Do Something Great with the BBC’s Sky at Night

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Image credit: BBC/Sky at Night

A week and a half ago, during a trip to visit Oxford Zooniverse Headquarters, I traveled to Mullard Radio Astronomy Observatory outside of Cambridge to meet with the Sky at Night’s co-presenter  Dr. Maggie Aderin-Pocock. We talked about main-belt comets and how the public could get involved in Comet Hunters to  search for these elusive breed of comets residing in the Solar System’s asteroid belt. In particular, I discussed the new HSC survey data that recently went live on the project. website.

Below is a link to a clip from Maggie encouraging people to join Comet Hunters.

This is part of the BBC’s Do Something Great Campaign, which promotes and encourages ways for everyone to get involved in volunteering and doing good. We’re thrilled to be involved in this effort with the Sky at Night.

Help astronomers find main-belt comets today at and if you’re based in the UK check out the Sky at Night’s latest episode on iPlayer.

More on the Hyper-SuprimeCam Survey Main-Belt Comet Search

By now, hopefully many of you have had the chance to try out the newest iteration of our Comet Hunters main-belt comet search that features data from the Hyper-SuprimeCam (HSC) Subaru Strategic Program, or the HSC Survey for short.  This survey is a ~300-night, 5-year observing program on the 8-meter Subaru telescope (which is the telescope used to obtain all of the data you’ve been previously classifying for the original Comet Hunters archival data search, though using a different camera) that aims to address a wide variety of scientific areas from cosmology to galaxy evolution to searches for distant objects in our own solar system.  While HSC survey observations are not specifically optimized for searching for main-belt comets (see below), with a few tweaks to our original classification interface, we still hope to use the data to search for previously unknown comets, with the added advantage of the data being relatively new compared to the data being used in our archival search, and also set the stage for an even bigger future expansion of Comet Hunters.

The main difference between HSC survey observations and the archival observations that we have asked you to review until now is that each HSC survey image has an exposure time of several minutes or more.  By comparison, for our archival search, we have tried to only use images with exposure times of less than 1 minute each.  Exposure time is how long the camera’s shutter remains open collecting light for a particular image.  For regular hand-held cameras that you might be used to, longer exposure times can be used to take photos in low-light conditions.  For astronomy, longer exposure times are used to study very faint objects.  The usual analogy used by astronomers is that of a bucket collecting rain drops.  The longer you leave the bucket out, the more rain drops it will collect (or for astronomy, the more photons from an object in the sky it will detect).  For a very faint and/or distant object for which only a very small number of photons reach us on Earth, we want to leave the camera shutter/bucket open for a longer time to collect more photons/rain drops.  As a side note, the size of a telescope’s primary mirror corresponds to the diameter of our hypothetical bucket, so by using a large telescope like Subaru and using longer exposure times, we can study very faint objects indeed!

The issue for us though is that long exposures work great for studying objects that don’t move in the sky (other than the steady, predictable motion caused by the Earth’s rotation), but not so much for nearby things in our solar system, like asteroids, which typically appear to move in the sky relative to background stars.  You can think of asteroids as fence posts along a road while you’re driving, while more distant objects like stars and galaxies are mountains far in the distance.  From your perspective, the nearby fence posts appear to move (whizzing past you as you drive) while the distant mountains appear to be essentially stationary.  Using the short exposure times for our archival search, the total apparent motion of asteroids compared to background stars was relatively minimal.  However, with the longer exposure times used by the HSC survey, the motion of the asteroids we are trying to study causes their images to be noticeably elongated (e.g., somewhat sausage-shaped), just as a photo of a fence post (or other nearby objects) might appear smeared out if you tried to take a picture while driving past.


What this means for Comet Hunters is that identifying comets just became a bit harder.  For the archival search, we asked you to compare the appearance of each asteroid with reference stars chosen from the same image and make a note of any differences you might see.  With the HSC survey data, every asteroid image will look different from the background stars because they will be elongated.  Furthermore, any cometary activity that might be present will also be “smeared out”, possibly making it harder to see.  Nonetheless, given the large size of the Subaru telescope, we expect to find some comets with activity bright enough to detect even when smeared out.  Then the trick is just to try to train your eyes to spot what elongated comets might look like, since they will not really look like most people normally think of when they think of what a comet looks like.  To help you out, we have generated some images of what elongated comets could look like and included them in the HSC Survey comet search tutorial (if you need a refresher, click on the “Show the project tutorial button” at the bottom of each classification page and go to the third panel).


The other major change that experienced Comet Hunters will notice is that instead of asking you to compare the appearance of a single asteroid to two comparison stars, we now ask you to compare the appearances of a single asteroid that has been imaged (at least) twice in the same night.  In part, this is due to the fact mentioned above that comparisons to “stationary” background stars are less useful when most of the asteroids we will show you appear elongated.  The other big reason we’ve made this change is to see if this helps to distinguish overlaps (or blends) from real comets.  This subject has been discussed in previous blog posts here and here, so we will not discuss them much here, except to say that background objects (mostly stars and galaxies) that might mimic cometary activity typically will not appear to move in the same way as our target asteroids.  So, by only focusing on asteroids that consistently show activity from one image to the next, we hope that you will be able to immediately identify cases where “activity” is only present in one image of an asteroid, rather than having to do a time-consuming manual check (as described here).

While it may initially take some getting used to, we hope that you will get the hang of searching for comets in HSC data before too long.  As mentioned in previous blog posts, the exciting thing here is that this data is much more recent than the archival data we have previously been having you review, meaning that if we discover any comet candidates, we may be able to trigger immediate follow-up observations to confirm the activity and study it further.  Another exciting aspect of this sub-project is that there is a lot more archival data available than we are currently using for our original SuprimeCam archival search.  As mentioned above, for this initial search, we intentionally restricted ourselves to short-exposure images, but if our attempt to use elongated asteroid images to search for comets is successful, we will be able to draw on the even larger pool of long-exposure SuprimeCam data, and then even include long-exposure data from other medium and large telescopes.  As I also mentioned above, astronomers like to use long exposures in tandem with large telescopes to allow them to study very faint objects, so being able to take advantage of such archival observations to do comet searches will greatly increase the amount of data available to us.  Since we expect that main-belt comets will be relatively rare compared to inactive asteroids, screening a large number of asteroids is key to finding the rare active ones, so the more data we can use, the better!

If you have any other questions about our new search, please comment below.  Otherwise, we thank you in advance for helping out with the new search, and wish you happy hunting!

An Introduction to Hyper Suprime-Cam (HSC)

The Hyper Suprime-Cam  (HSC) is the next generation camera on the Subaru Telescope, replacing its’ predecessor  Suprime-cam that had been used for 18 years. The field of view (FOV) has been dramatically increased from 0.16 to 1.5 square degree (10 times!!!). The HSC has not only a large FOV but it is also mounted on one of the biggest telescopes in the world. The camera’s ability and efficiency are the mightiest in the current observatories. HSCs physical extent is larger than three meters. Its focal plane (60 cm in diameter) is paved with 116 CCDs (including focus and tracking chips), operating in -100 degrees centigrade. The diameter of the front lens is 82 cm, the length of the lens barrel is 165 cm. The total weight is 890 kg. Every exposure includes 870 million pixels.

(c) Subaru Telescope, NAOJ

Before the HSC era, most of the cameras with large sky coverage were installed on  medium or small telescopes (48-inch-a few meter telescopes), e.g. GigaPixelCamera on Pan-STARRS 1 (1.8m), MegaCam on the  Canada-France-Hawaii Telescope (3.6m) and Magellan(3.6m), Dark Energy Camera on the Blanco Telescope (4m). Although they can cover a few square degrees, the sensitivity is  25% less than what you can achieve on an 8-meter class telescope. In some astrometry topics, like micro-lensing and large structure in the universe, both large aperture and FOV are vital. The enough sample will lead astrometers to a significant and compact conclusion.


(c) Subaru Telescope, NAOJ

The HSC Subaru Strategic Program (SSP) is most important and largest programs o the  Subaru Telescope in this decade. This survey started in 2014, finishing at 2019. This program will survey 1400 square degrees, using optical to near-infrared filters (g, r, i, z and y), reaching a 26.5 magnitudes in stacked images. The survey regions are fixed on the equator (Dec = 0) and cross with Ecliptic plane where are the locations including a lot of solar system bodies. Hence, beside cosmology science, this survey data is quite valuable for Solar System science. Now with the HSC Survey Search, you can search for cometary activity in asteroids imaged in the HSC survey on Comet Hunters.

Introducing the Hyper Suprime-Cam Survey Main-belt Comet Search

As of today, Comet Hunters has a new dataset and a new look. You’ll notice there’s now a button called ‘HSC Survey Search’ on the front page of the website.  We are thrilled to announce the incorporation of data from the Hyper Suprime-Cam Subaru Strategic Program. Hyper Suprime-Cam (HSC) is the largest field-of-view camera ever stuck on an 8-10-m class telescope. HSC covers nine times the size of the full moon in a single pointing!

What makes this so exciting is that the asteroid images you can review now on Comet Hunters from this survey are as from as close to right off the telescope as we can get. This means we can follow-up and try to catch the asteroid still in the act if Comet Hunters spots a tail. No one has ever looked at these images for main-belt comets before. Your eyes will be one of the first to view these images. Who knows what we’ll find!

The old Comet Hunters classification interface you know and love is still around. It’s now under the ‘Archival Data Search’ on the Comet Hunters front page. Looking for main-belt comets in the archival Suprime-Cam data is still extremely useful, and we’ll be keeping that classification interface going in parallel to the HSC Survey Search. You’ll notice the HSC images are a bit different than the Archival Data Search. There’s a tutorial and help buttons that will show you how find tails in the HSC images. You can also find more information on the Research and FAQ pages as well.

Dive into the HSC Survey data and help search for main-belt comets today!

Meet the Team: Shiang-Yu Wang

Today we have the next post in our Meet the Comet Hunters Team series. This time we’re featuring Shiang-Yu Wang from the science team.



Name: Shiang-Yu Wang

What is your current position and where/institution?

Research fellow at Academia Sinica, Institute of Astronomy and Astrophysics

Where are you originally from/where did you grow up?

I was born and grew up in Taipei, Taiwan.

What is your role in Comet Hunters?

My role is to provide some ideas of how to make the project better and to find the budget to support the activities

Beyond Comet Hunters, what else do you work on?

I work on large astronomical instruments and telescope systems.

In 3 lines explain your PhD thesis?

It is for a new kind of IR detectors. With artificial solid state quantum structure, you can detect the low energy IR photons. My thesis is focused on the new structures to improve the performance.

Why are you interested in main-belt comets?

It is a fairly new discovery and it might tell us more about the water on Earth.

Name one hobby of yours?


What is the latest book you have read?

Le Capital au XXI siecle (Chinese version)

Who is your favorite singer/band/musical artist?


What’s one thing most people don’t know about you?

I am pretty lazy.

Favorite cocktail or beverage?

Red wine

Dome Opening

I found this online today, and thought I’d share. The engineers for Hyper Suprime-Cam on the Subaru Telescope put together a video of the Subaru dome opening during twilight, You can find the original video here on a blog about the commissioning of Hyper Suprime-Cam, Subaru’s newest wide-field camera (Note:  the blog is in written in Japanese).

When you’re observing you don’t often get this view as sunset is one of the busiest times when you’re an astronomer getting ready for the start of your night (likely of one or a handful that semester) on the telescope. The data you currently review on Comet Hunters is the public archival data from Subaru’s Suprime-Cam. Each of those nights when the weather was good, something like below happened as the observatory prepared to start the nightly calibrations.

Video credit: Yousuke Utsumi

Blends, Blends Blends

The science team is working on incorporating data from the Hyper Suprime-Cam (HSC) survey into Comet Hunters.  We started with the archival Suprime-Cam data first to get a better understanding of what are the false positives and challenges for identifying Main-Belt Comets (MBCs) in data from 8-10-m class telescopes. We’ll continue with both datasets as there’s more Suprime-Cam asteroids, but when we have the chance we’ll move to reviewing the new HSC observations hopefully a few days after they’re taken.Most previous asteroid detection surveys are using 1-3-m class telescopes, so there are bound to be surprises that we wanted to know about before we developed the decision tree for the HSC snapshots on to the site. So we launched Comet Hunters with the archival Suprime-Cam images first. Now that things are going smoothly, we can turn our attention to the HSC data.

We combined your classifications from the first batch of Suprime-Cam images and had 125 candidates in need of further vetting. Thanks to volunteer Tadeáš Cernohous who on Talk went through our list comparing repeat images of the asteroid at slightly different positions in the same batch of subjects. What we learned that all of the candidates are unfortunately blends with stationary background sources. There are lots of faint background blobs that the asteroid moves on top of overlapping in the images creating very tail-like features. All of these images the science team would have had said has a tail.

A few examples are below (all blends with faint background sources):


Looks like a candidate tail, but a blend with a background source. We’d want this marked as ‘has a tail’ in the classification interface.


Looks like a candidate tail, but a blend with a background source. We’d want this marked as ‘has a tail’ in the classification interface.


Looks like a candidate tail, but a blend with a background source. We’d want this marked as ‘has a tail’ in the classification interface.


Looks like a candidate tail, but a blend with a background source. We’d want this marked as ‘has a tail’ in the classification interface.

