101: The Great Debate
This is the first in a new series of blog posts under the title of ‘Galaxies 101’. These posts aim to explore the history and basics of the science of galaxies. I’ll be covering some of people who helped us understand these ‘Island Universes’ as well as some of the basics that would be taught during a first year undergraduate galaxies course at university.
It is fortunate that these posts are beginning in the week of the 90th anniversary of The Great Debate which occurred on April 26th, 1920. The Great Debate – or the Shapely-Curtis Debate – took place at the Smithsonian Museum of Natural History between two eminent astronomers, Harlow Shapley and Heber Curtis. Shapely was arguing that the ‘spiral nebulae’, that were observed at the time, were within our own Galaxy – and that our Galaxy was the Universe. He also argued that the Sun was not at its centre. Conversely, Curtis argued that the Sun was at the centre of our Galaxy but that the ‘spiral nebulae’ were not inside our Galaxy at all. He suggested instead that the Universe was much larger than our Galaxy and that these nebulae were in fact other, ‘island’ universes.
Below is a drawing of the ‘spiral nebula’ M51. This is an observation by Lord Rosse, drawn in 1845 using the 72-inch Birr Telescope at Armagh Observatory in the UK.
With 90 years of hindsight we can now say that Shapely and Curtis were both right and wrong. The Sun is not at the centre of the Galaxy and the Galaxy is only one of hundreds of billions of galaxies in the Universe. But how was the argument resolved? The answer, in part, comes from a very famous name in astronomy: Hubble.
Less a decade after the Great Debate took place, Edwin Hubble used the largest telescope in the world – the 100-inch Hooker Telescope on Mount Wilson – to observe Cepheid variable stars in the Andromeda Nebula/Galaxy. Cepheid variables are a type of pulsating stars whose pulsation periods are precisely proportional to their luminosities. This makes Cepheid variable stars a ‘standard candle’ – an object where the brightness is a known quantity. If you can observe the apparent brightness of a standard candle, then you can determine its distance by a simple inverse square law. Since Cepheid variable stars have pulse rates proportional to their luminosity, if you can measure the pulse rate of a Cepheid variable anywhere in the Universe, then you can determine how far away it is. This is what Edwin Hubble did in 1925 and he calculated the distance to Andromeda as 1.5 million light years.
At the time, Shapely thought that our Galaxy was around 300,000 light years across and Curtis believed it was around 30,000 light years. Hubble’s measurement placed Andromeda well outside our galaxy and showed that Curtis was correct in thinking that the ‘spiral nebulae’ could indeed be other galaxies. Today we think the Milky Way is about 100,000 light years across and that Andromeda is 2.5 million light years away.
The discoveries of the 1920s started a whole new adventure for astronomy. The Universe had gotten a lot bigger and was about to expand much, much more. It is important to remember that Shapely, although wrong about the nature of the nebulae, did correctly assert that the Sun was not at the centre of the Galaxy. This is the kind of Copernican shift that makes people think about things differently and it is important to realise that the issues discussed during the Great Debate were complex. For our benefit though, the Great Debate is a starting point for exploring the relatively new study of galaxies. Humanity’s view of the Universe, and our place within it, has changed an awful lot since 1920. The study of galaxies has had a lot to do with that.
If you want to read more about the Great Debate, and what else helped to resolve the arguments I can recommend this excellent NASA site. You can also read the published text of the debate online.
[Andromeda image credit: Robert Gendler]
Galaxy Zoo: Hubble
The Galaxy Zoo project has evolved once again – now we are classifying galaxies from the incredible Hubble Space Telescope! Galaxy Zoo: Hubble is the new incarnation of the Galaxy Zoo project and it continues to allow you to help astronomers with real scientific research by asking you to to visually classify galaxies online.
The original Galaxy Zoo and Galaxy Zoo 2 both used data from the Sloan Digital Sky Survey and recently, after reaching 60,000,000 classifications those projects began to wind down. The timing is excellent though and it allows Galaxy Zoo: Hubble to launch today, for the 20th anniversary of the space telescope. Images of galaxies taken using the legendary space telescope are there for everyone to classify and I recommend that you go and do just that.
A lot of the fainter galaxies look like those seen in the Sloan catalogue from Galaxy Zoo 2 (this is a good sign, since we don’t want galaxies to change wildly depending on what telescopes we use!) however in amongst these there are some real gems to be discovered in the Galaxy zoo: Hubble data. I just found a couple in my first tentative classifications, I’ve shown them here to whet your appetites.
Hubble has now been in orbit for 20 years. In that time it has helped us to understand the age of the Universe, to see more distant galaxies than ever before, to detect the presence of black holes in the centre of galaxies, to witness a comet collide with Jupiter, and much more!
Hubble has captured the imagination of people all around the world and it has given us some of the most iconic images of space that exists in the public consciousness. The image at the top of this post was taken during Servicing Mission 4, just after the Space Shuttle Atlantis captured Hubble with its robotic arm in May 2009, beginning the mission to upgrade and repair the telescope. Thanks to that upgrade, Hubble will continue to provide amazing images and science for many years.
So that’s enough chat from me – go and classify some Hubble galaxies!
XMM-Newton is observing Hanny's Voorwerp TODAY!
Hi all,
Just a quick note – our observations of IC 2497 and the Voorwerp have been scheduled for today and are taking place now. Since we’re observing in the X-rays, our “quick snapshot” to see what is going on actually takes almost a whole day. XMM-Newton‘s eye isn’t very sharp, so we won’t get a pretty picture. What we will get however is a really great spectrum of the X-ray emission of the black hole in IC 2497 (if it’s munching on stars and gas) and perhaps also the hot gas in the Voorwerp.
We won’t get the data right away though. First, the folks at the European Space Agency (esa) who are controlling XMM need to check out whether the data is OK and do some basic processing on it. Only then can they send it to us to have a look and that may take a few weeks.
Stay tuned!
Kevin
60 Million Classifications
Well, you’ve done it, more quickly than we would ever have thought possible. We have now reached a critical point – 60 million classifications means an incredibly robust, well-defined and scientifically valid catalogue of Sloan Digital Sky Survey galaxies. Congratulations to those who won prizes, and thanks to everyone who took part.
So what happens now? The site is still here, as you can see, and every classification you make will still improve our results, and will be saved in our database. To encourage you to keep clicking, we’re still giving away individual prizes to one person at random for each collection of 250,000 classifications. To take part, all you have to do is what you do best – classify galaxies – and it will help if you make sure your Zooniverse email address is up to date so we can contact you if you’re a winner.
What 60 million really means is that we can move on to the next phase of the project – and you won’t have long to wait…
How to handle Hubble images
While we’re squirreling away processing the Hubble data on IC 2497 and Hanny’s Voorwerp, and starting to get some science out of them, here’s a guide to the kinds of things needed to get science from Hubble images and make them presentable. To demonstrate, I’ll use a galaxy that shows up in the opposite corner of the field in exposures with the Wide-Field Camera 3 (WFC3). Read More…
Zoonometer Approaches 60 million
Having only announced the race to 60 million, only ten days ago, the Zoonometer is showing that we are now making the final 500,000 classifications! The response has been quite incredible and you can now start to see the winners going up on the Zoonometer page. We are still contacting winners as the classifications are made.
There is still one more prize draw to be made, at the 59,750,000 mark – when one classification from the previous 250,000 will be selected at random. Beyond that we await our 60,000,000th galaxy classification. The lucky person that makes that fateful classification will win a cool bundle of prizes:
- An original Sloan Digital Sky Survey plate
- A Galaxy Zoo mug and mousepad
- A Zooniverse t-shirt
Those of you that are wondering what will happen to Galaxy Zoo after the 60 million mark need not worry. We have a nice surprise in store for everyone very soon, but classifications will continue beyond 60,000,000 in the meantime. 60 million marks our minimum, best database. Every galaxy classified afterwards is still just as valid and useful as the 60,000,000 that preceded it and thus Galaxy Zoo will continue.
So if you want to be in with a chance of winning our prize for the 60,000,000th classification then go forth and classify! Watch this blog for more news and updates on the future of the Galaxy Zoo project.
[Image credit: NASA, ESA, K. Sheth (Spitzer Science Center, California Institute of Technology), and P. Capak and N. Scoville (California Institute of Technology)]
Machine Learning Paper Accepted!
Exciting News from Manda Banerji on the Machine Learning paper:
Hi Everyone!
