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Science | Edge Cases Science | Earth, Water, Atmosphere & Celestial World
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The Glory

Why Coloured Rings Can Form Around Your Shadow on a Cloud

Big Question: Why does light scattered almost directly backward by cloud droplets organise into coloured concentric rings instead of a featureless bright patch?

Quick Answer

A glory forms close to the antisolar point—the direction exactly opposite the Sun. Sunlight encounters many small spherical droplets in cloud or fog. Their scattering is strongly wavelength- and size-dependent. Near the backward direction, wave-optical contributions interfere and can produce enhanced backscattering in rings whose colours and angular size depend on droplet size distribution.

NASA describes glories as coloured rings formed when water droplets scatter sunlight back toward the light source. More detailed physical descriptions require wave scattering rather than a single geometric-optics ray path, which is why glories differ from ordinary rainbows.

NASA — A Slice of Glory →

What You Will Learn

• Where the antisolar point is.
• Why the observer’s own shadow often marks the centre.
• Why glories need small cloud or fog droplets.
• Why a glory is not simply a small rainbow.
• How scattering differs from refraction through one raindrop.
• Why wave interference matters near exact backscattering.
• How droplet size controls ring diameter.
• Why narrow droplet-size distributions make clearer rings.
• How aircraft, mountain and satellite views differ.
• What a Brocken spectre is and why it is not the same phenomenon.
• How polarisation can help test scattering models.
• Why the full microscopic mechanism is richer than one classroom ray sketch.

Part 1 — Find the Antisolar Point

Draw a line from the Sun through your head and continue it forward into the sky or cloud below you. The opposite direction from the Sun is the antisolar point.

Your shadow lies along this direction, which is why glories are often centred around the observer’s shadow rather than somewhere arbitrary in the cloud.

Part 2 — Why the Ordinary Rainbow Model Fails

A primary rainbow is commonly explained using refraction into a raindrop, internal reflection and refraction back out. Its angular geometry places the bow tens of degrees from the antisolar point.

A glory is much closer to exact backward scattering and often spans only a few degrees. It therefore belongs to a different scattering regime.

If you use only the familiar rainbow ray path, the ring spacing and intense near-backward return are not explained properly.

Part 3 — Small Droplets Turn Light Into a Wave-Scattering Problem

Cloud droplets are often only tens of micrometres across. Their size is not enormously larger than visible wavelengths.

That means diffraction and interference cannot be ignored. The scattered electromagnetic field from a spherical droplet contains many wave contributions whose phases depend on wavelength, droplet radius and scattering angle.

Part 4 — Why Backscattering Can Be Enhanced

Near the backward direction, different scattering paths can arrive with phase relationships that reinforce selected angles while weakening others.

The result is not one bright point but a structured angular pattern. Different wavelengths peak at slightly different angles, producing coloured concentric rings.

Laboratory studies have also observed glory-like optical backscattering from spherical bubbles, confirming that the geometry belongs to a broader wave-scattering problem rather than to atmospheric mythology.

Physical Review Letters — Glory in Optical Backscattering From Air Bubbles →

Part 5 — Droplet Size Controls the Pattern

The relevant dimensionless comparison is droplet size relative to wavelength.

Smaller droplets generally produce broader angular scattering structures; larger droplets can make tighter rings. If cloud droplets cover a very wide size range, slightly different ring systems overlap and blur.

A glory can therefore reveal something about the microphysical uniformity of a cloud layer.

Part 6 — Why Colours Appear in the Opposite Order From Some Other Atmospheric Effects

Each wavelength has its own scattering phase and angular response. Red and blue light therefore peak at slightly different positions.

NASA descriptions commonly note red on the outside and bluer colours toward the centre in visible glories. The exact appearance depends on droplet size distribution and viewing conditions.

Part 7 — Why Your Shadow Seems Special

The glory is not physically attached to one person’s body.

Each observer sees the antisolar direction from their own line of sight. Two people separated by some distance can therefore see glories centred on their own respective shadow directions.

The phenomenon is observer-centred because the required scattering angle is defined by the Sun–droplet–observer geometry.

Part 8 — Glory vs Brocken Spectre

A Brocken spectre is the enlarged shadow of an observer projected onto nearby cloud or mist, often distorted by perspective and moving fog.

A glory may surround that shadow, but the shadow geometry and the coloured backscattering rings are different jobs.

shadow enlargement ≠ coloured-ring scattering mechanism.

Part 9 — Aircraft and Satellites See Different Slices

An aircraft passenger can sometimes see nearly complete rings around the aircraft shadow on clouds below.

A satellite sensor samples a different viewing geometry. NASA’s MODIS imagery can show portions of the glory as coloured bands rather than a full circle because the instrument views only part of the angular scattering pattern at each location.

NASA Earth Observatory — A Slice of Glory →

Part 10 — Failed Model → Better Model

Naive model	Why it fails	Better model
It is just a small rainbow.	The angular location and scattering geometry are different.	Use near-backward wave scattering by droplets.
Each colour follows one simple ray.	Ring structure depends on interference among wave contributions.	Use a wave-scattering model.
The glory belongs to the shadow.	Each observer has their own antisolar direction.	Track observer–Sun geometry.
Any cloud should show sharp rings.	Droplet size distribution and optical depth can blur them.	Include cloud microphysics.

How Do We Know?

• Photograph ring radius at known wavelength bands.
• Compare aircraft geometry with the antisolar direction.
• Use cloud droplet probes to measure size distributions.
• Compare observed colours with electromagnetic scattering calculations.
• Measure polarisation of the backscattered light.
• Reproduce glory-like scattering with controlled spherical droplets or bubbles.
• Use satellite observations to test how ring structure varies across cloud fields.

Observation vs Inference

• Observation: coloured rings occur near the antisolar direction in fog or cloud.
• Measurement: ring size changes with droplet-size distribution and wavelength.
• Inference: coherent wave scattering and interference create the angular ring structure.
• Boundary: simple one-ray stories are pedagogical approximations; quantitative glory theory uses full electromagnetic scattering or related asymptotic descriptions.

Checkpoint Questions

1. What is the antisolar point?
2. Why is a glory often centred on your shadow?
3. Why is it not an ordinary rainbow?
4. Why do cloud droplet sizes matter?
5. Why does interference create coloured rings?
6. Why can a broad size distribution blur the pattern?
7. What is the difference between a glory and a Brocken spectre?
8. Why can two observers see different glory centres?
9. How can a satellite see only part of the ring system?
10. What measurement would test a scattering model?

Answers

Open after attempting the questions

1. The direction exactly opposite the Sun from the observer.
2. The observer’s shadow lies along the antisolar direction.
3. Its angular geometry and wave-scattering mechanism differ from primary-rainbow refraction/reflection.
4. Scattering depends strongly on size relative to wavelength.
5. Different wave contributions reinforce at selected angles and wavelengths.
6. Different droplet radii produce overlapping ring spacings.
7. The spectre is the projected shadow; the glory is the coloured scattering pattern.
8. Each has a different Sun–observer line.
9. Its viewing geometry samples only part of the angular pattern.
10. Ring radius, wavelength dependence, polarisation and independently measured droplet sizes.

Primary Science Bridge

• light can be scattered by tiny droplets;
• colour depends on wavelength;
• shadows depend on light direction;
• the same object can look different from different viewpoints;
• not every rainbow-like colour pattern is a rainbow.

Secondary → JC Bridge

• diffraction and interference;
• Mie-scale electromagnetic scattering;
• polarisation;
• angular scattering functions;
• droplet-size distributions;
• remote sensing of clouds.

Unfamiliar Transfer Challenge

A sensor sees a coloured backscatter ring from a spray of nearly equal droplets in a laboratory chamber. Do not call it a rainbow merely because colours are present. Measure scattering angle, droplet radius and wavelength dependence, then ask whether the structure is a glory-like backscattering pattern.

Edge Resolution — The Simple Ray Picture Stops Too Early

Atmospheric optics is full of phenomena that can be partly sketched with rays. The glory is a useful boundary case because quantitative prediction requires wave optics. Its rings are not an embarrassment to ray optics; they are a sign that the wavelength of light and the scale of the scatterer have become inseparable.

Public-Safe eduKateAI Direction Routes

• If the learner asks “why around my shadow?” → route to the antisolar point.
• If the learner asks “is it a rainbow?” → compare angular geometry and scattering mechanisms.
• If the learner asks “why rings?” → route to diffraction/interference in backscattering.
• If the learner asks “what changes the size?” → route to droplet radius relative to wavelength.

Evidence Boundaries

• Glory ≠ ordinary rainbow.
• Brocken spectre ≠ glory.
• One ray path ≠ full quantitative mechanism.
• Visible rings ≠ identical droplet size.
• Observer-centred geometry ≠ phenomenon physically attached to the observer.

Manual Summary — KNOW → CONNECT → EXPLAIN → APPLY → CHECK

KNOW: antisolar point, scattering, droplet, diffraction, interference, polarisation.

CONNECT: droplet size to wave scattering and wave scattering to coloured backscattering rings.

EXPLAIN: why a cloud can form coloured rings around an observer’s shadow direction.

APPLY: distinguish a glory from rainbow, halo and shadow phenomena.

CHECK: locate the Sun and antisolar point before naming the effect.

Research Sources and Further Reading

• NASA — A Slice of Glory
• NASA Earth Observatory — A Slice of Glory
• Physical Review Letters — Glory in Optical Backscattering From Air Bubbles