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The night sky

Different branches of astronomy focus on different part of the universe

Earth’s motions

Earth undergoes 2 distinct motions: rotation and revolution

Effects of earth’s rotation

Day and night

Planets and Retrograde motion

Greeks called the 5 bright points wandering stars. Retrograde motion is the apparent slowing, reversal and looping of a planet in its path, occurs because the earth travels faster some planets

Perihelion and Aphelion

Perihelion is the point where earth is closest to sun, around Jan and aphelion is the point where earth is farthest away, around july.

Precession

Earth’s axis traces a circle every 26000 years, changing where the axis points.If the axis was extended to reach the star called Polaris and the name of the imaginary line is North Celestial Pole.

Effects of earth’s revolution

The earth’s revolution is going around the sun once, a revolution takes 365 ¼ days to complete on its elliptical path.

The seasons

The tilt of the axis causes the seasons. When the tilted side of the earth faces the sun (earth is closer to aphelion), that is summer. When the tilted side is facing away from the sun (closer to perihelion), it’s winter.

Constellations

Astronomers recognize 88 different patterns of stars, any other pattern between stars are not considered official constellations, like the Big Dipper. Those are called Asterisms.

Celestial Sphere

The celestial sphere was a model used by ancient astronomers to explain the sky in relation to the earth. This model, with the stars, planets, and sun held together in fixed positions as they spun around earth, was eventually replaced about 2000 years later. The celestial equator divides the night into 2 hemispheres, the plotting system is set up to mark longitude and latitude to show position of stars.

Plane of the ecliptic and Equinoxes and Solstices

Plane of the ecliptic is the path taken by the sun marked by the 12 constellations. Equinoxes occur during March 21 and Sep 22 when the sun crosses the celestial equator and Solstices occur when the sun reaches either highest and lowest positions in the sky in june 21 or dec 21.

Circumpolar constellations

Some constellations never disappear below the horizon as earth rotates, such as the Ursa Major and Ursa Minor and Cassiopeia.

Phases of the moon and Lunar cycle

The moon causes ocean tides, responsible for eclipses. The moon’s phases have 8 distinct stages, New->Waxes->Full->Wanes->New again

Eclipses and Tides

Sun and moon appear as the same size in the sky and cover the other. Solar eclipses occur when This only occurs every 2 years. Tides are the alternative rising and falling of the surface of large bodies of water, the gravitational pull of the moon on earth results in the ocean bulging in the direction of the moon. Neap tides are when the sun and moon are perpendicular to earth, weaker than spring tides. Spring tides are when sun->earth->moon.

Formation of the Solar system

Nebula consists of hydrogen and helium and, to a lesser extent, iron, rock and ice. Properties from a supernova that moved closer due to gravity.-> Nebula collapses due to internal pressure and temperature increase. Continues to collapse as particles are drawn to it. When the nebula is large enough, reactions within start to occur.-> Reactions =explosions. At the core of the nebula, the sun is forming and starts to rotate due to condensing gaseous material. Eventually, the increased speed causes matter to spread out.-> The bulge in the middle is the sun, and smaller cool matter begin to appear, called protoplanets.-> Protoplanets forced together by gravity, condensed to form planets that follow defined orbital paths, sweeping up leftover debris, becoming bigger in the process.

Outer planets and Terrestrial planets

Gaseous planets, consists of mainly hydrogen and helium gases, have low densities; planets similar to earth with solid chunks of matter molded together, slow rotations, solid metal cores, solid surface and no rings, respectively

Formation of the Moon, The Big Splash Theory and Apollo

Smaller objects were attracted to larger objects by the gravitational pull of the larger body of mass. 4.5 million years ago, an object the size of mars collided with earth caused extreme high temperatures and pressure making dense materials into earth’s core while less dense material flew away. Some materials were in the same region and gravity pulled them together to form our moon. Apollo landings supported evidence when no less dense material found on surface, something that happens when there was extreme heating and a smaller core made of nickel.

