A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of
light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc.
--Wikipedia [my emphasis]
Yes, the rainbow is always in principle or in its aim a full circle. We rarely see it that way, but sometimes in gorges or waterfalls or from helicopters and planes and in skydiving it can be witnessed in full. You can find YouTube's that show it, for instance here.
In group, as part of our practice of knowing ourselves to be energetic or subtle beings as well as physical beings, we have experimented with an exercise called The Rainbow Carwash. It is the simplest thing in the world.
Standing, with eyes closed, you picture a full circle rainbow above your head. It is horizontal to the earth, like a huge hat or halo for you. You allow the rainbow to sink slowly down through your body: head, neck, shoulders, arms and torso, hips, legs, feet. A bit below your feet, it reverses direction and rises through your body: feet, legs, hips, torso and arms, shoulders, neck, head. All along the way, you feel the pervasive, permeating effect of the sparkling light.
When the rainbow has returned to its original position above your head, it swivels 90 degrees and becomes and upright disc, body-high, confronting you from a few inches in front of your standing form. It slowly moves through you from front to back. Once it has left you to the back, it returns through you to the front.
Now the rainbow shifts around to your right and, still an upright disc, passes through your body from right to left. Then it reverses and moves through you from left to right.
All through this process, you allow the richly saturated, brilliant colors to enliven your mind and body, transmuting your every part and particle into living light. If the feeling of freshness lags at any point, you can bring it back by pausing, briefly draining the rainbow of all color and so seeing it as in a black-and-white photograph, and then letting the vibrancy of the colors return in full force before continuing the procedure.
At the end, you let the rainbow dissipate and focus for a moment on the felt sense of a refreshed, cleansed and spacious body/mind. From this position it is easier to engage, as a distinct but form-free someone, with the energetic world around you.
All blessings to all,