By Vinita Domier
Ever wonder how astronomers determine physical properties of distant stars such as their chemical composition, surface temperature, luminosity, etc.? How they infer the speeds of stars and galaxies relative to the Earth? Or how they calculate the vast distances of stars and galaxies from the Earth?
If so, then please come to the Davis Astronomy Club’s next free meeting on Saturday at Explorit Science Center, 3141 Fifth St. in Davis, starting at 7 p.m., for a presentation on some of the observational techniques that astronomers use to answer these and other fundamental questions about the universe. All ages are welcome to attend the featured presentation indoors, followed by the star party outdoors.
Starlight emanating from a star’s extremely hot and dense photosphere produces a continuous spectrum of visible light when dispersed through a spectroscope. When this light passes through the relatively cooler and less dense gasses enveloping the star’s surface, dark lines appear in the continuous spectrum. There are more than 600 distinct dark lines in the sun’s visible spectrum.
The chemical composition of the star’s cooler gasses can be determined by comparing the dark line patterns in its spectrum to the signature patterns produced in the laboratory by the 92 naturally occurring elements in their neutral and ionized states. The chemical make-up of the star’s interior can then be surmised to be similar to its surface, with the thickness of the lines indicating relative proportions of the elements.
Dark spectral lines also indicate stellar surface temperatures as elements ionize at different temperatures. The absence of dark lines of elements in stars can mask the fact that the elements do exist, but are in a completely ionized. If the temperature of a star exceeds an element’s ionization temperature, that element can still exist in the star even though it does not produce dark lines. Visual colors of the stars also indicate their temperatures, with blue stars being hottest and red stars being coolest.
Join us Saturday to find out more about spectral analysis and the wonders of the galaxy.
Saturday, Oct. 19: You’re invited to our October fundraiser “Touched by Science, Touched by Explorit Celebrating 30 Years of Putting Hands On Science,” from 5:30 to 8 p.m. Enjoy food, wine, special guests and get your own commemorative long-STEM wine glass! Explorit members and UC Davis Alumni Association members can purchase discounted tickets to this fundraiser. For more information and to buy tickets, visit http://www.brownpapertickets.com/event/437033.