Earth Science Past Paper PDF - BS Psychology

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Frances Tiffany R. Otanes

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astronomy earth science observational astronomy general science

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This document is a student's notes on earth science, possibly for a 2nd year BS Psychology course. It contains material on astronomy, observational astronomy, and the origin of the solar system. The document includes details about telescopes, observing sites, and general areas of study.

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Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY The “Laboratory” for Observational Astronomy EARTH SCIENCE Ground-based...

Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY The “Laboratory” for Observational Astronomy EARTH SCIENCE Ground-based and Space-based Telescopes Computers - for processing data The internet - for transferring and sharing data, access to journals, etc. The classroom - where ideas are shared and developed with the next ASTRONOMY generation of astronomers Primary Goal: Understanding the nature of the universe and its constituents Good Observing Site Means: Equipment building, research, teaching Minimal number of cloudy nights Minimal atmospheric turbulence General Areas Of Study Away from bright lights/cities Low water vapor ★ Solar – the study of the sun ★ Planetary – the study of planets, comets, asteroids, and debris around other Telescopes are thus located on Mountaintops stars ★ Stellar – the study of stars Mauna Kea Observatories, located on Mauna Kea on the Big Island of Hawaii ★ Galactic – the study of our Galaxy Elevation above sea level = 13,800 ft ★ Extragalactic – the study of other galaxies ★ Cosmology – the study of the origin & evolution of the universe In Desert Valleys ★ Owens Valley, California Research – Scientific Detective Work, the process of seeking out knowledge ★ Hypothesis In Space ★ Tools/Sample to Test Hypothesis The “Seeing” at various sites: ★ Propose for Observations Long Island, NY: > 5” ★ Obtain Observations Kitt Peak, AZ: ~ 1.5” ★ Reduce & Analyze data Mauna Kea, HI: ~ 0.5-0.8” ★ Modify Hypothesis HST: 0.05” Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY Not all wavelengths of light hit the ground Origin of the Solar System This is one reason why some air/space-borne missions are necessary Observing Mauna Kea 1. A cloud of gas & dust contracted (got smaller) to form a disk-shaped solar Observers sleep at a dormitory located at 10,000 ft nebula. Then drive to the summit with the telescope operator 2. The solar nebula condensed to form small planetesimals. 2 person rule - due to dangers of working at altitude 3. The planetesimals collided to form larger planets. Mauna Kea with Maui in the distance When the Solar System formed: ★ Clouds typically are below 10,000 ft 1. Radioactive age-dating indicates the Solar System is 4.56 billion years old. Gemini Telescope on Mauna Kea How the Solar System formed: How things move (dynamics) ★ All planets revolve in the same direction. ★ Most (but not all) planets rotate in the same direction. ★ Planetary orbits are in nearly the same plane. What they are (chemistry) Sun: Mostly hydrogen (H) and helium (He). Jovian planets: Rich in H and He, low density. Terrestrial planets: Mostly rock and metal, high density. A cloud of gas & dust contracted (got smaller) to form a disk-shaped solar nebula. The Solar System started as a large, low-density cloud of dusty gas. Such gas clouds can be seen in our Milky Way and other galaxies today. Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY Outer Solar System: The gas cloud initially rotated slowly. As the cloud contracted under its gravity, it ★ Metal and rock = solid planetesimals rotated faster. Quickly rotating objects become flattened. ★ Water, ammonia, and methane = solid ★ The flat, rapidly rotating cloud of gas and dust was the solar nebula. Hydrogen helium, and gaseous are everywhere. ★ The central dense clump was the protosun. ★ Similar flat, rotating clouds are seen around protostars in the Orion The planetesimals collided to form larger planets. Nebula. ★ The contraction of the solar nebula made it spin faster and heat up. ★ Planetesimals attracted each other gravitationally. (Compressed