UA Science

You are here


UArizona Spacewatch discovered the larger of the twin asteroids targeted in NASA's upcoming DART mission

On a spring night in 1996, a camera on the University of Arizona Steward Observatory's 36-inch telescope atop Kitt Peak captured three important images of a bright object sweeping across a backdrop of seemingly static stars.

The object turned out to be a half-mile-wide, potentially hazardous near-Earth asteroid, caught on camera by Joseph Montani, a member of the university's Spacewatch group in the Lunar and Planetary Laboratory. Originally dubbed 1996 GT, the asteroid would later be renamed Didymos – which is Greek for "twin" – at Montani's suggestion. The name was inspired by the discovery in 2003 that the asteroid has a small companion, only 525 feet across.

That companion – named Dimorphos, meaning having two forms – is the target of an upcoming NASA mission designed to test technology that could redirect asteroids that potentially threaten life on Earth.  

Dimorphos and Didymos both orbit the sun, and the smaller of the pair orbits the larger one about once every 12 hours. Though Didymos and Dimorphos pose no threat to Earth, NASA identified Dimorphos as an ideal target to test asteroid redirection technology that could help protect Earth from future asteroid threats.

On Sept. 26, 2022, NASA's Double Asteroid Redirection Test, or DART, mission spacecraft will slam into Dimorphos, and scientists will closely study how the impact alters the smaller asteroid's orbit around Didymos. DART launched on Nov. 24, 2021.

Spacewatch is led by principal investigator Melissa Brucker. She is also on the science investigation team for DART. Spacewatch and other research groups plan to collect data on the light reflected from the two asteroids after impact.

"We'll take a long series of images to measure the brightness of the system over time. Didymos and Dimorphos will look brighter when they're next to each other than when one is in front. In a series of images, we will be able to determine how long it takes Dimorphos to orbit Didymos," Brucker said. "Working on this mission is very exciting. I've been working on near-Earth asteroid tracking for eight years, so being able to participate in the first planetary defense demonstration is a really great opportunity."

Spacewatch has long history of asteroid discovery

Spacewatch was founded by UArizona planetary scientists Tom Gehrels and Robert S. McMillan in 1980.

The original goal of Spacewatch was to survey and discover small objects orbiting the sun, such as asteroids and comets, to better understand the evolution of the solar system. Spacewatch started shifting focus in 1998 and now follows up on discoveries made by astronomical surveys, such as UArizona's Catalina Sky Survey, by monitoring the positions and movement of newly discovered potentially hazardous objects so that they do not become lost.

Spacewatch continues to use the Steward Observatory 0.9-meter (36-inch) telescope atop Kitt Peak, as well as the Lunar and Planetary Laboratory's 1.8-meter (72-inch) telescope, which has been operational on Kitt Peak since 2002.

New asteroids and comets are discovered by groups around the globe constantly, with astronomers slicing the sky into regions that telescopes survey multiple times a night, snapping images at each pass. Surveys capture each region three to four times a night.

Astronomers then compare the positions of moving objects to background stars in an image. They send the resulting measurements to the International Astronomical Union's Minor Planet Center, which takes the observations and determines orbits for the objects.

As one of the longest running asteroid tracking groups, Spacewatch can claim many firsts.

It was the first group to use a charge-coupled device, or CCD, camera to routinely survey the sky for comets and asteroids. It also claims the first CCD-discovered near-Earth asteroid, 1989 UP (now called 496816), and comet, dubbed 125P/1991 R2 Spacewatch. Spacewatch was also the first astronomical group to develop automated, real-time software for moving-object detection and the first to discover a near-Earth asteroid by software – 1990 SS (now called 11885 Summanus).

Between May 1984 and June 2022, using UArizona telescopes on Kitt Peak, Spacewatch submitted 15,777,248 astrometric records of asteroids and comets to the Minor Planet Center. Of those 151,805 were of 15,072 unique near-Earth objects, including 1,883 potentially hazardous objects.

NASA’s James Webb Space Telescope presents a new perspective on the Tarantula Nebula

NASA’s James Webb Space Telescope presents a new perspective on 30 Doradus, or the Tarantula Nebula, a region well-know to astronomers studying star formation.  Its nickname once came from its resemblance to the spider itself, but in Webb’s view the overall region takes on the appearance of a tarantula’s home – a burrow lined with its own spun silk.  The Tarantula Nebula shelters thousands of you and still-forming stars, many revealed by Webb for the first time. 

