Space physics Flashcards
Order of solar system
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
How does the earth rotate around the sun?
The Earth is a planet that rotates from west to east on its axis, which is tilted, once in approximately 24 hours at an angle of approximately 23.5°
How does the way the earth rotates around the sun affect daily apparent motion of the sun?
Because of this rotation (counterclockwise from west to east), an observer on Earth sees the Sun appear to rise in the east, move across the sky, and set in the west. This is known as the apparent daily motion of the Sun
What happens during equinoxes?
- day and night are approximately equal in length
- the Sun appears to rise exactly in the east and set exactly in the west
What is the cycle of day and night caused by?
- Day and night are caused by the Earth’s rotation on its axis
- One full rotation takes approximately 24 hours, which means the half of the Earth’s surface facing the Sun experiences day and the other half of the Earth’s surface, facing away from the Sun, experiences night
How long does it take the Earth to orbit the Sun?
the Earth orbits the Sun once in approximately 365 days
What does the earth axis of rotation mean for hemispheres?
one hemisphere tilts towards the Sun and receives more solar radiation while the other hemisphere tilts away from the Sun and receives less solar radiation (six months later, the hemispheres tilt in the opposite direction)
What happens when it’s summer in the northern hemisphere?
When it is summer in the northern hemisphere the northern hemisphere is tilted towards the Sun meaning it receives a greater proportion of solar radiation
the southern hemisphere experiences winter because it is tilted away from the sun receiving a smaller proportion of solar radiation
It is opposite for winter in northern hemisphere/summer in southern hemisphere
What happens during spring and autumn in terms of solar radiation?
When it is spring or autumn, both hemispheres receive about the same amount of solar radiation
What happens during 20th March?
Spring equinox in NH
Autumn equinox in SH
means equal hours of day and night
What happens during March, April, May?
NH: spring (days are longer than nights hours of daylight increase)
SH: autumn (days are shorter than nights hours of daylight decrease)
What is on 21st June?
NH: summer solstice (longest hours of daylight)
SH: winter solstice (shortest hours of daylight)
What happens during June, July, August?
NH: summer (days are longer than nights, hours of daylight decrease)
SH: winter (days are shorter than nights, hours of daylight increase)
What is on 23rd September?
NH: autumn equinox (equal hours of day and night)
SH: spring equinox (equal hours of day and night)
What happens during September, October, November?
NH: autumn (days are shorter than nights, hours of daylight decrease)
SH: spring (days are longer than nights, hours of daylight increase)
What happens on 21st December?
NH: winter solstice (shortest hours of daylight)
SH: summer solstice (longest hours of daylight)
What happens during December, January, February?
NH: winter (days are shorter than nights, hours of daylight increase)
SH: summer (days are longer than nights, hours of daylight decrease)
Properties of the moon
The Moon is a natural satellite that orbits around the Earth in a roughly circular orbit
- takes about one month (28 days) to complete one orbit
- rotates on its axis once every 28 days so the same side always faces the Earth
- It is visible in the night sky because it reflects the light from the Sun
- orbits counterclockwise
What happens on day 0 moon cycle?
On day 0, a new moon is observed, where: the Moon is positioned between the Earth and the Sun
- the side of the Moon facing away from Earth is fully illuminated
- none of the Moon’s surface is visible from Earth
days 1-6 of the moon cycle
Waxing crescent moon
(when shape is thickening, illuminated on left side)
day 7 of moon cycle
On day 7, the first quarter phase is observed
days 8-13 of moon cycle
Waxing gibbous (like 3/4 of moon is illuminated from left side)
day 14 of moon cycle
On day 14, a full moon is observed, where: the Earth is positioned between the Moon and the Sun
- the side of the Moon facing towards the Earth is fully illuminated
- all of the Moon’s surface is visible from Earth
Day 14-20 in moon cycle
Waning gibbous (3/4 of moon is illuminated from left side)
Day 21 of moon cycle
On day 21, the last quarter phase is observed
Day 22-28 of moon cycle
Waning crescent
What does solar system contain?
