Space Physics Details/Definitions Flashcards
The Earth orbits the Sun once in…
approximately 365 days
Nature of the rotation of the earth
-Rotates on its axis(which is tilted)
-Complete rotation takes approximately 24 hours
Impact of rotation of the Earth on day and night cycles
-In areas where the sun is not facing that side of the Earth, it would be nighttime.
-In areas where the sun is facing that side of the Earth, it would be daytime.
Why day and night are not of equal length(in most places in the world)
The axis of the Earth is tilted
Why the nature of seasons is periodic
Because of the tilt in the Earth’s axis(different parts of the planet are tilted further or closer away from the sun)
Time it takes for the moon to orbit the Earth
Approximately one month
Why the moon has phases
-As the Moon orbits around the earth, different parts of it are illuminated by the Sun
-As the same side of the Moon always points toward Earth, some of the illuminated part faces away from us
Structure of the Solar System
-The Sun(the only star)
-The eight named planets
-Minor planets(eg. dwarf planets like Pluto and asteroids in the asteroid belt)
-Moons that orbit the planets
-Smaller solar system bodies(eg. comets and natural satellites)
The orbits that planets, minor planets and comets have are…
elliptical(oval-shaped)
The Sun is only at the centre of the orbit when…
the orbit is approximately circular
The planets(in order from the sun)
-Mercury
-Venus
-Earth
-Mars
-Jupiter
-Saturn
-Uranus
-Neptune
The four planets nearest to the Sun are…
rocky and small(compared to those furthest from the Sun)
The four planets furthest from the Sun are…
gaseous and large
At the surface of a planet, the strength of a gravitational field depends on…
the mass of the planet
the strength of a gravitational field around a planet decreases as…
the distance from the planet increases
Why do planets orbit the Sun
The Sun contains most of the mass of the Solar System
Force that keeps an object in orbit around the Sun
The gravitational attraction of the Sun
As the distance of a planet from the Sun increases…
-the strength of the Sun’s gravitational field decreases
-the orbital speeds of the planet decreases
An object in an elliptical orbit travels faster when closer to the Sun(T/F)
True
Features of the Sun
-A star of medium size
-Consists mostly of hydrogen and helium
-Radiates most of its energy in the infrared, visible and ultraviolet regions of the electromagnetic spectrum
What stars are powered by
Nuclear reactions(which give out energy)
In stable stars, the nuclear reactions(that power them) involve…
the fusion of hydrogen into helium
Galaxies are made up of…
many billions of stars
The galaxy which the Sun is in
The Milky Way
Astronomical distances are usually measured in…
light-years
Light-year
the distance travelled in (the vacuum of) space by light in one year
(In metres) One light-year is equal to…
9.5 × 10¹⁵m
Life cycle of a star
-A star is formed from interstellar clouds of gas and dust that contain hydrogen
-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
-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
Protostar
an interstellar cloud collapsing and increasing in temperature due to its internal gravitational attraction
What happens to red giants
They form a planetary nebula with a white dwarf star at its centre
What happens to red supergiants
-They explode 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 the supernova may form new stars with orbiting planets
Diameter of the Milky Way
100,000 light-years
Redshift
an increase in the observed wavelength of electromagnetic radiation emitted from receding stars and galaxies
Redshift in the light from distant galaxies is evidence that…
the Universe is expanding
Light emitted from distant galaxies appears…
redshifted in comparison with light emitted on the Earth
Microwave radiation of a specific frequency is observed at all points in space around us(T/F)
True
Cosmic microwave background radiation (CMBR)
microwave radiation that is observed at all points in space around us
When was CMBR produced
Shortly after the Universe was formed
How the speed at which a galaxy is moving away from the Earth can be found
By observing the change in wavelength of the galaxy’s starlight due to redshift
Hubble constant
the ratio of the speed at which the galaxy is moving away from the Earth to its distance from the Earth
Estimate for Hubble constant(H₀)
2.2 × 10⁻¹⁸
Features of the equation:
distance(d)/speed(v) = 1/H₀
-Represents an estimate for the age of the Universe
-Is evidence for the idea that all matter in the Universe was present at a single point
