Bakersfield College

June 2, 2012

Bakersfield Night Sky – June 2, 2012
By Nick Strobel

My trip north for the May 20th annular solar eclipse was a great success. I met up with members of the Kern Astronomical Society in Red Bluff to view the exactly New Moon pass directly in front of the Sun. We had one section of a park reserved with a clear view of the western sky and several passersby also joined us to view the eclipse through one of the spare eclipse glasses or the large solar viewer (a SolarScope) my wife manned. The SolarScope projects an image of the Sun from a small telescope onto the white sunshade through which the telescope sticks after it bounces off a very small mirror near the focal point of the telescope. While a telescope or camera offers a view to individuals one at a time, the solar viewer enables several people to see the 3.5-inch diameter at once. The image is sharp enough to see the sunspots. I'm glad my wife volunteered to run the solar viewer while I snapped over a hundred photos with my telephoto lens during the eclipse. I posted a sequence of five of the images showing the stages of the eclipse on the William M Thomas Planetarium's homepage I hope to create a time lapse movie with all of the images this summer.

I have experienced several lunar eclipses (when the Moon goes into the Earth's shadow at exactly full phase directly opposite from the Sun) but this was my first annular solar eclipse. A few years ago, my wife and I traveled to China to try to view a total solar eclipse but the weather did not cooperate. We did experience the rapid nightfall of totality but the clouds prevented us from seeing the totally covered-up Sun with the halo of the corona around the dark Moon, looking like a hole had been punched in the sky. We'll have to wait until August 21, 2017 for the next solar eclipse to happen in the United States. That one will be a total solar eclipse going right through the heart of the United States from northern Oregon to South Carolina and passing through southern Idaho, the center of Wyoming, Nebraska, and Missouri, western Kentucky (where the greatest time length will be), and eastern Tennessee. I don't suppose there's any chance of Bakersfield College and the local K12 schools starting a week later than usual as August 21st will fall on the usual first day of the fall semester. The next solar eclipse after that to happen in the United States will be in October 2023, right in the middle of the semester and that will be an annular solar eclipse.

Now, I'm a pretty calm, rational person but when I looked at the Sun directly with my eclipse glasses and saw a huge chunk of the central part of the Sun disappear for those four minutes, the rational prefrontal cortex part of my brain had to work overtime to keep the emotional striatum and amygdala parts of the brain from taking over as I reminded myself several times that the life-giving Sun had not disappeared and that I'm an astronomer who knows all about the perfectly natural and normal phenomenon going on. Experiencing an annular or total solar eclipse in person (not viewing it vicariously on some computer screen or someone else's pictures) makes you understand at a gut level how people long ago could feel fear during a solar eclipse. With our modern understanding of what's going on during an eclipse, we can experience a solar eclipse as a really cool, awe-inspiring event (a truly unique astronomy thrill ride).

A solar eclipse happens somewhere in the world usually three times within a year's span but a very rare event is taking place in three days time—the Venus transit of the Sun. On Tuesday, June 5th Venus will cross the face of the Sun from 3:06 PM to 9:45 PM as seen from Bakersfield—see the graphic below. The graphi shows the path that Venus will take across the Sun as seen during our afternoon. The next time Venus will transit the Sun as seen by anyone on the Earth will be in 105 years, in the year 2117. On June 5th, all of North America, all of Central America and northwestern South America will be able to view the transit in our hemisphere. Most of Europe, eastern half of Africa, all of Asia and Australia will be able to see it during their morning of June 6th (remember that they are many timezones ahead of us). Only special solar filters are safe enough for directly looking at the Sun—dark sunglasses, even several put together, are NOT safe for your eyes! Here in Bakersfield, the Kern Astronomical Society will have solar telescopes set up at Russo's Books in the Marketplace Mall from a little before 3 PM to sunset. Stop by for a look! It won't happen again for another 105 years.

