Earth and Space

Content
No. Title Page Number
Content
Introduction
i
ii
1.0
1.1
1.2
Observation Report
Sketch of horizon of night sky
Observation Aids
1
4
11
2.0
2.1
2.2
2.3
Reflection of Observation
The Celestial Sphere
Relationship between motion of celestial objects
and the observed night sky
Predictions, analysis and explanation of
difference in observations with change in
location, time and direction
12
12
13
13
3.0
3.1
3.2
3.3
Discussions
Changes occurring in apparent movement of
celestial bodies throughout a year
Rotation and revolution of earth and the rising
and setting of stars
Use of computer applications and software in
increasing understanding the relationship of the
earth and celestial bodies
18
18
20
21
4.0 Conclusions 27
5.0 References 28

Introduction
Astronomical objects or celestial objects are naturally occurring physical entities,
associations or structures that current science has demonstrated to exist in the observable
universe. The universe means objects in the sky including planets, satellites, stars, galaxies,
asteroids, meteoroids, comets and many others. The sun is the center of the solar system
surrounded by planets and celestial bodies in space. Eight major planets orbit the sun are
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. All the planets in the solar
system moves around the sun in space.
All the planets except Mercury and Venus have natural satellites that constantly orbit
the planet. Natural satellites named “Moon”. The moon does not emit light but reflects light
from the sun. Planet moving at maximum speed when approaching the sun and moving with
minimum speed limit when away from the sun. Each planet also rotates on its axis at different
speeds and have the force of gravity which vary also. The gravitational pull of the sun will
prevent the planets and other objects in the solar system of floating in space. At the same time,
the forces resulting from rotational movements of planets and prevent it from being pulled
down into the center of gravity of the sun. Due to the distance of the planets is far from Earth,
then the planets can not be seen with the naked eye.
At night we can see different types of stars in the sky. There are about 6000 stars may
be seen with the naked eye without the aid of a telescope or binocular. There are billions of
stars in the universe. Most of them are too far away to be seen even with a telescope or
binocular. Stars appear to twinkle as the light travels through the earth’s atmosphere.
Among the important factors in assessing the movement of the Earth and the celestial
objects was taking pictures in the sky. Thus, computer applications such as Google Sky Map,
Planetarium Softeare, The Night Sky or Stellarium is used in making observations. Then,
make a reflection about the movement of the earth and the celestial objects change with time
during the night. In addition, the celestial objects changes over the course of a night should
also be studied

1.0 Observation Report
As the Sun sets, and the sky gradually grows darker, the stars begin to appear. They
are always there, but while the Sun is shining, the atmosphere is lit by its brilliance and the
stars’ faint light is lost in its glare.
Movement of the stars from Earth were observed on the night of October 21, 2014
(Tuesday) for four hours, from 8:00pm until 11:00pm. The location was chosen to make the
observation is in Ipoh, Perak. The time recorded is starting from 8:00pm to 11:00pm. On that
observation night, many groups of stars are appeared but the moon and planets do not visible.
The horizontal, orientation and the stars are sketched in Figure 1.1.1, Figure 1.1.2, Figure
1.1.3 and Figure 1.1.4 according to the certain time, such as 8:00pm, 9:00pm, 10:00pm and
11:00pm. The Figure 1.1.5 have shown how the position of the celestial objects change over
the course with time during the night.
Based on the observations that have been made, it appears the stars move through the
sky, they remain in the same pattern. Namely, the ‘distance’ between any two stars never
change. Which remain outstanding pattern encourages us to connect the dots to create mental
pictures, called constellations. One particular star pattern can move across the sky and turned
to the side or upside down, but it will not grow larger or smaller, or change its shape in any
other way.
Figure 1.1.1 have shown the stars that exist at 8:00pm. When he arrived at 9:00pm,
the stars also sketched in Figure 1.1.2. After that, 10:00pm is the time to sketch the stars at
the third time in Figure 1.1.3 and Figure 1.1.4 is at 11:00pm. After combination of the four
observations in Figure 1.1.5, we can see that certain stars are moving upwards on the sketch,
it means that the stars move westward. Based on sketches made, it appears the stars are
moving from bottom to top, such as from east to west. Actually, the stars do not move on
space, it is due to the movement of the earth in space. Found that the earth moved from west
to east, this situation has caused us seen the stars move from east to west. The software
“Stellarium” has been used to take pictures of planetary motion and the stars. Please refer to
Figure 1.1.6, Figure 1.1.7, Figure 1.1.8 and Figure 1.1.9.
During the time that it takes the sky to gradually darken, the positions of the stars are
gradually changing. They do not change position relative to each other. In fact, their positions
relative to each other are so permanent and unchanging that we sometimes refer to them as

