Exploring the Heavens – Week 4

The main focus for this week was ‘The Characteristics of Stars’. For this lass I was back to my usual Tuesday class time, and I had been looking forward to this session for quite some time.

The session started outside at the observatory waiting for the ISS to fly across the Sydney sky at 30,000 km/h. I had never seen this before so I was pretty excited to see a spaceship fly through the sky. It happened at 6.20pm and lasted for a couple of minutes. Incredible to think there are people inside the ISS doing science experiments at 30,000 km/h all day everyday.

iss

Then inside for another amazing 3D presentation by Dr Paul Payne about stars. Starting with the Sun, which produces an enormous amount of light and heat for billions of years. Stars are huge, 100,000 to 400,000 million kilometres across. The Sun is turbulent and the surface, photosphere, can have dark spots and bright patches that can flare up to 1,000x brighter.

Stars vary greatly in temperature, size and brightness. Stars do not burn, as this would not produce enough energy to keep them alive very long, they are nuclear power reactors where hydrogen is fusing to form helium and this processes keeps them alive for billions of years.

The most important property of a star is its mass as it determines everything about it – size, light, length of life. When a star dies it crushes itself to a fraction of its original size leaving behind either a white dwarf, neutron star or a black hole.

The formation of stars

Stars are formed from nebulae – an interstellar cloud of gas (mainly hydrogen and helium) and dust. The contracting ball of gas throws out rings of material to make planets and what was left is the central star. As the central star compressed it gets hotter and hotter and gravity keeps on compressing it even further. With a core temperature of about 10 million degrees atoms of hydrogen in the core move with such immense speeds that they collide and fuse together – called nuclear fusion. This reaction produces an enormous amount of energy and is a million times more efficient at generating energy that during the equivalent amount of coal.

Our Sun

Our Sun is stable and is currently fusing hydrogen at its core, a process that lasts for 90% of its life. Energy from the core radiates through the dense central layers and slowly makes its way to the surface in the form of x-rays and gamma rays. The journey could take a million years to happen. At the surface gas is not as dense so to expel the energy it uses a convection process. Gas below the surface moves in packets carrying heat energy. At the surface each packet radiates energy out into space, and we on Earth see this energy in the form of visible light.

The appearance of the Sun looks cellular, however, each cell is approx. 1000 km across. Small bright patches are where gas is radiating and darker veins are cooler areas where energy has fallen back into the Sun. The temperature of energy varies from 15 million degrees at the core to 5700 degrees at the photosphere. This is why the Sun looks yellow, because more yellow light is produced at this temperature than any other colour.

A sunspot is a region on the surface where the gas is cooler than its surroundings, approx. 4000 degrees cooler. The spot generates less light so appears darker. Galileo correctly recognised them and was able to measure the period of rotation of the Sun. The Sun does not rotate as a solid ball, each latitude rotates at a slightly different rate, for example the equator takes 27 days to rotate once and at a latitude of 40 degrees it takes 29 days.

656472main_solar-rotation_946-710

Solar eruptions are more frequent as the amount of sunspots increases. These eruptions are also called flares, where a small area may increase in intensity and temperatures of a million degrees may be generated so particles are exploded and hurled from the Sun that may even reach Earth and cause auroras visible near the poles.

The Life of the Sun

The Sun will fuse hydrogen for about 9 billion years. The leftover helium ash will build up the core. The Sun is stable during this time. It will eventually start running out of fuel at the core and it will prepare to die. It will take another billion years or so and its energy output will vary, called a variable star, where its brightness may vary.

The Death of the Sun

Eventually the core will collapse causing heat that will drive nuclear reaction faster resulting in the Sun swelling. It will grow to over 100x its present size and be 1000x brighter. The surface will cool and it will become a Red Giant. Finally the ignition of helium in the core, fusing to form carbon, nitrogen and oxygen, generating enormous power. It will glow with a brilliant red, something that happens to all stars prior to dying.

At this stage the star will produce heavier elements than helium up to iron. Elements heavier than iron when fused will not produce energy but absorb it, making the star very unstable. A planetary nebula is then produced, shells of gas are released cocooning itself in a cloud of its own material. They appear as faint blue discs surrounding dying stars. When the star tries to fuse iron the reaction absorbs energy from the core and the interior behaves more like a refrigerator than an oven. The core collapses, gravity compresses the star the size of the Sun to the size of Earth. It is extremely dense, a sugar cube sized peeve of its material would weigh 5 tonnes. The star is dead, it does not produce energy and it slowly cools off, it is now a white dwarf.

