Galaxies, Nebulae and Star Clusters

Milky Way

Composited panorama of the Milky Way; source: European Southern Observatory
The Milky Way is our home galaxy. Our sun is one of an estimated 100 to 400 billion stars in this galaxy.

The Milky Way is a barred spiral galaxy with a diameter of about 1.85 million light years.

The center of the Milky Way is a supermassive black hole of about 4.1 million solar masses. It can be pinpointed by an intense radio source known as Sagittarius A*.
There is no consensus on the nature of the Milky Way's spiral arms.

Most commonly, there are thought to be four major spiral arms starting near the Milky Way's center and a number of minor spiral arms.

Our Sun is located in one of the minor arms, the Orion–Cygnus Arm, some 27,000 light years away from the center.

We travel at a speed of 141.5 miles per second (828,000 km/h) around the center, taking 230 million years to complete one circle.

Before the invention of the telescope, the Milky Way was observed only as a hazy band of light in which no individual stars could be distinguished. Today's common name Milky Way was derived from the Latin via lactea (Milk Road) and the Greek γαλαξίας κύκλος (Milk Circle).

The Greek word γαλαξίας (galaxias = milky) became the modern word Galaxy.

Source: Wikipedia

Artists depiction of a Milky Way model with four symmetric spiral arms from Wikipedia
Click here for a large image without notations.
© Xing-Wu Zheng & Mark Reid BeSSeL/NJU/CFA

In other cultures, the Milky Way is seen as a road, a river, a track of birds or a snake (among others).

Click here for myths about our home galaxy.

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