The Universe Flashcards
Theories on universe (geocentric, heliocentric)
Brightest celestial object
Venus (brightest major planet)
Venus is so bright because its thick clouds reflect most of the sunlight that reaches it (about 70%) back into space, and because it is the closest planet to Earth
Why can we see planets
They do not produce their own light, but reflect the sun’s light -> not like stars
Stars are
immense spherical masses of hydrogen gas undergoing a fusion reaction, producing helium and enormous amounts of light and heat energy
self-luminous astronomical object/celestial body of gas held together by self-gravity visible in the sky, especially at night
illuminating the sky, all born in nebulae (clouds of dust and mostly hydrogen gas) - begin life as protostars or hot cores formed by the collection and collapse of dust and gas - as it becomes hotter hydrogen nuclei inside cores begin to fuse and create helium -> called thermonuclear fusion which generates star’s heat and energy and causes it to shine
They are categorised by certain characteristics, such as surface temperature (spectral classes - hot-obafgkm-cool), amount of light they emit (luminosity classes - small, less bright white dwarfs -> large + extremely bright hypergiants).
Why do stars die
finite life and eventually exhausted the supply of fuel sustaining a fusion reaction in its core
most stars have enough fuel to last billions of years. When hydrogen runs out, stars that are about the size of the Sun expand and become a red giant — up to one hundred times their original diameter. As a red giant loses heat its core loses mass, blowing off outer layers and shrinking to become a white dwarf star.
brightest star in the sky
Sirius
closest star to our solar system
Proxima Centauri
‘apparent magnitude’ + determined by
amount of light a star emits used to describe/measure how bright an object appears in the sky from Earth/relative brightness of stars viewed from Earth
^ result of star’s distance from the Earth and how much light it emits.
idea of a magnitude scale dates back to Hipparchus (around 150 BC) who invented a scale to describe the brightness of the stars he could see.
DETERMINED BY: size (larger usually brighter), surface temperature (brighter -> higher -> white colour/cooler -> lower -> red)
magnitude scale
tellls us relative brightness (categorised)
Astronomers use the term ‘apparent magnitude’ when referring to the relative brightness of stars viewed from Earth.
- developed by the ancient Greeks around 150 BC
- put the stars they could see into six groups (brightest stars were placed in group 1, and called them magnitude 1 stars. Stars that they could barely see were put into group 6. So, in the magnitude scale, bright stars have lower numbers)
- a star that is one magnitude value lower than another star is about 2.5 times brighter. For example a magnitude 4 star is 2.5 times brighter than a magnitude 5 star and so a star that is five magnitude numbers lower than another star is 2.55 or 100 times brighter.
- extended to include those brighter than 1 and dimmer than 6
distance between the Earth and the sun
averages 150 million kilometres
why do stars twinkle?
This is because the light travelling from a star is distorted by the Earth’s atmosphere. The light is bent in all directions as it passes through the moving air of the atmosphere. This causes the image to change slightly in brightness and position and hence twinkle.
Pockets of warm and cold air in the Earth’s atmosphere bend light from a star, making the star appear to twinkle. - refraction when it passes through different mediums
Because of earth’s atmosphere, the light travelling from a star is distorted (affected by winds in the atmosphere and by areas with different temperatures and densities), which causes the image we gain of it to change slightly in brightness and position and hence twinkle. In space, there is no atmosphere to make the stars twinkle, allowing a much clearer image to be obtained.
why do telescopes get clear images
one of the reasons the Hubble telescope in orbit high above the Earth is so successful at capturing clear images of celestial objects. In space, there is no atmosphere to make the stars twinkle, allowing a much clearer image to be obtained.
constellation
A certain grouping of (visible) stars (located close-ish) forming a recognizable/perceived patternor outline that typically represent an animal, mythological subject or inanimate object (forming a picture if you imagine lines connecting them). They are traditionally named after its apparent form or identified with a mythological figure.
The group of stars within the 88 regions the sky is divided into.
Astronomers of ancient civilisations grouped stars according to the patterns or shapes they seemed to form. These shapes were usually of gods, animals or familiar objects.
distance between stars in constellations
When viewed from Earth, the individual stars in a constellation may appear to be very close to each other. However, they can be separated by huge distances in space and in fact have no real connection to each other at all. The stars that make up the constellation Orion, for example, are at very different distances from Earth.
constellations visible and not - their ‘movement’
Stars appear to move around the celestial poles due to the spin of the Earth
The constellations visible on any given night depend on the time of year. For example, Gemini and Leo are clearly visible in March but not in October.
