Sky Oddities • Atmospheric Optics • Ice Crystal Phenomena
Sundogs, also called parhelia or “mock suns,” are bright patches of light that appear on one or both sides of the Sun. They form when sunlight passes through tiny plate-shaped ice crystals in the atmosphere, creating colorful sky spots that can look like extra suns.
TL;DR: What Are Sundogs?
Sundogs are atmospheric optical phenomena caused by sunlight refracting through flat, hexagonal ice crystals. They usually appear about 22 degrees to the left and right of the Sun, often as bright white or rainbow-colored patches when the Sun is low.
Why Does the Sun Sometimes Have Two Fake Companions?
Sundogs can look dramatic: two glowing lights flanking the Sun, sometimes linked by a faint halo, sometimes blazing like miniature suns on the horizon. They have inspired myths, omens and viral “two suns” claims, but the explanation is beautifully simple.
The atmosphere occasionally fills with tiny, flat ice crystals that drift like microscopic mirrors and prisms. When these crystals align horizontally, they bend sunlight toward the observer and create bright patches on either side of the Sun. The result is a parhelion — from Greek roots meaning “beside the Sun.”
What Causes Sundogs?
Sundogs form when sunlight enters one side of a plate-shaped hexagonal ice crystal and exits another side. This bending of light is called refraction. Because the crystals act like tiny prisms, they can also separate sunlight into colors.
- Ice crystals: usually flat, hexagonal plates in cirrus or cirrostratus clouds.
- Low Sun angle: sundogs are most visible near sunrise or sunset.
- Horizontal crystal alignment: falling plate crystals tend to float with their flat faces parallel to the ground.
- Refraction angle: sundogs often appear near the 22-degree halo position.
This is why sundogs often appear together with a faint circular halo around the Sun.
How to Recognize a Sundog
A sundog usually has several telltale features:
- It appears to the left or right of the Sun, not randomly anywhere in the sky.
- It is often located at roughly the same height as the Sun.
- It may show red on the side closest to the Sun and bluish-white light farther outward.
- It is most common when the Sun is low and high thin clouds are present.
- It may appear alone, as a pair, or with a 22-degree halo.
The easiest safe way to observe one is to block the Sun with a building, tree, pole or your hand and scan the sky on both sides of it.
Sundogs vs Halos vs Light Pillars
| Phenomenon | What It Looks Like | Main Cause | Where to Look |
|---|---|---|---|
| Sundog | Bright spot beside the Sun | Refraction through plate-shaped ice crystals | Left or right of the Sun |
| Solar halo | Ring around the Sun | Refraction through ice crystals with varied orientations | Around the Sun |
| Light pillar | Vertical beam above or below a light source | Reflection from flat ice crystals | Above the Sun, Moon or artificial lights |
| Circumzenithal arc | Upside-down rainbow high in the sky | Sunlight through plate crystals | High above the Sun |
Why Are Sundogs Sometimes Rainbow-Colored?
Sundogs can show color because ice crystals separate sunlight into different wavelengths. The red side usually faces the Sun, while blue or white light appears farther away. However, many sundogs look mostly white because the colors overlap or because the crystals are not perfectly aligned.
The brighter and more orderly the ice crystal layer, the sharper and more colorful the sundog can become.
Best Conditions for Seeing Sundogs
- Time of day: sunrise or sunset is best.
- Cloud type: thin cirrus or cirrostratus clouds.
- Temperature: ice must be present aloft, but the ground does not need to be freezing.
- Sun position: low Sun angles create stronger, more visible sundogs.
- Viewing safety: never stare directly at the Sun.
Why Sundogs Are Often Mistaken for UFOs, Portals or “Two Suns”
Sundogs can be surprisingly bright, especially when the Sun is hidden behind a cloud or building. This can make the side patches appear more mysterious than the real Sun itself. In photos and videos, they may look like glowing orbs, portals, extra suns or strange atmospheric lights.
But sundogs follow predictable geometry. If the bright object sits beside the Sun, at roughly the same height, and appears with thin high clouds or a halo, the culprit is probably ice crystal optics — not a second Sun sneaking into the solar system like a cosmic tax evader.
Sundogs & Parhelia FAQ
What is a sundog?
A sundog is a bright patch of light that appears beside the Sun when sunlight is refracted through plate-shaped ice crystals in the atmosphere.
What does parhelion mean?
Parhelion is the scientific term for a sundog. It means a bright optical phenomenon appearing beside the Sun.
Why do sundogs appear on both sides of the Sun?
Sundogs can appear on both sides because horizontally aligned ice crystals refract sunlight symmetrically to the left and right of the Sun.
Are sundogs rare?
Sundogs are not extremely rare, but many people miss them because they occur close to the bright Sun and are easiest to see when the Sun is blocked from direct view.
Can sundogs appear around the Moon?
Similar phenomena can occur around the Moon and are sometimes called moon dogs or paraselenae, but they are much dimmer because moonlight is weaker than sunlight.
Are sundogs a sign of bad weather?
Sundogs can appear in high clouds that may precede a weather system, but they are not a reliable storm warning by themselves.