At only 161,000 light-years away in the Large Magellanic Cloud galaxy, the Tarantula Nebula is the largest and brightest star-forming region in the Local Group, the galaxies nearest our Milky Way. It is home to the hottest, most massive stars known. Astronomers focused three of Webb’s high-resolution infrared instruments on the Tarantula. Viewed with Webb’s Near-Infrared Camera (NIRCam), the region resembles a burrowing tarantula’s home, lined with its silk. The nebula’s cavity centered in the NIRCam image has been hollowed out by blistering radiation from a cluster of massive young stars, which sparkle pale blue in the image.

The region takes on a different appearance when viewed in the longer infrared wavelengths detected by Webb’s Mid-infrared Instrument (MIRI). The hot stars fade, and the cooler gas and dust glow. Within the stellar nursery clouds, points of light indicate embedded protostars, still gaining mass. While shorter wavelengths of light are absorbed or scattered by dust grains in the nebula, and therefore never reach Webb to be detected, longer mid-infrared wavelengths penetrate that dust, ultimately revealing a previously unseen cosmic environment. 


100 Years of Public Evening Lectures


Lavinia Steward made her historic contribution of $60,000 to the University of Arizona “…TO BUY TELESCOPE OF HUGE SIZE,” on October 18, 1916.  However, the United States entry into World War I delayed the construction of the Steward Telescope and its 36-inch mirror.  That original Steward Telescope was finally used for the first time on July 17, 1922.  It would take another 9 months before the Steward Observatory and Telescope would be formally and officially dedicated on April 23, 1923.

The Telescope, however, was ready to be used before the official dedication date and Prof. Andrew Ellicott Douglass, the first Director of Steward Observatory, did not leave the telescope idle. He invited members of the campus and Tucson communities to view the wonders of the night sky through this new, large (for the time) telescope.  The date was September 28, 1922, and the Steward Observatory Public Evenings were born.

We are thrilled to able to celebrate 100 years of presenting lectures on astronomy and telescope viewing to the public by offering a special Public Evening Lecture on the 100th Anniversary of the very first Steward Public Evening.  


Lecture Information - Fall 2022 - Mark Your Calendars!


Monday, September 19

100 Years of Steward Observatory

Dr. Thomas Fleming and Dr. Buell Jannuzi, Steward Observatory


Wednesday, September 28 - Celebrating 100 Years!

The Webb Telescope: Starting Steward Observatory's Next 100 Years

Dr. Marcia Rieke, Regents Professor, Dr. Elizabeth Roemer Endowed Chair, Steward Observatory


Monday, October 3

Imaging Black Holes with the Event Horizon Telescope

Dr. Daniel Marone, Steward Observatory


Monday October 17

Floating Above Antarctica: The GUSTO Mission

Dr. Christopher Walker, Steward Observatory


Location:  Steward Observatory N210

Doors open at 7:00 pm and Lectures begin at 7:30 pm MST

Nearest parking 2nd Street or Cherry Ave Garage

Telescope viewing follows at 8:30 PM - Weather Permitting


In-Person or Watch via NEW ZOOM link


UA Astronomer, Dr. George Rieke, comments on new James Webb Space Telescope images

Regents' Professor George Rieke, the Science Lead for the JWST MIRI Instrument, gives us his view of the first images from JWST:

"It is gratifying to see how the first images and results from the James Webb Space Telescope have swept the world and given so many people a respite from humanity’s problems. If it is possible, it is even more gratifying to the teams at Steward Observatory who have been working and supporting the development of two of the four instruments on Webb – the Near Infrared Camera (NIRCam) and the Mid-Infrared Instrument (MIRI). Our roles in these instruments began more than twenty years ago for a few now-grizzled veterans, and as long as ten years ago for the many young astronomers who joined us. They took a huge gamble with their early careers by investing their energies in something with an uncertain and, on their timescale, far future payoff. But it has worked out for them, and amazingly well since the Webb observatory is working even better than predicted.