In ancient times, it was thought the stars wandered through the night sky; today we explain the stars’ apparent movement in terms of the motion of the Earth through space as it orbits the sun.
Over the course of an evening, the positions of constellations appear to move from east to west. This is due to the Earth’s spin. Just like the sun and the moon, stars rise in the east and set in the west. A time-lapse photograph of the stars taken over several hours shows the changing positions of the stars due to the Earth’s spin.
ecliptic
the path that the sun traces in the sky during the year
the zodiac
twelve constellations with a special significance -> they pass through what is known as the ecliptic -> ancient greeks
the south celestial point
The central point around which the star trails appear to rotate. It indicates the Earth’s axis of rotation.
similarities + difference between star, planet and moon
A star is a sun which produces energy from nuclear fusion. A moon is a rocky celestial body orbiting another body. A moon normally orbits a planet, but a moon can orbit another moon until it gets pulled away by something larger. A planet is a large body orbiting a sun.
- all in common - gravity
- planets + moons - orbits
- moons + stars - visible in night sky from earth
Stars
A giant ball of gas that produces heat and light
large, glowing balls of hot gases, mostly hydrogen and helium. Typical properties are: Brightness, Color, Surface temperature, Size, Mass, Magnetic field, Metallicity, Luminosity, Movement, Wavelengths of light emitted (produces its own light)
Planets
- It must ORBIT A STAR (in our cosmic neighborhood, the Sun).
- It must be big enough to have enough gravity to force it into a spherical shape. -> LARGE ENOUGH TO BE ROUND
- It must be big enough that its gravity cleared away any other objects of a similar size near its orbit around the Sun -> CLEARED ITS ORBIT OF DEBRIS
All of them rotate in their own axis and revolves around the Sun. All are circular or oval in shape, they have a core.
Moon
objects that orbit planets
a celestial body that revolves around other bodies, specifically the planets (can also be dwarf planets or large asteroids - just not a star)
Most moons’ atmospheres are extremely tenuous (VERY THIN), so much so that their constituent molecules never collide with each other. Such collisionless atmospheres are called exospheres. The Moon has an exosphere, as does the planet Mercury
Gravity
An attractive force between objects that have mass; it keeps objects in orbit
Orbit
the path taken by one object around another because of gravity; for example, earth’s path around the sun
Satellite
any object in space that orbits around a larger body; such as the Moon or a space station that orbits Earth
Terrestrial planet
a planet that is mainly composed of rocks or metals and has a solid surface
Gas/jovian planet
a planet that is mainly composed of gases
Galaxy
a concentration of stars, gravitationally linked
a cluster of stars, dust and gas held together by gravity, such as the Milky Way
a system of millions or billions of stars (+ stellar remnants, interstellar gas, dust, and dark matter), together with gas and dust, held together by gravitational attraction.
larger, hotter stars appearance
slightly more blue compared to a smaller, cooler star
earth type of planet
terrestrial planet
The Local Group
made up of the Milky Way, the Andromeda galaxy and a few smaller galaxies.
The Milky Way, along with our neighbouring galaxy, the Large Magellanic Cloud, forms part of the Local Group of galaxies.
our local galactic neighbourhood, called the Local Group, is a collection of more than 30 galaxies within approximately 4 million light years of the Milky Way and gravitationally bound together. Two spiral galaxies, the Milky Way and Andromeda, are the two largest members of the Local Group. which also includes many dwarf galaxies such as the Magellanic clouds.
The Interstellar Neighbourhood
Local interstellar neighborhood is the grouping of nearby stars that can be easily observed and have parallax measured to.
sector of the Orion Arm of the Galaxy.
The virgo supercluster
The Universe
Observable universe
The region of space that is visible to us (either by our own eyes or with the aid of technology) - everything we have been able to see/observe up to this point
smallest to largest (virgo supercluster, sun, universe, milky way, solar system, local group)
sun, solar system. milky way, local group, virgo supercluster, universe
A group of galaxies is called
A cluster
The Hubble Space Telescope
Launched April 24, 1990
astronomers have traced the evolution and formation of galaxies, discovered that most galaxies contain supermassive black holes, and mapped the presence of the mysterious dark matter that makes up most of the universe’s mass and structure.
The James Webb Space Telescope
Replaced Hubble:
Launched 25 December 2021 at 11:20 pm AEDT, on an Ariane 5 rocket from Europe’s Spaceport in French Guiana, on the northern coast of South America.
