Frequently Asked Questions

1.1 How can I participate?

Please create an account at the login screen (see the figure below) and then login to participate in the GALAXY CRUISE galaxy classification. We require accounts to allow us to manage everyone's classification results. For more information about the registration process, please see “2. About Account Registration.”
* You can access pre-login content without registering.

login screen


1.2 What do I need to participate?

To participate in this project, you need a PC or tablet connected to the internet. GALAXY CRUISE’s website is optimized for PC and tablet browsers. Please perform the classification with your device connected to the internet so that you can load image data and save your classification results. A reasonable internet speed (16 Mbps or higher) is recommended.
Test your internet speed

1.3 Can I participate from my smartphone?

We recommend using a PC or tablet to participate in this project; however, a smartphone with a smaller screen can also be used for galaxy classification.

1.4 Can I view the images of galaxies without registration?

The same images that are used in GALAXY CRUISE can be accessed through hscMap image viewer allows you to browse the images captured during the HSC Subaru Strategic Program (HSC-SSP). It is publicly accessible and does not require registration. However if you want to participate in the galaxy classification, you need to register with GALAXY CRUISE.
 Exploring the Universe with Subaru Telescope Data  (About hscMap)


2.1 Where can I create my account?

You can create your account from the login screen. First click the “CREATE ACCOUNT” button, then enter your e-mail address and create a password. Then click the “Register” button (see the left figure below). You should then receive an automatic e-mail with a link. Please click on the link in the e-mail to display the registration screen for your account name and other information (see the right figure below). A simple questionnaire will be displayed upon registration, so please fill it out. Please complete the required information and click the “Register” button to complete the registration process. Registration is of course free. 
* Your account name is your virtual identity that will be displayed on the rankings screen after login.
* These questionnaire items will be used for future programs. Attributes and motivation are analyzed as statistically, separately from personal information, and individuals will not be identified.



2.2 Why didn’t I receive the automatic e-mail?

Please check your e-mail settings. The possible causes are:
・The e-mail was automatically sorted into your spam folder.
The e-mail might have been delivered to your spam folder instead of your inbox.
・Spam protection is active.
If your cellphone is set to only receive e-mails from specific domains in order to avoid spam, it might have blocked the automatic e-mail. Please modify your e-mail settings to allow messages from the following three domains:,, and
・An incorrect e-mail address was registered.
Please double check that the e-mail address entered into the registration form is correct. If the e-mail address you provided us with is not correct, we will be unable to send you the confirmation e-mail.
*If you try these three solutions and the problem still persists, please contact us.

2.3 Why can’t I log in?

To log in, you need your registered login ID (your e-mail address) and password. (If you haven’t yet registered, please create your account first.) Please verify that all the required information is entered correctly and then try to log in again. Note that all information must be entered in single-byte characters. 
* If you have verified the registration information but still cannot log in, please contact us.

2.4 What should I do if I forget my login password?

Click “Reset Password” on the login screen and create a new password. 

2.5 How can I modify my registration information?

After login, click the suitcase-shaped icon at the bottom left of the screen and open the “Voyage Log” (see the figure below). If you click the “Change Registration Information” button, another screen will pop up where you can change your account name and password.



2.6 How can I display my avatar on the Ranking screen?

First, click the “Change Registration Information” (see “2.5” above for more information about the "Change Registration Information" button) and open “Registration Information” (see the figure below). To display your avatar, select the “Use Gravatar” and “Show my Gravatar on Rankings” boxes on the bottom left of the page. When selected, a checkmark (✓) should appear in the box. Finally click the “Save” button on the bottom right to save your changes. 
* If you remove the checkmark from the “Show my Gravatar on Rankings” box, your avatar will appear only on the “Registration Information” screen.
* Creating a  Gravatar (Globally Recognized Avatar) is the only way to upload your avatar image to this website.


2.7 How can I create a Gravatar?

To To create a Gravatar, you need an account on If you don’t have one, visit the official website of “Gravatar” and click the “Create Your Own Gravatar” button to sign up. Upon signing up, please make sure to use the same e-mail address you used to register for GALAXY CRUISE. (If you have a account, click the “Sign In” button to access your account.) Once you have created your avatar at the “My Gravatars/Manage Gravatars” page after login, you can view your avatar image on the “Voyage Log.” (Provided you have selected the “Use Gravatar” box on the “Registration Information” screen explained in “2.6” above.)

2.8 Can I delete my account?

Yes. To delete your account, open “Voyage Log” (as explained in “2.5” above) and click the “Delete Account” button to delete your registration information (such as e-mail address) and the number of galaxies you have classified. However, your classification results are stored separately from your account-related information, and will be used in future research. Note that you cannot delete your classification results.