A closer look at the planets

The sun and most planets have magnetic fields that extend into space.

Mercury

Closest to sun, daytime temperature =427*c and nighttime temperature=-173*c because it has no atmosphere to trap heat. Rarely visible during night because too close to sun. many craters because of collisions with meteorites. Orbits at 50 km/s, the fastest out of all the planets, sluggish rotation, only 3 every 2 revolutions. Transit is when people can watch mercury pass in front of sun 13 times each century.

Venus

Atmosphere composed of carbon dioxide, C2O act like glass of greenhouse, keeping temperatures high enough to melt lead. Temperature =462*c.Volcanoes on surface. Besides moon and sun, brightest object because of closeness and atmosphere reflect sunlight, sometimes called morning or evening star. Harsh surface. Transits occur in pairs. Share similar qualities to earth. Rotate in clockwise direction.

Earth

Ideal for life,atmosphere contains nitrogen, oxygen and water vapour. Has ozone that filters some radiation from sun and maintaining level temperature between day and night. 70% water. Many impact craters. Rich fertile land for plant life. Weathering, erosion, volcanoes and earthquakes changing surface of earth, still considered stable. Has magnetic field, reason for auroras.

Mars

Temperature ranges from -90*c to -5*c. Called red planet because of red soil. Dust storms engulf mars periodically. Dry and barren land today but evidence shows it had water and volcanoes, possible life existed there.

Other objects in our solar system

Objects beyond Neptune known as trans-neptunian objects, consisting of planetoids, kuiper belt, and the oort cloud.

Aboriginal Legends

Aboriginal people and other cultures hold traditional views of universe that differs from a scientific view, trying to interpret astronomical objects and events. Kwakwaka’wakw- lunar eclipse, Menomini- meteors, Haida- origin of universe Tsimshian- stars and moon formed.

Ancient Science

One of oldest sciences, used sun and moon cycles to create calendars to decide harvest and feast times. Chinese created 365 calendar and mayan accurately maps stars.

Ptolemy

Endorsed by catholic church and roman emperors, tried to explain sun and planet motions using a geocentric model, helped creating the christian calendar. Knew earth was sphere.

Copernicus

Geocentric model supported by church and any opposition taken as a threat to the church. Found mathematical errors on geocentric and created heliocentric but not made official because it raised to many questions against church.

Brahe

Man of Learning, dubbed by denmark king. Witnessed a supernova.

Galileo

Made telescopes, discovered jupiter’s moons and saturn’s rings, called father of scientific method. Forced to house arrest and take back his beliefs.

Kepler’s Laws of Planetary Motion

Planets travel in elliptical orbits around off center Sun at one focal point. The speed of planet depends on distance from sun. Close->faster and far->slow.

Newton

Force of gravity depends on mass of object and distance between them. Closer = more gravitational pull.

Modern Astronomy

Prediction of returning comet by Edmund Halley. Williams Herschel discovered uranus and moons outside of solar system. George-Henri Lemaitre (priest) credited with big bang theory.

Origins of the universe and Expanding universe

Hubble confirms existence of other galaxies and expanding universe. Galaxies moving away from us . Hubble relied on spectroscope to discover the elements in stars and whether it’s moving away.

Big Bang and Modern support

13.7 million years ago, an enormous fireball hurled everything outward in a big bang. Using a microwave antenna in 1965, detected radiation coming from every direction and the belief is that these are the remnants of big bang and probably represents outer boundary of our universe.

COBE and WMAP

Revealed a structure in the early universe that led to the formation of the galaxies.

Measuring distance in space

Vast distances in space are measured using parallax, cepheid variables and red shift.

Cepheid variables

Unstable, yellow supergiants about 1000 times brighter than our sun and pulse, change in size and brightness. Are called Standard Candles, object’s bright and predictable behaviour used to measure distance from earth.

