Author Topic: Alice's MSc Astrophysics reports  (Read 37334 times)

JohnF

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Re: Alice's MSc Astrophysics reports
« Reply #15 on: September 29, 2011, 06:26:31 pm »
Good luck with your course and your write-ups Alice, its a bit like putting your head over the parapet, which I did when I went live with my websites.

Interesting RAS Presidental Address (Roger Davies, 2011) in the latest issue of 'Astronomy & Geophysics' entitled 'New Views of Old Galaxies' - talks about the tuning-fork classification of galaxies.
John C. Fairweather - http://www.jcfwebsite.co.uk

JeanTate

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Re: Alice's MSc Astrophysics reports
« Reply #16 on: September 29, 2011, 07:44:48 pm »
This is fantastic Alice!

The best part is, IMHO, that you're having fun, and that your fellow students (and university staff, etc) are nice and are also having fun.  ;D

I wanted to jump in and comment on a few things, but I see that Edd already picked up on the most important (again, of course, IM(ns)HO  :P).

Just this one (or two) though:
The flux can be compared with the luminosity, and a telescope can do this. (NB I need to find out exactly what "flux" means; I have heard it before!)

Back to the standard candles. Edwin Hubble used Cepheid variables as standard candles, to determine how far away other galaxies were. To use a standard candle, you need to know how much energy it emits - this seems to be the "flux" again. However, Hubble's estimate of the expansion of the Universe was severely wrong - and that was because he was mistaking one type of standard candle for another! His mathematics was quite right - he just needed more knowledge of what was there. At the time, nobody believed him because his measurements suggested that the Universe was younger than the Earth.
"flux" is an infuriating unit (or concept)!  >:(

I won't say more just now, other than to suggest that you keep poking at it, keep thinking about it, because it's quite important. Oh, and perhaps the most infuriating part is that the term is not used consistently! :o  In any one paper (or chapter of a textbook, or ...) it means just one thing (well, it should); however, in a different paper (or textbook), it may mean a quite different thing. When in doubt, look for (or ask for) a clear definition; an analogy: in physics words like 'force', 'energy', 'work', and (mostly) 'intensity' have very precise definitions, ones which differ (quite a bit) from the everyday meanings the words have.

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This seems to suggest no new galaxies could form now; is that correct? What about irregular galaxies - have they always been there? Since the generation of galaxies, that is? It seems unlikely given their starforming rates. But I may be quite wrong.
Hold onto these questions!  ;)

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Apparently, even if a standard candle is wrong, the linear distance is correct. Dark energy saved Hubble. Sorry - I have no clue what this means. But I'm putting it here in case anyone does know.
Perhaps you could bookmark this? At the end of the course, you'll be, um, interested in your own reaction, upon re-reading it.

jules

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Re: Alice's MSc Astrophysics reports
« Reply #17 on: September 29, 2011, 07:55:05 pm »
I'm hanging on your every word Alice! Thanks so much for taking the time to write up your notes for us. :-* :)

waveney

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Re: Alice's MSc Astrophysics reports
« Reply #18 on: September 29, 2011, 08:18:39 pm »
This is fantastic Alice!

Quote
This seems to suggest no new galaxies could form now; is that correct? What about irregular galaxies - have they always been there? Since the generation of galaxies, that is? It seems unlikely given their starforming rates. But I may be quite wrong.
Hold onto these questions!  ;)


Edd and Jean have filled in a lot, this is an area where you know I have some answers and hope to have more next year...   ;)
Join the Irregular Classifiers
We all help at the cutting edge of ignorance.

Alice

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Re: Alice's MSc Astrophysics reports
« Reply #19 on: September 29, 2011, 11:57:50 pm »
I was hoping you would have something to say about that, Waveney . . . ;D ;D ;D

Thank you all for your wisdom and encouragement. It is wonderful to think that in a way I am not just doing this course for me, but for all of you too - and to write things down not just for exams, but because I love them and because I look forward to telling you all about them later. 8)

It is amusing to see the reactions of people who have clearly studied this before, and who know when I should not forget my early thoughts and questions . . .

This evening we had our first Research Methods lecture. It was brilliant - all the stuff I really wish they'd told us on day 1 of undergraduates!! >:( - but if you will forgive me, I am going to put those off too. I'm already feeling like I've written enough today and it's nearly 1am. I need to get into the habit of cooking something to eat when I get back at 10pmish after these lectures - I've had greasy fry-ups after both of them! :D

paulrogers

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Re: Alice's MSc Astrophysics reports
« Reply #20 on: September 30, 2011, 02:06:47 am »
I was hoping you would have something to say about that, Waveney . . . ;D ;D ;D

The noisy student ;) is going to be "loaded for bear" when she get gets back to class? ;D ;D ;D

