The four solar terms in the revolution of the earth are _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.

When the earth revolves around the sun, the axis of the earth forms a fixed angle of 66.5 with the orbital plane, so that the direct point of the sun's rays regularly moves between the tropic of cancer in a year. When the sun shines directly on the equator, it is the vernal equinox or autumnal equinox in the northern hemisphere. When the sun shines directly on the Tropic of Cancer, it is the summer solstice in the northern hemisphere; When the sun shines directly on the tropic of Capricorn, it is the winter solstice in the northern hemisphere.

So the answer is: vernal equinox; Summer solstice; Vernal equinox; Solstice of winter.