Projecte Educatiu d'Agrupament

PartA

Prova prova prova prova

The Council of the Animals

(music here)


The Council of the Animals
every age is hold
to review the virtues
that God to us bestowed.

The snake, the whale, the lion,
the ever gentle dove,
each one is invited,
for each one is beloved.

Do you hear the singing?
So an animal you're too!
Come quick to the party
before the time is due!

Let it be told.

The Council of the Animals
every age is hold
come with your key virtuethat God to you bestowed.

El color del cel

Comic de xkcd

Molt encertat. Molt divertit.

Som Riu: Txarango

Catalonia should excercise the right to selfdetermination

Tracking the Expansion of the Universe with a Million of Galaxies

This is the 2.5 meter telescope used by the SDSS
 collaboration at the Apache Point Observatory. 

More that one million galaxies have been observed in the last three years by the 2.5 meter telescope from the Apache Point Observatory in New Mexico. In the picture above you can see the telescope (and me) just before sunset during a visit I made to the observatory some years ago. We, some of the astronomers and cosmologists of the Sloan Digital Sky Survey, had met nearby to discuss the science that can be done with the forthcoming observations. But now the data is already here.

When you have in your pocket observations of the positions and colors of more than one million galaxies, there are a lot of questions about the universe that can be investigated.  In this post, I will focus on explaining how we have measured the expansion of the universe from the distribution of galaxies of the BOSS survey, which is part of the Sloan Digital Sky Survey.

BOSS, the Baryon Oscillation Spectroscopic Survey, have targeted 1.35 million galaxies covering approximately 10,000 square degrees.  Galaxies are observed by setting optical fibers in the focal plane of the telescope. The light of each galaxy is then carried to an spectrograph where it is diffracted into a spectrum (of wavelengths or frequencies, this is, colors) and the data is stored.  

As the light travels from the galaxy where it was originally emitted to us, the spectrum of colors of the galaxies shifts towards the red. This is, the galaxies are seen reader than their original color. We call this change in color redshift, and we can measure it because we know the color/frequency of a particular atomic transition as it would have been observed in the galaxies when it was emitted. The amount in the color -the redshift- is an important cosmological quantity and tells us about how much the universe have changed in size since that light was emitted. If the universe have doubled its volume since then, then the wavelength of the light that we observe have doubled too.

Now, to know the expansion history of the universe we need to figure out how big the universe was at different times. To achieve this we could use different sets of galaxies. If for each set of galaxies we can determine how old was the universe when their emitted their light, and how big was the universe then, we have solve the problem. The first part, how big was the universe when the light of the galaxies was emitted, we have just obtained by using the redshift. The second part, which is how old was the universe when the light of the galaxies was emitted, is what we need to sort out next. In fact, we only need times differences. This is, we only need to know old was the universe when that light of each group of galaxies was emitted in comparison of how old the universe is now, which is the same as asking how long ago the light of each group of galaxies was emitted. And, since the light travels at a constant speed, this is equivalent to ask how far that group of galaxies is from us.

This is a map of some of the galaxies observed from the SDSS telescope.
Courtesy of M Blanton and the Sloan Digital Sky Survey

The Figure above show slices through the SDSS 3-dimensionalmap of the distribution of galaxies. Earth is at the center, each point represents a galaxy, typically containing about 100 billion stars. The outer circle is at a distance of 2 billion light years. The original distance between the edges is was not mapped by the SDSS because dust in our won Galaxy obscures the view of the distant universe in this directions. Both slices contain all galaxies between -1.25 and 1.25 degrees declination.
 
As it can be seen in the Figure above, galaxies in the universe are not distributed randomly. Galaxies tend to cluster in groups of galaxies because they attract each other. Galaxies also have a particular separation that they are more likely to be found as opposed to a little shorter or a little larger distances. This separation comes from plasma physics - it is the Baryon Acoustic Oscillation characteristic distance - and we know it is about 4,5 10²¹ km. This distance is not the distance between us and any set of galaxies, but a shorter one, the distance that galaxies "like" to be between themselves.