the fixed stars. However, gradually move across the sky, rising in the east and setting in the
west in the same way that the Sun does during the day. The motion of the stars like a mirror
image of the rotation of the Earth. As we rotate around our axis of rotation, anything not
attached to the Earth appears to move in the opposite direction from the motion of the Earth.
The Earth’s rotation is toward the east, so the stars move toward the west.
The rising and setting points of celestial bodies such as the stars and planets are
determined by their positions on the celestial sphere. The celestial sphere is an imaginary
sphere with the earth at its center. The sky overhead is the half of the sphere we see from
earth, appearing as a dome, even though the sky extends infinitely into space. The other half
of the sphere is below the circle of the horizon.
Figure 1.0.1 : The celestial sphere
The sphere appears to be rotating from east to west every twenty-four hours, so
celestial bodies appear to rise in the east and set in the west. The earth’s rotation creates the

illusion that the celestial sphere is rotating. The Celestial Sphere rotates on the Celestial Axis,
which goes through earth’s north and south poles and extends out to the Celestial Sphere
intersecting it at the North Celestial Pole (NCP) and the south Celestial Pole (SCP). The
Celestial Equator is an imaginary line around the middle of the Celestial Sphere, equidistant
from the NCP and SCP and on the same plane as the earth’s equator. It intersects the Circle
of the Horizon at East and due West.

1.1 Sketch of Horizon of Night Sky
Figure 1.1.1 : Observation of night sky facing east at 8:00pm

Figure 1.1.5 : Combination of four observations

Figure 1.1.6 : Night sky facing east at 8:00pm

1.2 Observation Aids
Observation aids used for this assignment include binoculars and the computer
application Stellarium. Binoculars are an ideal option for beginners, as they are able to show
a wide field of vision, making it easy to look for celestial objects in the night sky. This is
good for first-timers, as a higher-power telescope magnifies only a particular spot in the sky.
Using binoculars also enables a right-side up and straight view of the sky, unlike a more
advanced astronomical telescope where the view is usually upside down and sometimes even
mirror-imaged. Binoculars used for astronomical purposes should best have larger front
lenses and high optical quality.
A computer application, Stellarium, was also used to complete this assignment. The
Stellarium software is extremely useful, showing a three-dimensional and realistic sky that
shows what is visible and even celestial bodies that are not visible to the naked-eye. Tools
provided in the software are highly practical and versatile. Celestial objects present can be
identified, and even constellation lines can be drawn. These are just a few of the many
various ways the software can be utilized.

2.0 Reflection on Observation
2.1 The Celestial Sphere
Celestial objects in the sky appear to move when seen from Earth. This observation is
in fact due to, not the stars and planets moving around earth, but instead due to the rotation of
the Earth itself within the celestial sphere. The celestial sphere is an imaginary sphere
centered on the Earth with the same center point and rotational axis. The celestial objects
such as the stars, moon and planets are situated somewhere within this non-rotating celestial
sphere. Thus, as Earths rotates from west to east, we will consequently observe the movement
of the celestial objects from east to west. Stars observed in the sky will therefore appear to
move from east to west as the Earth rotates within the celestial sphere. However, there is a
difference in the way these movements would appear depending on the origin of observation,
that is, the location from where the observer stands. For instance, observers located at the
equator, the pole, and a location between the equator of the pole would observe different
movements. This concept will be explained in further detail in later discussions.
Figure 2.1.1 : The celestial sphere and its components