The power of stars

Stars are rated like light bulbs. Some stars produce 100,000x more power than our Sun. To measure the power we have to measure the brightness and how far away it is. If we know any two of power, brightness and distance we can find the third quantity.

Stars are hot!

The surface temperature of a star can be measured by its colour. Cool stars are red at 3000 degrees. Hot stars are blue at 15,000 degrees on the surface. We can see the colours of stars at night with the naked eye. We notice blue stars more as they generate more power. Examples are Sirius, Rigel. They are blue stars and are 8 and 815 light years away respectively. Examples of red stars, which do not last as long in the night sky, are Betelgeuse, Antares and Gamma Crucis.

Composition of stars

The composition of a star can be measured from the light from it. Telescopes equipped with a spectrometer can break the light into its different component features, called an absorption spectrum. Dark lines throughout the spectrum, like a barcode, reveal the elements, such as hydrogen and helium. The spectrum can also reveal the velocity as the lines will be red-shifted, meaning the star is moving away from us. The greater the velocity the greater the shift. If the star is moving towards us it will be blue-shifted. This shift in spectral lines is called the Doppler Effect.

An emission spectrum is produced by a glowing cloud of gas, like a nebula. Dark lines are now bright and the bright, rainbow continuous spectrum background is gone. Bright lines coincide with light lines and can measure all the properties listed for an absorption spectrum.

98A-pic-spectrum-types

A supernova is a very violent event in the universe when a massive star explodes. Elements heavier than iron are produced in the explosion. Gravity is the driving force behind the collapse of the core. The remnant is a compressed star smaller than a white dwarf, even 20 km across. A sugar cube sized piece can weigh 5,000,000 tonnes. This is known as a neutron star. It emits pulses of light, like a light house. Two beams of light are generated from the magnetic poles and as it rotates the beams are swept out into space. An example is the Crab Nebula Pulsar which flashes at 30x per second, meaning it rotates 30x per second.

Black Holes

A star with 3x the mass of our Sun can collapse to form a black hole. This is when the star pulls itself out of existence due to the amount of gravity it has. Nothing can escape a black hole, not even light. The star is reduced to a singularity into which all matter is pulled to. An envelope of space around it is called the event horizon, this is the point of no return. A typical size would be 10km. They are small and black so very hard to detect, we can only hope to detect their gravitational influence on objects around them. A famous black hole is in the binary system called Cygnus X1.

Cyg X-1 generic

Binary Stars

Most stars come in pairs. What appears as one point of light in the sky is actually the accumulation of two stars close together. These stars are in orbit around each other, this is called a binary system.

Next week… Telescopes.

Exploring the Heavens – Week 3

The topic for this week was ‘The Characteristics of the Solar System’. The main items covered were the formation of the solar system, the planets and other celestial bodies such as comets and asteroids.

Due to being ill this week I attended the Thursday class instead of my usual Tuesday class, but the format was exactly the same. Paul’s 3D presentation was fantastic as it put us right in the middle of the solar system and we could experience it from many different angles and points of view, which really helped in developing our understanding of how it all works.

One of the main themes throughout this course has been the ‘ecliptic’ – a plane on which all the planets sit and orbit the Sun. Our solar system consists of our star – the Sun – an object which dominates our neighbourhood, consisting of 99% of the mass and also gravitationally. The 8 planets and countless comets and asteroids all belong to the Sun. The unit by which we measure the distance of the planets from the Sun is called an astronomical unit, and the Earth is 1 AU from the Sun (approx. 150m km). It is possible that the distances of all the planets from the Sun can be explained with a mathematical formula that proves they are not just random distances.

A sidereal period is the time it takes a planet to orbit the sun. The further the planet from the Sun the greater the period. Kepler’s third law – the law of periods – found a simple relationship between the distance and the period. The ratio of the average distance from the Sun cubed to the period squared is the same constant value for all planets.

kep8

His equation:

kep3

Our best guess at how our solar system was formed is called the Solar Nebula theory. Any theory has to explain the characteristics of our system:

  1. The order of the orbits of planets
  2. The categories of planets – terrestrial and jovian
  3. The amount of comets and asteroids
  4. Anomalies

formation

  1. Our solar system formed from the gravitational collapse of a large cloud of gas and dust
  2. As the cloud collapses, conservation of energy, momentum and angular momentum flatten it out into a disk
  3. The diffuse clouds end up as a spinning disk of gas and dust with the young protosun at the middle
  4. The spinning disk is hotter at the centre and colder on the outside, so closer in are more material of rock and iron, further out more hydrogen compounds such as methane, explaining the makeup of our planets
  5. Finally the Sun ignites and releases a strong solar wind to clear away the remaining dust other material. We are left with the planets we have now

We talked about all of the planets and their characteristics. When we were outside looking up we could clearly see Jupiter and Mars on the ecliptic. The signs of the Zodiac pass through the ecliptic. This is a good way to find a planet!

