The Stellar Distance Uncertainty
The Stellar Distance Uncertainty
| Group Name | err |
| Reference | The Hipparcos and Tycho Catalogues (ESA 1997) |
| Prepared by | Brian Abbott (AMNH/Hayden) |
| Labels | Yes |
| Files | stars-err.speck, stars-err.label |
| Dependencies | none |
| Census | 9 stars with uncertainty data |
The position of each object in the Digital Universe has an uncertainty associated with it. To illustrate this, we demonstrate distance uncertainty with several stars of various distances and luminosities.
From Earth, we can measure a star's two-dimensional position in the sky to great accuracy. However, the star's distance remains elusive. Our most accurate distances come from the measurement of an angle in the sky that is imperceptible to the naked eye. This angle is called the trigonometric parallax [see “Parallax and Distance” for more information], and the uncertainties and errors in the measurement of this angle translate into uncertainties in the star's distance.
| Star Name | Other Name | Distance | Range | Uncertainty |
| (light-years) | ||||
| Ain | ε Tauri | 155 | 149-161 | 12 |
| Bellatrix | γ Orionis | 243 | 226-262 | 36 |
| Spica | α Virginis | 262 | 245-282 | 37 |
| Betelgeuse | α Orionis | 368 | 352-544 | 192 |
| Pleione | 28 Tauri | 387 | 351-431 | 80 |
| Polaris | α Ursae Minoris | 431 | 405-460 | 55 |
| Antares | α Scorpii | 469 | 460-876 | 416 |
| Rigel | β Orionis | 773 | 648-956 | 308 |
| Deneb | α Cygni | 2,150 | 2,063-7,409 | 5,346 |
Representing Uncertainty
In the Atlas, uncertainties are represented by red lines. These lines consist of a series of points that, when viewed from a distance, appear as a line. Each point is spaced 1 light-year from the next. We leave a space in this line for the published parallax distance. More often than not, the star will be found in this gap, but there are some stars that have a weighted mean distance and are placed elsewhere along the line of sight. Betelgeuse and Antares are good examples. Both are placed closer than their trigonometric parallax distance because of the large error in the parallax measurement.
Labels, in light-years, denote the near distance uncertainty, the published distance (from the parallax angle), and the far distance uncertainty.
The star Ain in the Hyades star cluster in Taurus is the closest star in this sample. At 155 light-years away, it has a small uncertainty, only 12 light-years. Compare that with Pleione in the Pleiades, a star cluster that is nearby in the sky but lies about 250 light-years beyond the Hyades. Pleione has an 80-light-year uncertainty. As you view the Atlas of stars, nebulae, and galaxies, consider that there is uncertainty associated with each of these objects and often the uncertainty for non-stellar objects is far greater.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott