# j15

### Hubble constant & Critical density?

For a Hubble constant of 70km/s/Mpc, the critical density is 9 x 10^-23kg/m^3.

1-How much mass does this correspond to within a volume of 1 cubic astronomical unit?

2-How large would a cube be required to enclose 1 Earth mass of material?

I know the answers, but I can't seem to get them right no matter how I go about solving. Please explain how.

1-Answer: 30,000 tons

2-Answer: 2.8 PC

2 AnswersAstronomy & Space8 years ago### What is the flatness problem in the universe?

What is the flatness problem and why has it been a problem for cosmologists?

3 AnswersAstronomy & Space8 years ago### Fraction of our galaxy's mass made of dark matter?

I seriously have no idea how to start this problem and have been working on it for a while. Can anyone help me out, at least on how to start it. Thanks!

Although the flat rotation curve indicates that the total mass of our galaxy is approximately 8 x 10^11 MS, electromagnetic radiation associated with normal matter suggests a total mass of only 3 x 10^10 MS. Given this information, calculate the fraction of our galaxy's mass that is made up of dark matter.

Any guidance would be much appreciated!

3 AnswersAstronomy & Space8 years ago### Orbital speed of M87?

My problem:

On the basis of the data presented in the text, calculate the orbital speed of material orbiting a distance of 0.5 pc from the center of M87.

The text tells me "Measurements of the gas velocity on opposite sides of the disk indicate that the mass within a few parsecs of the center is approximately 3 x 10 ^9 solar masses; we assume that this is the mass of the central black hole."

Using the equation for orbital velocity: v = sq rt. GM / r

r = 0.5pc

M = 3 x 10^9 solar masses

G = 6.67 x 10^-11

yet no matter what I know I'm doing something wrong because plugging this in my calculator gives me a decimal answer.

The answer is : 5080

Please help explain this one?

1 AnswerAstronomy & Space8 years ago### Finding luminosity & M for a quasar?

The problem I am working on is:

What are the absolute magnitude and luminosity of a quasar with a redshift of 5 and an apparent magnitude of 22?

I have a ton of equations and even the final answer... yet I'm stuck. I'm feeling that this is probably a lot easier then I think it is, yet the teacher never taught it & the book gives no examples.

Please help to get me started?

m - M = 5log10 (d/ 10pc)

L = R^2 T^4

redshift = v / c

Answer: M = -22.5 & 1.5 x 10^8 solar luminosities

2 AnswersAstronomy & Space8 years ago### distance from the sun of deflection?

This is part D, to my homework question. I got parts A-C & checked them in the back of the book & they are correct. However I'm not even sure how to start this part.

Please solve & explain?

A future generation of space astronomy missions may be able to measure angles as small as 10^-6 arcsec accurately. At what distance from the Sun would this deflection occur?

The answer is: 8100 AU 5 0.039pc

2 AnswersAstronomy & Space8 years ago### Deflection in arc seconds?

I'm trying to estimate the deflection of a beam of light that just grazes the surface of the moon.

So I have the equation:

deflection (arc seconds) = 1.75 x M (solar mass) / R (solar radii)

So I looked up M & R for the moon:

M = 7.474 x 10^22 kg

R = 1,737.4 km

However I know I've already done something wrong as my text books says the answer is 26 micro arc seconds, & that doesn't seem to work with the numbers I am plugging in.

Please solve & explain?

1 AnswerAstronomy & Space8 years ago### Astronomy mass of black hole?

A star is observed in a circular orbit about a black hole with an orbital radius of 1.5 x 10^11 kilometers (km) and an average speed of 2,000 km/s. What is the mass of this black hole in solar masses?

So this is as far as I got....

;

Starting with Schwartz formula: v = sqrt of 2GM / r

I rearranged it t solve for m.

v x r ^2 / G = m

I know:

v = 2,000 km/s

r = 1.5 x 10^11 km

g = 6.674 x 10^-11

so...

(2,000 km/s)(1.5 x 10^11km)^2

----------------------------------------- =6.74

(6.674 10 ^-11)

yea... so that's my best try.

Can you please help me solve this & explain it?

Thank so much!

3 AnswersAstronomy & Space8 years ago### Pass no Pass: College?

Is it better to get a low grade in a class, or to just have a P on your transcript?

I am uncertain about how my grade will be for one of my classes this term, and since I have never done a pass no pass, and currently have a GPA of 3.92 (after 130 credits), I'm afraid of getting a low grade that will hurt my GPA.

Also do grad schools care or notice this?

The class is not within my major, & is simply part of my general studies so...

Advice?

Thanks!

5 AnswersHigher Education (University +)8 years ago### Astronomy help: orbital speed?

Calculate the orbital speed of matter in an accretion disk just above the surface of a 0.6-solar-mass, 15,000-km-diameter white dwarf.

I think I'm supposed to use the equation sq rt. of GM/r

But I can't seem to get the right answer.

