The Sun as a Star: Photosphere, Corona and the Activity Cycle · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

The Sun wears a hot crown

Science · Astronomy & Astrophysics · ages 21-22
Name ______________________   Date ____________

  1. Considering only photosphere, chromosphere and corona, which row correctly gives placement, observing methods and the general density trend? Middle and outer refer to these three regions. UV means ultraviolet.

    • Chromosphere: outer, ~10000 K, narrowband/UV; corona: middle, coronagraph/X-rays; density falls outward
    • Chromosphere: middle, ~10000 K, narrowband/UV; corona: outer, coronagraph/X-rays; density falls outward
    • Chromosphere: middle, ~10000 K, coronagraph/X-rays; corona: outer, narrowband/UV; density rises outward

  2. Which effective temperature and visible spectral pattern describe the Sun's photospheric light?

    • About 5800 K, with absorption lines
    • About 1000000 K, with absorption lines
    • About 5800 K, with only X-ray emission

  3. About how many years does one sunspot activity cycle last, averaged over many cycles?

    Answer: ______________

  4. Which description identifies a solar flare rather than solar wind or a coronal mass ejection?

    • A steady outflow of charged particles from the solar atmosphere
    • A rapid magnetic energy release producing a radiation burst
    • A large cloud of coronal plasma and field expelled into space

  5. A pair of sunspots marks an emerging magnetic loop. Why do the spots look darker than nearby photosphere?

    • Orbiting planets block sunlight and cast cool shadows on the photosphere
    • Gas above the spots absorbs light, hiding photosphere at its usual temperature
    • Strong fields reduce convective heating, making the photospheric gas cooler

  6. A flare and an Earth-directed CME occur together. Which forecast correctly separates radiation arrival, plasma arrival and storm severity?

    • Flare light: minutes; CME: possibly days; severity also depends on the cloud's magnetic field
    • Flare light and CME plasma: both about eight minutes; their shared arrival time determines storm severity
    • Flare light: days; CME plasma: minutes; the earlier plasma arrival alone determines storm severity

  7. Why does the corona, much hotter than the photosphere below it, require ongoing heating, and what must a proposed explanation demonstrate?

    • Passive heat from cooler gas maintains it; a temperature image alone establishes enough energy deposition
    • Passive heat is insufficient; deposited heat must balance losses and fit the observed heating pattern
    • Low density rules out high temperature; a magnetic-loop image alone establishes enough energy deposition

  8. A model links solar gas motions to sunspots and flares. Which account correctly connects the dynamo, differential rotation and magnetic activity?

    • Gas motions sustain the field; every latitude rotates together, and a thermal cycle alone causes sunspots and flares
    • Gas motions erase the field; unequal rotation stops loops from emerging, and surface fusion produces solar flares
    • Gas motions sustain the field; unequal rotation reshapes it; loops form spots and magnetic energy powers flares
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Answer key

For grown-ups. Fold this page away before handing over the rest.

The Sun wears a hot crown W1-mt_AMIkiU7wRz-s1

  1. Chromosphere: middle, ~10000 K, narrowband/UV; corona: outer, coronagraph/X-rays; density falls outward · The chromosphere lies between photosphere and corona; parts reach about 10000 K and are studied in narrowband visible or ultraviolet images. Coronagraphs and X-rays reveal the corona. Density generally falls outward.
  2. About 5800 K, with absorption lines · The Sun's effective temperature is about 5800 K. Its photospheric visible spectrum contains a continuum crossed by absorption lines.
  3. 11 · The activity cycle averages about eleven years. The typical spot-pair polarity pattern reverses between activity cycles, giving a magnetic polarity cycle of about twenty-two years.
  4. A rapid magnetic energy release producing a radiation burst · A flare rapidly releases magnetic energy and produces radiation. Solar wind is a continuing plasma outflow; a CME expels a cloud of plasma and magnetic field.
  5. Strong fields reduce convective heating, making the photospheric gas cooler · Strong magnetic fields inhibit convective heat transport. Sunspot gas becomes cooler and emits less light than the surrounding photosphere.
  6. Flare light: minutes; CME: possibly days; severity also depends on the cloud's magnetic field · Flare light reaches Earth in about eight minutes. CME plasma may take days, depending on speed and path. Arrival time alone does not determine storm severity; the cloud's magnetic field affects its interaction with Earth's magnetic environment.
  7. Passive heat is insufficient; deposited heat must balance losses and fit the observed heating pattern · Passive heat flow from the cooler photosphere cannot maintain the hotter corona. A proposed process must deliver energy, deposit enough heat to balance radiation and other losses, and match the observed heating pattern.
  8. Gas motions sustain the field; unequal rotation reshapes it; loops form spots and magnetic energy powers flares · Conducting-gas motions sustain the dynamo by converting motion into magnetic energy. Differential rotation reshapes the field. Emerging loops can form spot pairs, and reconnection can release magnetic energy in flares.
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