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Thank you all for your wisdom and encouragement. It is wonderful to think that in a way I am not just doing this course for me, but for all of you too - and to write things down not just for exams, but because I love them and because I look forward to telling you all about them later. 8)

In my experience that's the best possible thing you could do to reinforce your memory of the lecture. 
« Last Edit: September 30, 2011, 02:26:15 am by paulrogers »

paulrogers

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Re: Alice's MSc Astrophysics reports
« Reply #21 on: September 30, 2011, 02:25:29 am »
Well my first report on my first lecture is that I feel really exhiliarated - but also exhausted! I didn't get home until after 10 - it's a long walk from the train station - and having set off shortly after 5, I hadn't had dinner yet, so then it was make and eat and wash up that. So if you don't mind, I'm going to write up the notes tomorrow :D

Once and only once in college I ate lunch including rapidly digested carbs before an early afternoon exam.  The body considers the stomach more important than the higher functions of the brain, so too much blood went to my tummy and too little to brain power.  Proteins and fats are slower to digest, and don't monopolize your blood supply so much.  I think you did the right thing.  If your classes are all in the evening, maybe your schedule could be for a generous lunch maybe around 2PM, giving your digestion 3hrs to finish with its priority demands on your blood supply.

I've also found eating fats in the evening leads to GERD, gastric esophageal reflux disease.  Didn't notice it when I was younger, but now I'm careful about what I eat in the evening.

paulrogers

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Re: Alice's MSc Astrophysics reports
« Reply #22 on: September 30, 2011, 03:35:52 am »
Then came the really devastating part. He asked us how long we thought cosmology could exist: forever? 3 million years? Another few silly figures? One person put their hand up for 3 million years - not me - and they were right. If the Universe continues to expand at its current rate, in only three million years' time we won't be seeing much in the way of other objects in it.

I felt shattered to hear this. Three million years is nothing in a 13.7 billion year old universe. It's nothing even on the geological timescale. The dinosaurs were around 165 million years ago. Three million years ago there were probably animals very similar to humans. (I should know.) It seems we've come in the nick of time - just slightly slower development and we'd have been too late.

It's generally considered that we shared an ancestor with chimps, Pan troglodytes, some 5MYA.  Lucy, the famous Australopithecus afarensis, is dated to 3.2MYA, just about the right time.

The hey-days of dinosaurs were essentially in the Cretaceous Era, 145-65MYA, ending with the Chicxulub impact event and the KT boundary.

FWIW, I saw it on a visit to my Dad's before he passed away at the Royal Tyrell Museum in Drumheller, Alberta, the thin black line halfway up the coulee.  That was far more impressive to me than the full mount inside of an Albertasaurus! ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D ;D

Before that was the Jurassic, 199-145MYA, and both (Oops, guess I can't say "both" and then list three!) herbivorous sauropods, 'lizard hipped' saurischians, and the "up and coming" 'bird-hipped' ornithischian carnivores.  So, indeed dinosaurs were around 165MYA, though I wonder if you were thinking of the 65MYA end of the big, plodding dinosaurs.  But we might point to the birds as the dinosaurs among us.
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He told us that stars the size of the Sun don't forge any elements heavier than carbon. You will never find oxygen in a white dwarf, he said - only in supernova explosions. The girl sitting next to me and I both opened our mouths in protest - I am sure that is not correct, I'm sure I've seen oxygen rich white dwarves in the news and here on the zoo!

Does the fact that they may be Pop I stars that got their oxygen during their formation give him an "out"?
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At scales of 50-100 Mpc (megaparsecs), the Universe is homogenous and the structure is pretty much the same. Rather like a mixture of veins and holes, I think when I see the pictures.

I admit to being a bit vague about the relative size of parsecs, beyond the mere definition.  But I remember when the great voids were discovered and some (woman?) astronomer made this "large scale" image that looked sort of like a stick figure of a human from one direction.  So that sounds a little strange to me.
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Apparently, even if a standard candle is wrong, the linear distance is correct. Dark energy saved Hubble. Sorry - I have no clue what this means. But I'm putting it here in case anyone does know.

We do have an awful lot riding on "standard candles".  So much that I regard them with some trepidation. I know.  I know they've been tested, but if they ever crumble under the weight of everything we pile on them, we're gonna have a helluva mess to pick up!

« Last Edit: September 30, 2011, 06:46:58 pm by paulrogers »

Mikyle

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Re: Alice's MSc Astrophysics reports
« Reply #23 on: September 30, 2011, 06:17:42 am »
Tuesday 27th September: Cosmology (1)

Then came the really devastating part. He asked us how long we thought cosmology could exist: forever? 3 million years? Another few silly figures? One person put their hand up for 3 million years - not me - and they were right. If the Universe continues to expand at its current rate, in only three million years' time we won't be seeing much in the way of other objects in it.


