TESS Shows Ancient North Star Has Eclipses
- Visualizations by:
- Chris Smith
- Written by:
- Francis Reddy
- Produced by:
- Chris Smith
- View full credits
This animation illustrates a preliminary model of the Thuban system, now known to be an eclipsing binary thanks to data from NASA’s Transiting Exoplanet Survey Satellite (TESS). The stars orbit every 51.4 days at an average distance slightly greater than Mercury’s distance from the Sun. We view the system about three degrees above the stars’ orbital plane, so they undergo mutual eclipses, but neither is ever completely covered up by its partner. The primary star is 4.3 times bigger than the Sun and has a surface temperature around 17,500 degrees Fahrenheit (9,700 C), making it 70% hotter than our Sun. Its companion, which is five times fainter, is most likely half the primary’s size and 40% hotter than the Sun. Thuban, also called Alpha Draconis, is located about 270 light-years away in the northern constellation Draco.
Credit: NASA's Goddard Space Flight Center/Chris Smith (USRA)
Watch this video on the NASA.gov Video YouTube channel.
The eclipses are brief, lasting only six hours, so ground-based observations can easily miss them.
The system ranks among the brightest-known eclipsing binaries where the two stars are widely separated, or detached, and only interact gravitationally. Such systems are important because astronomers can measure the masses and sizes of both stars with unrivaled accuracy.
Alpha Draconis, also known as Thuban, lies about 270 light-years away in the northern constellation Draco. Despite its “alpha” designation, it shines as Draco’s fourth-brightest star. Thuban’s fame arises from a historical role it played some 4,700 years ago, back when the earliest pyramids were being built in Egypt.
At that time, it appeared as the North Star, the one closest to the northern pole of Earth’s spin axis, the point around which all of the other stars appear to turn in their nightly motion. Today, this role is played by Polaris, a brighter star in the constellation Ursa Minor. The change happened because Earth’s spin axis performs a cyclic 26,000-year wobble, called precession, that slowly alters the sky position of the rotational pole.
Discovering eclipses in a well-known, bright, historically important star highlights how TESS impacts the broader astronomical community. In this case, the high precision, uninterrupted TESS data can be used to help constrain fundamental stellar parameters at a level we’ve never before achieved.
Credits
Please give credit for this item to:
NASA's Goddard Space Flight Center
Animator
- Chris Smith (KBRwyle) [Lead]
Science writer
- Francis Reddy (University of Maryland College Park) [Lead]
Producer
- Chris Smith (KBRwyle) [Lead]