Topic Summary: Earth and Universe
A. Model of the universe
Human in their curious mind has tried to make sense of their place in the universe ever since they throw their gaze to the sky. In general, there are 2 prevalent theories, or models that try to answer this ques�on.
1. Geocentric model
The geocentric model puts the Earth at the center of the universe, with all celes�al bodies orbi�ng around it. This model was the predominant descrip�on of the cosmos in many European ancient civiliza�ons, such as those of Aristotle (Greece, 4th century BC) and Ptolemy (Egypt, 2nd century AD).
Two observa�ons supported the idea that Earth was the center of the Universe:
• First, from anywhere on Earth, the Sun appears to revolve around Earth once per day. While the Moon and the planets have their own mo�ons, they also appear to revolve around Earth about once per day. The stars appeared to be fixed on a celes�al sphere rota�ng once each day about an axis through the geographic poles of Earth.
• Second, Earth seems unmoving from an earthbound observer's perspec�ve; it feels solid, stable, and sta�onary.
• Although the model can explain some aspects of the solar system, it fails to explain several phenomena such as: o The geocentric model could not explain the retrograde mo�on of some planets, which appeared to
move backward in the sky at certain �mes.
o The varia�on of seasons, which depended on the �lt of Earth’s axis and its distance from the Sun.
The geocentric model assumed that Earth’s axis was always perpendicular to its orbit and that its distance from the Sun was constant.
2. Heliocentric model (Current model)
The heliocentric model puts the Sun at the center of the solar system, with all planets, including Earth, orbi�ng around it. This model was first proposed by Aristarchus of Samos in the 3rd century BC, but it was not widely accepted un�l the Copernican Revolu�on in the 16th century.
The heliocentric model was supported by the observa�ons and calcula�ons of Copernicus, Kepler, Galileo, and Newton, who showed that the mo�ons of the planets were ellip�cal and governed by the laws of gravita�on. The heliocentric model also explained some phenomena that were difficult to account for in the geocentric model, such as the phases of Venus, the retrograde mo�on of Mars, and the varia�on of
seasons. Figure 1: Nicolaus Copernicus
B. The earth
• The Earth takes 24 hours to rotate once on its axis. (This makes a day). It rotates 360° in a 24 hour period, so the Earth rotates at a rate of about 15° per hour. Therefore, the Earth has been divided into 24 �me zones.
• Time Zones are a geophysical world globe division of 15o each, star�ng at Greenwich, England, created to help people know what �me it is now in another part of the world. These lines on a globe are called Time Meridians.
•
The star�ng point for the standard �me zones is the Prime Meridian, 0° (which passes through Greenwich, England)• To calculate the �me at 2 different loca�on, you can determine its difference first, then use the differences to figure out the answer. Here are some examples.
Ques�on:
The clock in Jakarta (GMT+7) shows 20:00. Determine the what the clock will show in:a. Jayapura (GMT+9)
Time difference = Target City Time Zone – Origin City Time Zone
1) The �me difference between Jayapura (target city) and Jakarta (origin city) is
(+9) – (+7) = +2
Target City Time = Origin City Time + Time Difference (in hour) 2) Time in Jayapura (target city) is
20:00 + 2 (hour) = 22:00
b. Mexico City (GMT-6)
1) Time difference between Mexico City and Jakarta is
(-6) – (+7) = -13
2) Time in Mexico City is
20:00 + (-13 hour) = 7:00
• The day and night cycle can have profound effects on various aspects, including life.
Effects of day and night life cycle towards life on earth.
• The day and night cycle regulates the circadian rhythms of many living organisms, which are biological processes that follow a 24-hour cycle. These rhythms influence sleep paterns, hormone levels, body temperature, metabolism, and behavior.
Human feel sleepy at certain time of the day Nocturnal animal active during night
• The day and night cycle also influences the ciralunar rhythms of some living organisms, which are biological processes that follow a lunar cycle. These rhythms affect migra�on, naviga�on, reproduc�on, and other ac�vi�es that depend on the phases of the Moon.
Turtle lay egg at certain lunar phase
• The day and night cycle affects the �des of the oceans, which are caused by the gravita�onal pull of the Moon and the Sun. The �des create dynamic habitats for marine life, such as inter�dal zones, coral reefs, and estuaries. The
�des also influence the distribu�on of nutrients, salinity, temperature, and oxygen in the water.
Many marine animal depends on the cycle of tidal pool
• The day and night cycle affects the light that reaches the Earth’s surface, which is essen�al for
photosynthesis, vision, and biological clocks. Light also affects the colora�on, camouflage, communica�on, and preda�on of many animals. Ar�ficial light can disrupt the natural balance of light and dark, causing nega�ve impacts on wildlife and ecosystems.
This Photo by Unknown Author is licensed under CC BY-NC-ND
• Day and night are caused by the Earth spinning on its axis and making one complete revolu�on every 24 hours.
• The Earth is a planet of the Sun travelling in a nearly circular orbit around the Sun, and the Moon orbits the Earth as a satellite.
• The seasons occur due to the mo�on of the Earth around the Sun once in approximately 365 days.
• Always remember that seasons on earth occur due to the unequal distribu�on of solar energy on earth surface, due to earth shape and its �lt
• The more direct solar radia�on fall on earth, the higher its energy is being concentrated. More energy means warmer season.
C. The Moon
• The moon is a satellite of the Earth and travels round it in an approximately circular orbit approximately once a month at an average distance away of about 400 000 km.
Like Earth, the Moon has a day side and a night side, which change as the Moon rotates. The Sun always illuminates half of the Moon while the other half remains dark, but how much we are able to see of that illuminated half changes as the Moon travels through its orbit.
Earth's Moon's rota�on and orbital periods are
�dally locked with each other, so no mater when the Moon is observed from Earth, the same hemisphere of the Moon is always seen. Most of the far side of the Moon was not seen un�l 1959, when photographs of most of the far side were transmited from the Soviet spacecra� Luna 3.
• Moon formed during a collision between the Earth and another small planet, about the size of the planet Mars. The debris from this impact collected in an orbit around Earth to form the Moon.
• Tides is the fluctua�on in the level of water on earth. High �de is when the water level reach the highest point while low �de is when the water level at its lowest point.
Ocean bulging due to moon gravity
It might seem strange that the ocean would bulge on the side farthest from the Moon as well as the side closest to it. This happens because the Moon’s gravity affects the en�re Earth, pulling at every point on our planet. The strongest pull occurs on the points closest to the Moon, and the weakest on the points farthest away, but every bit of water is affected.
Demonstration on why there are 2 sets of tide each day
As Earth rotates within this layer of water, its
landmasses pass through the two bulges. These bulges are Earth’s high �des. Most shorelines experience two high and low �des per day. One high �de to high �de cycle (or low �de to low �de cycle) takes a litle over 12 hours.
Spring �de is a period where the sun, earth and moon align, crea�ng a larger than usual �des. This is due to the moon and sun gravity reinforcing each other. Neap Tide refers to a period of moderate �des when the sun and moon are at right angles to each other. In this posi�on, moon and sun gravity’s effects on the ocean is counteract ech other.
• What is an eclipse? An eclipse happens when a planet or a moon gets in the way of the Sun’s light. Here on Earth, we can experience two kinds of eclipses: solar eclipses and lunar eclipses.
• Why don’t we have monthly solar/lunar eclipse? The Moon’s orbit is �lted about 5 degrees compared to the plane of Earth’s orbit around the Sun. Because of this �lt, the Moon as seen from Earth’s perspec�ve usually passes above or below the Sun when it passes between us and the Sun. The �lt of the Moon’s orbit prevents us from having monthly solar and lunar eclipses.
• Why staring directly at solar eclipse is dangerous? During a solar eclipse, the moon blocks some or all of the sun’s brightness, making it seem less harmful. However, even a small amount of exposure to the sun’s rays can cause serious harm to your eyes, namely burned re�na among other effects.
D. Objects in the solar system and galaxies
1. Planets
a. Etymology: Greek word for wanderer b. Characteris�cs:
i. Enough mass to be rounded by its gravity ii. Cleared space debris in its orbit
c. Classifica�on
i. Inner planet: Mercury, Venus, Earth & Mars ii. Outer Planet: Jupiter, Saturn, Uranus & Neptune
Tabel 1 Difference of Inner and Outer planets
Inner Planet Outer Planet
Size Rela�vely small Rela�vely large
Density Rela�vely dense Rela�vely less dense
Composi�on Mostly rock and metal Mostly gas
Atmosphere Rela�vely thin Rela�vely thick
Loca�on Between asteroid belt and sun Between asteroid belt and Kuiper belt
2. Dwarf planets
a. Characteris�cs:
i. Enough mass to be rounded by its gravity ii. HAVE NOT Cleared space debris in its orbit
b. Loca�on: asteroid belt, Kuiper belt, scatered disk (beyon Kuiper belt) c. Example: Pluto, Eris, Ceres, Makemake
3. Asteroid
a. Characteris�cs
i. Not enough mass to be rounded by its gravity ii. No atmosphere
iii. May made up of metal, rock, or ice
b. Loca�on: Mostly concentrated in the asteroid belt, between the orbit of Mars and Jupiter 4. Comet
a. Characteris�cs
i. Not enough mass to be rounded by its gravity ii. Made mostly of ice
iii. May made up of metal, rock, or ice
iv. They have eccentric orbits that can range from several years to millions of years v. Grow tail of dust and glow bright as they approach the sun
b. Loca�on: Kuiper Belt (short term comet) or Oort Cloud (long term)
Image 1: An asteroid Image 2: Comet as it approach sun Image 3: Eccentric orbit of the two comets