The synodic period is the time it takes for a planet to return to the same angle with respect to the Sun. The synodic period for Mars is 780 days for it to move from opposition to opposition. Prior to opposition is when the planets move in retrograde motion.

We had an amazing view of the Moon tonight through a telescope on the balcony at the observatory. This was my first time viewing the Moon through a telescope and it looked amazing, we could see so much detail. I can only imagine the view from the Moon looking back at Earth.

Moon

The Moon has a sidereal period (orbit) of 27.3 days and appears to go through its phases every 29.5 days (synodic period). The basis for our month. The phases of the Moon are due to the changing appearance relative to the Sun, however, we only ever see one side of the Moon as it has been locked in its orbit, due to the tidal effect from Earth.

The Moon is the major force behind tides on Earth. The gravity of the moon pulls the water  up towards it, creating an uneven distribution. The Earth and moon orbit a common centre of mass, located close to the surface of the Earth. As the Earth rotates on its axis each point on the surface is subjected to a sequence of high and low tides every 6 hours. These tides are also causing the moon to slowly drift further away from Earth at 3.7 cm per century.

Finally, we talked about eclipses, both solar and lunar. Paul said that we should all try to make it to a total solar eclipse, when the moon obscures the Sun. This happens when the 3 bodies are in exact alignment, which happens every 6 months or so. This phenomenon is possible because the Sun and Moon look the same size in the sky. The Sun is approx. 400x larger than the moon but is is 400x times further away, hence a total eclipse of the Sun is possible. Very few places on Earth will see a total eclipse due to the precision needed to make this happen.

Next week… The Stars!

Astronomy at Questacon in Canberra

Questacon in Canberra has a pretty cool section on space and astronomy. Check out the pictures I took in the gallery below.

This slideshow requires JavaScript.

A few of the highlights from this exhibition.

NASA WMAP

  • WMAP is the Wilkinson Microwave Anisotropy Probe
  • It launched on June 30, 2001
  • Has mapped fluctuations in the cosmic microwave background (CMB) radiation (the oldest light in the universe) and has produced a full map view of the microwave sky
  • Has determined the universe to be 13.77 billion years old
  • Determined the curvature of space to within 0.4% of flat Euclidean
  • Found that the universe is 24% dark matter
  • Found that dark energy makes 71.4% of the universe, causing the expansion rate of the universe to speed up

Morgan Keenan System (MKK)

  • Classification of stars based on temperature
  • Categories divided into Roman numerals, with sub-categories and classes
  • To completely describe a star the MK luminosity class is appended to the original Harvard classification for the star
  • The Harvard Spectral Classification assigns each star a spectral type with is further divided into 10 sub-classes depending on the absorption features present in the spectrum. E,g, our Sun has a temperature of 5,700 Kelvin and is classified as a G2 star
  • Our Sun is a main sequence star G2 and the full classification is G2V

Screen Shot 2016-05-15 at 10.27.10 AM

Types of orbit

  • The Moon does not orbit the Earth, the Moon and Earth orbit each other around their common centre of mass. The common centre of mass is inside the Earth
  • Kepler showed the orbits of the planets were ellipses with the Sun at one foci
  • Newton showed there were other types of orbit
  • Elliptical and circular orbits are both bound orbits
  • Parabolic and hyperbolic are unbound orbits
  • Comets and asteroids typically have hyperbolic or parabolic orbits, they zip around the Sun once and they go off never to be seen again because they do not have gravitationally bound orbits
  • Look at the circular cone above, how you slice the cone determines what kind of geometric cross-section you get – horizontal makes a circle, an angle creates an ellipse, increase the angle and get to the bottom of the cone you get a parabolic and cut the cone vertically you get a hyperbola
  • So 4 different types of orbits

Additional…

  • Newton’s laws of gravity showed that Kepler’s first 2 laws, ellipses and equal area in equal time are a consequence of the conservation of angular momentum (Mass x speed x distance = constant)
  • At perihelion the distance to the Sun is smaller so to keep the mass times the speed times the distance the same the conservation of angular momentum the plane must move faster
  • At aphelion, further away from the Sun, conversely the speed must decrease
  • P squared is a cubed (P^2 = a^3)
  • P is the period the time it takes to go around and the semi-major axis of a of the ellipse, a is the average orbital distance

Thank you F.X. Times at Arizona State University for some of the information included.

Exploring the Heavens – Week 2

The focus of this week’s class was Celestial Rhythms and the development of the constellations.

We started the class upstairs in the observatory and outside on the balcony with Paul describing our session and then identifying a few of the objects on display in the night sky, including a crescent Moon. Paul described how the Moon is moving around the Earth and how the position of the Sun in relation to the Earth and Moon affects the different phases of the Moon. He explained that next week the moon will have moved across the sky in counter-clockwise direction and showed us approximately where it would be.

We then headed downstairs and outside to a large model of the solar system painted on the ground, as seen in the image below during the daytime. We sat around the model and Paul described the motion of the Earth and other planets around the Sun. This demonstration was a great way to visualise our solar system and how various planets move in relation to the Sun. Paul also described how our view on Earth is affected by the Sun and how the Sun blocks various stars at certain parts of the year.

293564_home_hero.jpg

This session was about the importance of understanding how the sky moves during a night and throughout a whole year.

“The sky is on a continual march that presents us with different constellations at different times of night, and different times of year.”

After our outside demonstration and further observing of the night sky we moved back inside for a much needed tea break and to escape the chilly Sydney evening weather, should have taken a jacket!

After our break we headed downstairs to the 3D theatre and enjoyed another presentation by Paul. The focus of the inside session was to demonstrate the motion of the Earth travelling around the Sun and its rotation on its own axis, what causes the seasons as well as examine closely what makes a day and a year, which is not quite what we thought.

I learnt so much over our 2 and a half hour class. As we spin around our axis once per day we actually move about 1 degree around the Sun. We rotate and orbit in a counterclockwise direction and in a year there are 365.25 days. So, the Earth, rotating at 1360 km/h, must spin on its own axis 360 + 1 degrees to have the Sun reappear in the same position. A day as we know it is 24 hours long, this is actually a solar day as our clocks have been tuned to the combined motion of our rotation and orbit around the Sun.

A different kind of day is called a sidereal day, which is 23 hours 56 minutes and 4 seconds long. This is the time astronomers use to predict the location of stars on the night sky. All of this means that we will see a slightly different sky each night.

We all know we have four seasons on Earth and the seasons are caused by our axis of rotation being tilted by 23.5 degrees to the plane of our orbit, called the ecliptic. The axis points in the same direction as we orbit the Sun, and this is what causes the seasons and the variation in the length of a day throughout the year. Paul gave us examples of the equinoxes and the solstices. The equinoxes occur approx. half way between the solstices on March 21 and 21 September, the solstices on 21 June and 21 December. In June the axis is pointed towards the Sun so the northern hemisphere will see the Sun high in the sky and will receive many hours of sunbathed daylight. In the southern hemisphere people will see the Sun much lower in the sky and will experience less daylight compared to the northern hemisphere. The reverse is true for December. At equinox the day and night are the same length for both hemispheres – equal.

AxialTiltObliquity.png

“We spend our days and nights humbly on planet Earth. We suffer from the illusion that we feel stationary on the surface of the Earth and that the Sun and stars seem to revolve around us.”

Infant, our axis is slowly precessing, like a spinning top over a period of 26,000 years. This means that the celestial poles on the celestial sphere sweep out a circle every 26,000 years carrying our coordinate system of the stars with it. This small drift was actually measured by Hipparchus around 140 BC. Paul has recommended we purchase a planisphere, seen below, a dynamic map that can portray the night sky for a given location at any time of night throughout the year. These are only designed for one latitude and do not contain much information.

There are 88 constellations in the night sky. Each constellation is an area of the sky and are recognised and classified by the International Astronomy Union (IAU). We learnt heaps about the constellations:

  • Each culture developed its own constellations
  • Constellations often symbolised mythological creatures
  • Constellations are a reminder of a lesson or a seasonal event
  • Many originated in Babylonia
  • The Greeks adopted many and developed their own mythologies to explain them
  • The constellations the Sun passes through along the ecliptic are called the zodiacs
  • There are actually 13 zodiacs, including Ophiuchus, although the Sun does not spend too much time in this sign
  • The Babylonians set up the zodiacs and their counting system was based on base 12, so they stuck with just the 12 constellations and that is why we have 12 hours of day, 12 hours of night and 12 months a year
  • The Sun now spends more time in Ophiuchus than in some neighbouring constellations

I am a Pisces and here is my constellation from the IAU (http://www.iau.org/static/public/constellations/gif/PSC.gif)

PSC.gif

A few facts about Pisces:

  • One of the most ancient constellations
  • Depicts 2 fishes swimming in opposite directions with their tails joined
  • In mythology the two fishes represent Aphrodite (Venus) and Eros (Cupid)
  • One day they hide to hide in rushes along the Euphrates to escape a monster called Typhon. The two fishes swam away to safety
  • Pisces is watery and faint, it lies in an undistinguished part of the sky
  • Its brightest stars are only magnitude 4
  • One way to locate Pisces is by reference to the square of Pegasus
  • The Sun passes through Pisces between Feb 19 and March 20
  • The 12th sign
  • Famous Pisces include Steph Curry (Mar 14), Einstein (Mar 14), Steve Jobs (Feb 24), Daniel Craig (Mar 2), Jon Hamm (Mar 10)

Pisces stars

Pisces

Eta Piscium is the brightest star at 316x that of the Sun. It is 294 light years from Earth and is a G class bright giant star.

Pisces contains a Messier object called Messier 74, a spiral galaxy located between the stars alpha Arietis and eta Piscium. It is also known as the Phantom Galaxy, shown below.

M74

Messier-74

The grand-design spiral galaxy Messier 74 as photographed by the Hubble Space Telescope in 2007. Image: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration. Acknowledgment: R. Chandar (University of Toledo) and J. Miller (University of Michigan)

The red areas indicate pockets of hydrogen gas. They glow due to the radiation from hot, young stars. Astronomers call these areas H2 regions. The brighter stars are not part of the galaxy and are actually located a lot nearer to us. The galaxy appears face-on and is approx. 30 million light years from Earth. It is roughly the same size as the Milky Way with a diameter of 95,000 light years. Two supernovae have been seen exploding in recent years in this galaxy. It contains about 100 billion stars. It is not easy to observe due to low surface brightness and requires clear skies. The only other object with a lower surface brightness is M101, the Pinwheel Galaxy, shown below.

M101

M101-HST-GendlerS.jpg

The Phantom is an example of a grand design spiral galaxy with 2 clearly defined arms which extend for about 1,000 light years. The arms contain clusters of young blue stars and star forming nebulae. It is receding at a speed of 793 km/s.

Zoom into M74:

M74 was first observed in 1780 by French astronomer Pierre Méchain who told his good friend Charles Messier about it, Charles added it to his famous catalogue.

More about M74 here.

Thank you Hubble!

Exploring the Heavens – Week 1

On Tuesday 3 May I attended the first week of my new course on astronomy at Sydney Observatory. The course is titled ‘Exploring the Heavens’ and is led by Dr Paul Payne. The structure of the course is as follows:

  1. History of Astronomy
  2. Celestial rhythms
  3. The solar system
  4. The stars
  5. Telescopes

So the course started with Dr Payne’s two hour version of the history of astronomy in the Sydney Observatory 3D theatre. Some of the main figures covered included:

  • Aristotle (384 – 322 BC)
  • Claudius Ptolemy (~140 BC)
  • Nicolas Copernicus (1473 – 1543)
  • Tycho Brahe (1546 – 1601)
  • Johannes Kepler (1571 – 1630)
  • Giordano Bruno (1547 – 1600)
  • Galileo Galilee (1564 – 1642)
  • Isaac Newton (1642 – 1727)
  • Edmund Halley (1656 – 1742)
  • Charles Messier (1730 – 1817)
  • William Herschel (1738 – 1822)
  • James Bradley (1693 – 1762)
  • Friedrich Bessel (1784 – 1846)
  • John Adams (1819 – 1892)
  • Jean Le Verrier (1811 – 1877)
  • Albert Einstein (1879 – 1955)

Dr Payne kept the pace moving pretty quickly to cover all of these historical and important figures and more about the ancient Greeks, Romans, Babylonians, Renaissance as well as advancements in mathematics, engineering and technology.

Dr Payne also used his homemade 3D graphics to help demonstrate certain themes and concepts, including retrograde motion of planets, constellations and the movement of the moon and planets from Earth’s point of view. The graphics were great and they certainly enhanced the presentation putting us firmly in the cosmic realms.

I was surprised at how important astrology was in ancient times and how seriously it was taken to predict future events. People were also very superstitous and heavenly objects played an important role in how people lived their lives, including Roman emperors. It is also amazing at how much people knew about the solar system hundreds and thousands of years ago without even the aid of a telescope.

