Wednesday, August 9, 2017

Eclipse Corner #14 Stars and Planets During the Daytime

     During totality of the solar eclipse, the darkened sky will reveal four planets to the unaided eye near the eclipsed Sun. In order of brightness, Venus will be on the right (west) of the Sun, and Jupiter on the left (east). Less bright are Mars, above (northwest) and Mercury closest to the left (east) shining as well. Some of the brighter stars will also be visible. The Sun is in the constellation Leo who’s brightest star is Regulus. Among other stars and constellations are, the constellation Orion with stars Betegeuse and Rigel and our sky’s brightest star Sirius all southwest of the Sun.


Chart courtesy Larry A Stevens editor of Totality  -   Inset showing the star Regulus with Sun.

     Brightness in astronomy is measured in magnitude which was first set up by Greek astronomer Hippachus in 150 BC. His brightest star was given the magnitude 1 and the next brightest class 2 until he had 6 classes. Today’s apparent magnitude scale has a better mathematic logarithmic background but still poses a semblance to Hipparchus’ thinking. The larger the number of the magnitude, the less brightness. In fact as objects get brighter like a full Moon their magnitude number will be lower, therefore often in the negative numbers.  For example, the Sun is at -26.7, Sirius is the brightest star in the night sky at -1.42, and Rigel from the constellation Orion is 0.12.  All of these measurements are the apparent magnitude or simply the brightness we see.
     When the distance from earth is calculated into the brightness formula, astronomers call it the absolute magnitude. To measure absolute magnitude of a star, the brightness of objects is measured at an equal distance of 32.6 light-years or 10 parsecs from earth. The Sun, with apparent magnitude -26.7 is so close but at 32.6 light-years away would have an absolute magnitude of 4.2. Rigel with a 0.12 apparent magnitude is at its distance away of 1,400 light-years, so Rigel would have a -8.1      absolute magnitude.  Thinking and understanding about apparent and absolute magnitudes with the dimensions of space is interesting.
     The brightness for the planets, being so close, is always measured in apparent magnitude and the brightness does change because their distance to the earth is always changing as the planets all orbit the Sun. The calculated apparent magnitudes for the planets seen during the August 21 eclipse totality are: Venus -4.0, Jupiter -1.8, Mars +1.8, Mercury +3.3 (Space.com)


From the Americaneclipseusa.com

     Do not spend too much of your few minutes of totality checking the planets and stars. The solar corona as well as the total horizon around you will be amazing as well. More information about the solar eclipse will be forthcoming.                                                                                                            –Dan Slais


Dan Slais is a retired 8th grade earth science teacher from Waynesville, MO.  He has taught Astronomy and Geology for Columbia College and has worked as a seasonal National Park Ranger for seven seasons. 

Join us August 18-21, 2017 for Midnight at Noon, a four day music festival and eclipse viewing event in Owensville and Rosebud, MO.  For more information click HERE

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