Stellar Orbits
Stellar Orbits
| Group Name | starorbits |
| Reference | Sébastien Lépine (AMNH) |
| Prepared by | Sébastien Lépine (AMNH), Brian Abbott (AMNH/Hayden Planetarium) |
| Labels | Yes |
| Files | starorbits.speck |
| Dependencies | none |
| Census | 7 star orbits |
Everything in the Universe moves. We experience the rotation of Earth when day turns to night, and we experience Earth's orbit around the Sun as the seasons change. Unbeknownst until the 20th century, the Sun and its family of planets, asteroids, and comets move through the Milky Way galaxy at about 500,000 miles per hour. We orbit the Milky Way in a relatively stable orbit; one circuit around—our “galactic year”—takes about 225 million years. The last time the Sun was in the same spot in the Galaxy, dinosaurs ruled Earth.
In this data group, we illustrate orbital trajectories for seven stars with varying speeds and directions. There are a few hundred billion stars in our Galaxy, and here we see how seven of them will move over the next one billion years.
The Sun, our host star, is the most stable of the seven. It travels in a fairly consistent orbit in the disk of the Galaxy. Currently, it is heading in the direction of the constellation Cygnus and lies about 50 light-years above the plane of the Galaxy. The Sun's position oscillates above and below the plane every 38 billion years, reaching a maximum of about 260 light-years above or below the plane. Imagine how our night sky changes due to this periodic motion. When we are centered on the plane of the Galaxy, the band of light across the sky will be at its thinnest. Conversely, when we are 260 light-years above or below the plane, the band of light will appear a little thicker, occupying a little more sky. Beyond the appearance of our night sky, some scientists believe that our position above or below the Galactic plane may even cause mass extinction events on Earth.
Barnard's Star, the fourth-closest star to the Sun, has the highest proper motion of any star in the night sky [see nearby stars for more on proper motion]. While its path generally remains in the Galactic disk, its radius from the Galactic center varies greatly. Currently, the Sun and Barnard's star are moving toward one another as we travel along our Galactic orbit. In about 10,000 years, Barnard's star will be only 3.8 light-years away, making it the closest star to the Sun.
Not all stars are so well behaved. Some move wildly above and below the Galactic disk. Imagine how your night sky will appear under these circumstances. If we were living on a planet whose host star was high above or below the disk, we would have a magnificent, face-on view of the Galaxy. The star PM J13420-3415 is an example of such a star. At its maximum distance above the Galactic disk, the night sky on a planet similar to Earth would appear fully illuminated by the Galaxy for part of the year, and appear dark the remaining time as we look away from the Galaxy.
PM J13420-3415 is only one of billions of stars that orbit the Galaxy in this fashion. The Milky Way contains a population of old, mainly dim, stars that are distributed spherically about its center. Astronomers call these halo stars. We cannot see many of these stars, let alone derive accurate distances to them. The most visible objects in the halo are the globular clusters, which are dense concentrations of halo stars.
Hidden Orbits
For clarity, we show only 4 trajectories by default. To display the other three stars, open the mw.cf file and follow the instructions in the starorbits group. Alternatively, you can change the color of the trajectories and labels in Partiview. For example, to see the seventh star LSR J0822+1700, type cment 7 1 1 1 and textcment 7 1 1 1. The “7” represents the seventh star's orbit, and the “1 1 1” is the red-green-blue color, which in this case is white. Frankly, it is easier to open the config file in a text editor and decide what you want to see, just scroll to the starorbits group in the mw.cf file.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott