PHYS1160 APOD Assessment Isaac Gunay Ada
Term 2, 2021 z5113412
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SOLAR AND LUNAR
ECLIPSES
What’s all the
fuss about?
Hello there! My name is Dan, and I will be guiding you through a
series of questions relating to one (or two) of the most broadcasted
and unifying cosmic events that people enjoy from the comfort of
their own backyards – eclipses!
Often, when eclipses are reported on television, we are told very
little about what they are and how they occur. The reports are met
with many tens of thousands of eager people that flock to
observation areas to share in the moment when an eclipse occurs.
But why has there always been a widespread appreciation for the
event? Dating back to the Ugarit Eclipse of 1375BCE [1], eclipses
have been observed throughout most known human civilisations.
They confirmed Aristotle’s arguments that the Earth is round, and
contributed to proving Einstein’s Theory of Relativity [2]. What
exactly are eclipses and how many different types are there? How
can you best prepare to view one?
These questions, and many more, will be answered below.
Happy exploring!
PHYS1160 APOD Assessment Isaac Gunay Ada
Term 2, 2021 z5113412
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To understand solar and lunar eclipses, we must first consider some basic facts regarding the three celestial
objects involved: Sun, Moon and Earth.
Nicholas Copernicus famously said “We revolve around the Sun like any other planet” [3]. This heliocentric
model of the solar system places the Sun at the centre and the Earth as one of the orbiting planetary objects.
It was then Johannes Kepler’s laws of planetary motion which matched astronomical observations of
planetary motion with heliocentrism [4]. It has since been understood that the Sun is positioned at the focus
of the Earth’s elliptical orbit. There is another elliptical orbit within Earth’s orbit: The Moon. And this time,
Earth is at its focus [5].
With these orbits within orbits, you should expect there to be times when the Sun, Earth and Moon align in
their positioning with respect to each other. If that is your expectation, you are correct!
To help us mentally visualise such phenomena, let us first consider the distances between these objects and
their sizes relative to each other.
At the centre of the solar system, the Sun is approximately 150 million kilometres away from Earth [6]
compared to 384,400 kilometres between Earth and the Moon [7]. The means that the Sun is positioned at
390 times the distance between Earth and the Moon.
Let’s start at the beginning
Not to scale
Not to scale
With respect to relative size, the Sun’s diameter is
approximately 109.1 times the diameter of the
Earth, with the moon’s diameter less than one third
the diameter of Earth [8].
Therefore, the apparent size of the
Sun from an observer on Earth
would be considered similar to
that of Moon because despite the
Sun being much larger than the
Earth, it is also much further away
when compared to the moon [9].
PHYS1160 APOD Assessment Isaac Gunay Ada
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On the left of Figure 1 [22] is a digitally configured
image of a total lunar eclipse. The moon appears
reddish [10].
On the right of Figure 1 [22] is a digitally configured
image of a total solar eclipse. You might not be able
to tell, but Dan is wearing a pair of eclipse watching
glasses. To him, the moon appears very dark with a
ring of light emanating from around it.
LUNAR ECLIPSE SOLAR ECLIPSE
What is a lunar eclipse?
A lunar eclipse occurs when the Earth blocks the
Sun’s light from reaching and being reflected off the
Moon – in effect, the Earth’s shadow is being cast on
the Moon [11].
What is a solar eclipse?
A solar eclipse occurs when the Moon blocks the
Sun’s light from reaching Earth – in effect, the
Moon’s shadow is being cast on Earth [12].
The Sun’s light casts two shadows [13]:
Umbra (smaller shadow) and Penumbra (larger shadow)
What exactly am I looking at?
Although the Moon orbits the Earth once every 29.5 days [14], we do not see lunar
and solar eclipses occurring once every month. This is because of the Moon’s orbital
tilt: a 5 degree tilt of the Moon’s orbit from the Earth’s orbital plane [15]. It is for this
reason we see different types of lunar and solar eclipses.
The size of the Moon’s umbral shadow can
reach 250 kilometres in diameter when cast
on Earth’s surface [19]. This umbral shadow
zone generates a path as the Earth rotates:
this is called the path of totality [19].
