Sunlight, Sun Bright

Click on the photos to see larger images and additional information.

Background

The Sun is the brightest object we can see in the sky, and without it, we would not be alive. 

   

The Sun gives off light and heat, and we need both to make the Earth a warm, comfortable place to live.  Plants use light from the Sun for photosynthesis, creating food for animals and oxygen for us to breathe.  Sunlight makes our days bright, and it reflects off the Moon to give us light at night.

 

Try making a list of all the things on Earth that would not be the way they are now if we did not get light and heat from the Sun.  Think about plants, animals, water, weather, even the way the Moon and stars look in our night sky.  What would our world be like if it was closer to the Sun, like the planet Mercury?  What would it be like if we were further from the Sun, like the planet Neptune?

The Sun is not solid, like the Earth.  It is a huge ball of dense gas, mostly hydrogen and helium, so there is no surface for you to stand on or land a spacecraft on.  Even if there was, you would melt or burn up before you even got to the Sun.  

Many people think that the Sun is on fire, but this is a misconception.  The Sun does not burn, giving off smoke and leaving burnt charcoal behind, like a candle or campfire does.  It is more like a light bulb or a burner on an electric stove -- it gets hot, and shines brightly, but it does not burn up.  Unlike a light bulb, the Sun does not use electricity, but creates energy with a reaction called nuclear fusion.  In nuclear fusion, two small atoms of hydrogen are pushed together to form a bigger atom, helium.  Every time this happens, energy is given off as heat and light.

The Sun is not the same all the way through. Nuclear fusion happens in the core of the Sun, and the resulting heat and light flow up through the Sun to the photosphere, the part of the Sun that we see.  The chromosphere is a thin layer above the photosphere.  Above that, the corona, or solar atmosphere, extends far into space.  We do not usually see these parts of the Sun because they are not as bright as the photosphere, but during a total eclipse they are visible because the Moon blocks the light from the photosphere. 

              
Image Credit: NASA

The surface of the Sun -- the photosphere, the part that we see -- is not smooth or still.  It is constantly moving, like a pot of boiling water, and it turns just like the Earth does.  Sometimes cooler, darker patches form on the Sun, called sunspots.  Sometimes huge storms, called prominences, explode out into space, releasing more energy in a second than all of the bombs ever built by humankind.  Sunspots and prominences can be many times bigger than the entire planet Earth.

The Sun is huge -- more than 100 earths could be lined up side-to-side across its middle.  The Sun looks small because it is so far away from the Earth -- 93 million miles away.  When light is given off from the Sun, it travels as fast as it can toward us, and still it takes about 8 minutes for it to arrive!

Our Sun is a pretty normal star, but it is special to us because it is the closest star.  A beam of starlight from our next nearest neighbor, Proxima Centauri, takes 4.2 years to get to Earth!  When you look out at the night sky, almost every glowing dot you see is a far away, fantastic, explosive, energy machine as powerful as our Sun, or even bigger.

The Pleiades Star Cluster


Sunrise and Sunset

Every morning, we see the Sun rise in the east.  Every evening, it sets in the west.  The Sun seems to move across the sky each day, but this is an illusion.  Really, we are moving, as the Earth turns around its axis once every day.  

Materials

Modeling Activity

Shine light on one side of the globe, pointing the light at the equator.  The half of the globe that is bright is experiencing day, and the half that is dark is experiencing night.  Pick a spot on the globe and pretend that you are standing there.  (A sticker or paper person may help younger students visualize this location.)  What time of day or night is it?  Turn the globe toward the left (counter-clockwise when looking down over the North Pole).  When does your spot on the globe experience sunrise?  Sunset?  When is it noon, with the "Sun" high in the sky overhead? 

Observing Changes in Sunrise and Sunset

You can do an interesting experiment from your own home.  Over several months or even a year, record the rising and setting points of the Sun.  On clear days, once or twice a week, mark where the Sun rises or sets on a drawing you've made of the horizon.  You'll notice that the Sun is changing the places that it appears to come up and go down.  

For your drawing to be good, you must stand in exactly the same spot each time you make your observations.  Try to pick a place without too many trees or tall buildings to get in your way.  It may be useful to get a chart of the sunrise and sunset times in your area, so that you know when to be outside.  This U.S. Naval Observatory site will help you create a chart for your location.


