Bakersfield Night Sky - July 15, 2017
Bakersfield Night Sky - July 15, 2017
By Nick Strobel
“Twinkle, twinkle little star, how I wonder what you are.” Cute song and a lot of astronomy in it! During this past couple of weeks, I visited family in Oregon and took walks with my wife in some beautiful green places. On one of those walks she suggested I write about why stars twinkle and what would the constellations look like from one of the other planets in our solar system. In my astronomy class, we spend about half a lecture on the effect of the atmosphere on star light, one week on how we measure the properties of the stars, and another week on the structure of stars and how they shine. Let's take a closer look at “twinkle little star” but brief enough to fit within the space of a newspaper column.
Our atmosphere makes it possible for life to exist on the surface of Earth but it sure is a nuisance for doing astronomy. The air above is made of ever-shifting layers of gases of varying temperatures and densities that cause light rays to bend and scatter about. Like looking at someone standing at the edge of a swimming pool while you're under water, the stars shimmer and dance about as we look at them from the surface of Earth. Since at least ninety percent of our atmosphere is within about ten miles of the surface, the shimmering—twinkling— is noticeably lessened from the top of a tall mountain, just a couple of miles above sea level.
Under high magnification, the pretty twinkling star is revealed to be a fuzzy blob made of many tens to a few hundred distorted images of the pinpoint star that shift wildly about in fractions of a second. I show a real-time video of a high-magnification image of a double star to my astronomy classes and wish them good luck in seeing a double star in all that mess. I have a link to that video in the telescope chapter of my Astronomy Notes website if you want to try finding the double star in the fuzzy blob.
Astronomers have figured out how to remove the effects of the turbulent atmosphere. When I was an undergraduate, a computer-intensive image processing technique called speckle interferometry was used to recover the true image of the objects we were looking at. That was replaced by something called “adaptive optics” which uses thin mirrors that can be quickly deformed to counteract the distortion of the star light by the atmosphere.
Large telescopes on the ground are now able to achieve images of some objects that are sharper than those from the Hubble Space Telescope. Hubble can make super-sharp images for any object and it has a truly black sky background. It also can observe over a larger swath of wavelengths, from UV to near-infrared, than what telescopes can do from the ground.
We find out that the stars are giant nuclear fusion reactors by measuring their distances from us and spreading out the star light into a rainbow of colors to make a spectrum. For the nearby stars we can use a technique called trigonometric parallax to measure their distances, that is similar to what surveyors use to measure large distances on Earth. From the database of nearby star distances, we can calibrate how star brightness changes with distance, so that we can use star brightness to determine a very distant star's distance.
Putting a star's brightness together with its distance enables us to find out the star's true power output—the wattage of those big light bulbs. The rainbow spectrum enables us to measure the temperature of stars extremely accurately. Even the coolest and dimmest stars have a power output of six followed by twenty-two zeros watts and are over a couple thousand degrees Celsius on their surface.
We find out how much material they contain (their mass) by measuring how much the star changes the motions of objects near it. Usually the other object near the star is another star, so the measurements give us the total combined mass of the two stars. Then measuring how much each star moves relative to its companion star, enables us to proportion out how much of the total mass goes with each star. Even the smallest star has a mass eighty times greater than Jupiter.
Using the laws of gas physics we can figure out what the conditions are like in the centers of stars. The density of the gas is greater than the densest rocks and metals and the temperature is above eight million degrees Celsius. Super-hot and super dense gases are just the thing you need for nuclear fusion, where low-mass atomic nuclei like hydrogen are smashed together to make higher-mass nuclei plus some energy as described by Einstein's famous equation, E = mc2. Measuring the particles called neutrinos confirms that nuclear fusion is occurring in the star cores. If you want just a wee bit more detail about how we figure out what stars are like, then see my Astronomy Notes website. “Twinkle, twinkle little star, now I know what you are (and you're not that little).”
Now for the view of the constellations as seen from other places in our solar system. Our solar system is so very teeny, tiny in comparison with the distances between the stars, that Pluto's view of the constellations is the same (very, very nearly exactly so) as what we see from Earth. I illustrate this in one of the field trip Planetarium shows. Even the view from the nearest star to the sun, the Alpha Centauri system, is very similar to what we see from Earth.
At the end of the month, Saturday July 29, will be another free public star party hosted by the Kern Astronomical Society at Panorama Park near where Linden Ave runs into Panorama Drive. Stop by between sunset and 10-ish for a free look through their telescopes. Did I mention that it is free?
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Nick Strobel
Director of the William M Thomas Planetarium at Bakersfield College
