What Is a Sun Halo? The Ring Around the Sun Explained
Ever seen a ghostly ring around the Sun? Read what they're all about and why they form.
Quick Reference
- What it is: a ring of pale rainbow light around the sun, caused by ice crystals in high cirrus clouds.
- Angle: 22 degrees from the sun (the most common halo). A wider 46-degree halo is rare.
- Color order: red on the inside, blue on the outside.
- Forecast clue: sun halos usually mean rain or snow within 12 to 24 hours. Old lore says: “A ring around the sun or moon means rain or snow is coming soon.”
- Cousin: sundogs (parhelia), bright patches that sometimes appear on the halo to the left and right of the sun.
A sun halo is the pale, ghostly rainbow ring that sometimes appears around the sun. It is one of the most striking sky phenomena you can see without a telescope, it is harmless to look at if you keep the sun blocked, and it is a reliable forecast for rain or snow within a day. Here is what causes it, what to look for, and how the old weather lore lines up with modern meteorology.
What Causes a Sun Halo
A sun halo is caused by sunlight passing through millions of tiny ice crystals suspended in thin, high cirrus or cirrostratus clouds. Cirrus and cirrostratus clouds form between 20,000 and 40,000 feet up, where the air is cold enough year-round for ice to form. The crystals in these clouds are hexagonal, six-sided columns. When sunlight enters one face of the crystal and exits another, it bends. The bending is called refraction. Different colors of light bend by slightly different amounts, which spreads white sunlight into its component colors the same way a prism does.
The geometry of a hexagonal ice crystal forces most of the bent light to come out at a 22-degree angle from the original ray. Multiply that across millions of randomly oriented crystals and the result is a ring of light at 22 degrees from the sun, with red on the inner edge (least bent) and blue on the outer edge (most bent). The halo looks pale because most of the light passes through the cloud without being refracted, so the inside of the ring is brighter than the outside, and the colored edge is faint compared to a true rainbow.
The 22-Degree Halo (and Its Rare 46-Degree Cousin)
The standard sun halo is the 22-degree halo. Twenty-two degrees is roughly the angle covered by your outstretched hand at arm’s length, fingers spread. If you cover the sun with your thumb, the ring should sit just outside your pinky finger.
A second, rarer halo can sometimes appear at 46 degrees from the sun. The 46-degree halo is fainter, larger, and harder to spot. It is caused by light passing through the ice crystals at a different geometry (entering one end of the hexagonal column and exiting through a side face). The 46-degree halo shows up only when the crystals are particularly well-aligned and the cloud cover is thin and uniform. Most readers will go years without ever seeing one.
Sundogs (Parhelia): The Halo’s Bright Cousins
Sometimes a sun halo appears with a pair of bright spots on it, one to the left of the sun and one to the right. Those bright spots are called sundogs. The scientific name is parhelia, from the Greek words meaning “beside the sun.” A single one is a parhelion. Sundogs are caused by the same ice crystals as the main halo, but they form when the crystals are oriented horizontally rather than at random angles, which concentrates the refracted light into the two bright patches at the same height as the sun.
Sundogs are most common in winter, when the cold air higher up extends down to lower altitudes and the ice crystals can form closer to the surface. They are most striking near sunrise and sunset, when the sun sits low and the sundogs flare brightly on either side. The full halo plus a pair of sundogs together is one of the great sights of cold-weather sky-watching.
What a Sun Halo Forecasts
Cirrus and cirrostratus clouds, the clouds that produce sun halos, almost always show up at the leading edge of an approaching warm front. Warm fronts bring rain or snow within 12 to 24 hours of the cirrus clouds passing overhead. That is the science behind the old weather lore couplet:
A ring around the sun or moon
means rain or snow is coming soon.
The reading is reliable. Studies of weather lore against National Weather Service data show the halo-precedes-rain pattern holds true the majority of the time, especially in fall, winter, and spring. In summer the rule is less consistent because cirrus clouds can also drift in ahead of dry weather systems. As a household rule of thumb, a halo in the afternoon or evening means tomorrow will probably be wet.
The same physics works at night. A ring around the moon is the lunar version of the sun halo, formed by the same ice crystals refracting moonlight. The forecast meaning is the same: rain or snow within a day. See our fuller piece on moonbows and lunar halos for the night-sky equivalents.
How to See and Photograph a Sun Halo Safely
The biggest practical issue with sun halos is that you have to look toward the sun to see them. Looking directly at the sun for more than a moment can damage your eyes. Use this method instead:
- Block the sun with your hand, a streetlamp, a tree, or a building edge.
- The halo sits 22 degrees out from the sun, so once you have the sun blocked you should see the ring around your hand or the tree.
- Sunglasses help with general sky brightness but they are not a substitute for blocking the sun directly.