IMG_2648.JPG

As well as learning about the history of astronomy Dr Payne gave us a tour of the night sky on what was a beautiful and clear evening in Sydney. Some of the notable objects we spotted were: Mars, Jupiter, Alpha Centauri, Sirius, Betelgeuse, as well as some notable constellations.

Jupiter-planet

The final part of the evening involved us moving to the south dome of the observatory to use the telescope to view the night sky. We were lucky enough that the sky was clear from clouds and we were treated to an amazing view of Jupiter and the Galilean moons Ganymede, Io, Europa and Callisto.

IMG_2640

Image of the telescope in the south dome of Sydney Observatory.

This telescope is the oldest working one in Australia and was built in 1874 by Hugo Schroder in Hamburg, Germany. An interesting article about the telescope can be found here.

This was actually my first time looking through a telescope and the view did not disappoint. I was amazed by how clear Jupiter appeared, being able to clearly identify its white zones and brown belts, both of which are cloud systems with winds that blow in opposite directions. The Galilean moons, although tiny, were very bright and also so clear to see. This is exactly what I had been hoping to see and has just added more fuel to my growing love for astronomy.

Looking forward to week 2!

Introduction to Solar Systems Astronomy Design Project

Earth’s twin: No oxygen, no water, scorching temperatures and a runaway greenhouse effect. What else do we know about our closest neighbour, Venus?

Arizona State University’s AST111

Introduction to Solar System Astronomy

Design Project evidence

Learning objective

Describe the origins, structure, contents, and evolution of our solar system.

Project goal

“Venus favours the bold” – Ovid

Describe the planet Venus, how it became so hot and examine the scientific impact resulting from the many missions to Venus, otherwise known as Freya’s planet.

venus.jpg

Image courtesy of http://www.space.com/images/i/000/044/599/original/venus-surface-magellan-spacecraft.jpg

Venus fact file

  • Second planet from the Sun, 67 million miles apart (0.72 AU)
  • Second brightest object in the night sky, behind the Moon. Venus’ clouds are highly reflective, making it shine bright in the night sky
  • Named after the Roman Goddess of love and beauty
  • Has no moons or rings
  • Spins very slowly in a clockwise direction (retrograde rotation), backwards to the other planets in the solar system. Backwards spin is probably due to a cosmic collision early in its history
  • Venus is very nearly a perfect sphere, thanks slow rotation!
  • 80% size of Earth, similar mass and both rocky worlds
  • Hottest world in our system, 480 degrees celsius on the surface, hot enough to melt lead
  • Runaway greenhouse effect. It is thought Venus used to have oceans but due to extra heat from the Sun these oceans evaporated and the water vapour trapped more heat in the atmosphere warming the planet further, trapping more heat until the oceans were no more
  • Has a cratered and volcanic surface
  • 1 year on Venus is equal to 225 Earth days, and 1 day on Venus lasts 243 Earth days – making a day last longer than a year on Venus
  • Atmosphere consists mainly of carbon dioxide (~96%), Nitrogen (~4%)
  • More than 40 spacecraft have explored Venus

Venus in culture

The Venus de Milo is ancient Greek statue created between 130 and 100 BC. It depicts Aphrodite, the Greek goddess of love and beauty, known as Venus to the Romans. It is on permanent display at the Louvre in Paris.

Venus_de_Milo_Louvre_Ma399_n2

Men are from Mars, Women are from Venus. This book published in 1992 has sold over 50 million copies around the world. It states that common relationship problems between men and women are a result of fundamental psychological differences between the sexes because they are from ‘different planets’.

menarefrommars

Beyond Apollo – Barry M. Malzberg. A novel about a 2 man mission to Venus which is aborted and when the mission returns to Earth the captain is missing and the other man cannot explain what happened to him. The novel tries to get to the bottom of this mystery and overall it represents humanity’s incompetence at the enormity of space exploration. The book is listed as in development on IMDb so look out for a motion picture soon. (http://www.imdb.com/title/tt2403823/?ref_=fn_al_tt_1)

beyond apollo

For a twin planet, Venus is very different to Earth

4 billion years ago Venus was thought to be a lot like Earth, with evidence pointing towards Venus supporting bodies of water (H2O), perhaps even oceans. However, 4 billion years ago the Sun was less powerful that it is today and was only 70% as bright. Over time as the Sun became much hotter any bodies of water on Venus evaporated and water vapour was driven into the atmosphere, causing major greenhouse changes. Water vapour can trap heat, acting as a blanket around a body. At the top of the Venus atmosphere water molecules were split into hydrogen (H) and oxygen (O), under the full intensity of sunlight and ultraviolet rays. Much of the hydrogen (H) escaped into space whilst the oxygen (O) combined with carbon to form carbon dioxide (CO2), a great absorber of heat. Oxygen also bound with sulphur (S) and created sulphur dioxide (SO2) which created droplets of sulphuric acid (H2SO4). Could this runaway greenhouse effect ever happen here on Earth?

