Look up at the stars on a crisp, clear evening, and you’ll see countless lights shimmering throughout the sky — but in reality, you’re only looking at about 15 percent of what’s really there.

The other 85 percent is made up of dark matter and dark energy, totally invisible to the naked eye and really any instruments that we have today — only its gravitational effects on things that we can see let us know it’s there.

Which is why it’s so impressive that hundreds of scientists working together were able to map out a quarter of the sky that measures dark energy. They used complex measurements and created a 3D model of 650 billion cubic lights years of space that includes 1.2 million galaxies.

Dark energy is perhaps the biggest mystery in science — what it is, why we can’t see it, and what impact it has on our universe. Many scientists believe it is responsible for the acceleration of the expansion of the universe, or even the cosmological constant described by Albert Einstein. Still others suggested it may be a sign that gravity itself was deteriorating.

But whatever it is, scientists want to know more, and this new map could help them do just that. The map is based on data from the past decade by scientists at a number of astronomical institutions.

The measurements were made by determining the size of what are known as baryonic acoustic oscillations, which are basically pressure waves from just after the Big Bang, leaving their own special footprint on the universe.

“We have spent five years collecting measurements of 1.2 million galaxies over one quarter of the sky to map out the structure of the Universe over a volume of 650 cubic billion light years,” says Jeremy Tinker of New York University, a co-leader of the scientific team carrying out this effort. “This map has allowed us to make the best measurements yet of the effects of dark energy in the expansion of the Universe. We are making our results and map available to the world.”