In the sky, this typical separation between galaxies appears as an angle. For each set of galaxies that we select as having emitted their light at a particular moment of the expansion of the universe, the typical separation of the galaxies between themselves appears to us as a given particular angle.  Each set of galaxies have a particular angle that gives the typical separation of the galaxies between themselves. And, since we know the value of this separation between galaxies from physics, r, and the angle its subtends by observation, θ, using the basic geometry of a triangle, we can know the distance between us of these galaxies, d. This is shown in last figure.

This shows a person observing two galaxies
separated a typical distance r,  if we know the
angle θ, we can measure the distance from 
us to the galaxies. 

Finally, because of the constant speed of light, we know how long ago the light of the galaxies was emitted and we have completed what we needed to deduce the expansion history of the universe.

In summary,  to know about the expansion rate of the universe we select several samples of galaxies. Each sample have emitted its light at a different time, and therefore it is at a different distance to us. We can measure this distance from geometry by observing the typical angle at which galaxies are separated. Once we have the distance to each sample of galaxies, we have also a measure of how long ago they emitted that light. Now, from the colors of the galaxies (the redshift) we know also how big the universe was at that time.  For each set of galaxies we know therefore the age of the universe at a particular moment and how big the universe was (in comparison to now). We have therefore determined the expansion of the universe.

This is what BOSS survey have done using three sets of galaxies at different distances.


You can read more here:


Lauren Anderson, Eric Aubourg, Stephen Bailey et al. (BOSS collaboration paper) 
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: Baryon Acoustic Oscillations in the Data Release 10 and 11 galaxy samples 

Endavant

Com proposa la seva família, recordem Joana Raspall amb un dels seus poemes.
Gràcies Joana, et recordarem. 

'Endavant!'

Respira fort, que l’aire és teu
i l’aire i tot et poden prendre.
Un cop ja l’hagis respirat
és carn com tu,
és alè teu que no es pot vendre.
Respira fort, que l’aire és teu.

Trepitja fort, que el lloc és teu!
On hi ha el teu peu no n’hi cap d’altre.
La terra té per a tothom
camins oberts.
Fuig de qui vulgui entrebancar-te.
Trepitja ferm, que el lloc és teu!

Parla ben clar, que el mot és teu
i el pensament ningú no el mana.
Si creus la teva veritat
llança-la al vent
i que s’arbori com la flama.
Parla ben clar, que el mot és teu!

(de Ales i Camins) 

My handsome litte vampire

Halloween, as almost every year, has been awesome!

I even wrote a poem,
a fragment reads:

A vampire comes to bite
in the secret of the night
Let him in or let him not?
Flesh and blood. 

Happy halloween to everyone.    

Monasterio dos Jerónimos, Lisboa

Visita al telescopi

 

Foto al telescopi des d'on s'observen les galàxies amb les que treballo. 

Foto del meu viatge amb barco

Fins quan ens caldrà aguantar?

TV3 ja no es pot veure enlloc del País Valencià des d’aquest dijous, 17 de febrer de 2011, a dos quarts de deu del vespre, després de 26 anys d'emissió

La llibertat d'informació, la llibertat pura i nua, i l'espai de comunicació en llengua catalana reben, d’aquesta manera, un colp immens.

Durant vint-i-quatre hores VilaWeb no emetrà perquè tots compartim la pèrdua d'una finestra de comunicació i perquè siguem ben conscients que és una derrota de tot el país, una derrota que ens afecta a tots, onsevulla que residim.

Davant aquest atac antidemocràtic, un atac a un poble i a la llibertat d'informació, davant d'aquesta situació més pròpia d'Egipte o Iran que no d'europa, què feu vosaltres? 

Excursió als ports

Heus aquí les fotos de l'excursió als Ports que vaig fer a finals d'estiu amb el Bernat. Company, gràcies per les fotos! Com veieu va ser tota una aventura.

Com sempre, els vostres comentaris seràn benvinguts.

31 aniversari!

