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70 Falmouth Street Portland, Maine 04103
43.6667° N 70.2667° W
Founded January 1970
Julian date: 2457659.16
"Heavens above!"
THE DAILY ASTRONOMER
Tuesday, September 27, 2016
Pandora's Return!
We intended to mention this before and, honestly, we probably shouldn't mention it now, but we have set a goal for ourselves. By or before August 4, 2017, we want to answer at least 100 -preferably 2,000- Pandora parchments. For those who've just jumped aboard this renegade comet nucleus of a ride, Pandora parchments are those scraps of ancient paper on which we inscribe all the astronomical questions we receive. These questions come from planetarium patrons, DA subscribers, "Radio Astronomy" listeners, Facebook friends, 8th century wizards who are too embarrassed to ask people in their own time period, and so forth, We store them in a nifty little vessel we have dubbed "Pandora's Jar," after the troublesome lady who released all of the world's troubles, leaving only hope behind. We tucked this vessel away in the planetarium's dome shadows, where we also keep the Irish King's amulet (long story), the wind chimes that play only UV light (longer story) and various other little trinkets we've accumulated over our 46-year history. Just before September 1st -when the new school year commenced- we resolved to answer at least 100 questions before the school year ends on August 4th. Quite understandably, we knew that we'd have to dig into Pandora's depths by at least September 5th to make a good start. Well, look at the date...ha ha!
So, without any further adieu, we return to Pandora's Jar. As we do so, we'll number the questions to keep track of them! Wish us lazy sods luck, because we're starting late.
PANDORA 1: CURVED LIGHT
"Is distant light still believed to "curve" around a mass ? Or is that debunked theory?" -Shawn Dow, Hollis, Maine
Greetings, Shawn,
That theory is not debunked at all. In fact, astronomers now know that massive objects will distort their local space-time geometry. An object that is sufficiently massive will cause light to bend around it. Now, that we've answered the question, we should delve more deeply into the science.
Albert Einstein's General Theory of Relativity (1915) pertained to gravitation. Even though the math is straight out of a 29th century sorcery book, the basic idea is that massive objects bend space-time. Space-time is the continuum combining the three spatial dimensions and one time dimension. Think of a taut rubber sheet. Place a bowling ball on that sheet and you will produce a small indentation around the ball. Then, imagine rolling ball bearings across the sheet. Those bearings closest to the ball will be drawn toward it by the indentation. The indentation won't affect the more distant bearings A massive object such as the Sun induces a "indentation" in space-time and the planets that revolve around it are trapped in this indentation. One can also regard it as a gravity well. According to Einstein, this indentation would affect light paths as well as massive objects. Gravity could actually "bend" light.
The Sun's "Gravity Well." The Sun distorts its local space-time geometry and in so doing "traps" the planets within this well. Here, we see Earth at different positions along its Sun-centered orbit. (Not to scale). The space-time "dents" produced by massive objects affect photons as well as massive objects. Image by Carlos Clarivan
Einstein's assertion that gravity resulted from space-time, itself was dismissed as preposterous by most, as it directly contradicted Newtonian's ideas of absolute space and time. However, in May 1919, British astronomer Sir Arthur Eddington (1882-1944), led an expedition to photograph the sky during a total solar eclipse. When an eclipse is at totality, the stars behind the Sun become visible. Eddington's team photographed the sky during this eclipse and determined that the stars' positions had been affected slightly by the Sun, just as Einsteins predicted. This first piece of evidence in support of General Relativity elevated Einstein to the status of global celebrity overnight and forever changed our view of space-time.
Throughout space astronomers see examples of massive objects bending light. Over vast distances, we can see examples of gravitational lensing: how light paths are shifted around highly massive objects such as galaxies. A single light source can appear as multiple light sources due to this lensing effect. See image below.
A simplified example of "gravitational lensing." Here, we see a light source which bends around a massive object located between it and Earth. As the light moves around this object, it appears to be two light sources. IMAGE: NASA/ESA
Whew....only 99 more Pandora parchments to go....
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FROM THE CATACOMBS OF INFINITE KNOWLEDGE
The Cross Overhead!
It is admittedly difficult to discern one's directions in the night sky. However, it is easy to simply look directly overhead. Tonight, mid latitude observers will be able to peer up at the zenith and behold the Great Northern Cross. This star pattern comprises most of Cygnus the Swan, a constellation within the Summer Triangle.
The Northern Cross. Otherwise known as "Cygnus the Swan," the Northern Cross looms high overhead early this evening. Even though its brightest star, Deneb, is par of the Summer Triangle, the Northern Cross is a prominent celestial sight in early autumn. Image by Bob King.
The Northern Cross consists of a long axis of stars with a shorter axis nearly perpendicular to it. The Northern Cross is larger than the more famous Southern Cross (which is only visible at latitude south of 30 degrees N.) . The Northern Cross will remain in our eastern sky until early winter, when it will set high in the northwestern sky at dusk. Although Deneb is Cygnus's brightest star, the "head" star Albireo is an exquisitely beautiful binary (double) star. One component star is golden, the other one is sapphire. One can resolve this star into its member stars even with small telescopes. This practise, called "splitting Albireo" is a favorite activity of many recreational astronomers.
Venture outside and seek the Northern Cross yourself. It is easy to find right now. Just go out and literally look up!
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