There’s a lot more blends than we had anticipated given some of the team’s past experience with 2-m asteroid survey data. It’s still very much worth digging into the rest of the Suprime-Cam archive to look for MBCs. There might be many blends, but there could still be undiscovered MBCs too! Knowing that the background blends rate is much higher  because of the increase in the photon collecting bucket is extremely useful. From the candidates, we could see the blends are faint blobby structures that would be likely hard to get a source extractor to pick up in all cases.  Because of the quality of the HSC data and the repeat observation cadence we can try and take this into account possibly by checking the image of the asteroid and the repeat image of the same position take later on in the same night (not all Suprime-Cam images will have that and are taken in all types of sky conditions).

Now the Comet Hunters team is thinking about how best to develop a classification interface for the HSC data to include this. In the meantime, there are new Suprime-Cam images in need of review at if you have a minute or two to spare.

New Comet Hunters Data Available!

Thanks to everyone who has helped out with Comet Hunters so far.  As noted in a previous blog post, with your help, we’ve completed the first batch of images from launch and have compiled a preliminary list of potential comet candidates based on your classifications, and are currently in the process of vetting those candidates.

We are pleased to announce that new data is now available!  We’ve fixed some issues with our data processing software (in particular, a bug that led to a large number of off-center asteroids that many of you noticed), and so this new set should be easier to analyze and classify.  With the newly uploaded batch of brand-new images as well as some re-processed images that we’ve shown before, we hope to identify many more main-belt comet candidates with your help.  Good luck and happy hunting!

First Set of Images Complete but More Coming Soon

You might have noticed the blue banner currently on the Comet Hunters website. That’s because thanks to your help, we’ve completed the classifications needed to retire all the images that were live on the site. The team has been working to process a new batch of asteroid images. We’ve taken our time to improve on some of the data reduction issues you might have noticed in the launch images (streaked asteroids, more off center asteroids images, and some bad quality images). By having people spot and comment on these features in the images, we’ve been able to refine the data processing pipeline for this next batch of images. We will have those images live ASAP. Stay tuned to this space.

Most of the Comet Hunters science team  chatted today, and we’ve decided to put on Talk our top comet candidates based on your classifications. As we’ve found thanks to your classifications and Talk comments, overlaps with background sources are a huge source of false positives for 8-m class telescope images of asteroids when you’re searching for comet-like tails. If you’re interested, we could use your help to review other images to see if the potential tail is a background galaxy or star when you view the same area after the asteroid has moved. More details here.

Meet the Team: Meg Schwamb

Today we have the next post in our Meet the Comet Hunters Team series. This time we’re featuring Meg Schwamb from the science team.

Photo credit: Sundar Srinivasan

Photo credit: Sundar Srinivasan

Name: Meg Schwamb

What is your current position and where/institution?

Postdoctoral fellow at the Institute for Astronomy & Astrophysics at Academia Sinica

Where are you originally from/where did you grow up?

Long Island, New York on the Northeast cost of the United States

What is your role in Comet Hunters?

I’m a member of the science team and serve as project scientist. I help organize the science team efforts and the day-to-day logistics of the project.

Beyond Comet Hunters, what else do you work on?

I work on studying small bodies in the outer Solar System in the Kuiper belt and beyond. I’m part of the ColOSSOS (Colours of the Outer Solar System Origins Survey) project to study the surfaces of ~13o Kuiper belt objects. I’m also currently involved in the Planet Four and Planet Four: Terrains Zooniverse projects to study the seasonal processes on Mars’ south pole.

In 3 lines explain your PhD thesis?

Studying the icy bodies orbiting past Neptune, in the region known as  the Kuiper belt and beyond. I used a wide-field survey to look for more objects like dwarf planet-sized Sedna, whose highly distant and eccentric orbit  cannot be explained by the current architecture of the Solar System. I  was able to place constraints on the size and properties of these populations.

Why are you interested in main-belt comets?

This is one of the newest reservoirs of water in the Solar System. I’m interested to learn how this population may have delivered water to the Earth, and what main belt comets can tell us about the Solar System’s birth and evolution.

Name one hobby of yours?


What is the most recent tv show you have watched?

House of Cards (US version)

What is your favorite movie?

Batman Returns

What is the latest book you have read?

The Assassination of Margaret Thatcher by Hilary Mantel

Who is your favorite singer/band/musical artist?

Nine Inch Nails/How to Destroy Angels

What are five of the top ten most played songs on your iTunes/spotify/etc playlist?

Warriors by Imagine Dragons

Radioactive by Imagine Dragons

Of the Night by Bastille

Breathe by Alexi Murdoch

Silhouettes by Of Monsters and Men

What’s one thing most people don’t know about you?

I saw Star Trek: Nemesis in the movie theater  four times

Favorite cocktail or beverage?

Champagne/sparkling wine

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