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  • Astronomer, Dr Sara Webb is fascinated about viewing distant galaxies. She is a galaxy hunter and explores the universe through the eyes of many different telescopes using online tools.

    This article has been republished from The Conversation under Creative Commons licence CC BY-ND 4.0.

    Rights: Sara Webb

    Night sky

    Astronomers use many cutting-edge technologies to capture the night sky, hoping to eventually tackle some of our biggest questions about the universe.

    This asset has made use of the VizieR catalogue access tool, CDS, Strasbourg, France (DOI : 10.26093/cds/vizier).

    By far my favourite thing about my job as an astronomer is those rare moments when I get to see beautiful distant galaxies, whose light left them millions to billions of years ago. It’s a combination of pure awe and scientific curiosity that excites me about “galaxy hunting”.

    In astronomy today, much of our work is handling enormous amounts of data by writing and running programs to work with images of the sky. A downside to this is that we don’t always have that “hands-on” experience of looking at every square inch of the universe while we study it. I’m going to show you, though, how I get my fix of wonder by looking at galaxies that only a select few people will ever have seen, until now.

    In just our observable universe we estimate there are over 2 trillion galaxies!

    Galaxies at your fingertips

    Only a few decades ago astronomers had to tediously examine photographic plates after a long, cold and lonely night of observing. In the 21st century we have access to information any time, anywhere via the internet.

    Automatic telescopes and surveys now provide us with so much data we require machines to help us analyse it. In some cases human eyes will only ever look at what the computers have deemed is interesting! Massive amounts of data are hosted online, just waiting to be admired, for free.

    Go online for a universe atlas

    Aladin Lite is one of the greatest online tools available to look at our universe through the eyes of many different telescopes. Here we can scan the entire sky for hidden galaxies, and even decipher information about their stellar populations and evolution.

    Let’s start our universal tour by searching for one of the most visually stunning galaxies out there, the Cartwheel Galaxy. In the Aladin interface, you can search for both the popular name of an object (like “cartwheel galaxy”) or known co-ordinates. The location will be centred in the interface.

    Rights: Public domain

    The Cartwheel Galaxy

    Online view in Aladin Lite of the Cartwheel Galaxy, a lenticular/ring galaxy 500 million light years away from Earth discovered in 1941 by iconic astronomer Fritz Zwicky. This is from optical imaging by the Digitised Sky Survey.

    This asset has made use of the Aladin Sky Atlas developed at CDS, Strasbourg Observatory, France. Image released into the public domain by NASA.

    The first image of the Cartwheel Galaxy we see is from optical imaging by the Digitised Sky Survey. The colours we see represent different filters from this telescope. However, these are fairly representative of what the galaxy would look like with our own eyes.

    A general rule of thumb as an astronomer is that “colour” differences within galaxies are because of physically different environments. It’s important to note that things that look blue (shorter wavelengths) are generally hotter than things that look red (longer wavelengths).

    In this galaxy, the outer ring appears to be more blue than the centre red section. This might hint at star formation and stellar activity happening in the outer ring, but less so in the centre.

    To confirm our suspicions of star formation we can select to look at data from different surveys, in different wavelengths. When young stars are forming, vast amounts of UV radiation are emitted. By changing the survey to GALEXGR6/AIS, we are now looking at only UV wavelengths, and what a difference that makes!

    Rights: Public domain

    A different view of the Cartwheel Galaxy

    An online view in Aladin Lite of the Cartwheel Galaxy with the survey changed to GALEXGR6/AIS – now you only see the UV wavelengths.

    This asset has made use of Aladin Sky Atlas developed at CDS, Strasbourg Observatory, France. Image released into the public domain by NASA.

    The whole centre section of the galaxy seems to “disappear” from our image. This suggests that section is likely home to older stars, with less active stellar nurseries.

    Aladin is home to 20 different surveys. They provide imaging of the sky from optical, UV, infrared, X and gamma rays.

    When I am wandering the universe looking for interesting galaxies here, I generally start out in optical and find ones that look interesting to me. I then use the different surveys to see how the images change when looking at specific wavelengths.

