Features of the Moon

People who observe the moon usually notice two areas of the surface. One of these areas is dark-grey, and relatively smooth. These are the lunar seas often called Mares. These areas of dark grey are called the lunar seas because astronomers once thought that they were rich with water. They are actually iron-rich basaltic rock. The other areas of the moon people usually notice are the light-grey (the highlands) parts which have huge numbers of craters. These areas are made of anorthosite which is a rough-grained type of rock. Because the lunar seas are smoother, this implies that the seas are ‘younger’.

Many of the moons small craters have been made by meteoroids from around the solar system but the larger craters such as the Tycho crater and the Copernicus crater were made by asteroids.

There are some types of features on the moon such as craters, wrinkle ridges and rilles (grooves). Rilles are narrow channels in the lunar seas which can be straight or smoothly curved and are believed to have been caused by lava flows. Wrinkle ridges are caused by the buckling of the lunar surface as a result of compressive forces.

Eratosthenes measures the Earth with a stick!

Eratosthenes was the first person to make an accurate determination of the Earths Circumference. He achieved this back in 300BC using a very clever experiment using the ideas that sticks in the ground at different latitudes cast different shadows.

Image form http://en.wikipedia.org/wiki/Geography_of_Egypt
Satellite image of the two places that Eratosthenes used to help him calculate the circumference of the Earth

On June 21st , because that is the date of the summer solstice, he knew that the Sun was going to be overhead of a well in Syene on the Tropic of Cancer. Since the Sun was overhead, sticks would not generate a shadow.He then had another stick placed at Alexandria and the measured the angle of the shadow at noon that day. He recorded the angle of the shadow that was created.

 

Image from http://www.juliantrubin.com/bigten/eratosthenes.html

He used the equation

Angle of the sun/360° = Distance to tropic of Cancer/Earths circumference

To find,

Earths Circumference= Distance to Tropic of Cancer x 360°/Ѳ of the sun 

Image from http://www.iucaa.ernet.in/~scipop/Obsetion/eratos/eratos_1.htm

To work out the circumference of the Earth, Eratosthenes put some numbers into his equation. He knew that the distance between Alexandria and Syene was 790km and he measured 7.2° as the angle from the Sun.

So 7.2°/360°=1/50 so when you flip the equation over you get 360°/7.2°=50

He then multiplied 50 by 790km and then concluded that the Earths circumference was 39500km.

The current measurement of the Earth’s circumference is 40075km, so Eratosthenes was only 1.4% out – 2400 years ago!

The layers of earth’s atmosphere

Earth has four layers in its atmosphere.

The troposphere is 12km up, this is the layer closest to the earth and where the weather occur (clouds). The air is the thickest here, its mass is about 80% of the total of all the layers of the atmosphere and most of the heat that comes from here is reflected back off the earth’s surface.

The stratosphere is the next layer, it goes to 50km up, and it has the ozone layer in it. Its pressure is 1/1000 of that at sea level.

Next layer is the mesosphere that is 80km up, this is the coldest layer at -100°C and has all the weather balloons in it and is where a lot of the meteoroids burn up because the density of air is just enough to start that happening.

http://en.wikipedia.org/wiki/File:Earth%27s_atmosphere.svg

The fourth layer and final is the thermosphere and the air is so thin that any change in heat is very extreme this why the temperature is very high, it can be 1500°C and goes all the way up to 350km above the earth’s surface. The aurora borealis also occurs in this layer. The exosphere is at the top of this layer. This is where the atmosphere begins to meet the vacuum of space and the international space station orbits here as well

Van Allen Belts - What are they?

The Van Allen belts are regions of charged particles that have become trapped in the Earth's Magnetic field and surround us in two distinct regions or "belts". They are named after James Van Allen who led the team of Physicists that discovered them.

A model of the Van Allen Belts
 

The Inner belt

The inner belt is a confined region of high-energy protons made when high energy cosmic rays from distance galaxies collide with our atmosphere. They are found between 600km and 1000km above the Earth. Prolonged exposure, say during a space flight, would be very hazardous to humans and equipment. This is why low orbit satellites follow paths between the poles of the Earth to minimize time spent in this region.

The outer belt

This is a much more diffuse (thinner) but larger region of particles that have become trapped from the Sun's solar wind.

Van Allen Belts - Discovery

The inner belt was first discover in January 1958 by the US satellite Explorer 1 (designed originally to detect and study the intensity of cosmic rays from greater distances than could be measured from earth) using a Geiger counter. The existence of this belt was later confirmed by similar instruments on board the US satellite explorer 3 and the Russian satellite Sputnik 3 later that year.

The outer belt was first discovered in December 1958, also using a Geiger counter. This was discovered by Pioneer 3 (although Russian scientists working on data collected by Sputniks 2 and 3 claimed to have detected evidence of this second radiation belt prior to this).