gas gets hotter.) ★ Planetesimals collided with each other to form Moon-sized protoplanets. The solar nebula condensed to form small planetesimals. Inner Solar System: Smaller planets, made of rock and metal. ★ Approximate condensation temperatures: Outer Solar System: Larger planets, made of rock, metal, and ice. ○ 1400 Kelvin: for metal (iron, nickel) ○ 1300 Kelvin: for rock (silicates) In addition, outer planets are massive enough to attract and retain H and He. ○ 200 Kelvin: for ice (water, ammonia, methane) Not every planetesimal was incorporated into a planet. ★ Inner solar system: over 200 Kelvin, only metal and rock condense. Comets = leftover icy planetesimals. ★ Outer solar system: under 200 Kelvin, ice condenses as well. Asteroids = leftover rocky and metallic planetesimals. As the solar nebula cooled, material condensed to form planetesimals a few km How does this “nebular theory” explain the current state of the Solar System? across. ★ Solar System is disk-shaped: It is formed from a flat solar nebula. Inner Solar System: ★ Planets revolve in the same direction: They formed from a rotating nebula. ★ Metal and rock = solid planetesimals ★ Terrestrial planets are rock and metal: They formed in the hot inner ★ Water, ammonia, methane = gas. region. ★ Jovian planets include ice, H, and He: They formed in cool outer regions. Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY VENUS (HOTTEST PLANET) PLANETS ★ Diameter: 12.104 kilometers (7.525 miles) ★ Mass: about 487 x 10 ^ 24 kilograms ★ Distance (Sun): 1082 million klometers MERCURY (CLOSEST TO THE SUN) ★ Length of Day: about 243 Earth days ★ Length of Year: about 225 Earth days ★ Surface Temperature: about 487 °C ★ Diameter of 4,880 km (3,032 miles), slightly larger than Earth's Moon. ★ Composition: The thick atmosphere may consist of carbon dioxide (about ★ High density due to a large iron core, making up 85% of its radius. 96.5%) with traces of nitrogen and other gases ★ Mercury has a thin exosphere ★ Greenhouse ★ Temperatures range from 430°C (800°F) during the day to -180°C (-290°F) at ○ Venus has one of the most extreme greenhouse effects in our solar night. system. It's thick atmosphere trap heat, resulting in scorching surface ★ The closest to the Sun; receives the most sunlight per unit area of any planet. temperatures shat can melt lead. ★ Completes an orbit around the Sun in 88 Earth days. ★ Thick Clouds ★ Takes 59 Earth days for one rotation; a single day on Mercury lasts 176 ○ Venus is blanketed by thick clouds composed mainly of sulfuric acid Earth days. These clouds make it nearly impossible to see the planet's surface. ★ First spacecraft to visit in the 1970s that mapped 45% of the surface ★ Volcanic Plain ★ Ice exists in permanently shadowed craters at the poles. ○ large volcanic feature called the Corona, which is a circular-shaped ★ Nmed after the Roman messenger god. ( Hermes) volcanic structure. These volcanoes and lava plains contribute to the planet's surface characteristics. ★ Inactive Plates ○ It lacks the movement of Earth's lithospheric plates, which leads to the absence of plate boundaries, earthquakes, and continental drift. ★ Retrograde ○ Rotates on its axis in the opposite direction (retrograde) compared to most other planets in the solar system. It spins from east to west, which is the opposite of Earth's rotation Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY ★ Has a weak magnetic field generated by its iron core. Its magnetosphere is ★ Mars has north and south poles like Earth, with polar ice caps covered in a much weaker than Earth's, providing limited protection from solar radiation layer of frozen carbon dioxide (dry ice). ★ Venus is the second closest planet to the Sun. ★ Martian days are called sols, short for solar day. ★ It is the hottest planet in the Solar System. ★ Mars has two small moons named Phobos and Deimos. ★ There are yellow clouds on Venus. ○ Phobos: The innermost and larger moon, heavily cratered with deep ★ Venus is the only planet in our Solar System that rotates clockwise. grooves on its surface. ○ Deimos: About half the size of Phobos, orbits two and a half times farther from Mars, and is covered in loose dirt that smooths its surface, MARS (RED PLANET) making it appear less pockmarked than Phobos. ★ Mars is one of the most explored bodies in our solar system. ★ it's the only planet where we've sent rovers to roam the alien landscape. JUPITER (GAS PLANET) ★ Named by the Romans for their god of war (Ares) due to its reddish color. ★ The Egyptians called it "Her Desher," meaning "the red one." ★ The largest planet in our solar system, named after the Roman god Zeus. ★ Diameter: 6,779 kilometers (4,212 miles) ★ Immense size, strong magnetic field, and a fascinating system of moons and ★ Distance from Sun: 228 million kilometers rings. ★ Length of Day: 24.6 hours ★ The fifth planet from the Sun. ★ Length of Year: About 687 Earth days ★ Diameter: About 86,881 miles; over 1,000 Earths could fit inside it. ★ Surface Temperature: -5°C to -87°C ★ The Great Red Spot, a gigantic storm larger than Earth, has been raging ★ Atmosphere Composition: Thin atmosphere, mainly carbon dioxide (95.3%), for at least 350 years. with traces of nitrogen and argon ★ Mars is called the Red Planet because of the iron in the soil. Orbital Characteristics ★ Mars is home to Olympus Mons, a dormant volcano and the largest volcano Orbit = the path one object takes as it travels around another object in space. and highest mountain in our solar system, standing 16 miles high and 600 km ★ Orbital Period: Has the shortest day of all planets, about 10 hours. across the base—three times the height of Mount Everest. ★ Rotation Period: Makes a complete orbit around the Sun (a year in Jovian ★ The biggest crater on Mars is Borealis Basin, spanning 5,300 miles and time) in about 12 Earth years. covering 40% of the planet’s surface. Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY Physical Characteristics ○ Io: The innermost of the four, the most volcanically active body in the solar system, with hundreds of volcanoes that can erupt plumes of ★ Size: With a radius of 43,440.7 miles or 69,911 km (twice as big as all the sulfur and gas reaching up to 300 miles into space. other planets combined). ○ Europa: The smallest of the Galilean moons, with a smooth, icy ★ Mass: 1.899 x 10²⁷ kg or 317.8 Earth masses surface. Beneath its crust lies a vast ocean of liquid water, raising the possibility of extraterrestrial life. Jupiter's Atmosphere ○ Ganymede: The largest moon in the solar system, larger than ★ Mostly hydrogen (about 90%) and helium (about 10%). Mercury. Features a mix of older, heavily cratered regions and ★ Distinct bands of clouds (belts and zones) created by strong jet streams younger, tectonically active areas. It also has its own magnetic field. moving in alternating directions. ○ Callisto: The outermost moon, heavily cratered with a relatively ★ Cloud Layers: intact surface. Offers clues about the early solar system and its ○ Upper Layer: Ammonia ice clouds, appearing white. formation. ○ Middle Layer: Ammonium hydrosulfide clouds, contributing to reddish-brown colors. ○ Lower Layer: Water ice and vapor clouds, which are not visible but SATURN (RINGED PLANET) affect weather patterns. ★ Note: Jupiter has no true surface. ★ Jupiter has a faint ring system made mostly of dust particles ejected from its ★ Massive ball made mostly of hydrogen and helium. moons by meteorite impacts. ★ second most massive planet in the solar system, about 95 times Earth's ★ The rings consist of three main components: the halo, main, and gossamer mass. rings ★ Saturn also has dozens of moons. ★ The farthest planet from Earth discovered by the unaided human eye, Moons (Io, Europa, Ganymede, Callisto IEGC) Saturn has been known since ancient times. ★ The planet is named for the Roman god of agriculture and wealth, who was Total Confirmed Moons: 95 also the father of Jupiter. Significant Galilean Moons: Io, Europa, Ganymede, and Callisto ★ Saturn's environment is not conducive to life as we know it. (discovered by Galileo Galilei in 1610). ★ Has the second-shortest day in the solar system. One day on Saturn takes only 10.7 hours. Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY Rings: ★ Uranus is not an ideal planet for human life due to its temperatures, pressures, and materials. ★ Saturn's rings are thought to be pieces of comets, asteroids, or shattered ★ A day on Uranus lasts about 17 hours. moons that broke up before they reached the planet, torn apart by Saturn's ★ Takes 84 Earth years or 30,678 days to complete a rotation around the Sun. powerful gravity. ★ Saturn is a gas-giant planet and therefore does not have a solid surface like Earth’s. But it might have a solid core somewhere in there. NEPTUNE (BLUE GIANT) ★ Strange hexagon-shaped jet stream around the north pole. ★ Saturn has a moon bigger than Mercury ★ Galileo Galilei was the first to observe Saturn's rings in 1610, although ★ The eighth and farthest known planet from the Sun. from his telescope the rings looked more like handles or arms. ★ at about 30 times the distance between the Sun and Earth (30 astronomical ★ Forty-five years later, in 1655, Dutch astronomer Christiaan Huygens, who units). had a more powerful telescope, proposed that Saturn had a thin, flat ring. ★ It is a cold, dark, and icy planet. ★ The only planet in our solar system not visible to the naked eye. ★ The surface is a hot pressurized ocean of water, methane, and ammonia ice surrounded by a layer of clouds. URANUS (ICED GIANT) ★ Atmosphere: Made of hydrogen, helium, and methane, which gives Neptune its rich blue color. ★ Core is 1.5 times the size of Earth, making up about 45% of the planet's ★ Uranus is a very cold planet, because of a collision that happened about 3 to mass, and is composed of water ice and silicate rock. 4 million years ago ★ Six rings encircle the planet: Galle, Le Verrier, Lassell, Arago, and Adams. ★ Four times bigger than Earth. ★ Only one spacecraft, Voyager 2, has visited Neptune. ★ Rotates almost at a 90-degree angle from its orbit. While Earth rotates ★ In 2011, Neptune completed its first 165-year orbit since its discovery in counterclockwise (prograde movement), Uranus rotates clockwise 1846. (retrograde movement) ★ The methane gas is responsible for Uranus’s blue color. ★ the first planet was discovered with the help of a telescope, on March 13, 1781, by astronomer William Herschel. ★ Uranus was named after the Greek god of the sky. Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY ★ Oort Cloud: Comets in the sphere-shaped outer edge of the solar system, CELESTIAL BODIES about 50 times farther from the Sun than the Kuiper Belt; known as long-period comets due to their significantly longer orbital periods. Why do we see it? COMETS (DIRTY SNOWBALL) ★ The gravity of a planet or star can pull comets from their homes in the Kuiper Belt or Oort Cloud, redirecting them toward the Sun. ★ Redirected comets follow long, stretched ovals. ★ Large objects made of dust and ice that orbit the Sun. ★ As a comet accelerates toward the Sun (As they approach the Sun, they heat up ★ Best known for their long, streaming tails, which are formed when they rapidly, causing solid ice to sublimate directly into gas.), it swings around behind approach the Sun. it and then heads back to its original location. Some comets plunge directly ★ Leftovers from the formation of the solar system 4.6 billion years ago. into the Sun, disappearing forever. ★ Comets orbit the Sun in highly elliptical paths, taking hundreds of thousands ★ When a comet enters the inner solar system, either on its way in or out, it of years to complete. might be visible in our skies. ★ Heating: As they approach the Sun, they heat up rapidly, causing solid ice to sublimate directly into gas. Parts of a Comet ★ The closest point in a comet’s orbit to the Sun is called “perihelion,” and the most distant point is called “aphelion.” ★ The nucleus is a solid body a few kilometers wide, made of volatile ices (mainly water ice) and dust particles. Tail Formation ★ The coma is the atmosphere around the nucleus that forms when the comet nears the Sun and the ices turn into gas, carrying dust with it. ★ This gas, which includes water vapor, carbon monoxide, and carbon ★ The dust tail, which is white or yellow, forms from these dust particles and is dioxide, forms the comet's distinctive tail. pushed back by solar radiation. Where do comets come from? ★ The ion tail, which is bluish, forms from ionized gases in the coma and is pushed away from the Sun by the solar wind. ★ Kuiper Belt: Comets found in a wide disk beyond the orbit of Neptune; referred to as short-period comets. Famous Comets ★ Halley: Last seen in Earth's skies in 1986 and will return in 2061 on its 76-year journey around the Sun. Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY ★ Comet C/1995 O1 (Hale-Bopp): Had a nucleus about 37 miles (60 km) FACTS ABOUT ASTEROIDS wide, was visible to the naked eye for 18 months in 1996-1997, and orbits the Sun every 2,534 years. ★ Asteroids have water gullies–in 2015, scientists observed water trails called gullies on the asteroid Vesta. ★ Comet Hyakutake: Discovered on January 30, 1996, it had a nucleus 1-3 km ★ They are rich in minerals and water–carbon, silica and metals are common in wide, reached perihelion on May 1, 1996, and displayed a tail up to 100 asteroids, and some of them include water ice trapped in the debris. degrees long. ★ Some asteroids became the moons of planets–Some asteroids became the moons of planetsSome of them get pulled into a planet’s gravity and become ASTEROIDS their moons. Some moons of Mars, Jupiter, Saturn, Uranus, and Neptune have origins this way. ★ Asteroids are small, rocky objects that orbit the sun. Although asteroids orbit the sun like planets, they are much smaller than planets METEOR, METEORITE, METEROID Asteroid Belt ★ Most of them live in the main asteroid belt—a region between the orbits of ★ METEOROIDS are small rocky or metallic objects in space, ranging from dust-sized grains to boulder-sized objects. They originate from various Mars and Jupiter. sources, including shattered asteroids, comet debris, and collisions with planets. Where did asteroids come from? ★ METEORS are usually visible as they pass through the thermosphere, ★ They are left-over from the formation of our solar system. When the solar burning up due to friction and air compression. BRIGHT METEORS are system began about 4.6 billion years ago when a big cloud of gas and cust called FIREBALLS while EXPLODING METEORS are known as collapsed. BOLIDES ★ METEORITES are typically the size of pebbles or fists.There are three Are all asteroids the same? main types of meteorites: stony, metallic, and stony-metallic, with further subcategories based on their composition ★ NO TWO asteroids are alike as they are formed in different locations at different distances from the sun COMPOSITION AND CLASIFICATION ★ They are not round, they have JAGGED and IRREGULAR shapes ★ They are hundreds of miles in diameter, but many more are as small as ★ Mostly contain nickel and iron pebbles ★ Some stone meteoroids contain chondrules and are called chondrites ★ Most of them are made of different kinds or rocks, but some have clays or ★ Most meteoroids that cause meteors are millimeter-size metals, such as nickel and iron Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY ★ Stony meteoroids without chondrules are called achondrites, often formed ○ Solar Eclipse from extraterrestrial igneous activity. ○ Lunar Eclipse Lunar Eclipses EFFECTS OF METEORS ON THE ATMOSPHERE ★ It occurs when the Sun, Earth, and Moon align. ★ During a lunar eclipse , the Earth gets in the way of the sun's light hitting ★ Ionization of atmospheric molecules. the moon. ★ Source of Dust Particles from the atmosphere. DIFFERENT TYPES OF LUNAR ECLIPSES METEOR AND METEOR SHOWER ★ Penumbral Lunar Eclipse ★ Millions of meteors occur in Earth's atmosphere daily ○ The Moon travels through Earth’s penumbra or the faint outer ★ Meteors may occur in showers when Earth passes through debris left by a part of its shadow. The Moon dims so slightly that it can be difficult comet to notice. ★ Partial Lunar Eclipse NOTABLE METEORS AND METEORITES ○ An imperfect alignment of Sun, Earth and Moon results in a part ★ THE CHELYABINSK METEORITE of the Moon entering Earth's shadow. In a partial eclipse, Earth's ★ ALLAN HILLS 84001 shadow appears very dark on the side of the Moon facing Earth. ★ THE WINCHCOMBE METEORITE The shadow grows and then recedes without ever entirely covering the ★ THE THUNDERSTONE OF ENSISHEIM Moon. ★ Total Lunar Eclipse ○ A total lunar eclipse occurs when the Moon and the Sun are on exact opposite sides of Earth. Although the Moon is in Earth's LUNAR ECLIPSE shadow, some sunlight reaches the Moon. The sunlight passes through Earth's atmosphere, which filters out most of the blue light. This Eclipse makes the Moon appear red to people on Earth. ★ An eclipse happens when a planet or moon gets in the way of the sun's Why don't we have a lunar eclipse every month? light. ★ Moon's orbut is tilted by 5 degrees Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY 4. Brightening 5. Final SOLAR ECLIPSE FACTS Solar Eclipse ★ Solar Eclipse Follows a Cycle– solar and lunar eclipses repeat themselves every 18 years ★ The Moon coming between Earth and the Sun so that the Moon’s shadow ★ Solar Eclipses Only Occur at New Moon–At that time, the sunlit half of the sweeps over Earth’s surface. Moon is turned away from us, and the Moon is invisible to observers on Earth. ★ Solar Eclipses Have Been Both Feared and Revered–Many believed they TYPES OF SOLAR ECLIPSE were bad omens and astrologers could potentially lose their lives if they failed to predict one. ★ Partial Eclipse ★ Eclipse totalities are different lengths–Earth is not always at the same ○ The Moon passes between the Sun and Earth but the Sun, Moon, distance from the Sun, and the Moon is not always the same distance from and Earth are not perfectly lined up. Earth. ★ Annular Eclipse ○ The moon is farther from Earth and appears smaller. During this, LOW TIDE AND HIGH TIDE the moon doesnt fully cover the sun thus leaving a ring light on the edges. TIDE ★ TOTAL ECLIPSE ○ The moon completely covers the sun and the sky becomes dark. It ★ It is a regular motion of the sea’s and ocean’s level. This phenomenon can last for several hours and totality can range from a few seconds makes the water either go up or down. to 7.5 minutes. HIGH TIDE SOLAR ECLIPSE STAGES ★ When the highest part, or crest of the wave reaches a particular location, 1. Shadow Band high tide occurs; the tide gets high when the sea or ocean is closer to the 2. Bailey’s Beads Moon (as the water is strongly attracted by it). 3. Totality Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY LOW TIDE SPRING TIDES ★ Low tide corresponds to the lowest part of the wave or its trough, The tide ★ These are exceptionally high, high tides and unusually low, low tides. will get low once the water surface is no longer in front of the Moon and ★ They occur when the sun, moon, and Earth align during the new or full attracted by the centrifugal force. moon phases, combining gravitational forces that enhance the lunar tide. How does the moon affect our oceans? NEAP TIDES ★ The ‘pull’ created by the moon’s gravity causes our oceans to bulge. ★ These are moderate tides occurring when the sun and moon are at right ★ Bulges on the ocean’s surface cause high tides to two main regions of angles with each other. Earth. ★ At this position, the solar tide partly counteracts the lunar tide. ★ The timing of high (and low) tide changes a little bit each day across the ★ Within a lunar month, there are two occurrences of spring tides and two month. occurrences of neap tides. ★ In general, coastal areas experience two high and low tides every day, with high tides occurring 12 hours and 25 minutes apart. TIDE TABLES SUN AND EARTH ★ Since the moon and sun move predictably, we can draw up tables of data years in advance about the timings of high (and low) tides in any location ★ Revolves around the sun every 365.25 days. worldwide. ★ While this occurs, Earth also rotates on its own tilted axis, resulting in the changing seasons. FACTS How does the sun affect our oceans? ★ The theory that tides were caused by the moon was introduced in 150 BC by Seleucus of Seleucia. ★ Although the moon considerably affects tides, the sun also generates tidal ★ Tides are caused because the moon's gravity is pulling the water up, while the forces. earth's gravity is pulling the water down. ★ Solar tides are about half the size of lunar tides. They are considered ★ Maximal tides are caused when the moon, earth, and sun are aligned as the variations in the lunar tidal patterns rather than separate tides. sun's gravitational force adds to the moon's gravitational force at these times. ★ The world's highest tides can be found in Canada at the Bay of Fundy in the province of Nova Scotia. Frances Tiffany R. Otanes 2nd Year- BS PSYCHOLOGY ★ In most places in the oceans, there are two low tides and two high tides each day, but some places only have one. ★ Spring tides (larger tides) happen when the new moon and full moon phase is occurring. When this happens the moon is on the same side of the earth as the sun. ★ Neap tides (weaker tides) happen when the moon is in its first quarter or last quarter phase. When this happens the moon is at a right angle to the earth-sun line.

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