki) and means comet.
せっき
sekki
せきどうきだん
equatorial air mass
あかいろ
communism
あかい
Red
あかじ
corrections (by a teacher or proofreader) written in red
あかちゃん
baby
せきどう
equator
せきはん
red rice (beans and mochi) for auspicious occasions
あかつち
dark-red paint
あかご
red cloth
あかちゃける
to turn reddish-brown
あかあか
bright red