2.2 Relationship between motion of celestial objects and the observed night sky
From the observation, we can also note the difference between the movement of the
stars and the movement of the moon. The difference can be explained by understanding the
motions of stars and the moon (and sun) in space with respect to Earth. As mentioned earlier,
the star movement observed is due to the rotation of the Earth. Due to the spin, we would be
able to observe the stars rise and set, similar to the sun and moon. However, in addition to
this rising and setting, the sun and moon have an additional motion across the sky. This is the
orbiting of the moon around the earth, and the orbiting of the Earth around the sun. Stars do
not orbit the Earth like the moon does, hence the difference in movement. The motion of stars
that can be observed over a single night is caused by the rotation of the Earth, whereas the
motion that might be observed over the course of several weeks or months is due to the
orbiting of Earth around the sun.
Now that it is clear that the rising and setting points of the celestial bodies are
primarily determined based on their positions on the celestial sphere, a deeper explanation to
the phenomenon can be explored. Going into further detail, as stars basically appear “fixed”
on the celestial sphere as it rotates, they can be identified by giving coordinates which are
given in two numbers: declination and right ascension, which represent imaginary lines, very
much like latitude and longitude on the Earth’s surface. The coordinates are therefore given
by the intersection of these declination and right ascension lines. Corresponding to Earth’s
rotation, right ascension is measured from 0 hours to 24 hours around the celestial sphere.
Accordingly, one hour represents 15 angular degrees of travel around the 360 degree celestial
sphere. Declination is further divided into arcminutes and arcseconds. In 1º of declination,
there are 60 arcminutes (60’) and in one arcminute there are 60 arcseconds (60”). Right
ascension hours are further subdivided into minutes and seconds of time.
2.3 Predictions, analysis and explanation of difference in observations with change
in location, time and direction
Based on the observation, the movement of the celestial bodies appears to occur in a
certain direction and pattern. However, what if we now consider changing some element of
observation? Would the movement be the same? The element that will be discussed here is
the position of the viewer. Consider the same experiment, or observation that was done in this

paper, is done by observers from different parts of the world. Their observations may not be
the same as ours. This is because the latitude where the observer is located affects the rising
and setting of stars. For instance, at the Equator, the Celestial Equator is seen to intersect the
Circle of the Horizon at a right angle; thus celestial bodies would appear to rise and set
perpendicularly.
How does the latitude where the observation is being made affect the rising and
setting of celestial objects? This will be explained with the aid of horizon diagrams. At the
equator, where the celestial equator intersects the circle of the horizon at a right angle,
celestial bodies will appear to rise and set perpendicularly. The north and south celestial poles
are on the horizon, and stars around these poles will appear to rise and set in half circles,
above the horizon for 12 hours.
Figure 2.3.1 : Direction of rising and setting of celestial objects at the equator
Moving farther north from the equator will result in the curvature of the earth
revealing more and more sky around the north celestial pole and less of the sky around the
south celestial pole. This means that the angle of the celestial equator tilts to the south in
relation to the plane of the horizon. The angle of tilt is equivalent to the latitude of where the
observer stands. The diagram below illustrates this with an example showing observation
being done in Hawaii.

Figure 2.3.2 : Direction of rising and setting of celestial objects at 20 º North
On the other hand, moving south from the equator has the opposite effect, where the
angle of celestial equator in relation to the plane of the horizon is tilted to the north.
Figure 2.3.3 : Direction of rising and setting of celestial objects at 20 º South
In the case of the northern hemisphere, celestial objects that are north of the celestial
equator will be above the horizon for more than 12 hours because the observer sees more than
half of their total 24-hour path around them. Celestial objects on the celestial equator will be
visible for 12 hours and those south of the celestial equator will only be above the horizon for
less than 12 hours, as less than half of their total 24-hour path is seen. The opposite is true in
the case of the southern hemisphere.

