Astronomy C

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Re: Astronomy C

Post by Name » September 7th, 2018, 7:09 pm

The rest wavelength of Hα is 6562.8 angstroms. Given the observed wavlength is 923.4 nm and the distance is 1795682000 parsecs determine the value of hubble's constant and determine the age of the universe in years
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Re: Astronomy C

Post by Knyte_Xjn » September 7th, 2018, 8:53 pm

Name wrote:The rest wavelength of Hα is 6562.8 angstroms. Given the observed wavlength is 923.4 nm and the distance is 1795682000 parsecs determine the value of hubble's constant and determine the age of the universe in years
First, we find the red shift. Z = (observed/emitted) - 1 = ~0.407 Next, we find the radial velocity. v = Z * c = ~1.22*10^5 km/s Hubble's constant can then be found: H = v/d = ~68.0 (km/s)/Mpc Given that the universe has been expanding at a constant speed since its beginning, the universe's age is 1/H, or 1.47*10^-2, which is then multiplied by 3.09*10^19 km/Mpc to cancel the distance units and then divided by 3.16*10^7 sec/yr to get the answer in years, which is 1.439*10^10 years
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Re: Astronomy C

Post by Name » September 8th, 2018, 8:53 am

Yup. You ask the next question
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Re: Astronomy C

Post by Knyte_Xjn » September 9th, 2018, 10:34 pm

Name wrote:Yup. You ask the next question
Sorry for the late response!
Suppose an astronomer observes an elliptical galaxy with a major axis with a length 3 times that of its semi-minor axis.
(a) What is the Hubble classification of this elliptical galaxy?
(b) Describe the type of stars that would be present in an elliptical galaxy such as this one.
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Re: Astronomy C

Post by PM2017 » September 13th, 2018, 1:54 pm

Knyte_Xjn wrote:
Name wrote:Yup. You ask the next question
Sorry for the late response!
Suppose an astronomer observes an elliptical galaxy with a major axis of 2.6 AU and eccentricity of 0.76.
(a) What is the Hubble classification of this elliptical galaxy?
(b) Describe the type of stars that would be present in an elliptical galaxy such as this one.
Could you double check the size of this galaxy? 2.6 AU is less than the diameter of Mars' orbit.
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Re: Astronomy C

Post by Unome » September 13th, 2018, 1:56 pm

PM2017 wrote:
Knyte_Xjn wrote:
Name wrote:Yup. You ask the next question
Sorry for the late response!
Suppose an astronomer observes an elliptical galaxy with a major axis of 2.6 AU and eccentricity of 0.76.
(a) What is the Hubble classification of this elliptical galaxy?
(b) Describe the type of stars that would be present in an elliptical galaxy such as this one.
Could you double check the size of this galaxy? 2.6 AU is less than the diameter of Mars' orbit.
"This galaxy would contain one star, and have a Hubble type of irregular"
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Re: Astronomy C

Post by Knyte_Xjn » September 13th, 2018, 2:33 pm

Unome wrote:
PM2017 wrote:
Knyte_Xjn wrote:
Sorry for the late response!
Suppose an astronomer observes an elliptical galaxy with a major axis of 2.6 AU and eccentricity of 0.76.
(a) What is the Hubble classification of this elliptical galaxy?
(b) Describe the type of stars that would be present in an elliptical galaxy such as this one.
Could you double check the size of this galaxy? 2.6 AU is less than the diameter of Mars' orbit.
"This galaxy would contain one star, and have a Hubble type of irregular"
I know that 2.6 AU is minuscule in comparison to what the major axis of most galaxies actually is, but the values wouldn't have prevented you from answering the questions. However, in the interest of making this question more realistic, I have updated it.
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Re: Astronomy C

Post by PM2017 » September 14th, 2018, 5:30 pm

Knyte_Xjn wrote:
Name wrote:Yup. You ask the next question
Sorry for the late response!
Suppose an astronomer observes an elliptical galaxy with a major axis with a length 3 times that of its semi-minor axis.
(a) What is the Hubble classification of this elliptical galaxy?
(b) Describe the type of stars that would be present in an elliptical galaxy such as this one.
a. The Hubble class for ellipticals is En, where n = 10(1-b/a), where b is the semi-minor axis, and a is the semi-major axis. Therefore, n = 10(1-1/3) = 10(2/3) = 6.66... So, the Hubble classification is E7. (Actually, I have always just assumed you round. Do you actually?)

b. Lots of old red and yellow stars.
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Re: Astronomy C

Post by Knyte_Xjn » September 14th, 2018, 8:07 pm

PM2017 wrote:
Knyte_Xjn wrote:
Name wrote:Yup. You ask the next question
Sorry for the late response!
Suppose an astronomer observes an elliptical galaxy with a major axis with a length 3 times that of its semi-minor axis.
(a) What is the Hubble classification of this elliptical galaxy?
(b) Describe the type of stars that would be present in an elliptical galaxy such as this one.
a. The Hubble class for ellipticals is En, where n = 10(1-b/a), where b is the semi-minor axis, and a is the semi-major axis. Therefore, n = 10(1-1/3) = 10(2/3) = 6.66... So, the Hubble classification is E7. (Actually, I have always just assumed you round. Do you actually?)

b. Lots of old red and yellow stars.
If you read the question closely, it says that the major axis is 3x the length of the semi-minor axis, so the semi-major axis is 1.5x the length of the semi-minor axis. Your equation was correct, but it should've been En = 10(1-2/3) = 10(1/3) = 3.33..., so the Hubble class would be E3. Yes, you do round the Hubble classification because it is a category, not continuous. Your answer to the second part looks good, but you could've been more specific by saying that most stars are Population II.
Your turn.
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Re: Astronomy C

Post by PM2017 » September 19th, 2018, 11:21 pm

A student at West High is angry he lost the tryouts for astronomy to PM2017. For this reason, he decides to throw PM2017's laptop into a black hole and seeing as he is actually better than PM2017 (and was unfairly disfavoured!) somehow observes that the laptop is, for some reason a perfect blackbody, and is normally blue (assume 470.00 nm). As the laptop passes through the event horizon, the student observes that the laptop seems to have a wavelength of 933.89 nm.

The student recalls from his studying that the mass of a black hole and the radius of its event horizon are related linearly. He dejectedly realizes that he can now use the wavelength data to find this relationship, but is too depressed to do so. Can you find the relationship between the mass of the black hole, in solar masses, and radius of a black hole, in kilometers?

Assume that G = 6.67e-11, c = 2.99e8, and a solar mass is 2.00e30 kg.

V = sqrt((2*G*M)/R)
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