faculae 光斑，耀斑

    Bright areas of the solar surface associated with sunspots and prominences.

    fall 落陨石

    A meteorite seen to fall. (See find.)

    false color 假色

    A representation of graphical data in which the colors are altered or added to reveal details.

    field (gravitational, electric, magnetic) 场

    A way of explaining action at a distance. A particle produces a field of influence to which another particle in the field responds.

    filar micrometer 动丝测微器

    An instrument that permits precise measurements at the telescope of the position of visual binary stars and similar objects.

    filtergram (filter) 滤镜

    A photograph (usually of the sun) taken in the light of a specific region of the spectrum -- e.g., an H-alpha filtergram

    find 寻陨石

    A meteorite that is found but not seen to fall. (See fall.)

    fission hypothesis 分裂假说

    The theory that the moon formed by breaking away from the earth.

    flare 闪焰耀斑

    A violent eruption on the sun's surface.

    flash spectrum 闪光谱

    The emission spectrum of the chromosphere that is visible for the few seconds during a total solar eclipse when the moon has covered the photosphere but has not yet covered the chromosphere.

    flatness problem 平坦问题

    In cosmology the circumstance that the early universe must have contained almost exactly the right amount of matter to close space-time (to make space-time flat).

    flat universe 平坦宇宙

    A model of the universe in which space-time is not curved.

    flocculent 丛毛状的

    Woolly, fluffy; used to refer to certain galaxies that have a woolly appearance.

    focal length 焦距

    The distance from a lens to the point where it focuses parallel rays of light.

    focus (of an ellipse) 焦点

    One of two points inside an ellipse that satisfy the condition that the distance from one focus to any point on the ellipse to the other focus is constant.

    forward scattering 往前散射

    The optical property of finely divided particles to preferentially direct light in the original direction of the light's travel.

    frequency 频率

    The number of times a given event occurs in a given time; for a wave, the number of cycles that pass the observer in 1 second.