Suggested Searches

 

Overlap Zoo

Galaxies, which are themselves vast collections of billions of stars, gas, and dust held together by gravity, are scattered across the immensity of space. Every so often, a rare cosmic coincidence occurs: two galaxies overlap one another in the sky, lining up perfectly from our point of view (on Earth or from a telescope in space). These rare overlapping galaxies let us study something normally invisible: the dust in the foreground galaxy.

As a volunteer in Overlap Zoo, you'll view images that volunteers in a different project (Galaxy Zoo) previously identified as containing overlapping galaxies. The Overlap Zoo project will teach you how to verify the presence of galaxy pairs in these images, classify key features of each galaxy, and mark their outlines. Your work will help build the first large-scale catalog of galaxy pairs suitable for dust studies and enable a huge step forward in accuracy of astronomical estimates.

Go to the project website! about Overlap Zoo

project task

Examining images

division

Universe

where

Online

launched

2026

What you'll do:

  • Learn how to recognize two types of galaxies, smooth and featured, in galaxy pairs. 
  • Examine images of galaxies and answer questions about the kinds of galaxies you see and their orientation in space by clicking buttons and drawing their outlines.
  • If you like, you can discuss what you find with other volunteers and scientists in an online Overlap Zoo Talk forum.

Requirements

  • Time: 10-15 minutes to complete the tutorial, then as much time as you like.
  • Equipment: An internet-connected computer.
  • Knowledge: None. The in-project tutorial provides all the necessary information.

Get started! 

  1. Visit the project website.
  2. Click on the “Classify” tab to Navigate to complete the in-project tutorial and learn how to recognize galaxy pairs, galaxy types, and galaxy orientation.
  3. Start reviewing images and recording the details you see.

Learn more: 

The Overlap Zoo project’s Research page gives an overview of the value of overlapping galaxies to astronomy, especially to scientists interested in learning more about cosmic dust and its impact on observational astronomical data. The Frequently Asked Questions (FAQs) page has additional, practical information relevant to doing the work of the project.

Overlap Zoo’s stylized, round logo. A white spiral galaxy stands out against a blue background with two stars. One spiral arm is overlapping the smooth side of a white elliptical galaxy in the the lower right. The whole is encircled by a white border and a thick black circle.
A space telescope view showing two large spiral galaxies, lined up one in front of the other. The foreground pinwheel-shaped galaxy is seen nearly face-on, with dark, swirling lanes of interstellar dust silhouetted against the bright glow of a larger background galaxy. The background galaxy is tilted both away from the viewer and roughly 45 degrees down to the left.
Data from the NASA/ESA Hubble Space Telescope was used to produce this image of a pair of overlapping galaxies called NGC 3314. While the two galaxies look as if they are in the midst of a collision, this is in fact a trick of perspective: the two are tens of millions of light years apart from one another, but they are in lucky alignment from the point of view of Hubble. Dust in the closer, featured spiral galaxy is made visible by light from the more distant smooth elliptical galaxy. More information about NGC 3314 can be found at https://science.nasa.gov/asset/hubble/lined-up-galaxies-show-rare-details-ngc-3314/.
Image credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and W. Keel (University of Alabama), from https://esahubble.org/images/heic1208a/.

Get to know the people of Overlap Zoo!

Selfie of Trevor Butrum.

Trevor Butrum

Project lead, graduate student in astrophysics, University of Louisville

Visit Team Page
Headshot of Benne Holwerda.

Benne Holwerda

Astronomer, Professor, University of Louisville

Visit Team Page
William “Bill” Keel in a room with space prints on the wall.

William “Bill” Keel

Astronomer, Professor Emeritus of Astronomy, University of Alabama

Visit Team Page