The Sun Is a Star

Scope on the Skies

The Sun Is a Star

Science Scope—September/October 2021 (Volume 45, Issue 1)

By Bob Riddle

Figure 1 Measuring the Sun’s altitude at the equator. — Figure 1

Although any month could be an appropriate period for studying the Sun, September and March are particularly good months for lessons about our nearest star, the Sun. These two months, the equinox months, are two of the four months during which seasons change. Using the Earth’s equator as a reference point, the Sun is directly over the equator at an altitude of 90° on September 22, 2021. During the March equinox, on March 20, 2022, the Sun will follow an apparent path across the sky similar to the one it followed in September.

By middle school, our students have learned about the “reasons for seasons” as caused by the Earth’s axial tilt and its revolution around the Sun—not having to do with distance. Often student attention is drawn to the equinox when they participate in an Eratosthenes project or measurement. This is where students would use shadows, the Sun’s altitude, and a bit of math to measure the Earth’s polar circumference (see Figure 1). They could explore how latitude determines the Sun’s apparent path on this day, or any day, at their home location (see “Location, Location, Location” in Resources). Another activity involving the Sun, and one that could be structured as a school-year-long activity, has the students use an equatorial star chart to track the Sun’s apparent daily motion along the ecliptic. Its apparent eastward motion can be followed weekly and be coordinated with midday altitude measurements of the Sun (see “Observing the Sun for Yourself” in Resources for several other ways to safely observe the Sun). Activities like these could, pardon the paraphrase, be a “gateway experience” to learning the importance and significance of studying the Sun and its relationship with our planet.

Space weather

Our Sun is observed and monitored from space, from our atmosphere, and from ground-based facilities gathering a host of data and information into what is called space weather. This is the science of heliophysics, the study of the connection between the Sun and the solar system, with a particular interest for obvious reasons in the Sun–Earth connection. So, what is space weather? (see Resources). It is the environment surrounding the Earth and other planets that is affected by the Sun’s solar wind. The solar wind is streams of charged particles coming from the Sun, some of which are harmful to life on Earth, but fortunately they are blocked by our atmosphere. While our students are aware of the solar wind and its interaction with the Earth’s magnetic field from pictures of the colorful auroras, understanding the importance of space weather is increasingly important as we live in a world that relies more and more on the use of electronics. There are times when the solar wind output has impacted the Earth more intensely than “normal,” resulting in problems with electrical power grids, radio, and cellphone communication, as well as potential harm to astronauts. One of the most powerful solar events is called the “Halloween solar storms of 2003.” This space weather event was triggered by a series of 17 large solar flares that disrupted radio communications and caused problems with orbiting satellites, power failures, and some very spectacular auroras visible in southern states where they are not often seen (see Resources).

Space weather, like atmospheric weather, is constantly changing and can sometimes go from seemingly tranquil conditions to storms from the Sun (see Figure 2; to view a larger image, see the link in Resources). These storms are very large releases of energy from the Sun associated with large solar flares and CMEs, or coronal mass ejections. They are classified by their characteristics into three types of solar storms, each having an effect scale ranging from 1 (minor) to 5 (extreme). A network of space-based solar observatories provides scientists with the tools and data needed for monitoring the active Sun and issuing warnings or advisories of potentially damaging space weather.

The most common type of space weather is a geomagnetic storm, where the Earth’s magnetic field interacts with charged particles in the CME. The material in a CME travels at millions of miles per hour, enabling the material to reach the Earth in a few days and allowing ample time for making any necessary safety preparations. One of two things will happen when the CME reaches the Earth’s magnetic field. If the magnetic field within the CME cloud aligns with the Earth’s magnetic field, then the CME has little to no effect. However, if the two magnetic fields do not align, then the charged particles within the CME interact with the Earth’s magnetic field to create the spectacular and colorful auroras, sometimes appearing further south. This is also a situation in which there can be damage to electronics in satellites, certain communication devices, and even electrical power grids.

Solar radiation storms are more intense flows of radiation within the solar wind but, for the most part, are not of a significant danger to anything within the Earth’s magnetic field, which extends out to about 40,000 miles (65,000 km). Energy within solar radiation storms take from approximately 30 minutes to several hours to reach the Earth’s magnetic field, thus limiting the amount of time between discovery and preparations. These space weather events can be intense enough to damage the ozone layer. However, the shielding effect of the Earth’s magnetic field helps prevent the loss of the ozone layer, which prevents harmful ultraviolet radiation from reaching the surface. During some of these events, and despite the shielding from the ozone layer, there could be damage to sensitive instruments on satellites, and radiation could even prove harmful to passengers in airplanes and astronauts in Earth’s orbit.

Radio blackouts are among the most commonly occurring space weather events and happen when a solar flare and the CME contain high-energy x-ray radiation. Traveling at the speed of light, the stream of x-rays takes about eight minutes to hit the upper regions of the Earth’s atmosphere, the ionosphere. This interaction creates a turbulence-like effect throughout the ionosphere. There could be serious consequences from these events, as turbulence within the ionosphere has an immediate effect on the transmission of certain aviation and marine radio frequencies as well as the accuracy of GPS, for example.

Space weather has a strong connection with the solar cycle of sunspots, an 11-year cycle of increasing, then decreasing, sunspot activity on the visible surface of the Sun, the photosphere. In 2021, there has been an increase in activity and the number of sunspots following the minimum a year or so ago (see Figure 3). Students may follow the daily activity of the Sun as viewed from space by the Yohkoh and SOHO satellites, or by logging into the Space Weather Enthusiasts Dashboard for space weather conditions and possible warnings. Additionally, students could use the PBS Learning Media’s interactive Helioviewer and observe the Sun for sunspots, flares, the Sun’s magnetic field, eruptions, CMEs, and other solar events. There are many suggestions for ways students could use the Helioviewer tool (see Resources).

Figure 3 Solar cycle graphic. — Figure 3

For students

1. Use data from the U.S. Naval Observatory to track the Sun’s daily position at rising, midday, and setting. Coordinate this with participating in an Eratosthenes project and calculate the Earth’s circumference.

2. Research and identify some notable examples of sunspot activity, solar flares, and CMEs that have occurred. (Teachers: see “Helioviewer—Teaching Tips” for suggestions on using the tool.)

3. Play the game “Radiation Hazards in Space”; choose your path to Mars, and deal with the hazards of space radiation.

4. Make a timeline that follows the Solar Storm of 2003 (see Resources).

Living With a Star

Living With a Star is the name of a proposed NASA mission to the Sun tentatively planned for a 2027 launch date (see Resources). This is also the title of an older but still available NASA publication (see Resources)—an educator’s guide with activities and web resources, albeit some of the URLs have changed since the publication was released. The publication is a good place to start as it lists and describes many of the NASA Sun–Earth missions and indicates whether there is a mission education page. Another good resource for lessons and activities about the Sun is “Solar Physics and Terrestrial Effects,” a curriculum guide for grades 7–12. Within the guide are directions and activities for observing and collecting data about the Sun, including interactions between the Sun, space, and the Earth. Because we are actively exploring Mars leading up to an eventual crewed mission, the board game Radiation Hazards in Space could be of interest to students. In this game students learn about harmful solar radiation. Working in small teams, they choose a path to Mars. Along the way, each team deals with the hazards of radiation. The team arriving with the best health record wins (see Resources). •

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