This is to let you all know that the Galaxy Zoo machine learning paper has now been accepted for publication in the Monthly Notices of the Royal Astronomical Society journal. The final version of the paper is at http://arxiv.org/abs/0908.2033. You can read all about the paper in my previous blog post at http://blogs.zooniverse.org/galaxyzoo/2009/08/05/latest-galaxy-zoo-paper-submitted/.
The paper has already attracted a lot of interest from the computer science community demonstrating that your classifications are proving useful and interesting to non astronomers as well!
60 Million Classification Giveaway
Yesterday, Galaxy Zoo launched a fun little competition to mark the approach of our 60,000,000th classification. This is the point at which we can create an amazing and powerful database from the Galaxy Zoo 2 data.
Galaxy Zoo’s ticking clock of classifications, The Zoonometer™, has been steadily ticking away, toward our target of 60 million classifications for a long time. We can hardly believe it, but we’re nearly there! To mark this historic moment in Galaxy Zoo’s history, we’re giving away prizes to the people that provide the clicks that take us to our target.
The person that makes the 60 millionth classification will receive a bundle of goodies, including a Galaxy Zoo t-shirt and mug, a Galaxy Zoo poster and an original Sloan Digital Sky Survey plate! As well as this, we’re giving away individual prizes to one person at random for each collection of 250,000 classifications.
The prizes kicked off with the 57,000,000th classification, which was achieved last night at about 2100 UT (see extremely geeky screenshot). One of the 250,000 classifications that led us to the 57,000,000 mark will now be selected at random to win a Galaxy Zoo mousepad. We will also be picking a winner from the 57,000,000 – 57,250,000 range as well. The winners will be posted on the Zoonometer™ page. We are appaoraching 57,500,000 as I type this.
If you want to take part, all you have to do is what you do best: classify galaxies! It will also help if you make sure you’re Zooniverse email address is up to date so we can contact you if you’re a winner.
60 Million Target Explained
With 60,000,000 classifications in the database, the Galaxy Zoo 2 project will have reached a critical point. 60 million classifications represents our minimum, ideal database. With that many classifications you, the participants, will have collectively classified every galaxy enough times to create an incredibly robust, well-defined and scientifically valid catalogue of Sloan galaxies. Beyond the 60 million classifications, every additional click still goes into the database – it just means that our minimum science goal is achieved.
What is an SDSS Plate?
The person who classifies the 60 millionth galaxy will win an original Sloan Digital Sky Survey plate. These plates are quite large and make amazing memorabilia, since they were actually used to observe galaxies by the SDSS. We are lucky enough to have one of these plates at Zooniverse HQ, to give away. 640 holes have been drilled into the plate, with each hole corresponding to the position of a selected galaxy, quasar or star in the sky. During observations, scientists plug the holes with optical fibre cables. The fibres simultaneously capture light from the 640 objects and record the results in CCDs. The plates are interchangeable with the CCD camera at the focal plane of the telescope. You can read more about how the SDSS performed observations on their own webpages.
She's an Astronomer: Elizabeth Siegel
Elizabeth Siegel lives in California in the USA. She is 57 years old and has worked as a registered nurse for the last 9 years after going back to college at 42 to do a nursing degree. She has two grown up kids – a son in college and a daughter who works in the aerospace industry.
- How did you first hear about Galaxy Zoo?
I found out about Galaxy Zoo through the science news page at Yahoo two years ago as the project was beginning. It was only on the page for one day, but I remembered the name and was able to find it on my own.
- What has been your main involvement in the Galaxy Zoo project?
My main involvement has been classifying galaxies. Specifically: Galaxy Zoo 1 and 2, mergers, barred spirals, AGN-clouds, and Irregular spirals. I have found a few asteroids and some possible gravitational lensens I did and OOTD on polar rings. I am an active member on the galaxy zoo forum, and have posted pictures in the pure art thread, not to mention one or two galaxies.. I’ve recently started working on the Solar Storm Watch, Supernova Zoo, and the Moon Zoo Beta test. Between these projects I have contributed around 200,000 classifications and spent almost 4000 hours on Galaxy Zoo.
- What do you like most about being involved in Galaxy Zoo?
I love looking at the galaxies, learning about them and discussing them with fellow zooites from around the world online or in person through group meets like the one we had in September 2008 at Chabot Observatory in Oakland California (West Coast Meet Ups Forum Thread).
- What do you think is the most interesting astronomical question Galaxy Zoo will help to solve?
