Teaching with the Show
Visualizations of the Sun and Earth are created from observations made by scientists using both ground-based and space-based telescopes.
To support a class discussion after viewing Journey to the Stars
, you may wish to review the main content points from each section of the show and then use the Guiding Questions
- We live on a planet that orbits a star that is one of hundreds of billions in our galaxy.
- Our star, the Sun, is a middle-aged yellow star of somewhat above average mass.
- Without nurturing light that carries energy from our Sun, life as we know it would not exist.
- And without the elements formed by stars that lived and died billions of years ago, we—and everything around us—would not exist.
Scientists use supercomputer models to understand star formation and star clusters. The first stars were massive-they burned hot and heated the surrounding gas (red, purple, white filaments). They lived fast and died young in supernova explosions (white region in center).
2. Stellar History
- Over 13 billion years ago (300 million years after the Big Bang), all that existed in the universe was dark matter and the elements hydrogen, helium, and trace amounts of lithium. Dark matter's gravity gathered the gas to form the first stars. Over the next few billion years, stars were born more rapidly than at any other period in the history of the universe. Stars now form at a rate one-tenth as high.
- About 4.5 billion years ago, within the Milky Way Galaxy, our Sun was born from a dense cloud of gas and dust, along with hundreds to thousands of other stars in a star cluster. As happens with many young stars, our Sun was ejected from its cluster. Since then it has traveled, along with its planets, in orbit around the center of the Milky Way.
- Except for hydrogen and helium, all the naturally occurring elements come from the life and death of stars. Together, they make up all the matter of daily life.
- Stars are different masses, temperatures, and colors. More massive stars are hotter and bluer, while less massive stars are cooler and redder. Yellow stars are in between.
The Voyager Space Probe has detected the outer edge of the Sun's solar wind and magnetic field, where they encounter the surrounding inter-stellar gas. This mission has extended the human footprint to the edge of the Solar System-it has traveled the farthest from Earth of any human-made objects
3. The Life of Stars: Our Sun as an Example
- Nuclear fusion in the core of the Sun generates energy (light of all wavelengths) that diffuses partway out as radiation. Energy is then carried the rest of the way to the surface by convection.
- The Sun, like all stars, performs a balancing act to keep itself together: the enormous outward pressure of hot gas is balanced by the inward pull of the Sun's own gravity. This is called hydrostatic equilibrium.
- The Sun continuously blasts a solar wind made up of charged particles (protons, electrons, and heavier ions). Magnetic explosions called solar flares produce storms in the solar wind and generate radiation. In rare cases, such storms can disrupt radio, cell phones, and GPS, or even cause blackouts on Earth.
Towards the end of its life, the Sun will become a red giant. Its outer layers will swell towards Earth.
4. Death of a Star: Our Sun
- In 5 billion years, our Sun will run out of fuel. Nuclear fusion in the core will cease, generating less energy, the pressure pushing outward will dwindle, and gravity will win. The outer layers will swell into a red giant, and ultimately blow out into the universe ejecting matter that may someday form other stars and planets. The core will collapse into a white dwarf.
- It will take tens of billions of years for the white dwarf, the remnant of our Sun, to cool and fade away. This is the way that nearly all stars end their lives.
Scientists find huge stellar nurseries like the Orion Nebula throughout the Milky Way Galaxy and the universe today.
5. Our Solar Neighborhood
- The stellar life cycle continues today. Stars still form, live, and die. The young Orion Nebula contains one of many clusters of newborn stars in the Milky Way. Some of them are just forming planets. The Pleiades, a mature star cluster, is ejecting stars. The Helix Nebula was expelled by a star at the end of its life.
- A brown dwarf shares properties of both stars and planets, having a mass that's in between. For every star like our Sun, there are hundreds of brown dwarfs. Scientists do not fully understand these objects or how they relate to planets and stars.
Scientists also observe the remains of stars, like the Helix Nebula, within which the star's core has already contracted into an extremely dense white dwarf.
- On Earth, the stars that we see in the night sky—and the one that we see during the day—each tell a story.