What is a rainbow?
A: A rainbow is a 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 what?
A: A multicolored circular arc.
Rainbows caused by sunlight always appear in what the
section of the sky?
A: The section of sky directly opposite the Sun.
Rainbows can be full what?
A: Circles.
However, the observer normally sees only what?
A: An arc formed by illuminated droplets above the ground and centered on a
line from the Sun to the observer's eye.
In a primary rainbow, the arc shows red on the outer
part and what on the inner side?
A: Violet.
In a double rainbow, a second arc is seen outside the
primary arc, and has what?
A: It has the order of its
colors reversed, with red on the inner side of
the arc.
This is caused by what?
A: By the light being reflected twice on the inside of the droplet before
leaving it.
A rainbow is not located at a specific distance from
the observer but comes from what?
A: An optical illusion caused by any water droplets viewed from a certain
angle relative to a light source.
Thus, a rainbow is not an object and cannot be what?
A: Physically approached.
Indeed, it is impossible for an observer to see a
rainbow from water droplets at any angle other than what?
A: The customary one of 42 degrees from the direction opposite the light
source.
Even if an observer sees another observer who seems
"under" or "at the end of" a rainbow, the second observer will see what?
A: A different rainbow—farther off—at the same angle as seen by the first
observer.
Rainbows span a continuous what?
A: Spectrum of colors.
Any distinct bands perceived are an artefact of what?
A: Human color vision.
No banding of any type is seen in a what?
A: Black-and-white photo of a rainbow.
Rainbows can be caused by many forms of what?
A: Airborne water.
These include not only rain, but also what?
A: Mist, spray, and airborne dew.
Rainbows can form in the spray of a what?
A: A waterfall (called spray bows)
Rainbows can be observed whenever there are water drops
in the air and sunlight shining from behind the observer at what?
A: A low altitude angle.
Because of this, when are rainbows usually seen in the
western sky?
A: During the morning and in the eastern sky during the early evening.
When do the most spectacular rainbow displays happen?
A: When half the sky is still dark with raining clouds and the observer is
at a spot with clear sky in the direction of the Sun.
What is the result?
A: A luminous rainbow that contrasts with the darkened background.
During such good visibility conditions what is often
visible?
A: The larger but fainter secondary rainbow.
Rarely, a moonbow, lunar rainbow or nighttime rainbow,
can be seen on what?
A: Strongly moonlit nights.
As human visual perception for color is poor in low
light, moonbows are often perceived to be what?
A: White.
From above the Earth such as in an airplane, it is
sometimes possible to see a rainbow as what?
A: As a full circle.
The sky inside a primary rainbow is brighter than what?
A: The sky outside of the bow.
Newton originally (1672) divided the spectrum into how
many main colors?
A: Five main colors: red, yellow, green,
blue and violet.
Later he included what?
A: Orange and indigo, giving seven main colors by analogy to the number of
notes in a musical scale.
Newton chose to divide the visible spectrum into seven
colors out of what?
A: A belief derived from the beliefs of the ancient Greek sophists, who
thought there was a connection between the colors, the musical notes, the
known objects in the Solar System, and the days of the week.
Scholars have noted that what Newton regarded at the
time as "blue" would today be regarded as what?
A: Cyan, and what Newton called "indigo" would today be considered blue.