- For photographs, hold up a finger or use the edge of a building to occlude the sun, and shoot in the direction of the halo. Most modern phone cameras handle the dynamic range well enough to capture the ring.
Best times of year for sun halos in most of the country are late autumn through early spring, when the upper atmosphere stays cold enough to produce ice crystals at lower altitudes. In the warmer months you still get them, but you need higher cirrus clouds and the halos tend to be fainter.
Other Halos and Optical Phenomena to Watch For
The 22-degree halo is the most common, but the same physics produces a whole family of less common sky-optics events. Once you start watching, you start spotting them.
- Circumzenithal arc: a smile-shaped rainbow high overhead, sometimes called an “upside-down rainbow.” It is the brightest of the rare halos.
- Sun pillar: a vertical column of light extending up or down from the sun, usually at sunrise or sunset. Caused by ice crystals reflecting (not refracting) sunlight.
- Tangent arcs: bright arcs that touch the top or bottom of a 22-degree halo, formed by horizontally-oriented crystals.
- Light pillars: at night in very cold weather, vertical columns of light over streetlamps or other ground lights, the artificial-light equivalent of a sun pillar.
For more on the physics and folklore of sky optics, see our pieces on sun dogs and sun halos, sun pillars, rainbows, and the green flash.
Reading the Sky Today
A sun halo is the easiest piece of weather forecasting most readers can do without any equipment. Spot the ring, count on rain or snow within a day, and plan accordingly. The Farmers’ Almanac long-range forecast covers the broader patterns months ahead, but the halo is the in-the-moment confirmation that the front you saw on tomorrow’s forecast is on its way.
Watch the sky. Read the ring.
Frequently Asked Questions
What is a sun halo?
A sun halo is a ring of pale rainbow light around the sun, caused by sunlight refracting through hexagonal ice crystals in high cirrus or cirrostratus clouds. The ring sits 22 degrees from the sun. Red is on the inner edge and blue on the outer.
Does a sun halo really mean rain is coming?
Usually yes. Sun halos form in cirrus and cirrostratus clouds, which almost always sit at the leading edge of an approaching warm front. Warm fronts bring rain or snow within 12 to 24 hours. The old saying about a ring around the sun or moon meaning precipitation soon is a reliable rule of thumb in fall, winter, and spring.
Why are sun halos circular?
Because the hexagonal geometry of ice crystals refracts sunlight at a fixed 22-degree angle in every direction around the sun. Multiply that bending across millions of crystals at random orientations and you get a complete circle around the sun at exactly 22 degrees out.
How is a sun halo different from a rainbow?
Two differences. First, the medium: rainbows are made by water droplets in low rain showers; sun halos are made by ice crystals in high cirrus clouds. Second, the position: a rainbow appears opposite the sun in the sky; a sun halo appears around the sun. Sun halos are also paler and have less vivid colors.
What is a sundog?
A sundog (scientific name parhelion) is a bright spot that sometimes appears on a sun halo, one to the left and one to the right of the sun. Sundogs are made by the same ice crystals as the halo, but oriented horizontally so the refracted light concentrates into bright patches. They are most common in winter near sunrise and sunset.
Can I look directly at a sun halo?
Looking at the halo itself is fine, but looking directly at the sun for more than a moment will damage your eyes. Block the sun behind your hand, a streetlamp, a tree, or a building edge first, then look at the ring around it. The halo sits 22 degrees from the sun, roughly the width of your outstretched hand at arm’s length.
Is a moon halo the same thing as a sun halo?
Yes. A moon halo is the night-sky version of the sun halo, caused by moonlight refracting through the same kind of ice crystals in high cirrus clouds. The forecast meaning is the same: rain or snow within a day. Moon halos are most visible during a full or near-full moon, when the moon is bright enough to produce a clearly defined ring.
This article was published by the Staff at FarmersAlmanac.com. Any questions? Contact us at questions@farmersalmananac.com.
- Farmers' Almanac Staff
- Farmers' Almanac Staff
- Farmers' Almanac Staff
- Farmers' Almanac Staff
Took a photo today of this sun halo — I’m in Arizona.
just seen my first sundog-it is beautiful=took several pictures-does anyone know what it means??
I just saw my first Hal8 rainbow yesterday on August 4, 2025 in Indiana. It was my nephew’s 1 yr death anniversary and a heavenly birthday for my mother in law.
This was gorgeous 😍
Just saw a partial halo with a sun dog..
Saw a Hali yesterday. June 22
This was yesterday over Roseburg Oregon.
WOW – gorgeous!!!!
6/11/24 over MI
Taken in west Tn 5-5-24
Port Orchard, WA, 2:42 pm
WOW! Gorgeous!!
From this morning El Paso tx
This is gorgeous!! Thank you for sharing with our community!