If observations were to be made somewhere at the pole, with Earth’s rotational axis
directly overhead, and the celestial equator on the horizon (see diagram), some stars may
appear to move in circles around the pole and never set below the horizon. These are known
as circumpolar stars. These stars remain above the horizon throughout the year. For example,
at 20ºN, celestial bodies with declinations within 20º of the north celestial pole will no longer
rise or set. These stars appear to circle the north celestial pole. On the contrary, stars that are
always below the horizon of the observer are known as never-rise stars; they will not appear
any time throughout the year from that position. Celestial bodies with declinations within 20º
of the south celestial pole cannot be seen at 20º N as they circle the south celestial pole below
the horizon, unseen.
Figure 2.3.4 : Positions of celestial objects that affect visibility; such as circumpolar stars and
never-rise stars

Figure 2.3.5 : Movement of circumpolar stars seen by an observer at the pole

3.0 Discussions
3.1 Changes occurring in apparent movement of celestial bodies throughout a year
The night sky does not remain the same throughout a year, or seasons. This means
that positions and movements of celestial objects, whether the stars or the moon, change
according to season. Therefore, the night sky observed tonight will not be the same if it is
observed 3 months, 6 months, 9 months or a year later, even if the observer was to stand in
the exact same location and face the same direction. This difference is primarily because of
the movement of earth around the sun, which takes time. It takes 365 days (equivalent to a
year) for Earth to orbit once around the sun, therefore the changes in star and moon position
cannot be observed over the course of just a day. Stars will appear to rise and set, but in order
to see which one will, for example, be at the highest position at a particular time, it will take
several weeks or even months.
To illustrate the changes occurring throughout seasons or at different times of the year,
computer apps such as stellarium can be used. By watching the sky of, for instance,
somewhere in the northern hemisphere with the passage of time, it is observed that stars
gradually shift westward while new stars move up from the eastern horizon to take their place.
This shift is actually due to the fact that Earth completes a single turn on its axis not in 24
hours, but 23 hours and 56 minutes. This cause a difference in four minutes each night,
consequently making stars appear to rise and set four minutes earlier each night. By simple
arithmetic, the time amounts to an entire hour earlier in 15 days, or two hours earlier in 30
days. A difference in two whole hours per month result in the cycle completing a full circle in
a year (12 months x 2 hours = 24 hours).
When a person is standing in a particular moment in the year, several variables have
to be taken into consideration. This includes the direction in which the observer is facing and
the time at the moment of observation. A difference in either or both elements would result in
a difference in, say, the constellation highest in the sky at the moment observed.
Depending on where the observation is made, stars viewed from different positions at
different times of the year will appear to vary. Circumpolar constellations will always be
visible, but their orientation and position in the sky changes from season to season. Other
constellations that rise and set will only be visible at certain times of the year. As Earth
revolves around the sun, different parts of the celestial sphere are visible at night during the

different seasons. Stars that are visible at night are in the direction facing away from the sun.
As the earth rotates on its polar axis, it makes a slightly elliptical orbital revolution about the
sun in 365.26 days. Earth’s revolution about the sun corresponds to the cyclic and seasonal
changes of observable stars and constellations, and other celestial objects on the celestial
sphere.
What causes the difference in visible stars at night at different times of the year? To
answer this, we should first know the two major motions that affect earth: its rotation around
its axis and its revolution around the sun. We know from the initial discussion that the
rotation of Earth on its axis is what causes the nightly movement of stars across the sky. At
different times of the year, however, the cause of seeing different stars is the revolution of
Earth around the sun.
Figure 3.1.1 : Effect of time of the year on stars observed
The illustration shows that on a given day, at a given position, an observer will only
be able to see stars that are facing away from the sun. Stars that are at the back of the sun will

