February - halos You are here: Home Photo gallery Atmospheric optics Light scattering Antisolar rays

Antisolar rays are sometimes seen in the direction opposite the sun, converging to the antisolar point (towards the shadow of your head). They are caused by sunlight being scattered from aerosols like dust particles and water vapor. Clouds or terrain may block the sun in some places, which causes rays of light to become visible. The rays are all parallel to eachother, because the sun is very far away. However, perspective causes the rays seemingly to diverge from the sun's position, or, in the case of antisolar rays, converge to the point opposite the sun (antisolar point).

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Observing tips

Solar and antisolar rays are caused by light scattering, and so there should be plenty of aerosols in the air (i.e. the air must not be too crystal clear). A slightly hazy sky makes for good opportunities to see these rays. Look for them when the sky is clear towards the direction opposite the sun, which should be low (between 0 and 20 degrees altitude, preferably).

Also, there should be clouds in the vicinity of the sun to cast shadows and create the rays. The rays may then be visible as pink bands of light contrasting with the blue sky (where it is in the cloud's shadow).

Antisolar rays are harder to see than the common solar rays, as most of the scattered light causing these rays is scattered in a forward direction, rather than backwards.

The rays are more distinct when the clouds covering some parts of the sky have clearly defined edges, like cumulus clouds. They may even be visible after sunset or before sunrise, when the clouds casting the shadows are so far away that they are below the horizon. The rays can then be seen converging into the dark shadow band of the earth (the twilight wedge) and the belt of Venus.