(Chapter 6.1) Describing the Universe Flashcards
Define star
A giant luminous ball of plasma, mainly consisting of hydrogen and helium, held together by its own gravity
Recall what feature of plasma makes it the fourth fundamental state of matter
A significant portion of plasma consists of charged particles – ions and/or electrons. The presence of these charged particles is what primarily sets plasma apart from the other fundamental states of matter
Define nuclear fusion
A reaction in which at least 2 atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles
Identify where nuclear fusion takes place in a star
Nuclear fusion takes place in the core of the star
Explain why stars emit light
Nuclear fusion converts mass into energy and electromagnetic radiation, such as visible light
Define apparent magnitude
Apparent magnitude (m) is a measure of the brightness of a star or other astronomical object observed from Earth
Identify the factors that impact the apparent magnitude
An object’s apparent magnitude depends on its intrinsic luminosity (energy output/distance), its distance from Earth, and any extinction of the object’s light caused by interstellar dust along the line of sight to the observer
Define absolute magnitude
The apparent magnitude an object would have if it were located at a distance of 10 parsecs
Recall the lifecycle of a star
- Birth from clouds of gas and dust
- Steady state - The star fuses hydrogen into helium to survive
- Old age - The star runs out of hydrogen fuel, expands and cools
- Death - The star implodes and the particles is blown away
Identify what property changes the colour of a star
The temperature of a star affects its colour
Identify the colour of a star in descending order of temperature
Blue, white, yellow, and red
Identify what property changes the brightness of a star
The size
True or False: “The size of a star is inversely proportional to the brightness”
False. The size of a star is proportional to the brightness
Define galaxy
A gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter
Define solar system
The gravitationally bound system of a central star (the Sun) and the objects that orbit it
Define nebula
A cloud of gas, predominately hydrogen, and dust in space and is the ‘birthplace’ of stars
Define planet
According to the IAU (International Astronomical Union), a planet is a celestial body that:
* is in orbit around the Sun;
* has sufficient mass for its self-gravity to overcome rigid body forces so it assumes hydrostatic equilibrium (a nearly round shape), and;
* Has “cleared the neighbourhood” around its orbit
Define planetary nebula
A type of emission nebula consisting of an expanding and glowing shell of ionised gas ejected from red giant stars late in their lives
True or False: “Planetary nebulae are related to planets”
False. Planetary are misnamed as when they were discovered, they were misclassified as planets
Identify another term for planetary nebula
Stellar nebula is another term for planetary nebula
Define asteroid
A small rock body that orbits the Sun
Define comet
A celestial object consisting of a nucleus of ice and dust and when it approaches the Sun, a ‘tail’ of gas and dust particles appears
Define meteoroid
A small rocky or metallic body that orbits the Sun
Define meteor
A small rocky or metallic body of matter from outer space that enters the Earth’s atmosphere, becoming incandescent as a result of friction and appearing as a streak of light
Define meteorite
A piece of rock or metal that has fallen to the Earth’s surface and previously was a meteor
Identify the most common minerals of meteors
The most common minerals are rock, iron, and nickel
Identify another term for apparent magnitude
Another term is stellar magnitude
Identify what property changes the lifespan of a star
The mass of a star affects the lifespan
Define accretion
The accumulation of particles into a massive object by gravitationally attracting more matter, typically gaseous matter, in an accretion disk
Define accretion disk
A structure formed by diffuse material in orbital motion around a massive central body, typically a star
Define binary star
A system of 2 stars that are gravitationally bound to and in orbit around each other
Define parsec
The radius of Earth’s orbit subtends an angle of one second of arc
Identify the elongated term for parsec
Parallax second is the elongated term for parsec
Explain what the stellar parallax is
The stellar parallax describes the effect of observing a star from different positions, which then the star’s position relative to other stars appears to be different
Explain why parsec is used to measure distances closer than 100 light-years
The parsec is used as it is an appropriate unit in terms of the number it produces
Define proper motion
The astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky
Recall the formula to calculate the distance of a star
d = 1/p
where:
d = distance (pc)
p = parallax angle (arc seconds) (1/3600)
Recall the conversion between parsec and light-years
1 pc = 3.26 light-years
Recall the speed of light
3 * 10^8 m/s
Contrast a solar system with a galaxy
A solar system is all the celestial bodies that orbit a cental star. On the other hand, a galaxy is the collection of stars, spanning a number of solar systems