“Our” instruments showed what they can do in the Early Release Observations. NIRCam provided the ultra-deep image of the sky centered on a massive cluster of galaxies. It shows intriguing arcs of galaxies far behind the cluster, whose light has been bent by the gravitational field of the cluster and concentrated toward our direction. This is a foretaste of the large program we will be conducting over the next year to search for proto-galaxies back toward the birth of the Universe.

Both NIRCam and MIRI were featured in the image of the Stephan’s Quintet – five galaxies, of which four are interacting and in the process of merging. The image by MIRI shows spectacularly the flocculent structure of the interstellar gas and dust in one of the galaxies, and is symbolic of the new perspectives that this instrument will provide by observing at longer wavelengths than NIRCam.

The Southern Ring highlights both instruments. Although this planetary nebula is 2000 light years away, NIRCam resolves details as small as the Solar System, a foretaste of the incredible detail Webb will show us for everything it looks at. Both images, but particularly that from MIRI, reveal complex scallops of dusty shells. These were thrown off as a star went unstable and pulsated while gravity pulled it to its ultimate demise, with only its core surviving as a faint white dwarf star in the center of the nebula."

Young Stars in Dwarf Objects in a Hostile Galaxy Cluster Environment

Steward Postdoctoral Research Associate Michael Jones and Associate Professor David Sand have identified five instances of a new type of stellar system. You can see three images HERE and HERE and HERE. They are around a million times less massive than our galaxy, likely containing only 10,000 to 100,000 stars, which are arranged in a clumpy and irregular configuration. These systems, colloquially referred to as "blue blobs", are dominated by young, blue stars, yet are surprisingly isolated, typically over 300,000 lightyears from the nearest plausible parent galaxy. Furthermore, all five reside in the nearby Virgo galaxy cluster (approximately 50 million lightyears away). Galaxy clusters are filled with hot ionized gas at millions of degrees, making them an extremely hostile environment for the cold gas that is needed to form new stars. Even relatively large galaxies, similar in mass to our own Milky Way, rapidly lose their cold gas content after falling into a galaxy cluster. Yet these tiny "blue blobs" are floating alone, embedded in this hostile, hot medium, and are actively forming new stars. This raises the questions, where did they come from and how did they manage to become isolated while still so young.

To answer these questions Dr. Jones,  Prof. Sand and Professor Kristine Spekkens (RMC, Kingston, Ontario) obtained Hubble Space Telescope and Very Large Array imaging of these systems, as well as observations with the Very Large Telescope in Chile, in collaboration with Dr. Michele Bellazzini (INAF, Bologna, Italy). These observations indicated that the "blue blobs" are rich in heavy elements, which is strong evidence that they formed from gas stripped from a large galaxy that had accumulated these elements as it built up its stellar mass over a long history. Material can be stripped from galaxies in two main ways, tidal stripping and ram pressure stripping. Tidal stripping occurs when two galaxies pass close by each other (or even merge) and their gravity pulls apart their outskirts, resulting in long tails of stripped material. Ram pressure stripping occurs when a galaxy moves rapidly through a gas medium, which forces its own gas out behind it. In either scenario, stripped gas clouds can collapse and form new stellar systems, analogous to "blue blobs." However, ram pressure stripping when galaxies fall into a cluster can occur at very high velocity (higher than can be achieved with tidal stripping) and this offers an explanation for how such young objects can be so isolated; they are just moving at very high speeds, perhaps over 500 miles per second.

These results were presented on Wednesday June 15th at a AAS 240 press briefing, and an accompanying UA press release. Check these out for more details.

Recent Advanced Degrees at Astronomy/Steward

Since May 1, 2022, three Astronomy grad students have received Doctorates: Katrina Litke Marslender on May 3, Ryan Endsley on May 18, and Minghao Yue on May 19. 

Photos can be seen HERE, HERE, and HERE. Congratulations to all of you, we are proud of you.

Also, in May, 2022, Hector Rico of the Department Office received  his Master's degree in Public Health with an emphasis in Health Services Administration. A photo of a celebration in the Dept. Office can be seen HERE.



For the public
For Public

Public events include our Monday Night Lecture Series, world-reknowned Astronomy Camp and Mt Lemmon Sky Center.

For Students

A good place to start if you want to become an undergrad major or grad student, or need to find our schedule of classes.


For Scientists
For Scientists

Find telescopes and instruments, telescope time applications, staff and mountain contacts, and faculty and staff scientific interests.