Venus atmosphere

The Venus atmosphere is extremely dense and hot. It is mainly composed of carbon dioxide with clouds of sulphuric acid, which gives Venus its yellow colour. It does rain sulphuric acid, but drops never reach the surface due to the extreme heat. The thick atmosphere traps heat and the tremendous amount of carbon dioxide adds to the runaway greenhouse effect on the planet. The weight of the thick, dense atmosphere creates enormous pressure on the surface of 90 times heavier than standing on the surface of Earth. The equivalent pressure on Earth is about 1 km beneath the surface of an ocean. The atmosphere is slowly being stripped away by the solar wind, a million tonne per second stream of material coming from the Sun. About 300 kg of the atmosphere is being lost every day from Venus.

Internal structure

Venus has an iron core approx. 3000 km in radius. This is similar to all terrestrial planets because of the effects of gravity, causing heavier material to sink to the middle of the planet whilst lighter material floated to the top. Venus does not have a magnetic field as it rotates too slowly.

InteriorOfVenus

Image courtesy http://astronomy.nmsu.edu/tharriso/ast105/InteriorOfVenus.png

Missions to Freya

Over 40 missions have explored Venus. The first craft to land on the surface was Venera 7 and was actually the first craft to land on another planet, after 15 failed missions. This Soviet mission in 1970 successfully landed on the surface and was able to send back 23 minutes worth of data, including a surface temperature reading of 475 degrees celsius and a pressure reading of 90. Not a very pleasant place to be!

venera_7_capsule-browse_732X5201

Image courtesy http://solarsystem.nasa.gov/missions/venera_07/galleries

There is presently an active Venus mission called Akatsuki. The goal of the mission is to study weather patterns, confirm the presence of lightning in thick clouds and search for signs of active volcanism. This mission suffered a huge blow early on in its mission when thrusters failed to fire and the craft ended up on a journey around the Sun rather than Venus. Over the next five years JAXA (the Japanese Space Agency) tested the various thrusters and came up with a strategy to fix the craft and send it back to Venus. To do this they dumped fuel from the broken thrusters and used the secondary control thrusters to orient the probe towards Venus. This happened in December of 2015 and the probe entered the orbit of Venus as originally planned.

Screen Shot 2016-05-01 at 12.07.30 PM.png

Image courtesy http://solarsystem.nasa.gov/galleries/space-tourism-posters

Magellan – mapping the surface of Venus. Launched in 1989 by NASA, the Magellan deep space orbiter was designed to map the surface of Venus down to a resolution of 120 to 300 metres. On 15 September 1990 the craft began to send high resolution radar images of the surface  clearly showing signs of vulcanism, tectonic movement, surface winds, lava channels and pancake shaped domes. During its first cycle it mapped 83.7% of the surface returning 1200 GB of data, an incredible amount at that time. After the second cycle it had mapped 96% of the surface and the third mapped 98%. Contact with the probe was lost on 12 October 1994 after it had plunged into the atmosphere to collect further aerodynamic data.

Magellan findings:

  • 85% of the surface is covered with volcanic flows
  • Complete lack of water
  • Extremely slow erosion process
  • Surface features persist for hundreds of millions of years

ESA goes express to Venus in 2005! The ESA sent the Venus Express to Venus in 2005 with the primary goal of studying the atmosphere. This was the ESA’s first mission to Venus and it was named Express due to the quick time the mission took to prepare and execute.

Artist_s_concept_of_lightning_on_Venus_node_full_image_2

Image courtesy http://www.esa.int/spaceinimages/Images/2007/11/Artist_s_concept_of_lightning_on_Venus

The magnetometer (MAG) on board ESA’s Venus Express detected wave signals that show evidence of lightning in the atmosphere.