INFO:
Andromeda
Distances of the furthest galaxies
Earliest and most distant supermassive blackholes
Identified composition of plantes atomsopheres
Chemical composition of stellar nurseries
Details about the atmospheres of extrasolar planets
More detailed images of every part of our universe in greater detail - allows scientists and researchers to gather and document more
Captured stars born in the pillars of creation through its capabilities as an infrared telescope - potentially helps us understand how stars form
Captured its first direct image of an exoplanet
Captured difficult to find Phantom Galaxy in infrared with Webb, showing the galaxy’s perfect spiral structure and its distribution of stars, arms extending outward from a radiant center. The image revealed fiber-like structures of heat-emitting dust and gas, emanating from a bright center rendered in vivid electric blue - shedding light on star-forming regions scattered amongst the galaxy’s spiral arms -> allows astronomers to pinpoint star-forming regions in the galaxies, accurately measure the masses and ages of star clusters, and gain insights into the nature of the small grains of dust drifting in interstellar space
Captured a Wolf-Rayet star
Made to observe the most distant galaxies in the universe (found 4)
Atmospheric data of Saturn’s moon - Titan
Discovered brown dwarf with sand clouds…
The Orion Arm
A minor spiral arm of the Milky Way Galaxy, 3,500 light-years (1,100 parsecs) across and approximately 10,000 light-years (3,100 parsecs) in length. The Solar System, along with Earth are contained within it.
nebulae
- considered star ‘nurseries’
- clouds/clumps of interstellar matter
- leftover/remaining dust may form planetary systems
Dust and gas are not evenly distributed in interstellar space. Some regions of the universe contain denser concentrations of swirling dust and gas. Within these currents, the density sometimes reaches the critical figure of 100 atoms per cubic centimetre. At this point, GRAVITY TAKES HOLD AND GAS AND DUST BEGIN TO COLLAPSE INTO BEGINNINGS OF A NEW STAR. The collapse continues under the influence of gravity, forming visible clumps in a nebula cloud. As the clumps collapse further, the original gas cloud begins spinning at ever-increasing speed. At the same time, the increasing pressure causes the temperature to rise and the conditions are right for a star to be born.
Stars differ from one another
how bright they appear to us and in their colour, some are close vs further away, age (young, middle, old, dying and exploded)
Magnitude data of stars display + who invented (2)
Ejnar Hertzsprung (denmark), Henry Norris Russell (U.S.A) -> Hertzsprung–Russell diagram sorts stars according to their absolute magnitude (or luminosity) and spectral type (which relates to the surface temperature).
plots absolute brightness (absolute magnitude - y-axis) of star against surface temperature (deduced from colour - x-axis ‘spectral type’)
^ bright on top
^hot on LHS
Majority fall into ‘main sequence’ - such as our sun
Main sequence group
majority of stars
continuous band extending from the upper left (hot, bright stars) to the lower right (cool, dim stars)
area on the Hertzsprung–Russell diagram where the majority of stars are plotted. Stars on the main sequence produce energy by fusing hydrogen to form helium. Such stars are at times referred to as being in their ‘adult’ stage, one of stability
Exactly where a star is found along the main sequence is determined by its mass. Low-mass stars tend to be cooler and less bright than high-mass stars.
Astronomers suggest that all stars begin their existence in the main sequence and spend the largest part of their life there
stars outside main sequence group
rarer: white dwarfs, red giants, blue giants and supergiants
The rarer types are stars that pass relatively quickly through later stages of development on the way to extinction as their nuclear fuel runs out.
Stars life cycle
Stars are ‘born’ within nebulae from gas and dust coming together through the force of gravity. During this process, the centre of the nebula may heat up and glow. Eventually sufficient hydrogen gas may accumulate to form young stars.
Stars then spend most of their life as stable ‘main sequence’ stars, and are powered by a fusion reaction within their core which converts hydrogen to helium. The size of a star determines how quickly the hydrogen in the core is used up. Small-to medium-sized stars like the sun have a life span of 10 billion years. The sun is currently 4.6 billion years old and in the main sequence phase, slowly consuming hydrogen gas.
Beta Centauri is a larger, hotter star and, because it consumes its hydrogen at a faster rate, will reach the end of its life within a relatively short 10 million years.