Besides being an extraordinarily rare phenomenon, Venus transits hold a special place in the history of finding the scale of the universe. Using trigonometry, astronomers centuries ago were able to figure out the proportional spacing of the planets in the solar system all relative to the Earth's distance from the Sun. They knew, for example, that Mars is 1.5 times farther from the Sun than is the Earth, Jupiter is 5.2 times farther from the Sun than is the Earth, etc. What they didn't know was the actual distance between the Earth and the Sun. The Earth-Sun distance is also needed in finding the distances to the stars. In the 1830s, astronomers were able to determine distances to the stars using the parallax effect and trigonometry. The basic idea behind parallax and using it to calculate distances (which is the name of the main game in astronomy) can be illustrated using your thumb. Hold your thumb up in front of your face about 6 inches from your nose and look at it with one eye and then the other. The thumb will appear to move with respect to whatever's in the background---that's the parallax effect. Do the same thing with your thumb held at arm's length and you'll notice that the parallax is smaller. If you did not know the distance to your thumb but you knew the distance between your two eyes, you could get the distance to your thumb by measuring how much of an angle by which your thumb shifted (get a protractor) and some trigonometry.

For the stars, we look at the nearby stars from opposite sides of the Earth's orbit and measure the size of the parallactic shift. Once you know a couple of angles and the length of one side of a triangle, you can get the rest of the triangle sides. The side of the triangle for the stars we need to know is the distance between the Earth and the Sun. Once we have the distances to the nearby stars, we use them to calibrate methods of finding distances for more distant objects such as the rest of the stars, nebulae, galaxies, quasars, etc. In order to determine the masses, 3D motion, sizes (diameter and volume), reflectivity, power output, and other properties of the planets, stars, the Milky Way, and other galaxies and compare them with the Earth we need to determine their distances. Their distances are also critical for determining the ages of the stars and the galaxies in which they reside plus finding out the age of the universe. When you trace all of this line of reasoning back to the start, you see that it comes back to knowing the distance between the Earth and the Sun. It is the fundamental baseline for our knowledge of the universe—the Astronomical Unit.

Edmund Halley (of Halley's Comet fame) figured out a way to use the parallax effect and trigonometry in determining the Astronomical Unit. His idea involves very careful time measurements of how long it takes to travel across the face of the Sun as seen from various parts of the Earth. Those different timings can be used to calculate the parallax angle of Venus and trigonometry gives us the distance to Venus and the distance from the Earth to the Sun follows from the proportional spacings of the planets worked out by Copernicus and Kepler. Nowadays we use radar to get the distance to Venus and trigonometry then gives us the distance to the Sun if we also measure the angular separation of Venus from the Sun on our sky when we do the radar measurement. (Trigonometry sure comes in handy!) Using radar to directly measure the distance to the Sun wouldn't work because the radio waves would get absorbed by the gas and the Sun's own radio emission would overwhelm any weak reflected radio wave anyway.

On June 5th you can participate in a 2012-version of Halley's method with your smartphone (iPhone or Android) by simply tapping the screen when you see Venus is all the way inside the one edge of the Sun and/or just touching the far edge of the Sun (when seen through your own solar filter or projected image). The phone app also has a simulation mode to enable you to practice using the app well before the time of the transit. Your observations will be combined with thousands of other observers from all over most of the world. Go to http://transitofvenus.org to download the phone app. Those of you without a smartphone or cannot make it to the KAS Venus Transit party at Russo's but have access to the web can participate in the transit events at NASA's Transit of Venus website at http://venustransit.nasa.gov/ and Astronomers Without Borders Transit of Venus website at http://tov2012.esri.com/ . The NASA site will have a webcast from Hawaii as will the The Exploratorium (http://www.exploratorium.edu/venus/). However, do not use the transit phone app with the webcasts unless you happen to be at the specific Hawaii sites from which the webcasts are taking place! The transit phone app is to be used to log Venus timings as seen from your location.

Finally, those of you who are night owls can view the partial lunar eclipse that starts at 3:00 AM tomorrow morning (June 4th) and ends at 5:07 AM. The Full Moon will pass through the edge of the Earth's umbra shadow and at deepest, 38% of the Moon will be in the Earth's umbra so it will look like a fat crescent Moon for several minutes. The deepest point of the eclipse will be at 4:03 AM. The June Full Moon will be 0.5% smaller than May's Full Moon.

In other space news, space industry took another step toward commercial, non-governmental space flight with the docking of the world's first commercial cargo craft, the SpaceX Dragon, with the International Space Station last Friday. Later missions of the Dragon capsule will ferry people to and from ISS. Near the end of this year, another company is scheduled to dock their capsule, the Orbital Cygnus, with the ISS.

Want to see more of the stars at night and save energy? Shield your lights so that the light only goes down toward the ground. See www.darksky.org for how.
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Nick Strobel
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com

Kern Community College District