Please solve and explain it to me.

Thank you.

2 AnswersAstronomy & Space8 years ago### Astronomy help? Mass transfer?

in typical binary systems a red giant can transfer mass onto a white dwarf at rates of about 10^-9 ms per year. roughly how long after mass transfer begins will the white dwarf undergo a type 1 supernova?

How does this length of time compare to the typical lifetime of a low-mass star?

(Assumer that a typical white dwarf starts with a mass of 0.6 ms)

Please answer and explain.

1 AnswerAstronomy & Space8 years ago### Radius-luminosity-temp relation help?

Us the radius-luminosity-temperature relation to explain how a protostar's luminosity changes as it moves from stage 4 (temp 3000 k, radius 2 x 10^8 km) to stage 6 (temp 4500 k , radius 10^6 km).

What is the change in absolute magnitude?

I know the radius-lum-temp equation is L = R^2 x T^4

But I'm still confused exactly what I'm supposed to do.

Please explain?

1 AnswerAstronomy & Space8 years ago### Astronomy question: estimate life expectancy?

Given that the Sun's lifetime is about 10 billion years, estimate the life expectancy of

(a) 0.2-solar mass, 0.01-solar luminosity red dwarf.

Could you please solve and explain this for me?

1 AnswerAstronomy & Space8 years ago### Astronomy help: Interior of sun?

Imagine that the source of energy in the interior of the sun changed abruptly.

(a) how long would it take before a neutrino telescope detected the event?

(b) when would a visible-light telescope see evidence of the change?

please answer and explain.

Thank you!

4 AnswersAstronomy & Space8 years ago### Peer reviewed sources help?

I am writing a college essay and need three peer-reviewed sources.

So far I have found one in my universities database but because I am working in a area with limited information I am going to have to look somewhere else for more sources.

Any areas to look? Or free online databases?

My paper is on the lotus flower in Japanese Buddhism and is for an Art history class.

Any info would be amazing. Thank you!

2 AnswersHigher Education (University +)8 years ago### Oil Painting Help/Advice?

1. I have been painting for some years now (with acrylic) and now I am taking a college painting class that only allows oil paints! (I didn't know this before hand).

Any advice/painting tips you can think of would be of great use!

Right now I am painting far far far below my ability and it is quite frustrating.

Also...

2. I figure it is not possible but can you think of anyway for me to paint with oil paints in my dorm room? I have homework assignments that need to be done. I was going to go to the class to paint over the weekend & filled out a form so that I could get into the building, but then I was told it would take 2 weeks for the form to be processed! I figure I will just have to do my homework once Monday comes around and the building is open again. (But it seems quite silly given I have the whole weekend where I could be working on it.)

Anyways... I could obviously use the paints it's just I don't have a way to clean up safely & dispose of the paint... So I suppose it's impossible. But I just thought I'd ask.

Thanks!

3 AnswersPainting8 years ago### drugstore primer for dry skin?

I have extremely dry skin and although I moisturize daily & wear a moisturizing bbcream/foundation my skin is still very flaky in some areas.

Is there a good primer that can help with this? I would prefer drugstore, or I could go high end (just nothing crazy too expensive.)

Or if you have any other tips for dry flaky looking skin?

Thanks!

3 AnswersMakeup8 years ago### google play/ itunes/ andriod phone?

I wanted to add some of the songs I bought on itunes to my android phone so I just hooked up my cell to my laptop & dragged & dropped the songs I wanted.

It seems like the only way to play them on my phone though is through google play.

Just checking, but google play won't charge me anything unless I directly purchase a song from it right?

thanks

2 AnswersGoogle8 years ago### Paypal!? Help! I don't know what to do?

Long story, sorry. But please HELP me!

I sold two items to two different customers through paypal. (each about 300 dollars)

Then both customers decided that they did not want to buy it before I sent the item.

I then sent them a refund & that was that.

Later however, although the history looked correct, paypal was charging me $600,

even though I didn't sell anything, or buy anything!

I called there help line and talked to a man with a heavy accent which I could hardly understand, & he didn't help at all.

I checked back to paypal a few days later because I got an e-mail saying they had resolved the problem, & it looked like it because I didn't owe anything.

Now I have both customers e-mailing me because they just got re-charged for the item they didn't recieved!

I don't know what to do!

I can try to stop the "re-charge back" by faxing paypal and going through all of these steps. But then I am just going to be charged again!

Does anyone know what I can do?

Please help! Thank you.

2 AnswersOther - Business & Finance8 years ago### Matched 3rd party content youtube question?

I got the "Matched 3rd party content" on a youtube video I uploaded.

It was a dance routine I did from 10 years ago, but I guess the audio that the dance was choreographed to was a problem. The video isn't even listed, I just put it up unlisted so I could show a few people.

How should I proceed?

I don't want to loose the audio or video for any reason.

Thanks!

3 AnswersYouTube9 years ago