The Earth Flashcards
Describe features of the Earth that distinguish it from other planets, including its water surface and atmosphere
70% of the surface of the crust consists of water in the form of the seas, oceans and lakes. The oceans regulate the Earth’s temperature, storing and releasing heat from the Sun. 30% is land mass made up of continents and islands.
Our atmosphere supports life. We breathe in Oxygen and breathe out Carbon Dioxide (which is what plants breathe in, then they breath out Oxygen). If there was one attribute that makes Earth unique in our Solar System it is that it supports life.
Other reasons why life exists are that:
We have a magnetic field which deflects solar particles from the Sun.
Our atmosphere also absorbs harmful rays from space.
Our planet is positioned in a habitable zone, where water can exist as a liquid to support life. This is a region far enough from the Sun to stay warm, but not near enough to evaporate.
Relate the blue sky to the preferential scattering of light in its atmosphere
Red, orange, yellow and green light carries straight on through this atmosphere but blue, violet and indigo get bounced around from molecule to molecule.
We see a blue sky as a result of all this bouncing around.
Why don’t we see an Indigo or Violet sky? Simply because our eyes do not see these colours very well. Blue is a more dominant colour.
Demonstrate an understanding of the benefits of the Earth‘s atmosphere to humankind
Benefits of Earth’s atmosphere
Oxygen allows humans and animals to breathe.
The atmosphere protects us from harmful ultraviolet radiation from the Sun
Makes the climate and temperature of Earth consistent
The atmosphere spreads out and scatters light from the Sun
Protects us from micro meteorite collisions from space
Describe some of the major causes of light pollution and demonstrate an understanding of why it is undesirable to astronomers
Optical pollution is light from human sources. If you go to the countryside or area outside a town on a clear night you will see many more stars than you would do in the city.
Chemical pollution comes from man-made and natural chemicals in the atmosphere obscuring the sky or affecting observations.
Describe how Eratosthenes made the first accurate calculation of the circumference of the Earth
He learnt that in the town of Syene, to the south, the Sun appears at the zenith (the highest point in the sky) on the summer solstice – it was well know that its reflection could be seen directly down a deep well.
By observing and measuring shadows in Alexandra, he calculated that the Sun was over 7.12 degrees from the Zenith on the same date. This is approximately 1/50th of a circle.
The distance between the cities was approx 5000 stadia (back then they measured by stadia – like football pitches are used to quickly illustrate lengths).
Eratosthenes made a calculation by multiplying the distance by the angle.
What is the shape of the Earth
Oblate Spheroid
What is Earths Diameter
13 000 km
Describe the evidence that the Earth is approximately spherical
There is evidence that early astronomers knew that Earth was round for a number of reasons:
The Moon is round.
The shadow of the Earth on the Moon during a lunar eclipse is round.
Travellers going north or south see different stars not visible from elsewhere.
Travellers recording shadows at different angles on the same date.
Tall ships appearing to ‘sink’ as they move over the horizon
What is Earths rotational period
23 hours 56 minutes
How long does it take to rotate though 1 degree
4 Minutes
Demonstrate an understanding of the Equator
The Equator lies exactly between the Poles at 0°. We refer to the Area above the equator as the Northern Hemisphere and below, the Southern Hemisphere.
The Sun is directly overhead at the equator at the Equinoxes on 2 days of the year.
Demonstrate an understanding of the tropics
The Tropics are a region where the Sun is directly overhead in the zenith at least once a year, and lie between approx. 23.5N & S.
Temperatures there are generally hotter than elsewhere and there is little seasonal difference except for dry and wet seasons.
The northern tropic is called the Tropic of Cancer, the southern is the Tropic of Capricorn.
Demonstrate an understanding of latitude
Latitude is a co-ordinate on the Earth’s surface that measures how far north or south a position is. It is measured from 0° at the Equator to 90° at the North Pole. Co-ordinates south of the equator are preceded by a minus sign, so the South Pole would be at -90°.
Demonstrate an understanding of longitude
Longitude is a co-ordinate on the Earth’s surface that measures how far west or east a position is.
A circle can be divided into 360° but for longitude we measure co-ordinates from 0°. Co-ordinates are located at up to 180° west or east of this location. The position of 0° is measured from the north-south line that intersects Greenwich, London.
The Equator and Tropics of Cancer and Capricorn are lines of Latitude.
Demonstrate an understanding of the poles
The pole is a point on the surface of the Earth at the axis of rotation, and both poles are located at 90° from the Equator.
The South Pole (90°S) is on a continental shelf (Antartica) and a United States Amundsen-Scott South Pole Station is located there. The North Pole (90°N) is in the Artic Ocean which is frozen for most months of the year.
Demonstrate an understanding of the horizon
The Horizon is the furthest visible point of the Earth’s surface from the observer’s position.
Demonstrate an understanding of the meridian
An imaginary line intersecting the Pole to the observer’s zenith.
It also refers to a specific imaginary line stretching between the poles of the Earth along points of longitude. For example the Greenwich Meridian which crosses the Greenwich Observatory in London.
Demonstrate an understanding of the zenith
The Zenith is a point directly above the observer’s head.
The opposite of Zenith is the Nadir, the point directly below the observers feet.
Demonstrate an understanding of the drawbacks to astronomers of the Earth‘s atmosphere and relate these to the need for optical and infra-red observatories to be sited on high mountains or in space
Frequently, larger observatories are built in remote locations ( normally on high mountains with less atmosphere to look though) far removed from light pollution.
Also they are located in areas that have good, dry weather and fewer clouds, so typically nearer the tropics or Equator.
Dry weather is especially important for infrared astronomy as water vapour in the atmosphere is an interference.
Less infrared light penetrates to the surface so a higher location is better for those observations.
Describe the features of refracting and reflecting telescopes (detailed ray diagrams not needed)
Refractor
A convex lens is used at the end of a tube to bring an image into focus at a point. Another convex lens called an eyepiece is used at the opposite end of the tube to magnify the image.
The lens is typically made of glass coated in a film to allow less light to be reflected and more to pass through the lens.
Reflector
A reflector collects light at one end of a tube and reflects it off a concave mirror. It is brought to a focus by a secondary mirror further up the tube at a 45 degree angle which is then magnified using an eyepiece.
Demonstrate an understanding of why the world‘s largest telescopes are reflectors rather than refractors
Higher resolution can be acheived with a smaller tube
Refractors suffer from chromatic aberration. This means that colour can sometimes be warped
Refractors suffer from lens sagging. The weight of the lens is supported by the edges and gravity distorts this. The maximum size refractor can be up to 1 metre wide.
Demonstrate an understanding that the Earth‘s atmosphere is transparent to visible light, microwaves and some radio waves
The light that we see from stars is just one form of observing we can do. ‘Invisible’ astronomy or ‘non-optical’ astronomy tells us a lot about space.
Visible light is a form of radiation travelling at a wavelength millionths of a metre wide. The light travels as a wave and the wavelength determines the colour seen.
Interpret data on the effect of the Earth‘s atmosphere on infra-red, ultra-violet and X-rays
Most infrared radiation is blocked by our lower atmosphere by water vapour.
A very small amount of ultra violet radiation penetrates our atmosphere; plants and life forms rely on it, although large amounts are harmful. The rest is blocked by the atmosphere.
We find it difficult to observe x- rays as our atmosphere blocks the rays, which is good as they are harmful
Describe where infra-red, ultra-violet and X-ray observatories are sited and explain the reasons why
X-Ray observatories are typically onboard spacecraft as are many ultraviolet and infrared observing stations.