Red shift

The farther an object’s spectral lines shifted to the red end of the spectrum, the faster the object is moving away. The connection is a direct result of our expanding galaxy. Useful way to measure distance of most remote galaxies.

Absolute magnitude and apparent magnitude

Absolute magnitude is the actual amount of light a star gives off, recorded at the standard distance. Apparent magnitude is the brightness of a star as it appears in the night sky.

Birth of stars, and the sun and Stellar birth

Life cycle: birth, midlife, end. When the thermal heat during the formation of the Sun becomes an enormous amount, it ignites.

Nuclear Fusion

Temperature and pressure high, hydrogen nuclei fuses to form helium nuclei. This causes a small loss of mass. Energy and subatomic particles go outwards and thermal expansion counteracts the force of gravity and stops the gravitational collapse of a star.

Stellar Midlife

Mass loss during H->He becomes energy. Might take hundreds of years to travel to outer layers of sun where it released as light.

Solar Anatomy

Core- radiative zone- convective zone- photosphere- chromosphere- corona

Sun’s Surface

Texture similar to boiling tomato soup and a tile mosaic, heated material rises, cools and sinks back. Sunspots are dark spots caused by disturbances in sun’s magnetic field.

Prominences and Flares

Regularly releases glowing hydrogen from photosphere called solar prominences. Solar flares occur above active sunspots, and is charged particles and gas caused by rapidly changing sunspots. Also emits x-rays and ultraviolet radiation. Sunspots in pairs have different polarities and thus cause the magnetic fields in between to loop and tangle.Solar wind disrupts our communications equipment and other electronic systems.

Star: old age, death, and new life

At the end of a star’s life, it either fades out or explodes in life re-newing cycle.

Hertzsprung-Russell diagram

Designed by Hertzsprung and Russell, shows temperature and luminosity(energy output). The sun is the set standard (in a diagonal band called main sequence). It also represents the different stages of a star’s life as fuel is consumed.

Red giant to white dwarf

Outward energy slows and core contracts-> heats up in core, restarts fusion-> outer layer expands then cools and sends out streams of gas and dust away until it loses enough solar mass to be a stable white dwarf (less than 1.4 solar masses).

Supernovas

Releases big amounts of energy and matter, creating a nebula, depending on mass of the star, produces either a neutron star or a black hole.

Neutron Star

If solar mass between 10-50 solar mass, supernova produces a neutron star. Core is made of neutrons tightly packed together that 250ml of core mass is millions of kg.

Pulsar

Type of neutron stars that sends out light and beams of high energy radio waves, rotates while giving off light like a lighthouse.

Black hole

Object’s mass and gravitational pull is immense, won’t even let light escape, no longer a star.

Galaxies and our home: the milky way and Local group

Has 200 billion years, is an average galaxy, part of the neighbourhood of galaxies called Local Group. Milky way's neighbouring galaxies that don’t move away as universe expands. Local group has over 24 galaxies and smaller systems.

The milky way

The number of stars in our neighbourhood is relatively low, if we were 6000 years closer to the center then the sky would be lit always.

Galaxy center

There is a black hole in the center of our galaxy, hidden behind clouds of dust and gas. The black hole has a mass of 2 x 10^6 solar masses and the diameter is 15 times the sun.

Quasars and galaxy

Quasars are starlike objects that emit powerful radio waves, thought to created when 2 galaxies collide. The largest black holes are thought to be found in large galaxy clusters.

Star clusters

Globular clusters are spherical, tight group of stars, ranging from new stars to old. The milky way has 150 globular. Open clusters have spiral arms, only a handful in cluster and easily influenced by other galaxies to spread apart.

Dark energy and the expansion of the universe

Oscillating theory contradicts the existence of clusters and is wrong. But what mass holds the galaxies together?

Dark matter

May be some form of particles yet to be discovered that gives the mass needed for the galaxy not to fall apart.

Dark energy

Stabilizing force that's strength increases with distance. It’s energy in empty space that works against gravity and speeds up the expansion of the universe.

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