- one star, the Sun
- eight planets
- minor planets that orbit the Sun, including
dwarf planets such as Pluto and asteroids in
the asteroid belt - moons, that orbit the planets
- smaller Solar System bodies, including
comets and natural satellites - artificial satellites
Orbit of planets
planets, minor planets and comets have elliptical orbits, and the Sun is not at the centre of the elliptical orbit, except
when the orbit is approximately circular
What is one light year equal to?
9.5 × 10^15m
Formation of a stable star
- A star is formed from interstellar clouds of gas and dust that contain hydrogen
- A protostar is an interstellar cloud collapsing and increasing in temperature as a result of its internal gravitational attraction
- A protostar becomes a stable star when the inward force of gravitational attraction is balanced by an outward force due to the high temperature in the centre of the star
Death of a star
- All stars eventually run out of hydrogen as fuel for the nuclear reaction
- Most stars expand to form red giants and more massive stars expand to form red supergiants when most of the hydrogen in the centre of the star has been converted to helium
- A red giant from a less massive star forms a planetary nebula with a white dwarf star at its centre
- A red supergiant explodes as a supernova,
forming a nebula containing hydrogen and
new heavier elements, leaving behind a neutron star or a black hole at its centre - The nebula from a supernova may form new
stars with orbiting planets
Sun properties
the Sun is a star of medium size, consisting mostly of hydrogen and helium, and that it radiates most of its energy in the infrared, visible and ultraviolet regions of the electromagnetic spectrum
How are stars powered?
nuclear reactions that release energy and that in stable stars the nuclear reactions involve the fusion of hydrogen into helium
What is a light year?
astronomical distances can be measured in light-years, where one light year is the distance travelled in (the vacuum of) space by light in one year
What are galaxies made up of?
many billions of stars
Where is the sun?
the Sun is a star in the galaxy known as the Milky Way
How far away are other stars that make up the milky way?
other stars that make up the Milky Way are much further away from the Earth than the Sun is from the Earth
Hubble constant definition
ratio of the speed at which the galaxy is moving away from the Earth to its distance from the Earth
Current hubble constant
2.2 × 10^–18
What does 1/H0 or d/v represent?
An estimate for the age of the Universe and that this is evidence for the idea that all the matter in the Universe was present at
a single point
redshift definition
an increase in the observed wavelength of electromagnetic radiation emitted from receding stars and galaxies
How does the light emitted from different galaxies appear compared to light emitted on Earth?
the light emitted from distant galaxies appears redshifted in comparison with light emitted on the Earth
Milky way properties
Milky Way is one of many billions of galaxies making up the Universe and that the diameter of the Milky Way is approximately 100,000 light-years
What is redshift evidence for?
Redshift in the light from distant galaxies is evidence that the Universe is expanding and supports the Big Bang Theory
How can the speed at which a galaxy is moving away from earth be found?
The speed, v, at which a galaxy is moving away from the Earth can be found from the change in wavelength of the galaxy’s starlight due to redshift
How can the distance of a far galaxy be determined?
The distance of a far galaxy, d, can be
determined using the brightness of a supernova in that galaxy
What is cosmic microwave background radiation (CMBR)?
microwave radiation of a specific frequency is observed at all points in space around us and it was produced shortly after the universe was formed
How is CMBR evidence for universe expansion?
Initially CMBR would’ve existed as short-wavelength gamma radiation. The shorter wavelength in the past indicates the Universe must have been very hot in the beginning. As the Universe expanded, the wavelength of the radiation increased and over time, it has been redshifted so much that it is now in the microwave region of the spectrum
What are the planets near the sun?
small, rocky
(have atmospheres apart from mercury)
What are the planets further from the sun?
large, gaseous
(mostly composed of hydrogen and helium gas)
What is an asteroid?
An asteroid is a small rocky object which orbits the Sun
(The asteroid belt lies between Mars and Jupiter)
What is a comet?
A comet is an object made of dust and ice which orbits the Sun in a highly elliptical path. The ice melts when the comet approaches the Sun and forms the comet’s tail
Why do planets orbit the sun?
the Sun contains most of the mass of the Solar System
What is the force that keeps an object in orbit around the sun?
The gravitational attraction of the Sun
