Lesson 2 of 6 · the solar wind
A flowing connection to the Sun
10 minute lesson · 3 checks along the way
Your goal for this lessonUse an upstream solar-wind measurement to estimate a conditional warning interval.
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A wind made of particles
The is an outward flow of from the Sun's hot outer atmosphere. Protons and electrons dominate, with other ions also present. It carries a magnetic field through interplanetary space. Sunlight reaches us as radiation, while solar-wind material must travel here. The two can originate from the same star without arriving together or interacting with Earth in the same way.
The flow is variable. Coronal holes, regions with magnetic connections extending outward, are associated with fast wind. Faster streams can catch slower material and produce compressed interaction regions. The Sun's rotation organizes large-scale patterns, but it does not make a forecast repeat exactly. Measurements of speed, density, and magnetic direction are needed because a single speed number cannot describe the whole disturbance.
Read an observation without overclaiming
The Solar Dynamics Observatory image in this lesson records extreme-ultraviolet emission, displayed in a visible orange color. The dark patch near the center-right is a . It is relatively faint in that instrument's band, not a physical opening through the Sun. Its appearance helps scientists identify a source region; it does not directly measure the speed of particles reaching Earth.
An upstream spacecraft instead samples material passing its instruments. DSCOVR operates around the Sun–Earth region, roughly 1.5 million kilometers sunward of Earth. Particle instruments and a can characterize the approaching environment there. Imaging provides broad spatial context, while a local measurement supplies detail at one location. Neither observes every point between the Sun and Earth's changing magnetospheric boundary.
Solar Dynamics Observatory recorded this extreme-ultraviolet view on March 28, 2013. Orange represents an invisible wavelength band. The dark coronal hole near center-right is a source region associated with fast solar wind; the picture is not a speed measurement at Earth.
Look closely
What does the dark patch measure directly, and which measurement would you add to estimate when a disturbance reaches Earth?
See what to notice
The patch is relatively faint in the observed band. A local solar-wind speed measurement and a stated propagation model are needed for a timing estimate; the image alone does not supply them.
Check 1 of 3
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Work through a decision
Turn a distance into a conditional lead time
Imagine a disturbance measured 1,500,000 kilometers upstream of a specified Earth reference point. Suppose it travels straight toward that point at a constant 500 kilometers per second. Distance divided by speed gives 3,000 seconds, or 50 minutes. This is a simplified from the measurement location, not the entire journey from the Sun and not a guarantee of a particular impact.
If delivery, processing, and the operator's decision consume eight minutes, 42 minutes of that model interval remain. Doubling the assumed speed halves the travel time to 25 minutes, leaving 17 after the same delay. Faster motion can produce a more urgent situation with less preparation time. Always attach the measurement time, assumed path, and speed to a quoted estimate.
Check 2 of 3
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Know what the estimate leaves out
Real disturbances have structure and can evolve. A front may be tilted, the sampling spacecraft is not precisely on an ideal straight line, and the relevant arrival is often at the rather than Earth's center. Those differences limit a simple distance-over-speed calculation. The magnetic field's orientation also matters for coupling energy into Earth's environment; a strong southward component can favor that coupling.
A useful forecast therefore combines remote observations, propagation models, and upstream measurements, then updates as new evidence arrives. Our calculation is a transparent check on scale and available time. It does not replace an operational forecast or indicate current conditions. Use archived spacecraft observations for this activity: the evidence comes from instruments and their documented measurements, with no direct solar viewing required.
Check 3 of 3
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Put it together
Your lesson progress
Each check connects to a part of the story. Complete all 3 to earn your 25-point lesson bonus.
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