El dia del meu aniversari va anar molt bé. Em vaig llevar més o menys d'hora i cap a les deu va arribar un amic meu que em va ajudar tres hores a prepara entrepans i fer truites de patates amb el que havia comprat el dia anterior. Com que al matí va ploure casi vaig estar a punt de cancelar el picnik al parc. Afortunadament no ho vaig fer i va sortir un dia rodó. Vaig estar al parc des de les dues del migdia a les vuit del vespre i van venir a saludar, menjar o jugar un bon grapat d'amics. Primer una mica de jugar a passar la bola amb les raquetes, després dinar amb pastís inclòs, mes tard un improvitzat partidet de futbol amistós, amb gent que s'estava pel park inclosa. Per les fotos a sobre podeu tenir una mica d'idea de com va anar. Fins una altra!

Marc

La mama vé de visita!

La meva mare ha vingut a veure'm a Nova York i ens ho estem passant molt bé. Ahir, dissabte, vam anar a Philadelphia i vam veure la famosa campana de la llibertat. Jo trobo que ja s'espavila bastant amb l'anglès, encara que ella diu que no. Apa!

Anem al zoo

Avui diumenge he anat al zoo amb un amic. Aquí teniu el resum de l'experiència.

Guanyador? Portsmouth

View Larger Map

Amics i amigues: després de dos dies sense dormir per l'estrés d'haver de decidir on serà casa meva els pròxims tres anys, finalment, el resultat: Portsmouth. Un petit poble a la costa sud d'Anglaterra. A vegades sóc tonto, mira que escollir Portsmouth podent-me quedar a Nova York, la veritat és que no sé que em va passar pel cap! En tot cas "la suerte está echada", així que desitgeu-me sort i veniu-me a veure, que encara no hi he anat i ja m'estic avorrint.

On et porti el vent

La vida del científic. Som a mig febrer i no tinc encara idea d'on estaré d'aquí sis mesos. La feina a Nova York s'acaba a l'agost i anant bé al setembre n'he de tenir una altra a punt. He fet un munt d'entrevistes per llocs tant diferents com: Niça (França), Cleeveland (Ohio, USA), Melboune (Austràlia = a les antípodes), Brookhaven (Long Island, USA), Porstmouth (Anglaterra), Edinburg (Escòcia), Bonn (Alemania), Los Angles (Costa Oest, USA). Tinc les meves preferències però encara cap oferta. 

Canviar de vida cada tres anys. Quina vida! Divertida i avorrida. Començar cada cop de nou a fer amics i tenir un amic o amiga arreu. Avui neva, i mireu m'he posat a escriure-us que fa molt que no ho faig. Tant que no sé ja si queda ningú mirant aquest blog. Us saludo i ja us esplicaré el resultat. 

Bufa el vent? I si bufa cap a on? 

Una abraçada,

Marc 

Thanksgiving

Pel dia d'acció de gràcies, és a dir el dijous passat, vaig fer igual que l'any passat, acceptar la invitació d'una amiga meva de la parròquia per anar a casa d'uns familiars seus. Hi érem, els seus pares, ella, el seu germà i promesa, la seva tia i marit i fills, i una monja gran de la família que va venir a passar una estona. Quan tingui la foto us la poso. Total, agafa el tren pleníssim fins a l'estat de Pensylvannia, i cotxe fins a la casa americana de dos pisos. Un menjador maco. Aperitiu que s'allarga mentre conversem en parelles o trios. Temps per fer uns croissants al forn - aquesta feina em va tocar a mi :-) -   i finalment tots a taula a mejar un gall d'indi gegant. Ahir encara en menjava sobres que em vaig emportar amb una carmanyola. La conversa interessant de tots temes, i molta història i geografia. Arribo a casa a la una de la nit. 

Apa i fins una altra.

PD. I ja que hi sóc aprofito a fer propaganda del meu altre blog http://www.teoforum.blogspot.com

Halloween

Ja sé que és una mica tard doncs estem a advent, però ara que m'han arribat les fotos de halloween aprofito per a posar-ne una. Com veieu vaig anar a una festa de disfresses i em vaig trobar una bona colla de catalans. Entre ells la Gemma i el Ferran, que també surten a la foto. Pels que no ho heu descobert vaig de ninja! Aha!