View east at sunset, Totaranui Beach, Abel Tasman National Park

On clear evenings, just after sunset, it is sometimes possible to see the beautiful phenomenon known as the “Belt of Venus” over the eastern horizon. The display begins a few minutes before sunset when, depending on the clarity of the atmosphere, the sky over the eastern horizon begins to turn a soft beige or brown colour. As the sun sets this colour quickly deepens into tones of pink and mauve and then, just a few minutes after the sun has disappeared, a dark blue shadow starts to work its way up from the eastern horizon, displacing the pink and mauve colours which by now form a well-defined band a few degrees above the horizon.

It is this distinctive pink band that is known as the Belt of Venus, or “countertwilight”, and is caused by the reflection of the sun’s last rays off particles of dust and haze in the lower atmosphere. The dark blue colour below is from the Earth’s shadow being projected onto the upper atmosphere, marking the gradual boundary between the day and night skies. As the setting sun slips further below the western horizon, the approaching darkness quickly lifts above the eastern horizon and the soft colours of the Belt of Venus dissipate.

Of course the same phenomenon can also be seen in reverse in the morning sky before sunrise, if one looks to the west about 15 minutes before the rising sun reaches the eastern horizon. As with the sunset display, all that’s needed is a clear sky and a good view of a distant horizon opposite the sun.