3.1 About the world view

Our Milky Way Galaxy is a shimmering isle of light in the black sea of intergalactic space. But we are not alone; innumerable galaxies lie scattered across the void like an archipelago full of diversity. GALAXY CRUISE is your chance to explore this cosmic archipelago. HSC mounted on the Subaru Telescope, one of the world’s best astronomy telescopes, has imaged countless galaxies scattered across a depth of billions of light-years of space. Likening the whole region of the sky surveyed by the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) to a nautical chart (the cruise map), with each galaxy you will come across wonderful scenery, as if you were on a cruise ship sailing on a world tour.
Cruise Map

3.2 What can I earn by participating in the galaxy classification?

As the voyage proceeds, you will earn “souvenirs” (commemorative illustrations) based on how many of the areas you have completed. You will also receive a departure stamp when you complete each town or continent. You can view your collections of souvenirs and stamps from the welcome screen when you login. The souvenir screen shown in the figure below, for example, shows the silhouettes of souvenirs you have not yet earned.
About Rewards
About the Welcome Page



3.3 Completion of the cruise

When you finish classifying all the galaxies and get the departure stamp at Stage 10, you will have completed the journey of GALAXY CRUISE. If you have explored around all the towns and continents, you will have classified nearly 8000 galaxies in total. Thank you for your generous support of astronomy research to unlock the mysteries of galaxy evolution. You can end your journey partway through if intervening circumstances arise. For more details, see “2.8 Can I delete my account?” 
* For those who have completed the cruise, we are currently preparing a “Continuing Journey GALAXY CRUISE.” If you are willing to support our research inspecting fainter galaxies to trace the history of galaxies back to earlier ages, please try it out. 

4.1 I have no idea which galaxies to classify.

White crosshairs will appear on a galaxy to be classified and if you zoom in on the galaxy, the crosshairs will disappear. If you lose track of which galaxy you are looking at, zoom out to display the crosshairs again. (You can zoom in and out by using your mouse wheel or touchpad.)
Classification Procedure

4.2 What should I do when white crosshairs or a green checkmark (✓) obscures the galaxies?

Using your mouse wheel or touchpad, you can zoom in to clear the white crosshairs on an unclassified galaxy or the green checkmark (✓) on a classified galaxy. Please magnify the images of galaxies so that you can inspect their detailed structures before classifying them.

4.3 I want to perform the classification while comparing galaxies to the training images.

On the welcome page, click the GALAXY CRUISE logo at the left edge of the menu bar (see the figure below) to open the home page in another tab. If you click the “Training” item in the menu bar on the home page, you can perform the classification while consulting the training images.
Welcome Page Menu Bar


4.4 In what situations should I adjust the brightness or convert to grayscale?

Faint structures, the remnants of galaxy collisions, may be lurking around the main body of galaxies. Sometimes it is easier to discover these faint structures by adjusting the brightness or converting to grayscale.

4.5 Can I check whether my classifications are correct?

No, you can’t. Even researchers cannot definitively classify galaxies. If you are worried whether or not your classifications are correct, we recommend redoing the training sessions or repeating the classifications in “Boötes Town” where you can compare your results with those of the Captain, until you gain confidence.
Practice in Boötes Town

4.6 My evaluation criteria seem to have changed over the course of the classification exercises.

Perhaps, you have gotten used to the tasks. As you gain experience progressing through the stages and the number of galaxies you have classified increases, your criteria will inevitably change. Don't worry about the change. Please proceed to the subsequent stages.

5.1 What does it mean for two galaxies to collide?

When two galaxies happen to be close enough, they are attracted to each other through their mutual gravitational force. As the galaxy pair gets closer, the gravitational force between them becomes stronger and disturbs their morphologies. This process through which neighboring galaxies distort each other is called “gravitational interaction.” On some occasions, these galaxies can “collide” and even merge to form a larger galaxy. Because galaxies consist mostly of empty space with scattered stars and nebulae, when galaxies "collide" they actually pass through each other for the most part. But the violent gravitational interactions caused by passing through each other severely disrupt the shapes of the galaxies. 

5.2 Are there occasions when two different features coexist?

Yes. Particularly, “tails” (tidal streams) and “distortion” (distorted halos) are likely to occur in the same galaxy, and telling the difference between the two is often difficult. Depending on the viewing angle, “tails” and “fans” are sometimes difficult to distinguish as well. Such distinctions are difficult even for professional astronomers.
*If you are unsure which one to select, select the multiple answers that you think are likely.

5.3 Can one feature of colliding galaxies be mistaken for a different feature depending on the viewing angle?

Although such cases are thought to be rare, it is possible. For example, a “ring” seen from any direction cannot be mistaken for a “fan.” However, seen from the side view a “fan” may resemble a straight “tail” (tidal stream).

5.4 Are there any features other than these four (ring, fan, tail, and distortion)?

You may encounter some features that cannot be neatly classified into the basic four categories. Multiple features can coexist, and in exceedingly violent collisions, their shapes could be smashed into unrecognizable pieces. When galaxies are in the midst of a collision, their particularly bright cores (galactic nuclei) are sometimes arranged side by side (see the image below), creating yet another different feature.
* In this galaxy, you can also see "tails" (possibly "fans") and "distortion".



