Q 01/05

A rainbow caused by sunlight always appears in which part of the sky?

A) Directly opposite the Sun

B) Directly around the Sun

C) Due north of the observer

D) Wherever the rain is heaviest

Answer · why

A) Directly opposite the Sun

The centre of the arc lies on a line running from the Sun through the back of your head.

Q 02/05

In a primary rainbow, which colour is on the outer edge of the arc?

A) Violet

B) Red

C) Green

D) Yellow

Answer · why

B) Red

Red light leaves the raindrop at the widest angle, so it forms the outside of the bow.

Q 03/05

At roughly what angle from the antisolar point does the primary rainbow appear?

A) 22°

B) 32°

C) 42°

D) 52°

Answer · why

C) 42°

Light returned from a raindrop piles up at that turning-point angle, and it does not depend on the size of the drop.

Q 04/05

Which three things happen to sunlight inside a raindrop to make a rainbow?

A) Reflection, ionisation and refraction

B) Diffraction, absorption and emission

C) Polarisation, Rayleigh scattering and fluorescence

D) Refraction, internal reflection and dispersion

Answer · why

D) Refraction, internal reflection and dispersion

The light bends on entry, bounces off the back of the drop and bends again on the way out, splitting into colours.

Q 05/05

Why are rainbows usually seen in the western sky in the morning?

A) The Sun is in the east and the bow sits opposite it

B) Morning rain clouds are usually pushed westward by wind

C) The air is cooler in the west at dawn

D) Dew evaporates first on the west side

Answer · why

A) The Sun is in the east and the bow sits opposite it

By early evening the geometry flips and the bow shows up in the east.