therefore not be visible on that day as they will be above the horizon at daytime, and we only
observe stars at night. After half a year, for example, the Earth will be on the opposite side of
its orbit, allowing us to observe stars that were not visible half a year ago (as they were
blocked by the sun). This explains the difference in stars observed over the course of a year.
3.2 Rotation and revolution of earth and the rising and setting of stars
In a year of cyclic seasonal change, the sun appears to travel completely around the
celestial sphere on the ecliptic and return to the vernal equinox. On the other hand, an orbital
revolution of Earth about the sun returns the sun to the same backdrop of stars. Seasons are
tied to the apparent movements of the sun and stars across the celestial sphere. In the
Northern Hemisphere, summer begins at the summer solstice (approximately June 21) when
the Sun reaches its apparent maximum declination. Winter begins at the winter solstice
(approximately December 21) when the sun’s highest point during the day is its minimum
maximum daily declination. The changes result from a changing orientation of Earth’s polar
axis to the sun that results in a change in the sun’s apparent declination. The vernal and
autumnal equinox are denoted as the points where the celestial equator intersects the ecliptic.
Corresponding to Earth’s rotation, the celestial sphere rotates 1 degree in four minutes.
Hence, sunrise, sunset, moonrise, and moonset all take approximately two minutes as both
the sun and moon have the same apparent size on the celestial sphere, that is, about 0.5°. We
know that the sun is much larger; however we should also take note that the moon is much
closer. Therefore, if measured at the same time of the day, the sun would appear to be
displaced eastward on the star field of the celestial sphere by approximately 1 degree per day.
Because of this apparent displacement, the stars would appear to “rise” approximately four
minutes earlier each evening and set four minutes later each morning. This further elaborates
the earlier discussion regarding the shift in stars caused by the four minute difference.
However, if measured at the same time each day, the moon would therefore appear to
be displaced approximately 13 degrees eastward on the celestial sphere in a day, therefore
rising and setting almost an entire hour earlier each day.

3.3 Use of computer applications and software in increasing understanding the
relationship of the earth and celestial bodies
Computer apps prove to be invaluable and extremely useful in further understanding
and exploring the apparent movement of celestial objects and how it affects what we observe
in the night sky.
We can use these computer apps to simulate what the sky would look like at a
particular place and time, and to observe how the stars appear to move as well as which stars
are visible and which are not. A connection can be made between the celestial sphere that
shows the entire sphere with the celestial objects around Earth, and the horizon diagram view
that shows what can be seen from a particular location at different directions.
Planetarium software can show us what the sky looks like in different latitudes of the
Earth, and how it would appear to move depending on which direction the observer is facing.
We can manipulate time, location, direction of observation and simulate night or even day
sky movement.
For example, using the rotating sky explorer, we can simulate the celestial movement
from, say, the United States:
Figure 3.3.1 : The rotating sky explorer application

The left diagram shows the position on Earth with respect to the celestial sphere. The
diagram on the right shows the horizon view diagram of the chosen location, and can be
manipulated to face any direction. Only stars above the horizon can be seen by the observer;
any star below the horizon is not visible.
By adding star constellations, we get the following:
Figure 3.3.2 : Observation from the northern hemisphere showing movement of the stars that
form the Big Dipper
The above example shows a person standing at the northern hemisphere (continental
US), and the star constellation of the Big Dipper has been added. From the animation (shown
in the diagram as a star trail, represented by the white lines), the Big Dipper is always visible
to the observer, and appears to move counterclockwise with time.
On the other hand, stars that form the constellation Orion (located close to the
celestial equator) rise very close to the eastern direction, and sets very close to the western
direction. The stars rise up and to the right (towards south):

form the Orion
The southern cross stars are positioned close to the south celestial pole:
form the Southern Cross