Main sequence star
stable
hydrogen fusion begins (change form protostar)
hydrogen is steadily turned into helium by the process of fusion. As helium builds up in the core of the star, the remaining hydrogen forms a shell around the core. The shell gradually expands and the star swells to 200 or 300 times its original size, cooling as it does so, to become a red giant. This will eventually happen to our sun, which will grow large enough to swallow up the inner planets, including Earth.
Red giant
hydrogen stops, helium fusion starts
In the core of a red giant, new fusion processes take place, turning helium into heavier elements such as beryllium, neon and oxygen. This increases the rate of energy production and raises the star’s temperature. A sun-like star which has become a red giant might shine 100 times more brightly than it did in its stable period.
Eventually red giants collapse inwards leading to the destruction of the star. The nature of its death depends on the size of the original star -> e.g. really big ones will die and result in a supernova/black hole
a very large star of high luminosity and low surface temperature. Red giants are thought to be in a late stage of evolution when no hydrogen remains in the core to fuel nuclear fusion/A red giant forms after a star has run out of hydrogen fuel for nuclear fusion, and has begun the process of dying/A red giant is a dying star in the final stages of stellar evolution. In about five billion years, our own sun will turn into a red giant/It has slowly swollen up to much bigger size Red giants can swallow up planets as they expand. -> hydrogen not fusing anymroe, instead In the core of the red giant, helium fuses into carbon
White dwarfs
For stars less than about eight times the mass of our sun, the destruction of a red giant begins when the outer layers are thrown off into space and the core flares brightly, forming a ring of expanding gas called a planetary nebula. The name ‘planetary nebula’ is misleading because it is not related to planets. But it does have the cloud-like nature of a nebula.
The remaining star fades to become a white dwarf, typically about the size of a planet like the Earth but with a very high density and a surface temperature of about 12 000 °C. It then slowly cools, becomes a cold black dwarf and disappears from view.
White dwarfs are hot, dense remnants of stars. They are the last observable stage of evolution for low and medium-mass stars/A white dwarf is what stars like the Sun become after they have exhausted their nuclear fuel. Near the end of its nuclear burning stage, this type of star expels most of its outer material, creating a planetary nebula. Only the hot core of the star remains/A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun’s/The vast majority of white dwarfs are formed after a dying star has shed its outer layers to form a planetary nebula/born when a star shuts down
violent end to stars (supernova)
Stars that are more than about eight times the mass of our sun come to a much more violent end. They swell into much larger red giants called super giants, then blow up in a huge explosion called a supernova. The matter making up the star is hurled into space along with huge amounts of energy. A supernova can emit as much energy in a month as the sun radiates in a million years. Observable supernova events in the Milky Way happen every 200 to 300 years on average. The supernovas fade from view within a few years. They are extremely important in the universe because it is within these violent explosions that the heavy elements such as iron and lead are produced.
What remains of a supernova is extremely dense; the pull of gravity becomes so great that even the protons and electrons in atoms are forced together. They combine to form neutrons and the resulting solid core is known as a neutron star -> the core is less than 3 times the mass of our
Sun, gravity and the pressure of the explosion,
collapses it inwards to form a super-dense ball
of neutrons only about 20 km in diameter.
If the remaining core has a mass more than about three times that of our sun, the force of gravity is great enough to ‘suck in’ everything — even light. Such a core becomes a black hole -> it keeps collapsing in on itself. Matter is
crushed to an infinite density and the core
becomes a “singularity” or “black hole”.
Any matter nearby is sucked into its immense
gravitational field. Even light waves cannot
escape… that’s why it’s black.
In-falling matter swirls around
the “event horizon” and is torn
apart before disappearing.
Twisted magnetic fields eject
“jets” of matter at high speed.
evolution of stars (small)
stellar cloud with protostars -> small star -> red giant -> planetary nebula -> white dwarf
evolution of stars (large)
stellar cloud with protostars -> large star -> red supergiant -> supernova -> neutron star/OR/black hole
how is star brightness defined
apparent magnitude - how bright star appears from earth
absolute magnitude - and absolute magnitude — how bright the star appears at a standard distance of 32.6 light-years, or 10 parsecs - intrinsic brightnes (compared to other objects)
Satellite
an object in space that orbits or circles around a bigger object
natural (such as the moon orbiting the Earth) or artificial (such as the International Space Station orbiting the Earth).
solar system
the collection of eight planets and their moons in orbit round the sun, together with smaller bodies in the form of asteroids, meteoroids, and comets. The planets of the solar system are (in order of distance from the sun) Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
- gravitationally bound
electromagnetic spectrum
the entire distribution of electromagnetic radiation according to frequency or wavelength.