The Primary mission of the Pioneer 3 probe was a lunar fly-by, but due to a fuel cut-out in the spacecraft’s main engine, the probe only managed to reach an altitude of 102,360km, this caused the probe to fall back to earth and burn up. However before burning up the probe’s Geiger counters provided important data that allowed Van Allen’s team to detect the existence of this second, outer belt. This was then confirmed by instruments on board the US probe, Pioneer 4 the following year.

Explorer 3

 

 

 

The Earth's Atmosphere!

The Earth’s atmosphere

The Earth’s atmosphere is made up of 78% nitrogen, 21% oxygen, 1% argon 0.04%, carbon dioxide and 1% of other gasses for example helium, neon and methane. As your height increases the atmosphere gets thinner and thinner as it merges with outer space at approximately 10000 km above sea level. The Karman line is defined as the edge of space by astronauts and is about 100km above sea level.

What does the atmosphere do?

There are lots of benefits to the earth’s atmosphere for example:

·         It gives us oxygen for us to breath

·         It absorbs ultra violet light from the sun this UV radiation can cause skin cancer and age skin.

·         The atmosphere also absorbs X-rays and gamma rays and regulates the temperature of the earth thus protecting us from extremes in temperature this is a good thing because it allows water to remain in its liquid form instead of being a gas or ice.

·         The atmosphere protects us from meteoroids by burning them up before they hit the earth this happens by the gases surrounding the meteoroids being compressed this compression creates large amounts of heat and makes the meteoroids burn up.

Although there are lots of benefits to the earth’s atmosphere there are also some drawbacks to it for astronomers for example:

·         Light is refracted and causes stars to twinkle and the clarity of images of the night sky to be effected.

·         The sky is made blue by gas light being scattered through gas molecules

·         The atmosphere is very good at absorbing UV light, gamma rays and X- rays this means that most observatories that require these things to be put on top of big hills where less of their rays will have been absorbed.

The Earth’s atmosphere successfully absorbs most electromagnetic waves but some can successfully pass further than others this picture explains that. The wavelength of the waves can affect how far they can pass and what they are reflected by.

·         The longest waves are reflected back by electrons

·         Slightly shorter wavelengths are absorbed by water vapour and oxygen

·         Infrared radiation is absorbed by water vapour, methane and carbon dioxide

·         Ultraviolet radiation is absorbed by ozone and oxygen

·         X-rays and Gama rays are absorbed by oxygen and nitrogen

 

 

Curiosity taking a break

The now famous 'Curiosity' Mars rover is taking a break from a solid 2 months of travelling across the Martian surface. 

Since the tense landing back in August 2012, the Curiosity rover has stayed within its landing square, waiting for the cue to start rolling towards its goal. It has waited almost a full year for the green light, but it started to gently roll forward in July of 2013. Now, after 2 months of silently creeping forward, the rover is going to make a stop at a group of Martian rocks, which have been dubbed "Darwin". This is the first waypoint of what the NASA officials hope to be 5, if no more interesting formations come to light, after which Curiosity will move on to Mount Sharp, the mountain that dominates the Gale Crater.

An image of the Darwin rock formation (source:www.jpl.nasa.gov)

The Curiosity rover will be analyzing the rock formation for "a few sols only" (a 'sol' is a Martian day, 39 minutes longer than an Earth day). During this time it shall only be using its remote sensing equipment, NASA has no intent to drill into the formation. Darwin will allow NASA to investigate what they are calling a 'conglomerate', a group of pebbles cemented together with a finer mineral, and compare it to formations found earlier in the mission. The mineral in question is believed to be similar to sediment that is deposited in rivers here on Earth, possibly proving that the Gale Crater and potentially Mars as a whole once flowed with water. This could also give us yet another hint as to whether Mars once accommodated life on its surface, breaking apart one of the most asked questions in Astronomical studies.

For more information on Curiosity's journey, feel free to click the following link to BBC News: http://www.bbc.co.uk/news/science-environment-24110442

Pluto moons get mythical new names

The recently discovered fourth and fifth moons of Pluto now have official names: Kerberos and Styx.

(from NASA)

The names - referring to a three-headed dog and a river separating the living from the dead, ranked second and third in an international public vote.

The two moons, formerly known simply as P4 and P5, were only discovered in July 2011 and July 2012, respectively. Both were spotted by a team using the Hubble space telescope, led by Mark Showalter, senior scientist at the Seti Institute.

Vulcan was a suggestion made by William Shatner of the television show Star Trek - the name of the home planet of character Mr Spock. Although it was a clear winner among the votes, the IAU opted not to use it, on the grounds that it has been used elsewhere in astronomy and not sufficiently associated in mythology with Pluto, the ruler of the underworld.