Fig. 1: Solar
and Lunar
Eclipses
PHYS1160 APOD Assessment Isaac Gunay Ada
Term 2, 2021 z5113412
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TYPES OF LUNAR AND SOLAR ECLIPSES
TOTAL Lunar Eclipse
A total lunar eclipse occurs when a full Moon
falls completely within Earth’s umbral shadow
[13]. Picture you are observing the Moon from
Earth:
The reddish appearance of the Moon is
caused by the Earth’s atmosphere refracting
the longer red wavelengths of the Sun’s light
toward the central umbral shadow region
[16].
PARTIAL Lunar Eclipse
A partial lunar eclipse occurs when only a part
of the Moon enters Earth’s umbral shadow
[13]. Picture you are observing the Moon from
Earth:
It is only the part of the Moon in the Earth’s
umbral shadow that will appear reddish [17].
PENUMBRAL Lunar Eclipse
A penumbral lunar eclipse occurs when the
Moon falls completely within Earth’s umbral
shadow [13]. Picture you are observing the
Moon from Earth:
These eclipses are difficult to spot, but you
should expect the Moon to simply darken
[18].
TOTAL Solar Eclipse
A total solar eclipse occurs when a full moon covers the
entire surface of the Sun [13]. You can observe this if you
are located within the path of totality.
Picture you are observing the Moon from Earth:
In the moments before the Sun is completely blocked by
the Moon, you will observe the phenomena known as the
diamond ring effect (see Fig. 2 [20]).
Fig. 2: A total solar eclipse
showing the diamond ring effect.
Once the Moon blocks the
entire surface of the Sun
as observed from Earth,
you will see a black Moon
with the Sun’s corona
emerging from around it.
PARTIAL Solar Eclipse
A partial solar eclipse occurs when only a part of the Moon
covers the surface of the Sun [13]. You can observe this if
you are located within the penumbral zone which is directly
outside the path of totality.
Picture you are observing the Moon from Earth:
You will only be able to see the portion of the Sun that is
unobstructed by the Moon.
ANNULAR Solar Eclipse
An annular solar eclipse occurs when you are located within
the path of totality, however the Moon does not cover the
entire surface of the Sun [13]. This happens during those
moments in the Moon’s elliptical orbit where the Moon is
further away from the Earth causing it to appear smaller.
You will observe the ring of fire (see Fig. 3 [21]).
Fig. 3: The “Ring of Fire”
PHYS1160 APOD Assessment Isaac Gunay Ada
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OBSERVING AN ECLIPSE
Lunar Eclipse Solar Eclipse
The next lunar eclipse is scheduled for 19
November 2021. It will be a partial lunar eclipse
and could be observed from any location across
Australia (See Fig. 4 [23]). This partial eclipse will
last approximately two and a half hours [24].
Fig. 4: Locations where the partial lunar eclipse of 19
November 2021 could be observed (shaded in red).
The next solar eclipse that would be observed
from Australia is scheduled for 20 April 2023.
The path of totality will cross Mount Hollister
in Western Australia – the only location in
Australia where a total solar eclipse will take
place with 100% coverage of the Sun (See Fig.
5 [25]). The further away from Mount Hollister
you are, the less coverage you will observe.
Sydney will be outside the path of totality,
however is within the penumbral path and
thus will observe a partial solar eclipse with
9.77% coverage of the Sun [25].
Fig. 5: Path of totality of the 20 April 2023 solar eclipse in
dark red, with penumbral paths extending beyond path.
How To Prepare For An Eclipse?
Fortunately, the alignment of the Sun, Earth and
Moon during a lunar eclipse involves the Earth
situated in between the Sun and Moon. This
means that you will not be looking directly at the
Sun. With a picnic blanket and some good snacks,
you can enjoy a lunar eclipse from your own
backyard with the naked eye. If you wish to have a
closer view of the phenomena, a telescope or a
pair of binoculars will assist! [13]
Unlike lunar eclipses, you cannot observe
solar eclipses with the naked eye as you will
be required to stare directly at the Sun. Lucky
for you, there are solar eclipse glasses that
you can purchase online which refracts and
reduces sunlight and blocks ultraviolet and
infrared radiation [26]. These glasses will help
you safely watch a solar eclipse.
Without these glasses, you can still have the
solar eclipse experience by observing your
surroundings – it will get dark for
approximately three minutes [13].
Before I provide you with some of my best tips for observing eclipses, let’s have a look
at when the next eclipses are scheduled to take place.
