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CEO
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Comets do not give off their own light but reflect light [#permalink]
 23 Sep 2003, 09:30
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16. Comets do not give off their own light but reflect light from other sources, such as the Sun. Scientists estimate the mass of comets by their brightness by their brightness: the greater a comet┬б┬пs mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halley's comet is composed reflects 60 times less light per unit of mass than had been previously thought.
The statements above, if true, give the most support to which one of the following?
(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halley's comet is composed.
(B) Previous estimates of the mass of Halleys comet which were base on its brightness were too low.
(C) The total amount of light reflected from Halleys comet is less than scientists had previously thought.
(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.
(E) Scientists need more information before they can make a good estimate of the mass of Halley's comet.
Explain your Choice
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i say the answer is C
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B
Per the recent satellite probe, the actual mass of Haley's comet should have been 60 times more than what was previously estimated.
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Brainless
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B) Previous estimates of the mass of Halleys comet which were base on its brightness were too low.
B says the estimates of the mass of Halleys comet were too low....but the estimates of Halleys comet WERE actually higher b/c the light that is ACTUALLY relflected is LOWER than they thought...thereby inflating the original MASS calculations.....
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CEO
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Brainless wrote: B
Per the recent satellite probe, the actual mass of Haley's comet should have been 60 times more than what was previously estimated. A very interesting one, isnt it? Brain is Correct Quote: the greater a comet's mass, the more light that comet will reflect
LOW Brightness => estimate ==> LOW MASS
But this method of estimation does not work for halley's comet...why?
because its material reflects 60 times less light.
Since the light reflected is MUCH MUCH lesser and the scientists estimated the mass based on THIS LOW value of reflected light.....this shows that the actual MASS is much larger.
Hope that helps
Thanks for a good discussion
Praetorian
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hmmm.....very confusing....
i completely missed where it said:
>>60 times less light per unit of mass than
--> the "unit of mass" part is very important
good eye Brainless
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praetorian123 wrote: Brainless wrote: B
Per the recent satellite probe, the actual mass of Haley's comet should have been 60 times more than what was previously estimated. A very interesting one, isnt it? Brain is Correct Quote: the greater a comet's mass, the more light that comet will reflect LOW Brightness => estimate ==> LOW MASS But this method of estimation does not work for halley's comet...why? because its material reflects 60 times less light. Since the light reflected is MUCH MUCH lesser and the scientists estimated the mass based on THIS LOW value of reflected light.....this shows that the actual MASS is much larger. Hope that helps Thanks for a good discussion Praetorian Indeed a good question ..
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Hey guys
i dont know what i am missing...
Why is C wrong.
and i still don't get why is B right..!!
Scientists predicted mass previously on brightness say X per unit mass.
Now they found out that actually it is X/60 per unit mass. This implies that comet is actually reflecting less light than what they thought previously, so its mass is less than what estimated before. Now howcome, previous estimates are low..!!
praet/brain/ Kindly clarify...
-vicks
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Vicky wrote: Hey guys
i dont know what i am missing...
Why is C wrong.
and i still don't get why is B right..!!
Scientists predicted mass previously on brightness say X per unit mass.
Now they found out that actually it is X/60 per unit mass. This implies that comet is actually reflecting less light than what they thought previously, so its mass is less than what estimated before. Now howcome, previous estimates are low..!!
praet/brain/ Kindly clarify...
-vicks
Vicks,
Look at the stimulus carefully,
The more brighter a comet is the more heavier its mass is
The more light a comet reflects the more brighter it is
So , now it has been revealed that Haleys comet actually reflects 60 times less of the light, so its brightness calculated was 60 times less, hence its mass..
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That's exactly my doubt. If it is "now" revealed that light reflected is actually 60 times less than what had been previously thought. That means previous estimate was on light that was 60 times brighter.. hence more mass according to previous estimates.
Why is C wrong.
please clarify.. i need to understand it.. may be missing something.
-vicky
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Vicky wrote: That's exactly my doubt. If it is "now" revealed that light reflected is actually 60 times less than what had been previously thought. That means previous estimate was on light that was 60 times brighter.. hence more mass according to previous estimates.
Why is C wrong.
please clarify.. i need to understand it.. may be missing something.
-vicky
Follow your own reasoning
If it is "now" revealed that light reflected is actually 60 times less than what had been previously thought. Correct
That means previous estimate of mass was on the light that was 60 times brighter.. hence more mass according to previous estimates. Wrong...
Previous calculation of mass was on the basis of 60 times less light which has been revealed by recent satellite probe.[/i]
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brain has done a great job at explaining this..but please let me know if you still need clarification on this one.
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why the hell i am not getting it... 
still not clear. praet, can u please give example of whats going on before and after the satellite probe (with numbers) so that i get an idea of whats going on.
And again, why is C wrong.
thanks
-vicks
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CEO
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Vicky wrote: why the hell i am not getting it... still not clear. praet, can u please give example of whats going on before and after the satellite probe (with numbers) so that i get an idea of whats going on. And again, why is C wrong. thanks -vicks lets forget individual choices for a while
First off, paraphrase...
Step 1... Vicks calculates the brightness of the comet
step 2.... based on the relationship between the brightness and the mass, vicks calculates the MASS.
Step3.... vicks sends a satellite probe...it finds that the material of the comet reflects lesser light PER UNIT MASS..
step 4... it is clear to vicks that he calculated the brightness correctly...why?
Because THE TOTAL AMOUNT of light is the same , its just the amount PER UNIT MASS is FAR FAR lesser....so what does vicks find out...
If the light reflected PER UNIT MASS is so less, the MASS has to be far far greater for reflecting the SAME TOTAL AMOUNT OF LIGHT.
Before satellite probe
BRIGHTNESS/unit mass * Mass = TOTAL AMOUNT
TOTAL AMOUNT = CONSTANT ...no questions there.
After satellite probe
Brightness /UNIT MASS is far lesser...so what happens to the MASS.. it should go way UP to maintain that CONSTANT TOTAL AMOUNT of light
The TOTAL AMOUNT of light does NOT change...so C cant be right.
good enough?
praetorian[/b]
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tons of thanks, praet. 
nice explanation.
oh man... i was solving it with wrong assumptions.
very good question. vicky9
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If brightness alone cannot accurately measure the mass of Halley`s Comet, then a new standard of comparison must be established.
(B)
1:46
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