Starship Asterisk*

[img3="Credit: Jaime Guarda/ESO"]https://cdn.eso.org/images/thumb700x/potw1622a.jpg[/img3][hr][/hr]

High upon the Chajnantor Plateau, a solitary vicuña — a relative of llamas, alpacas and camels — stands before the APEX antenna.

Both the animal and the antenna are well-equipped to handle the harshness of their remote and arid environment. At Chajnantor, some 5000 metres above sea level, temperatures can get fairly warm during the day, thanks to the intense sunlight beaming through the thin atmosphere. However, at night, the mercury plunges.

Engineers built the antenna of APEX to withstand the harsh weather, carefully crafting them to endure relentless sunlight, strong winds, and severe temperature changes ranging from +20 to -20 degrees Celsius.

The hardy vicuña, meanwhile, with its thick, wooly coat that traps hot air close to its body, can also handle nature’s quirks. The species, only found at high altitudes in the Andes Mountains, grazes on the tough grasses found across the otherwise barren slopes. Although the Chajnantor region is one of the driest places on the planet, at times the temperature swings can even bring snow to the plateau, an occurrence that the vicuña in this image is investigating!

[c][attachment=0]potw1622a[1].jpg[/attachment]Credit: ESA/Hubble & NASA;
Acknowledgement: Judy Schmidt[/c][hr][/hr]

This 10.5-billion-year-old globular cluster, NGC 6496, is home to heavy-metal stars of a celestial kind! The stars comprising this spectacular spherical cluster are enriched with much higher proportions of metals — elements heavier than hydrogen and helium, are in astronomy curiously known as metals — than stars found in similar clusters.

A handful of these high-metallicity stars are also variable stars, meaning that their brightness fluctuates over time. NGC 6496 hosts a selection of long-period variables — giant pulsating stars whose brightness can take up to, and even over, a thousand days to change — and short-period eclipsing binaries, which dim when eclipsed by a stellar companion.

The nature of the variability of these stars can reveal important information about their mass, radius, luminosity, temperature, composition, and evolution, providing astronomers with measurements that would be difficult or even impossible to obtain through other methods.

NGC 6496 was discovered in 1826 by Scottish astronomer James Dunlop. The cluster resides at about 35 000 light-years away in the southern constellation of Scorpius (The Scorpion).