PHYS1160 APOD Assessment Isaac Gunay Ada
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THE FUTURE OF ECLIPSES
The occurrence of eclipses rely on the alignment of the Sun, Earth and Moon.
However,
the Moon is gradually moving away from Earth by approximately three centimetres every year [27].
With this trend, it is estimated that the distance between the Moon and Earth will be so great that
the Moon will not appear large enough to cover the entire surface of the Sun [13].
BUT until then…we still have BILLIONS of more years to enjoy the awesome
cosmic event!
PHYS1160 APOD Assessment Isaac Gunay Ada
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REFERENCES:
[1] NASA, Solar Eclipses of Historical Interest (2008)
Accessed 23 July 2021.
[2] History, Eclipses (2017) environment/history-of-eclipses> Accessed 23 July 2021.
[3] NASA Earth Observatory, Planetary Motion: The History of an Idea That Launched the Scientific
Revolution (2009) Accessed 23 July 2021.
[4] Explaining Science, Johannes Kepler (2018) kepler/> Accessed 23 July 2021.
[5] NASA, Eclipses and the Moon’s Orbit (2012)
Accessed 23 July 2021.
[6] Space, How Far is the Earth from the Sun (2017) earth-from-the-sun.html> Accessed 23 July 2021.
[7] Space, How Far is the Moon? (2017)
Accessed 23 July 2021.
[8] British Astronomical Association, The size of things (2018)
MYjAraig2INI> Accessed 23 July 2021.
[9] EarthSky, Coincidence That Sun And Moon Seem Same Size? (2013)
Accessed 23 July
2021.
[10] NASA, Earth’s Moon (2021) and-eclipses/> Accessed 23 July 2021.
[11] Space, Lunar Eclipses: What are they & when is the next one? (2020)
Accessed 24 July 2021.
[12] Space, Solar Eclipses: When is the next one? (2021) eclipses.html> Accessed 24 July 2021.
[13] National Geographic, Lunar Eclipses 101 | National Geographic (2018)
Accessed 24 July 2021; National Geographic,
Solar Eclipse 101 | National Geographic (2017)
Accessed 24 July 2021.
[14] NASA Science, Earth’s Moon: Inside & Out questions/> Accessed 24 July 2021.
[15] NASA, Earth’s Moon: Moon in Motion
Accessed 24 July 2021.
[16] Business Insider Australia, The longest total lunar eclipses in a century happens this week – here’s
the difference between a lunar and solar eclipse (2018) eclipse-vs-solar-eclipse-difference-2018-7> Accessed 24 July 2021.
PHYS1160 APOD Assessment Isaac Gunay Ada
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[17] Time and Date, What is a Partial Lunar Eclipse? (2021)
Accessed 24 July 2021.
[18] Time and Date, What is a Penumbral Lunar Eclipse? (2021)
Accessed 24 July 2021.
[19] Vaonis, Path of Totality, Umbra and Penumbra (2017) and-path-of-totality-of-solar-eclipses> Accessed 24 July 2021.
[20] Time and Date, What Are Total Solar Eclipses (2021)
Accessed 24 July 2021.
[21] EarthSky, ‘Ring of Fire’ Solar Eclipse on June 10 (2021) solar-eclipse-on-june-10-2021/> Accessed 24 July 2021.
[22] NASA APOD, Astronomy Picture of the Day (09 February 2018)
Accessed 24 July 2021.
[23] Time and Date, Solar and Lunar Eclipses Worldwide – 2020-2029 (2021)
Accessed 29 July 2021.
[24] Time and Date, 18-19 November 2021 Partial Lunar Eclipse
Accessed 29 July 2021.
[25] Time and Date, Eclipse Map – 20 April 2023 Total Solar Eclipse
Accessed 29 July 2021.
[26] CNET, How to tell if your solar eclipse glasses are safe or fake
Accessed 29 July 2021.
Other
Male character
Vector Stock, Set male characters man boy person user vector image
vector-15870784> Accessed 29 July 2021.
Image of Solar eclipse on Page 1
Syfy, From Earth and from Space: The Wonder of a Total Solar Eclipse (2019)
Accessed 29 July 2021.
Image of cartoon Sun, Moon and Earth on Page 2
Primary Homework Help, The Moon (2013)
Accessed 29 July 2021.