Astronomers deduce that we are in the middle of one of the galaxy’s arms, 30,000 light-years from the core, halfway between the edge and the center. Astronomers just don’t pinpoint our location with certainty because we don’t have an exact “blueprint” of our galaxy. Precisely because we are inside it, far less is known about its shape than we know about others in our vicinity. “There is no photograph of the Milky Way. What astronomy does is deduce its shape from possible observations and comparisons with other galaxies”, says astronomer Rundsthen Vasques de Nader, from the Valongo Observatory, at the Federal University of Rio de Janeiro. In these pages, we show a representation of our galaxy made by the American space agency – NASA – and the main information about it.
We live on the periphery: Earth is 30,000 light years from the center of the galaxy
SIZE
Our galaxy has a diameter of 100,000 light years. The Andromeda Galaxy, for example, is the same shape and a little more than twice the overall diameter. The smallest galaxies of the Local Group (which we show on the previous pages) are 500 light years
TOTAL STARS
The most recent estimates suggest that the Milky Way has about 100 billion stars. With the naked eye, we can only see those that are at most 1,500 light years away – which is not even 1% of the total!
ARMS
From the center come the arms of the galaxy, which are regions with a lower concentration of stars, generally younger than those in the center. It is in this region that the “stellar nurseries” are located, areas conducive to the birth of stars
CORE
In the center of the galaxy there is a large concentration of stars, most of them old (from 10 billion to 15 billion years old). It is the thickest part of the galaxy, 6,000 light-years high.
BARRED SPIRAL
The Milky Way was classified as a spiral galaxy, but new observations have shown a bar in the center, where the arms come out. From there, the Milky Way entered the category of barred spirals.
ORBIT
All stars in the Milky Way revolve around the center. Our Sun moves at a speed of 200 km/s. It takes 250 million years to go around the galaxy completely. Since the galaxy’s emergence, 13.7 billion years ago, it has only circled the Milky Way 54 times!
SOLAR SYSTEM
The Sun is one of the stars in the Orion arm, also known as the local arm. It is about 30,000 light-years from the center of the galaxy, roughly midway between center and edge.
Galactic Plan
Thanks to the galaxy’s rotational motion and the gravitational forces acting on it, the stars farthest from the center have flattened into a plane, like a table top. The arms of the Milky Way are aligned in this region called the galactic plane, which serves as a reference to determine the position of the other galaxies in the Universe