Thus, the stars will not be visible to a person at continental United States because the
stars stay completely below the horizon.
Facing different directions will, of course, affect how the stars appear to move. Facing
north in the northern hemisphere will cause stars to appear to rotate counterclockwise around
the north star (Polaris); while in the southern hemisphere, facing south, stars appear to move
clockwise around the south celestial pole. Other directions such as east will cause star trails to
angle. In the northern hemisphere, observers facing east will see stars move up to the right
toward the southern part of the sky, while if they face west, the stars angle to the left instead.
Stellarium is another computer application that is very useful to gain better
understanding and simulate the night sky (or even day sky) at any time, date and location. It
can also be used as a reference when observing the actual night sky, to know which stars and
celestial objects we should look out for during our observation. The diagrams below illustrate
how I used Stellarium to visualize the different night skies at different times of the year. In
this example I position my observation to be in Ipoh, Malaysia, facing eastern.
Figure 3.3.5 : Night sky in January facing east at about 10pm

Figure 13: Night sky in March facing east at about 10pm
Figure 14: Night sky in June facing east at about 10pm

Figure 15: Night sky in September facing east at about 10pm
Figure 16: Night sky in December facing east at about 10pm

The example shown was a very simple and basic use. The application allows for many
other uses and enables exploration of celestial objects, their movements and constellations.
4.0 Conclusions
The observations conducted for this assignment appear to obey the theory of motion
of celestial objects in space that has been discussed. Possible sources of error include unclear
skies due to the rainy weather. Also, as the observations are shown based on drawings, the
drawings cannot completely show the exact points of celestial objects seen. Other errors may
be due to improper usage of equipment. These tasks have taught me to understand the basic
concepts of astronomical movements and the celestial sphere in general. I have also learnt
how to use various computer applications to boost my understanding in more complex ideas
and theories, and also to experiment on several different possible factors that affect the night
sky. By completing these tasks I now have gained a more solid knowledge on our earth and
the celestial space around it.

5.0 References
Astronomyasylum.com, 2012. Celestial Motion Tutorial. Viewed 13th October 2014.
Available from: <http://www.astronomyasylum.com/celestialmotiontutorial.html>.
Cornell University, Astronomy Department, 2003. Ask an Astronomer: Why do different stars
appear with seasons? Viewed 15th October 2014. Available from:
<http://curious.astro.cornell.edu/question.php?number=300>.
David J Griffiths (1999). Introduction to Earth (3nd ed.). Prentice Hall. hlm. pp. 559-562.
Garcia, L and Lochner, J, 2014. NASA: Ask an Astrophysicist. Viewed 14th October 2014.
Available from: <http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970518.html>.
Lerner, KL, 2014. Celestial Sphere: The Apparent Motion of the Sun, Moon, Planets, and
Stars. Viewed 15th October 2014. Available from:
<http://science.jrank.org/pages/1304/Celestial-Sphere-Apparent-Motions-Sun-Moon-
Planets-Stars.html>.
Polynesian Voyaging Society. Hawaiian Voyaging Traditions: The Celestial Sphere. Viewed
13th October 2014. Available from :
<http://pvs.kcc.hawaii.edu/ike/hookele/celestial_sphere.html>.
Rao, J, 2011. Why the Night Sky Changes With the Seasons. Viewed 14th October 2014.
Available from: <http://www.space.com/10821-night-sky-changing-seasons.html>.
University of California, Berkeley Astronomy Department, 2011. The Sun and Stars in the
Celestial Sphere. Viewed 15th October 2014. Available from:
<http://astro.berkeley.edu/~basri/astro10-03/lectures/CelestialSphere.htm>.
Schroeder, DV, 2011. Understanding Astronomy: Motion of the Stars. Viewed 14th October
2014. Available from: <http://physics.weber.edu/schroeder/ua/StarMotion.html>.
Strobel, N, 2010. Motion of Our Star the Sun. Viewed 13th October 2014. Available from:

<http://www.astronomynotes.com/nakedeye/s5.htm>.
Strobel, N, 2010. Reference Markers. Viewed 13th October 2014. Available from:
<http://www.astronomynotes.com/nakedeye/s4.htm>.
Williams, J.R. & Thwaits, D.I. 1994. Sceince in Suria System. Oxford: Oxford University
Press.

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