Major achievements of Venus Express include:

  • Discovery of a shape-shifting southern solar vortex. It can take almost any shape indicating complex weather patterns due to centre of vortex being offset to geographical pole
  • Evidence of recent volcanism, perhaps in the last few thousand to ten thousand years

venus2.gif

Double volcano on Venus. Image courtesy http://astronomy.nmsu.edu/tharriso/ast105/Ast105week08.html

A ten-fold increase in sulphur dioxide in the atmosphere has led scientists to question whether volcanos are still active today.

  • Venus’ rotation is slowing down, found by comparing data collected by the Magellan mission. Features monitored by Express could only be lined up with Magellan if the length of a day on Venus is on average 6.5 minutes longer than when Magellan tracked the same features
  • Discovery of a cold area 125 km above the surface where snow or ice could exist. The temperature of -175 degrees celsius means the carbon dioxide can freeze
  • Detection of a thin ozone layer approx. 90 to 120 km above the surface, far higher than on Earth where ozone exists at 15 to 50 km above the surface
  • Water loss due to splitting of water molecules in upper atmosphere by ultraviolet radiation from the Sun. The process creates two hydrogen atoms and one oxygen atom which are carried into space by the solar wind. Venus does not generate a magnetic field which can protect its atmosphere from the solar wind
  • Discovered mean wind speed of 400 km/h, an increase of 100 km/h over the 8 year mission

venus pancake domes.gif

Pancake domes on Venus. Image courtesy http://astronomy.nmsu.edu/tharriso/ast105/Ast105week08.html

Images from the surface – Venera 13. On 1 March 1982 Venera 13, a Soviet mission, set down on the surface of Venus and began relaying data back to Earth. It was able to transmit data for 127 minutes, far longer than the expected 32 minutes before the craft was crushed and melted by the extreme pressure and heat on the surface of Venus. It successfully relayed the first colour pictures of the surface of Venus, something previous missions had failed to do. It sent 8 panoramas showing fields of orange-brown rocks and loose soil. Soil analysis showed soil similar to terrestrial leucitic basalt with high potassium content.

Venera13Camera2

Image above shows Venus surface.

Future Venus missions?

1. The clockwork Venus rover. The solution to Venus landers not lasting longer than 2 hours could be a clockwork lander with no electronics. To send messages back home it would record data on a phonograph and then loft it on a balloon to rendezvous with a spacecraft overhead. (https://www.newscientist.com/article/mg23030693-600-our-top-5-wacky-nasa-missions-that-might-just-happen/)

The phonograph is a machine invented by Thomas Edison in 1877. It is a machine for recording sound on tinfoil coated cylinders. It has 2 needles, one for recording and one for playback. It is incredible to think that over one-hundred year old technology could be used to explore the solar system today.

2. Can sound help us detect ‘earthquakes’ on Venus? (http://www.astrobio.net/topic/solar-system/venus/can-sound-help-us-detect-earthquakes-on-venus/)

Researchers are planning to deploy an array of balloons in the atmosphere of Venus that could detect seismic activity on the surface using sound. A team of experts at the Keck Institute for Space Studies began thinking of ways to use infrasonic observations to get a better look at the geological dynamics of Venus. If we can get a better idea of the seismic activity on the planet this can tell us more about the history of the planet and its interior.

Escape velocity of Venus

During the course the mathematical labs have not been my strongest area, but I have learnt so much from attempting the challenges, something I really enjoyed doing. I would like to finish with a math problem I can do – the escape velocity of Venus. So here goes…

What is the escape velocity from the Venus exosphere, which begins about 220 km above the surface?

mass = 4.867 x 10^24 kg

radius = 6.05 x 10^6 m

height = 2.2 x 10^5 m

Formula:

Screen Shot 2016-05-01 at 2.16.56 PM.png

= 2 x 6.67 x 10^11 x 4.867 x 10^24 / (6.05 x 10^6 + 2.2 x 10^5) = 1.03 x 10^8

v = sqrt (1.03 x 10^8) = 10148 m/s = 10.1 km/s ~ 10 km/s

Please check the math and let me know if I have made a mistake along the way.

Watch BBC The Sky at Night Venus documentary https://www.youtube.com/watch?v=82fS9C9koxU for more information.

Finally…

Huge thanks go to Dr Frank Timmes for being an outstanding teacher during this course, your videos and notes were amazing, thank you sooo much! You have inspired me to learn more about the universe. Big thanks also go to the rest of the team at Arizona State University for putting together an amazing course and for all their support. This has been the best course I have enrolled in on edX and I would highly recommend it to anyone interested in astronomy.

https://courses.edx.org/courses/course-v1:ASUx+AST111x+2161B/info

Thanks for reading, bye bye!

venus hipster.jpg