What the Extra Bands Actually Are
Retrospective coverage note: the photograph described here was captured in 2018 along the Jersey Shore, after the remnants of Hurricane Florence had passed through. NASA's Astronomy Picture of the Day featured it on October 4, 2026. This article reviews that APOD feature and explains the physics behind the image; it is not breaking news about a new event.
On October 4, 2026, NASA's Astronomy Picture of the Day featured a photograph by John Entwistle titled "Supernumerary Rainbows over New Jersey." The image shows not just one rainbow but a stack of faint, extra bands nested inside the main arc, described in the APOD text as a "hall of rainbows." According to the same APOD text, at least five supernumerary bows were captured in the single shot, fading in and out over roughly half an hour as the Sun broke through after the remnants of Hurricane Florence had moved past the Jersey Shore in 2018.
That number comes from the APOD text and the photographer's account, not from an independent measurement. What is independently verifiable is the physics: supernumerary rainbows are a well-documented optical phenomenon, and their cause is one of the classic pieces of evidence that light travels as a wave.
A photograph can be striking without being mysterious. This one is interesting precisely because the extra bands are not a camera artifact or an editing trick. They are a reproducible consequence of how light behaves inside raindrops, and they appear only under fairly narrow conditions.
Supernumerary rainbows form only when the falling water droplets are all nearly the same size, and typically less than a millimeter across. Under ordinary rain, droplets vary widely in size, and the subtle extra bands blur away. After a hurricane, the drizzle that follows can be unusually uniform, which is exactly the condition needed. The APOD explanation links this droplet-size condition to an external optics reference (atoptics.org.uk), which describes the same requirement.
The mechanism is interference. Inside each raindrop, sunlight reflects and refracts, and light that follows slightly different paths through slightly different droplets arrives with slightly different timing. Because light is a wave, those overlapping rays can reinforce each other in some places and cancel in others, producing thin bands of extra color just inside the main rainbow, with colors in reversed order relative to the primary bow.
A simple analogy: drop a stone into a still pond and watch the ripples spread. If two sets of ripples overlap, crests meeting crests make a taller wave, while crests meeting troughs flatten out. Light does the same thing, but with electromagnetic waves instead of water. Where the light waves arriving at your eye reinforce, you see a bright band; where they cancel, you see a gap. Ordinary rainbows can be explained with simple ray tracing, treating light as straight lines bending at surfaces. Supernumerary bows cannot. They are a signature that light is not just a ray but a wave.
Historically, this mattered. In the early 1800s, when scientists such as Thomas Young were arguing about whether light was a stream of particles or a wave, the observed existence of supernumerary bows was treated as early evidence in favor of the wave picture. Ray optics alone cannot produce those faint extra bands; wave interference can, and the prediction matched what observers saw in the sky.
This is the same physics that underlies everyday technology. Interference and wave optics are the working principles behind anti-reflective coatings on eyeglasses, the resolution limits of microscopes, the behavior of light inside fiber optic cables, and the diffraction gratings used to separate wavelengths in spectrometers. When a rainbow shows supernumerary bands, it is demonstrating, for free and at planetary scale, a wave phenomenon that engineers rely on daily.
There is a modest practical takeaway for a sky watcher. If you notice faint green, violet, or pink bands just inside a rainbow's main arc, you are likely looking at very small, very uniform droplets, often from drizzle or lingering post-storm moisture, rather than heavy rain. The rainbow is encoding information about the droplets that produced it: nearly uniform droplets give crisp, multiple supernumerary bands, while a mix of droplet sizes gives a smooth, featureless arc. Meteorologists and atmospheric optics enthusiasts use this kind of visual cue, alongside more precise instruments, to infer droplet characteristics.