I am not a Astronomer so I really cannot answer that question. I do known as volunteers we are providing the Astronomers loads of information which would have taken them a long time to research otherwise. Of course there is Hanny’s Voorwerp that the scientist and zooites would like to learn more about. Personally it’s all the galaxies I like. I find Polar Ring galaxies to be the most interesting to me since there are so few of these type galaxies. If Astronomers could learn more about these galaxies that would indeed be cool.
- How/when did you first get interested in Astronomy?
When I was around 14 years old I had read a lot of books on the moon and meteorites and wanted to be an astronomer. That year my Christmas present was a telescope. One night, my friends and I decided that we were going to ride our bikes to Lick Observatory. We snuck out at one in the morning rode twenty miles East of San Jose California. We made it by mid-morning but of course everything was closed. There was an old man and he asked us what we were doing. We told him we had come to see the observatory. He smiled and said the best time to see the observatory was at night. He gave us some water to drink, and we smiled and thanked him for the water and information. But 20 miles up hill on bikes is a long way to go to be told to come back at night. The old man did not even show us around. When I found out that most of Astronomy had to do with math I lost interest in being a Astronomer as a profession since math was never my strong subject. Over the years I kept up on Astronomy though reading science articles watching programs like Nova etc. Then I found Galaxy zoo I can look at all the galaxies, stars, nebulae, clusters which is my favorite part of Astronomy
- What (if any) do you think are the main barriers to women’s involvement in Astronomy?
I have no idea.
- Do you have any particular role models in Astronomy?
I do not have any particular role models in Astronomy but I do admire the way the Galaxy zoo team has taken the original Galaxy zoo project and is now expanding it to the Zooniverse. I would like to invite everyone to come and participate in these wonderful zoo projects.
This post is part of the ongoing She’s an Astronomer series on the Galaxy Zoo Blog is support of the IYA2009 cornerstone project of the same name (She’s an Astronomer). We are listed on the She’s an Astronomer website in their Profiles.
- Zooites:
- Hanny Van Arkel (Galaxy Zoo volunteer and finder of Hanny’s Voorwerp). Hanny’s interview in het Nederlands.
- Alice Sheppard (Galaxy Zoo volunteer and forum moderator).
- Gemma Couglin (“fluffyporcupine”, Galaxy Zoo volunteer and forum moderator).
- Aida Berges (Galaxy Zoo volunteer – major irregular galaxy, asteroid and high velocity star finder). Entrevista de Aida en español.
- Julia Wilkinson (“jules”, Galaxy Zoo volunteer. Frequent forum poster, and member of irregular and HVS projects).
- Els Baeton (“ElisabethB”, Galaxy Zoo folunteer. Frequent forum poster, and member of most of the spin-off projects!). Els’s interview in het Nederlands.
- Hannah Hutchins (Galaxy Zoo volunteer, forum poster and co-creator of Galaxy Zoo APOD)
- Researchers:
- Dr. Vardha Nicola Bennert (researcher at UCSB involved in Hanny’s Voorwerp followup and the “peas” project). Vardha’s Interview auf Deutsch.
- Carie Cardamone (graduate student at Yale who lead the Peas paper).
- Dr. Kate Land (original Galaxy Zoo team member and first-author of the first Galaxy Zoo scientific publication; now working in the financial world).
- Dr. Karen Masters (researcher at Portsmouth working on red spirals, and editor of this blog series.)
- Dr. Pamela L. Gay (astronomy researcher and communicator based at Southern Illinois University).
- Anna Manning (Masters’ Degree Student in Astronomy at Alabama University working with Dr. Bill Keel on overlapping galaxies)
- Dr. Manda Banerji (recent PhD and author of the machine learning paper)
We’re almost done – this is the penultimate entry, and last Zooite we will be interviewing. Just one more researcher to go.
Who's looking at the Voorwerp?
I just got a notification from the XMM-Newton Science Operations Centre that our observations of IC 2497 and the Voorwerp have now been scheduled for April 19th. XMM-Newton is esa’s flagship X-ray satellite and can observe photons from 0.2-10 keV. We’ve already got our hard X-ray observations from Suzaku last year, so XMM will have a second, detailed look at the softer X-rays. Also, if there’s anything there, then XMM will give us a very rough image; Suzaku can’t take images, only spectra. After the data are taken, it may take a few weeks for esa to process the raw data before they send it to us. Stay tuned…
