The Astronomy Picture of the Day (APOD) for September 13, 2026, features a breathtaking time-lapse video capturing Comet C/2020 F3 (NEOWISE) ascending majestically over the Adriatic Sea, an event originally recorded on July 8, 2020. This particular celestial display, documented by astrophotographer Paolo Girotti, offered a rare glimpse of one of the few comets visible to the unaided eye in the 21st century, solidifying its place in astronomical annals as the "Great Comet of 2020." The video, a compilation of over 240 images taken across 30 minutes, vividly illustrates the comet’s ascent through a foreground adorned with bright, undulating noctilucent clouds, set against a backdrop of distant stars, providing both scientific insight and profound aesthetic appeal.
The Astronomy Picture of the Day: A Window to the Cosmos
APOD, a daily service provided by NASA and Michigan Technological University, has served as a pivotal educational resource and public engagement platform since its inception in 1995. Each day, the initiative presents a different image or photograph of the universe, accompanied by a concise explanation penned by professional astronomers. This consistent delivery of high-quality astronomical content has cultivated a global audience, making complex scientific phenomena accessible to millions. The program’s longevity and widespread appeal underscore its critical role in fostering public interest in space science and astronomy. Robert Nemiroff and Jerry Bonnell, long-standing editors, along with Cecilia Chirenti and Keighley Rockcliffe, curate this daily offering, which remains a cornerstone of NASA’s public outreach efforts.
The feature of Comet NEOWISE on September 13, 2026, exemplifies APOD’s mission: to highlight significant astronomical events, celebrate exceptional astrophotography, and provide educational context. It also serves as a poignant reminder of transient celestial phenomena that captivate human imagination. Notably, the APOD platform itself is undergoing a significant transition, migrating its main NASA site from apod.nasa.gov to science.nasa.gov/apod, reflecting ongoing digital infrastructure updates within the agency. This migration aims to enhance accessibility and integration within NASA’s broader science communication ecosystem, ensuring that the daily exploration of the cosmos remains readily available to all.
Comet C/2020 F3 (NEOWISE): A Celestial Wanderer’s Journey
Comet C/2020 F3 (NEOWISE) earned its distinction as the "Great Comet of 2020" due to its exceptional brightness and prolonged visibility to observers across the Northern Hemisphere. Discovered on March 27, 2020, by astronomers using the Wide-field Infrared Survey Explorer (WISE) space telescope – specifically its NEOWISE mission extension – the comet quickly became a subject of intense scientific scrutiny and public fascination. Its discovery came as a welcome surprise, particularly during a period when many major public events were curtailed, offering a unique opportunity for collective observation and shared wonder.
NEOWISE is a long-period comet, believed to originate from the Oort Cloud, a vast theoretical shell of icy objects far beyond Neptune’s orbit. Its highly eccentric orbit suggests a journey that will not bring it back to the inner solar system for approximately 6,800 years. The comet reached its perihelion – its closest approach to the Sun – on July 3, 2020, at a distance of about 43 million kilometers (0.29 AU). This close encounter with solar radiation significantly increased its activity, causing volatile ice to sublimate rapidly, releasing copious amounts of dust and gas. This process formed the comet’s characteristic tails and dramatically enhanced its brightness, making it a naked-eye object.
Following perihelion, NEOWISE made its closest approach to Earth on July 23, 2020, passing at a distance of about 103 million kilometers (0.69 AU). During its peak visibility in early to mid-July, the comet displayed two distinct tails: a broad, diffuse dust tail, yellowish-white in color, composed of tiny dust particles pushed away from the Sun by radiation pressure; and a narrower, bluish ion (or plasma) tail, formed by ionized gas particles accelerated directly away from the Sun by the solar wind. These tails, emanating from a nucleus estimated to be around five kilometers in diameter, provided valuable data for scientists studying cometary composition and dynamics. The comet’s nucleus, a conglomerate of ice, dust, and rock, exhibited remarkable stability despite its close solar pass, contributing to its sustained brilliance.
Capturing the Dawn: Paolo Girotti’s Adriatic Masterpiece
The video featured in the September 13, 2026 APOD entry is a testament to the dedication and skill of astrophotographer Paolo Girotti. Taken on July 8, 2020, from Italy, it captures Comet NEOWISE rising over the tranquil waters of the Adriatic Sea. This particular timing, just before dawn, was crucial for observing the comet as it emerged from the twilight glow, offering a striking contrast against the brightening sky. Girotti’s choice of location, with the Adriatic Sea providing an unobstructed eastern horizon, further enhanced the visual drama of the celestial event.
The creation of such a time-lapse video requires meticulous planning and execution. Girotti combined over 240 individual exposures taken over a 30-minute period, carefully processing them to create a seamless visual narrative of the comet’s ascent. The technical challenges include managing varying light conditions from pre-dawn twilight, ensuring precise tracking if using a motorized mount, and post-processing to balance the brightness of the comet with the delicate structures of the noctilucent clouds and the faint background stars. The resulting video not only documents a scientific phenomenon but also stands as an artistic interpretation of the universe’s grandeur, showcasing the power of long-exposure photography and time-lapse techniques in astronomy.
The geographical context of Italy also adds a layer of cultural significance to the observation. Italy has a rich history of astronomical observation, dating back to ancient Roman and Renaissance scholars like Galileo Galilei. Modern Italian astronomers and amateur enthusiasts continue this legacy, contributing to global astronomical research and public engagement. Girotti’s photograph, therefore, is not just a personal achievement but also a continuation of a long tradition of sky-gazing from the Italian peninsula.