5.5 Why do interacting galaxies have various features?

The various features come from various forms of collision. Some collisions involve a larger galaxy and a smaller one and other collisions involve galaxies with similar sizes. Some galaxy pairs collide head-on and others collide obliquely or just pass close to each other. You may also see galaxies just before or after collision and some galaxies have experienced more collisions than others. In other words, the various features of interacting galaxies reflect the details of the collisions.

5.6 How can galaxies collide while the Universe is expanding?

Although in the grand scale the Universe as a whole is expanding, on the scale of galaxies, it is possible for gravity to overcome the expansion in the local area and pull galaxies together. In fact, the typical separation between galaxies is only a little larger than the typical size of a galaxy. For example, our Milky Way is headed toward the Andromeda Galaxy and predicted to merge with it in about four billion years. If we scaled the Milky Way’s disk, measuring 100,000 light-years in diameter, down to 10 centimeters, the Andromeda Galaxy would be located only about two meters away. It wouldn’t be difficult to roll a disk to hit a target two meters away. As you can see, the distances between neighboring galaxies is only a couple dozen times greater than their diameters, and the closer the pairs of galaxies get, the more strongly they attract one another. Therefore, galaxies actually collide quite frequently.

 6.1 What should I do when I find an interesting object?

Please use the contact form to send us its coordinates and a brief description. To do so, move the object to the center of your display and save its image. If you click the “Screenshot” (camera-shaped) icon on the welcome page, the image will be saved and automatically downloaded. The coordinates of the object are shown at the bottom left of the screen as a pair of green numbers. In the case of the image below, for example, you should write “α=02:30:08.2909, δ=-04:32:04.5867” or “alpha=02:30:08.2909, beta=-04:32:04.5867” in the contact form.
You can also upload the downloaded image file on your Twitter or Instagram account with the #GALAXY_CRUISE hashtag instead of contacting us. In this case, please write "Credit: HSC-SSP/NAOJ" in addition to the coordinate.

* Currently, Screenshot is available only on Firefox, Google Chrome (greyscale only), and Safari. As of January 2020, Screenshot does not work on Microsoft Internet Explorer or Microsoft Edge. Please use Firefox or Safari until this problem is solved.

6.2 Can I name the galaxies I’ve classified?

Unfortunately, you can’t. Every newly discovered celestial object should be assigned a unique designation because of scientific necessity. But if you find strange-shaped galaxies or other interesting objects, please give them nicknames and share them on Instagram. Perhaps some of your nicknames will go viral. 
 GALAXY CRUISE Official Instagram

6.3 Is it possible that an image may contain something other than celestial objects?

Yes. Since the displayed images (observation data) are unprocessed, you may find camera artifacts or false features in them. You may also find fast-moving celestial objects, such as asteroids, traveling across the sky. In the image shown in question 6.1, for example, the spike-like line running horizontally at the bottom right is an artificial feature.
Strange Features in Images (from Exploring the Universe with Subaru Telescope Data”)

6.4 Can I use the image materials without permission?

You can use our image materials without prior permission within the following scope: 
- Extent of free use stipulated by Japanese copyright law (private use, educational use, news reporting, etc.)
- Usage in academic research, education, and learning activities
- Usage by news organizations
- Usage in printed media
- Usage in websites and social networks
When using the materials, you should include the following credit line: “Credit: NAOJ.” For more information, see the Guide to Using NAOJ Website Copyrighted Materials.

7.1 What is Citizen Astronomy (Citizen Science in Astronomy)?

Plase see About Citizen Science.

7.2 Why are you conducting this project?

Please see A Word from the Captain.

7.3 Is this the first attempt (in the world) to classify interacting galaxies?

It’s not the first. There actually are many examples where researchers have classified galaxies in telescope images, and some were even conducted as citizen science projects. Compared with the images captured by other instruments, however, those captured by HSC are overwhelmingly superior in the extent of the survey area and the "depth" (quality) of data which determines how well you can recognize dim and faint objects. Since the telltale signs of galaxy collisions are often faint, we expect HSC images will allow a detailed analysis that cannot be performed with other images.

7.4 How will the classified results be used?

Researchers will statistically analyze the data obtained for galaxies classified by multiple participants. When the analysis of the various galaxies moves ahead and is written up as a research paper, we would like to acknowledge the contribution of all the Citizen Astronomers, as a group, who helped with the classification.

7.5 Isn’t it better to apply machine learning than to have non-specialists classify galaxies?

Actually, attempts to search for interacting galaxies with machine learning are beginning, but so far classification with human eyes is still essential. Before using machine learning, we first have to create classification samples, or “teaching data,” of interacting galaxies. However, there are still no such data available for the classification of faint galaxies imaged with HSC or other instruments. To create the data, we first need to systematically analyze classification results provided by many people. In addition, by many people participating in the classification, we can share the pleasures of participating in real astronomy and determining the growth history of galaxies. More than machines, humans can better appreciate the stunning images captured by HSC!
Please see the NEWS article on September 1, 2020 "GALAXY CRUISE and Machine Learning" for more details.

Now, Let's Start on Your Adventure!