Why Does Comet Fluctuate in Size but Sun Doesn't?

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In summary, the conversation discusses the fluctuation in size of a comet compared to the stable size of the sun, and the possible explanation being the effect of color and our brain's perception. The poster also mentions conducting experiments to further understand the phenomenon. They also bring up color blindness as a possible factor in perceiving the fluctuation.
  • #1
Johninch
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The following picture has been posted in the Astronomy section (by Dave C426913).

https://www.physicsforums.com/file:///C:/Users/John/AppData/Local/Temp/msohtml1/01/clip_image001.jpg [Broken]
Source: http://www.space.com/4643-incredible-comet-bigger-sun.html

Why does the comet fluctuate in size but the sun does not? Why does it appear to get smaller but not bigger?

P.S. I was not able to post the image, but you can see it via the link. If you copy the picture to another document you will see the same effect i.e. the image fluctuation is not embedded.
 
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  • #2
I don't know. Perhaps the color or our eyes being accustomed to the sun and nothing much bigger? I don't know.
 
  • #3
Johninch said:
Why does the comet fluctuate in size but the sun does not? Why does it appear to get smaller but not bigger?

I'm not sure what you're talking about. What fluctuations?
 
  • #5
Drakkith said:
I'm not sure what you're talking about. What fluctuations?
The orange disk remains stable, while the blue disk repeatedly (at about 1 to 2 second intervals) "tries" to recede. The article referenced by Vanadium 50 explains it. I haven't finished studying the article yet, but it says that some people do not see the receding effect. So as I understand it, I am experiencing a receding effect because of the blue color, which my brain translates into a repeated reduction of disk size.

I am going to do some experiments with Excel using different colors and shapes.
 
  • #6
Interesting. Both images appear stable to me.
 
  • #7
I used to see that effect at times, and I thought it was due to tired eyes playing a trick.
Tthe effect I notice with the sun/comet image.
But not on any image from the Wiki article.
 
  • #8
Hmm. I wonder if the folks who have issues seeing the effects know their Ishihara color test scores for color blindness. Color blindness comes in two flavors, and varying levels of color perceptual ability. So it is possible to have a less than perfect Ishihara number and still be able to see colors - most of the time.

The reason I posted this is obvious - color plays a part in some of the wiki examples.

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0024265/

Eight percent of white males are color blind, females less than ~1 percent. Color perception alleles live on the X chromosome, females have 2, males one. Color blindness is most common among European males.
 

1. Why does a comet change in size but the sun doesn't?

Comets are made up of ice, dust, and small rocky particles, while the sun is composed mostly of gas and plasma. This fundamental difference in composition is the main reason for the difference in size fluctuation between a comet and the sun.

2. How does the composition of a comet contribute to its size fluctuation?

As a comet approaches the sun, the heat causes the ice and frozen gases on its surface to melt and turn into gas, creating a tail and expanding the comet's size. As it moves away from the sun, the gas dissipates, and the comet shrinks in size. This process does not occur with the sun, as it is constantly undergoing fusion and maintaining its size.

3. Are there other factors besides composition that contribute to a comet's size fluctuation?

Yes, the trajectory and distance of a comet from the sun also play a role in its size fluctuation. If a comet has a highly elliptical orbit, it will experience more extreme temperature changes as it moves closer and farther away from the sun, resulting in larger fluctuations in size.

4. Why is the sun considered a stable object while a comet is not?

The sun is considered a stable object because it maintains a relatively constant size and shape due to the continuous process of fusion occurring in its core. On the other hand, comets are considered unstable because they can change in size and shape as they orbit the sun and interact with its heat and radiation.

5. Can a comet's size fluctuation affect its orbit or trajectory?

Yes, a comet's size fluctuation can affect its orbit and trajectory. As a comet's size increases, it experiences more gravitational pull from the sun, which can alter its trajectory. Additionally, a comet's expanding tail can also create a drag force that can affect its orbit. These factors can make it difficult to predict the path of a comet, especially during its active phase near the sun.

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