Topic outline

  • Introduction

    Solar eclipse by society.excite.co.uk


    Written by: Suzanne Monir, Kimberly Tran, EIS Education Team Members, August 2016
    Title: Introduction to Solar Eclipses
    Grade (Age) Level: Grades 5-8 (Ages 10-14)

    Pre-requisites: There are no pre-requisites for this course but familiarity with the solar system is recommended. 


    This course is to teach students about the solar eclipse phenomenon. 


  • Glossary

    Phases of the Moon


    The moon has eight phases, with the moon orbiting the Earth once every 29 and a half days. Note, when the illuminated part of the moon is getting bigger, the Moon is waxing. When it is getting smaller, the Moon is waning. 

    The cycles are as follows: 

    • New Moon: The illuminated side of moon is facing away from the Earth (nothing is seen)
    • Waxing crescent: Less than half of the illuminated side of the Moon is facing the Earth (right crescent visible) 
    • First quarter: Half of the illuminated side of the Moon is facing the Earth (right half visible) 
    • Waxing gibbous: More than half of the illuminated side of the Moon is facing the Earth (right side visible)
    • Full moon: The illuminated part of the Moon can be fully seen
    • Waning gibbous: The illuminated part of the Moon begins to shrink, with more than half facing the Earth (left side visible) 
    • Last quarter: The illuminated part of the Moon shrinks, with half facing the Earth (left half visible) 
    • Waning crescent: The illuminated part of the Moon shrinks, with less than half facing the Earth (left crescent visible) 
    From here the cycle returns to the new moon.

    Parts of a Solar Eclipse


    Penumbra- The Moon’s faint outer shadow

    Umbra- The Moon’s dark inner shadow

    Antumbra- The part of the Moon's shadow that extends beyond the umbra. Here, the Moon is in front of the Sun but doesn't cover the Sun entirely so its outline can be seen around the shadow of the Moon 

    Solar Eclipse by www.fotosearch.com

    Corona- The gaseous envelope of the sun and other stars. The sun’s corona is only visible during a total solar eclipse when it is seen as an irregularly shaped pearly glow surrounded by the darkened disk of the moon



    • What is a solar eclipse?

      What is a solar eclipse? In general an eclipse  is when one object blocks an observer from seeing another. In a solar eclipse the Moon passes in front of the Sun and creates a shadow that falls on the Earth. While an eclipse can't been seen everywhere, for those in the shadowed areas the Sun appears dark. Solar eclipses only occur during the new moon phase and based on the position of the Moon, Sun and Earth there are four possibly types of solar eclipses that can be seen. This phenomenon lasts a few minutes and on average occurs every 18 months.

      This video clip by Bill Nye introduces solar eclipses and one way to view them safely. 

       
      Solar eclipses are the product of coincidence. With a diameter of 1.39 million kilometers the Sun is 400 times larger than the moon (with a diameter of 3,474 kilometers). However, the moon is roughly 400 times closer to the Earth than the Sun (384,400 km vs 149.6 million km). Something else to note is that the moon has been gradually moving away from the Earth since its formation billions of years ago. At its current distance, the moon is at the perfect position to appear in the sky as the exact same size as the Sun to block it out.

      • Solar Eclipse vs Lunar Eclipse

        Another type of eclipse that can be seen from space is called the Lunar Eclipse. In a lunar eclipse, the Earth moves between the Moon and the Sun blocking part of the Sun's light from hitting the Moon. When this happens, the Earth's shadow appears on the Moon. Lunar eclipses only occur on the night of a full Moon, and can be viewed by anyone on the 'night side' of the Earth.  Unlike Solar eclipse, this phenomenon lasts for hours and can be safely seen without eye protection. 



        In this video by Physics Girl, the differences between Solar and Lunar Eclipses is discussed. 
      • Types of Solar Eclipses

        As mentioned before, there are four types of solar eclipses. Below, we'll go over each type. 


        Total Solar Eclipse
        Total Solar Eclipse


        During a total solar eclipse, the moon casts its umbra upon Earth's surface; that shadow can sweep a third of the way around the planet in just a few hours. Those who are fortunate enough to be positioned in the direct path of the umbra will see the sun's disk diminish into a crescent as the moon's dark shadow rushes toward them across the landscape.

        During the brief period of totality, when the sun is completely covered, the beautiful corona — the tenuous outer atmosphere of the sun — is revealed. Totality may last as long as 7 minutes 31 seconds, though most total eclipses are usually much shorter.


        Partial Solar Eclipse

        Partial solar Eclipse

        A partial solar eclipse occurs when only the penumbra (the partial shadow) passes over you. In these cases, a part of the sun always remains in view during the eclipse. How much of the sun remains in view depends on the specific circumstances.

        Usually the penumbra gives just a glancing blow to our planet over the polar regions; in such cases, places far away from the poles but still within the zone of the penumbra might not see much more than a small scallop of the sun hidden by the moon. In a different scenario, those who are positioned within a couple of thousand miles of the path of a total eclipse will see a partial eclipse.

        The closer you are to the path of totality, the greater the solar obscuration. If, for instance, you are positioned just outside of the path of the total eclipse, you will see the sun wane to a narrow crescent, then thicken up again as the shadow passes by.


        Annular Solar Eclipse

        Annular Solar Eclipse

        An annular eclipse, though a rare and amazing sight, is far different from a total one. The sky will darken but with what appears as twilight also, since so much of the sun still shows. The annular eclipse is a subspecies of a partial eclipse, not total. The maximum duration for an annular eclipse is 12 minutes 30 seconds.

        However, an annular solar eclipse is similar to a total eclipse in that the moon appears to pass centrally across the sun. The difference is, the moon is too small to cover the disk of the sun completely. Because the moon circles Earth in an elliptical orbit, its distance from Earth can vary from 221,457 miles to 252,712 miles. But the dark shadow cone of the moon’s umbra can extend out for no longer than 235,700 miles; that’s less than the average distance of the moon from the Earth.  

        So if the moon is at some greater distance, the tip of the umbra does not reach Earth. During such an eclipse, the antumbra, a theoretical continuation of the umbra, reaches the ground, and anyone situated within it can look up past either side of the umbra and see an annulus, or “ring of fire” around the moon. A good analogy is putting a penny atop a nickel, the penny being the moon, the nickel being the sun.


        Hybrid Solar Eclipse

        Hybrid Solar Eclipse

        These are also called annular-total (“A-T”) eclipses. This special type of eclipse occurs when the moon’s distance is near its limit for the umbra to reach Earth. In most cases, an A-T eclipse starts as an annular eclipse because the tip of the umbra falls just short of making contact with Earth; then it becomes total, because the roundness of the planet reaches up and intercepts the shadow tip near the middle of the path, then finally it returns to annular toward the end of the path.

        Because the moon appears to pass directly in front of the sun, total, annular and hybrid eclipses are also called “central” eclipses to distinguish them from eclipses that are merely partial.

        Of all solar eclipses, about 28 percent are total; 35 percent are partial; 32 percent annular; and just 5 percent are hybrids.



      • How to View a Solar Eclipse

        You should never view a solar eclipse with unprotected eyes. This is because the Sun is too bright for the human eye to handle, resulting in retinal burn and blindness.. Even during a total eclipse while the Sun is covered by the Moon, it is still dangerous to view unprotected. Since a total solar eclipse makes the surrounding area dark, the human pupil dilates to allow more light in for a clearer picture. However the Sun may come out and 'surprise' viewers before they can turn away, making the resulting retinal burn even more dangerous with the eyes trying to let in as much light as possible. 

        To safely view a solar eclipse, it is important to protect your eyes. The following can be used to safely view a solar eclipse: 

        * Note- According to NASA, the  following materials should never be used to view a solar eclipse: 

        • Sunglasses
        • CDs or Computer floppy discs
        • Medical x-ray film with images on them
        • Colour film
        • Smoked glass


        Pinhole Projector

        This video by Videofromspace shows how to make an inexpensive projector using a shoe box. 


        Eclipse Glasses

        Eclipse glasses found on amazon.com

        Eclipse glasses can be worn to safely view an eclipse. Check your nearest museum or science center to see if glasses can be bought or rented, otherwise they can be found online for sale. 

        Welder's Goggles

        Welding goggles from weldinghelmetpros.com

        Welding goggles rated 14 can also be used to safely view a solar eclipse. These goggles contain the darkest lens shade available and can be found at welding supply outlets or online. 


        Aluminizied Mylar Sheeting/ Solar filters

        Aluminized mylar sheeting can be used as a filter to view a solar eclipse. It is easy to cut and attach to a box or viewing device. Alternatively, solar filters can be bought. These filters may be made form aluminized mylar or other material. 

        Ways to view a solar eclipse by nature-universe-photography.blogspot.com

      • Test Your Knowledge