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San Diego Phenomena

Phenomena in Science Education

Phenomena are the natural and man-made observable events that provide context for the work of scientists and engineers. Recent science standards changed the focus from learning about science to figuring out science. Phenomena are a powerful way to engage students and empower them to wonder and investigate.

Sometimes, we look too hard for the phenomenal events and miss the every-day occurrences that are just as intriguing. The list below is a constant work in progress and will be updated as new submissions are received and new occurrences are observed in and around San Diego County.

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Did you observe something that made you stop and wonder? Share your phenomena and any supporting material like photographs, videos or additional resources.

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King tides: high tide and low tide vary

Image: The Marine Room

While cycling into work one day, a staff member at San Diego Coastkeepers noticed that a section of the bikeway was under water. The cyclist hadn't seen water in this spot before and wondered what the cause was. 

The flooding was the result of a king tide. King tides are the highest of high tides that are naturally-occurring and predictable. The moon's position in relation to Earth is responsible for all tides, including king tides.

Why does the height of high tide vary? What is the relationship between the Moon and Earth that causes this variance? 


San Diego Coastkeepers: The King Tides Are Coming

NOAA: What is a King Tide?

California King Tides Project: Schedule of tides

NGSS & Grade

5-ESS1-2, ESS1.B: Earth and the Solar System

MS-ESS1-1, ESS1.B: Earth and the Solar System 

Monarch Butterflies migrate great distances

Image: Paul Mirocha

Each year, thousands of Monarch Butterflies choose San Diego as their overwintering site. In August, Monarchs arrive after traveling 1500 miles or more. Monarchs are known to return to the same location--and even the same tree--year after year. What makes this migration more amazing is that no single butterfly makes it more than once. Due to the short life-cycle of the butterfly, each migration is made by Monarchs three or four generations apart. 

What causes Monarchs to migrate in the first place? How do Monarch butterflies know when to migrate and how do the butterflies know to return to the same spots? How do butterflies, weighing less than an ounce, travel dozens of miles each day? 

The Fleet Science Center's film Flight of the Butterflies explores this migration and features the scientists who work to track them. Flight of the Butterflies is one of many films available for school group visits.  


Monarch Watch: Migration and Tagging

Paul Mirocha: Where do Monarch Butterflies Go?

NGSS & Grade:

K-LS1, LS1.C: Organization for Matter and Energy Flow in Organisms

K-ESS3-1, ESS3.A: Natural Resources

Green flash appears on the horizon


In the fleeting seconds just as the sun dips below the horizon, you may catch a brief green flash. This phenomenon, visible at both sunrise and sunset, is so famous yet so elusive in San Diego. Local restaurants and breweries have even adopted the name for their businesses. Sunset Cliffs in Point Loma is a popular location for spotting the green flash, although social media posts indicate it is visible from Ocean Beach, too. 

What causes the green flash? Why is it visible sometimes but not all the time? Popular sighting locations along Point Loma are above sea level -- does that vantage point make the green flash any easier to spot?


EarthSky: How to see a green flash

LA Times: Wait for the green flash on the Sunset Cliffs in San Diego

ABC News 10: Where to see a green flash in San Diego

San Diego Reader: San Diego's Green Flash Phenomenon

Times of San Diego: Rare green flash at sunset dazzles San Diego

NGSS & Grade:

MS-PS4, PS4.B: Electromagnetic Radiation

Air pollution spikes dramatically in July

Image: LA Times

On July 5, 2018, San Diegans received cell phone notifications warning of poor air quality in San Diego. Similar warnings went out in 2017 and 2016 around the same time.

The graph above from the LA Times was generated using 2017 data from the California Air Resource Board. The graph shows a dramatic jump in air pollution around Los Angeles, and graphs using data collected from air monitoring stations closer to San Diego show a similar spike.

  • What is the cause and effect relationship behind this pattern?
  • What human-made event is causing this impact on the environment?
  • Where does this air pollution go?
  • How can we balance holiday celebrations and care for the environment?

Resources:, California Air Resource Board

LA Times, Fourth of July brings some of the year's worst pollution, California

NGSS & Grade:

MS-ESS3-3, ESS3.C: Human Impacts on Earth Systems

Some rainbows are white

Image: Delinda, Ocean Beach Chronicle

Some rainbows are white and are called white rainbows or fogbows. The image above was captured in May 2018 near Ocean Beach in San Diego.

What do fogbows and rainbows have in common? What is different? What do you think might cause this difference? As the name implies, fogbows are the result of fog. When compared to rain, fog water droplets are much smaller, creating less diffraction and less visible color than rainbows. Fogbows can be completely white or contain faint traces of color. Many of the conditions necessary to create a rainbow, including the position of the sun (or light source), the viewer and the water droplets, are the same as with a fogbow.

Fogbows can be used to bridge physical science and earth science through the crosscutting concepts. 


Ocean Beach Chronicle, White Rainbow aka Fogbow

Popular Science, What the heck are white rainbows, and where do they come from?

Mashable, White rainbows are the phenomenon you've never heard of

NGSS & Grade

4-PS4-2, PS4.B: Electromagnetic Radiation

3-ESS2-1, ESS2.D: Weather and Climate

MS-ESS2-4, ESS2.C: The Roles of Water in Earth's Surface Processes



Rain disappears in mid-air

Image: NWS San Diego

When precipitation occurs, we expect to see and feel it on the ground. However, not all precipitation reaches the ground, and when this happens, we call it virga.

In August 2015, Jason Martinez from News 10 reported on virga in San Diego. Countless others have taken to social media to share rain that seemingly disappears as it falls to the ground. Of course, rain doesn't just disappear, it evaporates, and what we are witnessing is the mid-air evaporation of rain. This phenomenon can serve as an interesting entry-point into the water cycle and local weather.

What causes rain? Where does the rain go if it doesn't hit the ground? Why does virga happen sometimes but not others?


San Diego Union-Tribune, Rain falls on a sunny day

San Diego CBS 8, Matt's MicroClimate Definitions

NGSS & Grade

3-ESS2-1, ESS2.D: Weather and Climate

5-ESS2-1, ESS2.A: Earth Materials and Systems

MS-ESS2-4, MS-ESS2-5, ESS2.C: The Roles of Water in Earth's Surface Processes



Halos form around the Sun


In February 2017, this halo was spotted in San Diego and shared on Twitter. Halos are occasionally observed around the sun and moon. Halos are caused by ice crystals in high-altitude clouds and the appearance of a halo can indicate certain weather patterns.

Are halos like rainbows, and if so, how? What causes a halo to appear around the sun? What does the appearance of a halo tell us about the weather? Are sun halos always the same size?


EarthSky, What makes a halo?

Weather Channel, What are sun halos?

NGSS & Grade

3-ESS2-1, ESS2.D: Weather and Climate

Moon appears larger when closer to the horizon

Image: Moon rise through Downtown San Diego buildings. Craig Carter, @SeeMyPhotos

Like the sun, the moon rises and sets in the sky at predictable times. When the moon is close to the horizon during moon rise or moon set, it appears to be much larger than when it is above us. 

Is the moon larger at certain times of the day? How can we determine if the moon is a different size depending on its position in the sky?


National Geographic, Why the moon looks bigger near the horizon?

Discover Magazine, Why does the moon look so huge on the horizon?

NGSS & Grade

1-ESS1-1, ESS1.A: The Universe and its Stars

5-ESS1-2, ESS1.A: The Universe and Its Stars

MS-ESS1-1, ESS1.A: The Universe and Its Stars

The Catalina Eddy

Image: NASA Earth Observatory

On June 13, 2018, the National Weather Service reported a small but well-defined eddy off the coast near the border of Orange County and San Diego County. An eddy is a counter-clockwise circulation pattern of fog and clouds. The Catalina eddy typically brings cool moist air to the coast. A similar eddy was also reported in 2013 (pictured) by the NASA Earth Observatory.

Why do the clouds take on a whirlpool shape? What causes the Catalina eddy and when does it typically appear?


NASA Earth Observatory: Catalina eddy

San Diego Union Tribune: The beauty of a Catalina eddy

Times of San Diego: Catalina eddy phenomenon spotted off San Diego coast

NGSS & Grade

MS-ESS2-6, ESS2.D: Weather and Climate