Noctilucent Clouds: Ethereal Guardians of the Upper Atmosphere
Adding another layer of visual and scientific interest to Girotti’s video are the bright, undulating structures of noctilucent clouds (NLCs), also known as "night-shining clouds." These are the highest clouds in Earth’s atmosphere, forming in the mesosphere at altitudes of about 76 to 85 kilometers (47 to 53 miles). Unlike tropospheric clouds, which are composed of water droplets or ice crystals, NLCs are made of tiny ice crystals that form around meteoric dust particles. They are typically observed during twilight hours in the summer months at high latitudes (between 50 and 70 degrees north or south) when the Sun is below the horizon but still illuminating these extremely high-altitude clouds.
The presence of NLCs in the foreground of the comet’s ascent is particularly noteworthy. Their ethereal, electric-blue appearance, often described as wavy or filamentous, provided a stunning terrestrial counterpoint to the celestial visitor. The increasing frequency and brightness of noctilucent clouds in recent decades have been a subject of scientific study, with some research suggesting a potential link to changes in atmospheric composition and temperature, possibly influenced by climate change. Specifically, increased methane emissions contribute to more water vapor in the upper atmosphere, which can lead to more frequent and brighter NLCs. Therefore, while visually spectacular, their presence also serves as a subtle indicator of ongoing atmospheric dynamics and global environmental shifts, adding a layer of contemporary scientific relevance to Girotti’s already compelling footage.
The Public’s Comet: Engagement and Outreach
Comet NEOWISE’s unexpected brilliance in 2020 ignited widespread public enthusiasm for astronomy across the globe. Unlike many faint telescopic objects, NEOWISE was accessible to millions with just their naked eyes, fostering a direct connection to the cosmos. Social media platforms became vibrant hubs for sharing photographs, viewing tips, and personal accounts of sightings, effectively transforming a scientific event into a global community experience. Professional observatories and amateur astronomy clubs alike reported a surge in public interest, with many hosting virtual viewing parties and online educational sessions.
This surge in public engagement underscores the profound impact that accessible astronomical phenomena can have on inspiring curiosity and promoting scientific literacy. For many, NEOWISE was their first encounter with a "Great Comet," leaving an indelible impression and potentially sparking a lifelong interest in STEM fields. The event served as a powerful reminder that the universe, with its endless wonders, is often just a glance away, providing moments of shared awe and scientific discovery for individuals from all walks of life. APOD played a crucial role in amplifying this engagement, offering daily explanations and featuring a diverse array of images submitted by both professional and amateur photographers, including Girotti’s now-iconic video.
Scientific Legacy and Future Comet Observations
Beyond its visual spectacle, Comet NEOWISE provided invaluable scientific data. Researchers utilized ground-based telescopes and space-based observatories, including NASA’s Hubble Space Telescope, to study its composition, dust production rates, and the dynamics of its tails. Spectroscopic analyses revealed the presence of various molecules, offering clues about the early solar system’s chemical makeup, as comets are often considered pristine remnants from the epoch of planetary formation. The observations helped refine models of cometary evolution and activity, particularly concerning how comets behave during their close approaches to the Sun.
The study of NEOWISE also contributed to the broader field of cometary science, which aims to understand the origins of water and organic molecules on Earth. The continuous monitoring of newly discovered comets, facilitated by missions like NEOWISE and ground-based surveys, remains critical for predicting potential future "Great Comets" and preparing for their scientific investigation. While no other comet has matched NEOWISE’s visibility since, the astronomical community remains vigilant, knowing that the Oort Cloud holds countless icy bodies, any one of which could someday embark on a similar spectacular journey through our inner solar system. The transient nature of such events underscores the importance of rapid response and dedicated observation when these rare opportunities arise.
The APOD Editorial Team and Collaborative Endeavor
The consistent excellence of the Astronomy Picture of the Day is a direct result of the dedicated work of its editorial team and the collaborative support of multiple institutions. Robert Nemiroff, a professor of physics at Michigan Technological University, and Jerry Bonnell, a senior research scientist at NASA’s Goddard Space Flight Center (GSFC), have been the primary architects of APOD since its inception. Their expertise ensures the scientific accuracy and educational value of each daily explanation. More recently, Cecilia Chirenti and Keighley Rockcliffe have joined the editorial ranks, contributing to the diversity and breadth of the content.
APOD is presented as a service of the Astrophysics Science Division (ASD) at NASA/GSFC, NASA Science Activation, and Michigan Technological University. This multi-institutional collaboration underscores the commitment to public science communication and education. NASA’s involvement provides institutional backing and access to cutting-edge research, while Michigan Tech contributes academic rigor and computational resources. This partnership ensures that APOD remains a trusted and authoritative source for astronomical information, continuing to inspire and educate new generations of skygazers and scientists alike.
The re-featuring of Paolo Girotti’s video of Comet NEOWISE on September 13, 2026, serves as a powerful reminder of the enduring beauty of our universe and the vital role that platforms like APOD play in bringing these wonders to a global audience. As APOD transitions to its new home on science.nasa.gov/apod, its mission to "Discover the cosmos!" remains steadfast, promising many more captivating glimpses into the fascinating universe that surrounds us. Tomorrow’s picture, as always, holds the promise of another open space, another mystery to unravel, and another opportunity for shared celestial wonder.
