Current Event: Mapping the Milky Way

The European Space Agency (ESA) recently released a wealth of data gathered by the space probe Gaia that promises to revolutionize the study of our galaxy in the next several years. The probe pinned down the precise position and brightness of over a billion stars. Until now, astronomers had to guess what the Milky Way looks like by observing other galaxies with similar traits. Launched in 2013 by the ESA, Gaia traveled to a point behind Earth and began measuring the positions of over a billion stars as it orbited the sun. Gaia measures stellar distances using a technique called parallax. It first images a star against a background of other stars. Halfway around the sun, it takes another picture of the same star. Because the two pictures are taken many millions of miles apart, the star’s position changes slightly in relation to its background. And because scientists know how far away the two star pictures were taken, and how much the star appeared to move, they can calculate its distance from Earth. Gaia’s first map shows a two-dimensional plot of star density in the Milky Way. As Gaia orbits the sun, it will gather information on more and more points of light. It will then be able to refine its data to better define star positions. Astronomers are confident that future data from Gaia will allow them to create extremely accurate, three-dimensional maps of the galaxy.

Artist’s impression of Gaia mapping the stars of the Milky Way. Credit: ESA/ATG medialab/ESO/S. Brunier

Objective:

The Milky Way is the galaxy that contains the sun, Earth, and other objects in our solar system. It also includes hundreds of billions of stars besides the sun. Huge clouds of gas and dust lie throughout the galaxy, and they constantly form new stars. The Milky Way is so massive that about 10 smaller galaxies orbit it like satellites revolving around a planet. The name Milky Way also refers to the part of the galaxy that can be seen with the unaided eye. On clear, dark nights, this portion of the galaxy appears as a broad, milky-looking band of starlight stretching across the sky. When observed through an entire year, this band appears to circle completely around us in the sky. Dark gaps in the band consist of clouds of gas and dust that block out light from the stars behind them. The Behind the Headlines news story and related World Book articles explore the Milky Way and other astronomical topics.

Words to know:

• Astronomy
• European Space Agency (ESA)
• Galaxy
• Milky Way
• Orbit
• Parallax
• Planet
• Satellite
• Solar system
• Space exploration
• Star
• Sun

Discussion Topics:

1. The Milky Way is our home galaxy. Ask your students to name some objects in our solar system. (Students might say the sun, other stars, the moon, any of the eight planets [Earth, Jupiter, Mars, Mercury, Neptune, Saturn, Uranus, Venus], dwarf planets such as Pluto, asteroids, comets, or meteors.)

2. Ask your students to debate: “Is it worth it for countries to spend a lot of money on space exploration programs? Why or why not?”

3. Ask your students to use World Book’s Timelines feature to view or add to the Advances in Space Exploration timeline. (Students may wish to use World Book’s “Space exploration” article for help.)