Thread: Woah, any help?

Imagine that it is the year 3000 AD, and you are captain of the starship USS Drongo. Unfortunately, due to a malfunction in your warp drive, you have been flung into a parallel universe. Your mission is to find your way back to our own universe.
Your science team can rig up a wormhole generator which will take you back. But to do this, they need to know what the cosmology is of this strange universe into which you have been flung. Is it expanding like our universe? Or shrinking? Or doing something stranger still?
As far as you can tell from experiments in your spaceship, all the laws of physics are the same here as they are back home. But when you look around with your telescopes, you see a strange universe. There are stars, which look much like the ones back home. There is one very blue star (which you are calling "blue star 1") only 1.36 parsecs from your spaceship. But there are no galaxies, only dense star clusters like the one shown:

Your first step is to find out how far away the nearest of these star clusters (the one shown above) is. With great imagination you are calling it "Star cluster 1".
As viewed with your best telescope, you can pick out the individual stars. They come in a range of colours. You identified a star in this cluster which has almost identical colours to blue star one. You therefore hypothesize that it has the same luminosity as blue star 1.


DISTANCE TO STAR CLUSTER 1

(3 points possible)
Blue star 1 is 1.36 parsecs from you, and has a measured flux of 4.5×10−9Wm−2.
The similar colour star in star cluster 1 has a measured flux of 3.2×10−21Wm−2.
How far away (in Mega-parsecs) is star cluster 1?
unanswered


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SIZE OF THE STAR CLUSTERS

(3 points possible)
Another star cluster ("star cluster 2") lies 8.3 Mega-parsecs from the starship, and has an apparent radius of 8.3 arc seconds. You would like to know how big it is. Is it the same size as galaxies in our universe (i.e. tens of kilo-parsecs) or only as big as a star cluster in our universe (a few parsecs).
What is the physical radius of star cluster 2? (in kilo-parsecs)
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SO WHAT ARE THEY?

(1 point possible)
So - based on the size you measured, what are these star clusters?

Galaxies (i.e. several kilo-parsecs in size)?Star clusters (i.e. less than around 10 parsecs in size)Something quite different, unknown in our universe
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WHAT IS IT MADE OF?

(2 points possible)
You took a spectrum of star cluster 2, keen to see what it is made of. Here is that spectrum.
From this spectrum, you can tell that certain elements are present in this cluster. On the basis of this spectrum, which elements are definitely present? Click the boxes next to all that apply. If you click all the correct boxes, you will see a tick when you check the answer, but if you get any wrong or identify too many you will see a cross.

So - this looks like an assignment of some sort. Is that right?

I presume you have some reference or other study materials to work from.

You should work out your proposed answers / methods and check with us to see whether you're on the right track.

Originally Posted by adelady

So - this looks like an assignment of some sort. Is that right?

I presume you have some reference or other study materials to work from.

You should work out your proposed answers / methods and check with us to see whether you're on the right track.

It is a test for me. I sort of would like for others here to chime in on answers > I don't know if my answers are correct yet and have not any submitted of them. I think I figured out the distance in mega-parsecs to star cluster 1. I'll post that tomorrow. I haven't worked out the radius of the star cluster yet> but am pretty sure it is Hydrogen based because of the around 660 nanometer wavelength absorption., Good grief, this is my first day in the course! Pushy Aussies! :-)

Without going into too much detail, I think the answer to the first question is 1.612762 mega-parsecs. It boils down that to find the distance of the star in the cluster (Distance 2) it will equal Distance 1 (which is given) times the square root of flux 1 / flux 2 which are also given. The square root thing is because light intensity lessens with the inverse of the square of the distance. Inverse-square law - Wikipedia, the free encyclopedia

No-one here is going to do your homework for you. As Adelady said you should work out your proposed answers and methods and people will let you know if you are on the right track or not.

I mentioned the answer I got on Q1 in the post above. ! already took the test and got these all correct.

well done

Originally Posted by Mayflow

I mentioned the answer I got on Q1 in the post above. ! already took the test and got these all correct.

Are you going to share your answers and demonstrate what you've learned or just leave us all hanging?

Let's take this one first:




Looking at the following we can see which elements are absorbing the most light (the vertical axis of the graph shows this) The more the flux we measure, the greater the light intensity we are seeing) - There is a lot of Hydrogen (H) around 660 nm (wavelength) and also some calcium (CA) shown a bit under 400 nm.

Here is a way to see which elements absorb different wavelengths -