It is worth being precise about what is established and what is not. The photograph itself is the primary evidence: Entwistle's image as featured by NASA's APOD, dated October 4, 2026. The claim that at least five supernumerary bows were captured, and that they faded in and out over about half an hour, comes from the APOD text and the photographer's account, which APOD presents as a description of the featured image rather than as an independently verified measurement. The underlying physics, that supernumerary rainbows require nearly uniform sub-millimeter droplets and arise from wave interference inside raindrops, is well-established science supported by multiple references including the atmospheric optics resources linked from the APOD page itself.
No independent count of the bows in the photograph was performed for this article. The historical claim about the early 1800s, that supernumerary bows were treated as early evidence of light's wave nature, is a standard account in optics history, consistent with the APOD explanation and with the broader historical record on Thomas Young and wave optics.
APOD's explanation, retrieved from the primary NASA page on October 4, 2026, states in part:
Yes, but can your rainbow do this? After the remnants of Hurricane Florence passed over the Jersey Shore, New Jersey, USA in 2018, the Sun came out in one direction but something quite unusual appeared in the opposite direction: a hall of rainbows. Over the course of the next half hour, to the delight of the photographer and his daughter, vibrant supernumerary rainbows faded in and out, with at least five captured in this featured single shot.
Supernumerary rainbows only form when falling water droplets are all nearly the same size and typically less than a millimeter across. Then, sunlight will not only reflect from inside the raindrops, but interfere, a wave phenomenon similar to ripples on a pond when a stone is thrown in. In fact, supernumerary rainbows can only be explained with waves, and their noted existence in the early 1800s was considered early evidence of light's wave nature.
Attribution: NASA Astronomy Picture of the Day, "Supernumerary Rainbows over New Jersey," dated October 4, 2026, page credit "Credit & Copyright John Entwistle," with authors and editors Robert Nemiroff, Jerry Bonnell, Cecilia Chirenti, and Keighley Rockcliffe. The page is a service of the Astrophysics Science Division at NASA Goddard Space Flight Center, NASA Science Activation, and Michigan Technological University. The APOD page itself reserves copyright for the image to the photographer; the wave-optics explanation quoted above is from APOD's written explanation text, not a direct quote from the photographer.
For readers who want to see the phenomenon for themselves: watch for rainbows during or shortly after light, uniform drizzle, especially in the hour after a storm clears. Look just inside the main arc for faint, closely spaced extra bands. If you see them, you are seeing direct visual evidence that light travels as a wave, the same wave behavior that makes modern optics possible.
Why Uniform Droplets Matter
Supernumerary rainbows are not a separate kind of bow so much as a sharpened version of an ordinary one. Both form when sunlight enters a raindrop, reflects once off the back surface, and exits toward the observer, concentrated in a bright arc about 42 degrees from the antisolar point. What makes the supernumerary version special is that the droplets doing the concentrating are nearly identical in size. When droplet sizes match, the slightly different path lengths of light through neighboring drops produce a clean, repeating interference pattern: thin bands of color just inside the main arc, each with colors reversed relative to the primary bow. When droplet sizes vary, these interference fringes from different-sized drops overlap and wash out, which is why heavy, mixed-size rain usually produces a smooth arc with no visible extra bands.
The name reflects a historical habit of treating these extra bows as additional or surplus arcs beyond the standard primary and secondary bows, though physically they are interference fringes rather than independent bows formed at a different angle. Their appearance and spacing carry information about droplet size: tighter, more closely spaced fringes correspond to smaller, more uniform droplets. This is a well-documented relationship in atmospheric optics, described in detail by the atmospheric optics reference linked from the APOD page itself.
It is worth being clear about what is established and what is not. The photograph is primary evidence: Entwistle's image as featured by NASA's APOD. The count of at least five supernumerary bows and the half-hour fading description come from the APOD text and the photographer's account, not from an independent measurement for this article. The physics of supernumerary bows as interference effects requiring nearly uniform sub-millimeter droplets is well-established science, supported by the atmospheric optics references APOD links to and by standard optics literature. The historical claim about the early 1800s, that supernumerary bows were treated as early evidence of light's wave nature, is a standard account consistent with the APOD explanation and the broader history of wave optics, notably the work associated with Thomas Young.