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All life on our planet has developed under regular light and dark cycles caused by Earth;s daily rotations as we orbit around our star, the Sun. These cycles are what we call day and night. During the day our place on the earth is facing the sun. During the night we face away from the sun in the earth's shadow. With clear dark skies we can look out into the universe.

Actually there are two other light periods during a day called twilight, one in the morning when night brightens into day and the other in the evening when day fades into night.
Life on earth has adapted to these cycles of light to take advantage of those periods for feeding, or not being fed upon, to migrate – perhaps navigating by the stars, to breed safely or to find their mates with natural glowing lights.

Each period of the day has species that specialise in those conditions. Humans have adapted to be active in the day and to rest and recover at night. Daytime active species are called diurnal, nightime species are called nocturnal. Those active in the twilight zones are known as crepuscular.

Further natural light cycles are provided by the moon and by the seasons as we travel around the Sun.

These natural light cycles are essential characteristics that determine our ecosystem's (Earth's) integrity, form, functioning, and resilience.

Definitions

Ecosystem
An ecosystem is a community of living organisms (plants, animals and microbes) in conjunction with the nonliving components of their environment (things like air, water and mineral soil), interacting as a system.  Wikipedia

Environment
environment includes—
• (a) ecosystems and their constituent parts, including people and communities; and
• (b) all natural and physical resources; and
• (c) amenity values; and
• (d) the social, economic, aesthetic, and cultural conditions which affect the matters stated in paragraphs (a) to (c) or which are affected by those matters
NZ Resource Management Act

Intrinsic values
intrinsic values, in relation to ecosystems, means those aspects of ecosystems and their constituent parts which have value in their own right, including—
• (a) their biological and genetic diversity; and
• (b) the essential characteristics that determine an ecosystem's integrity, form, functioning, and resilience
NZ Resource Management Act

As we progress through the year and the seasons of summer, autumn, winter and spring, our night skies are directed to a different part of the universe and our local galaxy. In our southern summer we look outwards at night to the outer edges of our Milky Way Galaxy. In winter we can watch the central bulge of the Milky Way pass over head. In spring and autumn we are looking either upwards or downwards from the disk of the Milky Way.

With clear dark skies there is a changing parade of wonderful sights during the year. But how many stars can you see from your place? Do you live in a city, in the country, by the sea or in a Dark Sky Reserve? What you can see will depend on how many artificial outdoor lights there are and how they are designed and installed.

Globe at Night
You can take part in a worldwide citizen science programme to report on how many stars you can see from your place. Globe at Night
Follow 5 easy steps to report from your place on our planet. 5-steps