I died a little inside  :'(

Tuesday 27th September: Cosmology (1)

He told us that stars the size of the Sun don't forge any elements heavier than carbon. You will never find oxygen in a white dwarf, he said - only in supernova explosions. The girl sitting next to me and I both opened our mouths in protest - I am sure that is not correct, I'm sure I've seen oxygen rich white dwarves in the news and here on the zoo! But his general point was that you need a big star to form heavy elements, which is generally correct. (He didn't point out that the biggest stars would have been in the Universe's early days, so the Universe is generally already seeded with heavy elements from early supernovae. But I thought I'd point that out here while it's relevant. :D)


Wait so this isn't correct? If it is I'm making the same face I made when I found out everything I was taught about atomic structure was wrong; ಠ_ಠ

All in all this was a great read. Now instead if troubled dreams of exams and relationships I can sleep peacefully, my head full of dreams about supernovae and galaxies.

Edd

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Re: Alice's MSc Astrophysics reports
« Reply #24 on: September 30, 2011, 12:30:35 pm »
I admit to being a bit vague about the relative size of parsecs, beyond the mere definition.  But I remember when the great voids were discovered and some (woman?) astronomer made this "large scale" image that looked sort of like a stick figure of a human from one direction.  So that sounds a little strange to me.

That's the CfA stick man - https://www.cfa.harvard.edu/~dfabricant/huchra/2mass/public.php
It's basically at the scale of the veinyness Alice mentioned, about when it starts to average out. It's the Coma (super-)cluster I think, so it's on a scale of about 100Mpc.

« Last Edit: October 05, 2011, 11:02:05 pm by Edd »
When I look up at the night sky and think about the billions of stars out there, I think to myself: I'm amazing. - Peter Serafinowicz

klmasters

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Re: Alice's MSc Astrophysics reports
« Reply #25 on: October 03, 2011, 06:24:27 pm »
Nice idea Alice. Sounds like you're busy. I'm a little jealous of you getting to learn this all for the first time. Some great days ahead. :)

Alice

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Re: Alice's MSc Astrophysics reports
« Reply #26 on: October 03, 2011, 07:04:10 pm »
Do please drop in with me Karen. Then I can pelt you with questions as they occur to me :D :D :D

Alice

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Re: Alice's MSc Astrophysics reports
« Reply #27 on: October 05, 2011, 05:37:14 pm »
Right, apologies for the delay in writing up Thursday's lecture. I'll be a typical student and make a barrage of excuses: the heatwave (never does anything for my concentration), the tiredness, the culture shock of moving to another place - the sudden lack of privacy on the one hand and losing the familiar people to share a workload with on the other. I went into temporary shutdown over the weekend.

By the way, Paul has asked me to keep my separate lecture topics in separate threads. Personally I wouldn't have chosen to do this as the lectures are only twice a week, there won't always be that much to comment on and it will look really big-headed taking up that much of the library. However, a majority of you may agree with Paul. (I'm flattered that anyone would read my notes at all.) So please let me know your preference - I can always change things later by merging or splitting a topic.



Thursday 29th September: Research Methods (1)

There's far less I can say this time as it's very . . . well . . . course-specific. Let me start by saying that I wish we'd had this first thing at undergraduates. I wish all people studying sciences were actively taught about research. At undergrad level they never mentioned it. By final year they assumed we somehow knew it all. I didn't find out a single thing about research until I'd handed in my dissertation (which we did in autumn) and then had a group project to do a few weeks later, in which I met students who, due to their schools or their advisers or what have you, actually did know what they were doing. I felt stupid and cheated, as you can imagine - and totally unfit to go anywhere in science. It was Galaxy Zoo that showed me how science really works. Anyway, enough about the past - I brought up that issue because I am certain my sort of science education is what the majority will get.

This handout contains a lot of specific stuff about the course website and library and so on (you can't get in without a password, so sorry about that! :P :D - also, I would like to be able to keep sharing this material with you all!!) and please ignore that, but I wanted to show it to you anyway because the slides that describe how research is done, and the scientific method, are what I was just harping on about. ;D

Research, Jim (the professor) said, is furthering the understanding of some field - it usually builds on what has gone before. We need to know the background, or we'll make all the mistakes people before us have made. Literature is usually vast, so we need to get good at selection before reading it. For example, research projects usually start with this following, say, a calculation that hasn't been tried yet. In literature review we need to be a bit critical of others' work by checking it occasionally, even if it's just checking their maths. That's the way mistakes are found.

Astrophysics relies on observations. Observations are not experiments. Very few experiments are possible, except of course with nearby materials in the Solar System, such as Moon rocks. We cannot control observations as we can experiments, but we have to treat them as experiments anyway. We can't input the variables of our choice. The Universe does that for us.