Make a Sundial

As the Sun moves across the sky each day, the shadows on Earth change places.  Long ago, people carefully drew the locations of the shadows at different times of day, and created sundials.  Then they used the sundials to tell time accurately.  Today, sundials like the one in front of Morehead Planetarium are often considered just decorative, but they still tell time on sunny days.  You can too! 

 

Materials

Mark the Hours on a Sundial

Your stick will be your gnomon (NO-mon), the part of the sundial that "knows" what time it is and tells you by casting a shadow.  Support it, pointed end up, in the clay or styrofoam on the center bottom edge of the index card.  Make sure it points as straight up as possible (a carpenter's square or triangle can help if you want to be accurate).

Early one morning, just after the Sun rises, go outside and place your blank card and gnomon on a level place that will not be in shadow at any time during the day.  Put the gnomon edge of the card toward the south, and the blank edge pointing north.  Tape or weight down the card with rocks so that it won't blow away.  If you might have to pick up your card, use tape or chalk to mark exactly where to placed it so that all your measurements happen in the same place. 

Every hour, trace the gnomon's shadow and write the time that you traced it beside the line.  If you cannot finish the entire project in one day, don't worry.  Place it in the same place a few days later, and continue making marks.  

Extending the Activity

Your sundial will be accurate for many weeks, but at the seasons change, the location of the shadows will no longer match your original marks.  If you want to observe this, record the date you made the sundial on it.  About two months later, take it out again and observe where the shadows fall at the same times of day. 

Make a Pre-Printed Sundial

If you do not want to spend all day marking the hours on a blank sundial, download this PDF image of a sundial for North Carolina and similar latitudes.  Glue the dial and the gnomon to sturdy paper (a file folder works well) and cut out the gnomon.  Fold the gnomon on the dotted line and glue it over the shaded area of the sundial, and use a compass to point your sundial North.  Remember to adjust for Daylight Savings Time during the summer!  Your sundial will probably not quite agree with your watch, because sundials display local time, not the official time displayed on watches.

There are many other types of sundials that you can make, either by marking the hours yourself or by printing one designed for your latitude.  Follow the links below for some sundial facts, history, and ideas.


Sun Links

www.lmsal.com/YPOP/Spotlight/Tour/index.html  Surfing For Sunbeams is a hypermedia tour of our Sun provided by the Yohkoh Public Outreach Project with photos, hyperlinks, technical information, and several solar movies.

www.astro.uva.nl/demo/od95/  This is a multimedia tour with movies and photos of how the Sun works, the parts of the Sun, ways the Sun affects planet Earth, and what scientists currently predict will happen to the Sun.  

www.seds.org/nineplanets/nineplanets/sol.html  This site has Sun facts and photos, vocabulary terms explained, and links.  It is part of a large web site about the objects in our Solar System. 

www.solarviews.com/eng/sun.htm  This page is full of Sun facts and Sun photos.

imagine.gsfc.nasa.gov/docs/science/know_l1/sun.html  More information about the layers of the Sun.

www.astrocappella.com/sun.html This fun song about the Sun is free to download (you must be able to play WAV sound files). It includes some complicated scientific vocabulary and is intended advanced elementary and middle school students, but the upbeat a cappella singing is exciting even for younger listeners.

aa.usno.navy.mil/AA/data/docs/RS_OneYear.html  Get a chart of the sunrise and sunset times in your area from the U.S. Naval Observatory. 


Sundial Links

These pages have instructions for marking the hours on a blank sundial

www.mos.org/sln/wtu/activities/patterns.html  Similar to the activity on this page.

www.eren.doe.gov/roofus/sundial.html  Make a small sundial from a styrofoam drinking cup.

solar.physics.montana.edu/tslater/plunger/plunger.htm  Make a larger sundial with a toilet plunger, or on a window with tape.

cc.owu.edu/~mggrote/pp/physics/sundials2.html  Includes a detailed teacher's guide.

Adults -- please try to make and use these printable sundials before offering them to your students.  Some are difficult to construct!

www.grex.org/~jh/dial/  There are many different type of sundials, and this page describes them and allows you to customize them for your location.  The sundial image to download on this page was created at this site.

www.sundials.co.uk/projects.htm  More free sundials you can make!

kids.msfc.nasa.gov/earth/sundials/sundialmake.asp  Another free sundial to print and construct.


2001 Challe Hudson

This web page was produced for Morehead Planetarium during a North Carolina State University astronomy class taken in pursuit of a Masters in Science Education.