Dang, if the moon isn’t always up to something! Tonight, it’s a crescent and in conjunction with Jupiter and Spica low in the southwestern sky during evening twilight. Feel free to give a nod to our only natural satellite for the fine work it did on eclipse day.
Earlier sunsets and a shorter twilight mean we get to see the stars considerably earlier in late August. From the central U.S., nightfall happens around 9:30 p.m., a much easier time to get out under the night sky than in June and July. At nightfall, you’ll see two bright points of light in the bottom half of the southern sky. The brighter one on the left (further east) is the planet Saturn; the other one is the star Antares in the constellation Scorpius.
To the naked eye, Antares shines with a distinctly red-orange tint. That makes it somewhat unique as there are only a few obvious red stars in the night sky. The color tells us something of its character: Antares is a huge and relatively cool, red supergiant star in the late stages of its life.
Like the better-known Betelgeuse in Orion, it too is on its way to becoming a supernova one day. With a diameter of 558 million miles (898 million km), if put in place of the sun, Antares’ surface would reach to the middle of the asteroid belt.
A team of astronomers, led by Keiichi Ohnaka in Chile, recently used the European Southern Observatory’s Very Large Telescope Interferometer (VLTI) at the Paranal Observatory in Chile to give us the best image ever of the surface and atmosphere of any star other than the sun. The VLTI can combine the light from up to four telescopes to create a virtual telescope equal to a single mirror up to 656 feet (200 meters) across! This allows it to resolve fine details far beyond the capability of a single telescope alone.
Ohnaka was interested in how stars like Antares shed weight so quickly in the final phase of their evolution. Stars spew gas all the time, but supergiants lose massive amounts. Gravity at their surfaces is very low, so any turbulence in the star’s atmosphere blasts gas into space. Antares loses matter at a rate millions of times greater than the sun’s loss through its solar wind. The VLTI measured the gas motions in the atmosphere of Antares in hopes of identifying what’s driving the turbulence.
The team was able to calculate the difference between the speed of the atmospheric gas at different positions on the star and the average speed over the entire star to make a detailed map of the speeds across Antares’ entire surface — the first ever for a star other than the sun. Astronomers also discovered turbulence much farther from the star than predicted, too far for convection to occur. Convection is how a star transfers energy from its core to its outer atmosphere in the form of large “bubbles” of hot gas much like the way water bubbles rise from the bottom of a pot when boiling water on a stove. Some process, currently unknown, may be needed to explain the more distant turbulence.
Stars seem so quiet when we look at them at night, but they’re busy burning elements in their core (and sometimes in shells around the core), bubbling with heat and flinging bits and pieces of themselves into space. Know that when you make a wish upon a star, it may take some time for that preoccupied, fiery globe to get to it.