Astrophysics relies not only on predictions, but on numerical predictions. When you devise a theory, your assumptions may be wrong. A theory is what explains some known phenomena, and makes predictions about what will happen in different circumstances. (For example - this is my example, not the lecture's - Democritus thought that if everything was made of discrete atoms rather than a continuous substance, salt could dissolve in water because it would disintegrate into its smallest parts which would fit among the smallest part of the water. This was an accurate prediction, as of course he would have known - and you can make a lot more predictions by suggesting that everything is made of atoms.)

Some observations can be explained by quite different theories, and some theories are not testable at all. For example, the dark matter theory or modifying the inverse square law of gravity theory.

With such theories there are "error bars" - like you get on graphs - but Jim says this isn't a very good way of describing them, because that implies "OOOH the scientists are wrong". He prefers the term "uncertainty" - "we have this, to this much uncertainty". Usually, if there are two explanations, the simplest is right - Occam's Razor. (Not always, of course!)

Referencing is very important in scientific work - a) they show the reader where they can find more information and b) they tactfully give credit to those who have also done hard work.

If you want to find new theories, look in research papers, not books. Books will cover background material but not new ideas. This is generally because books take such a long time to publish that the fabulous new idea would be out of date by the time it came out!

Research papers have to say precisely what you did to get the result you're reporting, and be clear enough that anyone wanting to reproduce your work exactly what to do.

There are often LOTS of authors on a research paper, some of whom did not necessarily do any work towards it! (Two asides from me here. Firstly: I discovered by accident that my mum is an author on a medical research paper. She said she shouldn't have been an author as she only did "the donkey work". Which should have put her in the acknowledgements at least, I thought. Secondly: zookeeperChris, didn't you say one of your ambitions was to write a paper with more pages than authors?) For example, a paper about a satellite will list the entire satellite crew regardless of whether or not they contributed to the research at hand :D

We were then shown some examples of papers and their abstracts and I thought I'd share some of the definitions, used as search terms, with you:
- Proper motion: movement relative to the rest of the sky (planets which move around compared to the stars being the most obvious example)
- T-dwarf: a very cool type of star, cooler than M-stars, off the main sequence.
- Pan-STARRS1: survey with various telescopes, mostly from Hawaii.
- WISE: Wide Infra-Red Satellite Explorer.
In the case of this paper, which as you can probably imagine was about proper motions of T-dwarfs using Pan-STARRS1 and WISE, some of the data was probably 10 years old - which is a pretty good way to measure proper motion! T-dwarfs are usually found near us for the same reason as irregular galaxies: not because they are near, but because the only ones we can see are nearby. They're small and faint.

We then heard about the Lyman break, which is pretty interesting. At 121nm on a spectrum there is a sharp rise in flux. Shorter wavelength than that (I think) is hydrogen mopping up photons. This is an excellent method for getting a redshift of a galaxy. (I just Googled it, here's the Wiki page, which doesn't go much into the exact technique used.)

We were then shown the titles of various "respected" journals and warned that some are rubbishy and only there to make money - but it's pretty clear which ones have a bad reputation and which don't.

Citations are when another author writes a paper and references your paper. The first Galaxy Zoo paper has over 100 citations! ;D Of course, getting 100 citations might mean it's a fabulous paper that others are building their work on - or it might be that 100 people have pointed out why your paper is wrong. I wonder how many citations that faster-than-light-neutrino paper has?



That's it really, the rest was about how to use the system, and I ain't gonna tell you how to do that. :D I thought I'd tell you, though, that our assignment is to use the library to compare a real paper with what the media make of it. I think I'm going to enjoy doing that - not to mention should get on with it! :D :D
« Last Edit: October 05, 2011, 05:41:47 pm by Alice »

zookeeperKevin

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Re: Alice's MSc Astrophysics reports
« Reply #28 on: October 05, 2011, 06:31:52 pm »
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Citations are when another author writes a paper and references your paper. The first Galaxy Zoo paper has over 100 citations!  Of course, getting 100 citations might mean it's a fabulous paper that others are building their work on - or it might be that 100 people have pointed out why your paper is wrong. I wonder how many citations that faster-than-light-neutrino paper has?

Yep. Citations are really a measure of "interest" not "correctness". Lots of "wrong" and controversial papers are highly cited because they created a discussion in the community.

Alice

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Re: Alice's MSc Astrophysics reports
« Reply #29 on: October 05, 2011, 06:37:48 pm »
Quote
Citations are when another author writes a paper and references your paper. The first Galaxy Zoo paper has over 100 citations!  Of course, getting 100 citations might mean it's a fabulous paper that others are building their work on - or it might be that 100 people have pointed out why your paper is wrong. I wonder how many citations that faster-than-light-neutrino paper has?

Yep. Citations are really a measure of "interest" not "correctness". Lots of "wrong" and controversial papers are highly cited because they created a discussion in the community.

Like Galaxy Zoo threads ;D ;D ;D