    Universal Where’s Wally

    Now you’ve had a crash course in galaxy hunting, let the game begin! You can spend hours exploring the incredible images and finding interesting-looking galaxies. I recommend looking at images from DECalS/DR3 for the highest resolution and detail when zooming further in.

    The best method is to just drag the sky atlas around. If you find something interesting, you can find out any information we have on it by selecting the target icon and clicking on the object.

    To help you on your galactic expedition here are my favourite finds of the different types of objects you might see.

    Rights: Sara Webb

    Spiral galaxies

    Four examples of spiral galaxies found using Aladin online. Spirals are the most iconic galaxy shape and include many of the brightest galaxies in the nearby universe, like the Andromeda Galaxy.

    This asset has made use of the VizieR catalogue access tool, CDS, Strasbourg, France (DOI : 10.26093/cds/vizier).

    Spiral galaxies typically have a central rotating disc with large spiral “arms” curving out from the denser central regions. They are incredibly beautiful. Our own Milky Way is a spiral galaxy.

    Rights: Sarah Webb

    Elliptical galaxies

    This shows examples of elliptical galaxies. This type of galaxy has an approximately ellipsoidal shape and a smooth, nearly featureless image.

    This asset has made use of the VizieR catalogue access tool, CDS, Strasbourg, France (DOI : 10.26093/cds/vizier).

    Elliptical galaxies are largely featureless and less “flat” then spirals, with stars occupying almost a 3D ellipse at times. These type of galaxies tend to have older stars and less active star-forming regions compared to spiral galaxies.

    Rights: Sara Webb

    Lenticular galaxies

    This shows examples of lenticular galaxies. These are a type of galaxy intermediate between elliptical and spiral galaxies.

    This asset has made use of the VizieR catalogue access tool, CDS, Strasbourg, France (DOI : 10.26093/cds/vizier).

    Lenticular galaxies appear like cosmic pancakes, fairly flat and featureless in the night sky. These galaxies can be thought of as the “in between” of spiral and elliptical galaxies. The majority of star formation has stopped but lenticular galaxies can still have significant amounts of dust in them.

    There are also other amazing types of galaxies, including mergers and lenses, which are just waiting for you to find them.

    Related content

    Find out more about the special instruments used to detect 'hidden' light in Light and telescopes.

    In Colliding galaxies investigate galaxy clusters to help understand more the structure of the universe.

    Space revealed – introduction curates our telescope resources in one handy place. Meet some Kiwi astronomers who use telescopes to investigate planets, stars and galaxy clusters.

    Activity ideas

    Citizen science

    Teacher Matt Boucher used the Planet Hunters online citizen science project within a year 7/8 unit on light. Read the case study and accompanying unit plan with activities. Before introducing students to Planet Hunters, he used models to demonstrate how a dip occurs in the light intensity from a star when a planet passes in front of it. Students also used Agent Exoplanet, an online citizen science project to demonstrate how the light curves are constructed.

    Student activities

    Exploring with telescopes uses an interactive and an online or paper-based quiz to teach about different types of telescopes and the types of space objects they are best suited to view.

    In Hunt the planet, students plot graphs of light measurements from stars, searching for dimming that indicates the presence of a planet, and calculate its size.

    Useful links

    This article is part of a How to guides series explaining how people can learn the skills to participate in activities that academics love doing as part of their work.

    Follow the author, Dr Sara Webb on Twitter at @sarawebbscience.

    Sara was also one of the authors of another The Conversation article: To find out how galaxies grow, we’re zooming in on the night sky and capturing cosmic explosions.

    See The Universe within 14 billion light years – NASA Atlas of the Universe – this map gives a rough cosmographical estimate of the expected distribution of superclusters within the observable universe.


    This article was written by Sara Webb, Postdoctoral Research Fellow, Centre for Astrophysics and Supercomputing, Swinburne University of Technology.

    The article was originally published in The Conversation, 27 December 2021. Read the original article.

    Rights: The Conversation

    The Conversation

    The Conversation is an independent source of news and views, sourced from the academic and research community and delivered direct to the public.

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      Published 20 June 2022 Referencing Hub articles
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