There are also varying amounts of other stuff – aerosols, dust, haze, clouds, smoke and so on.
The light from the sun has to pass through this “stuff” to get to the surface of the earth. But some of the light does not make it, or if it does arrive at the surface, it gets there indirectly.
Why? Because the light – or more accurately, part of the light – is scattered by “stuff” in the atmosphere.
Visible light is an electromagnetic wave of a rather narrow range of wavelengths (roughly 390-700 nanometres, where 1 nanometre is 1 billionth of a metre) in the complete spectrum. This electromagnetic spectrum spans the very long wavelengths of radio to the extremely short wavelengths of gamma rays.
Within the visible portion of the spectrum red light has a longer wavelength than blue – 650 nm vs 450 nm.
When light is scattered in the atmosphere, the amount of scatter and the angle by which it is scattered depend on the wavelength and the size of the scatterer.
If the scatterer’s size is significant compared to the wavelength of the light being scattered, the shape of the scatterer becomes important too.
Molecules are the smallest scatterers, being about a factor of 1,000 smaller than the wavelength of visible light. For these molecules – such as nitrogen gas (N2) which makes up 78% of the atmosphere – the dependence of scattering on wavelength goes as the inverse fourth power of wavelength.
That is, comparing blue to red, we take the wavelength ratio (650/450) and raise that to the fourth power to calculate how much more likely (4.3 times, as it turns out) it is blue will be scattered than the red.
If you look away from the sun, blue light travelling from the sun through the earth’s atmosphere (but not directly toward you) is scattered by the molecules toward your eye.
Thus the sky looks blue because scattering from molecules is much more probable for blue light than red.
There is so much blue light from any particular direction that it completely dominates the light from the stars, which is nonetheless still there.
If you get close enough to space, the sky is black (see image below). This is just because there is nothing significant up there that will scatter the sunlight to your eye.
Conversely, if you look through a clean atmosphere (i.e. with no dust or smoke) towards the sun, a significant amount of the blue light is scattered away from the line of sight, which tends to give the sun a yellowish hue.
This sort of scattering – when the scatterer is considerably smaller than the wavelength of the light – is usually called “Rayleigh scattering”, after the 19th century British physicist Lord Rayleigh.
Near sunset, the path sunlight takes on its way through the atmosphere to you is especially long. In this case, so much blue light is lost (i.e. scattered away) that the sun appears orange or even red (see image below).
The water droplets and ice crystals that make up clouds are quite large compared to the wavelength of visible light (at least 20 times greater). In this case the scattering of light is strong and nearly independent of wavelength, over the visible range at least.
Because nearly all wavelengths of visible light are scattered, clouds appear white, or varying shades of neutral grey if they are in the shadow of other clouds.
If you consider the wavelength dependence of scattering for medium-sized particles, you find that for a narrow wavelength range the dependence reverses for a bit. That is, in this range – which can be as wide as the visible spectrum – the scattering is stronger for longer wavelengths, as opposed to weaker.
It is possible for the size of the particles to be just right for this to happen in the visible spectrum. In this case the sunlight that passes through air with these particles suspended has red light scattered away leaving the sun (or moon) looking bluish.
This is rare but has happened on occasion when volcanoes or forest fires load the atmosphere with particles of just the right size.
In contrast to Earth, the Martian atmosphere is quite dusty, and there the sky tends to be orange, sometimes with blue sunsets. This is because the dust particles are much larger than the carbon dioxide molecules which make up the atmosphere.
The fact that the atmosphere is very thin on Mars means scattering from dust is relatively more important than it would be on Earth.
So next time you’re lying in the grass looking up at white clouds float across a stunning blue sky, spare a moment to think about the physics responsible for what you’re seeing.
Murray Hamilton receives funding from the Sir Ross and Sir Keith Smith Fund.
“People are coming here, not now as a result of persecution, but because they’re economic refugees who’ve have paid money to people smugglers.
– Foreign minister Bob Carr, Meet the Press, June 9.
There is a political context to this statement as the government grapples with its perceived weakness on asylum seeker policy. Resurrected prime minister Kevin Rudd has backed Carr, saying there were a “whole bunch of people” arriving by boat as economic migrants purporting to be refugees.
The government has commissioned a review into the processing of asylum seekers in a bid to lower the acceptance rate – around 90% of asylum seekers who arrive by boat have been found to be refugees. The government’s view is that many are middle class Iranians and Sri Lankans, in particular, who are fleeing for economic reasons. “There’ve been some boats where 100% of them have been people who are fleeing countries where they’re the majority ethnic and religious group, and their motivations is altogether economic,” Senator Carr said last week.
The government says it has evidence to justify these claims, but so far we have not seen it. Putting aside the politics, the government’s assertions are not backed by the known facts.
Since the adoption of the Expert Panel Recommendations on Asylum Seekers, the “no advantage” test has been applied to all individuals who have arrived in Australian waters seeking asylum since August 13, 2012. This means they receive no benefit compared with people who stay in refugee camps waiting for processing. Because of this, as reported in The Guardian: “there has been virtually no processing of the claims made by the more than 20,000 refugees who have arrived since that time”. This was confirmed in the Legal and Constitutional Affairs Legislation Committee on May 27, 2013. So, if we have not processed claims, we have no idea whether recent arrivals by boat are “genuine” refugees or not.
We also know that the majority of asylum seekers are arriving from Sri Lanka, Iran and Afghanistan. Regarding Sri Lanka, the Human Rights Council on March 21, 2013, adopted the resolution on Promoting Reconciliation and Accountability in Sri Lanka, which called on its government to “conduct an independent and credible investigation into allegations of violations of international human rights law and international humanitarian law”.
The resolution expresses concern at:
…reports of continuing violations; concern at reports of enforced disappearances, extra-judicial killings, torture, threats to the rule of law, religious discrimination and intimidation of civil society activists and journalists.
As for Iran, this year the Security Council – of which Australia is a member state – extended the enforcement of sanctions. The Human Rights Council on March 22, 2013, passed a resolution on the human rights situation in Iran after hearing a report by the UN Secretary General. It concluded that:
…the Secretary-General remains deeply troubled by reports of increasing numbers of executions, including of juvenile offenders and in public; continuing amputations and flogging; arbitrary arrest and detention; unfair trials; torture and ill-treatment; and severe restrictions targeting media professionals, human rights defenders, lawyers and opposition activists, as well as religious minorities.
As for Aghanistan, the Security Council regularly hears from the United Nations mission in Afghanistan (UNAMA). In March 2013, it was reported to the council that there remains serious human rights violations and attacks on civilians by armed non-state actors. Regarding the likelihood of these asylum seeker claims meeting the UNHCR refugee definition – “the UNHCR has identified 859,305 refugees in need of resettlement, of whom 180,676 require resettlement in 2013”. Afghanistan remains the number one source country for successful refugee claims around the world.
In summary, these three major source countries for boat arrivals have been repeatedly found by the international community to be unable to protect persons that may fall under the refugee definition – someone with a well-founded fear of persecution on the grounds of race, religion, nationality, social group or political opinion.
Finally, on the question of “economic migrants” versus “refugees”, the UNHCR provided an important qualification in their 2011 issue of the UNHCR Handbook on Procedures and Guidelines for RSD. They noted the distinction is “sometimes blurred”.
“Behind economic measures affecting a person’s livelihood there may be racial, religious or political aims or intentions directed against a particular group.”
The handbook goes on to note that “objections to general economic measures are not by themselves good reasons for claiming refugee status. On the other hand, what appears at first sight to be primarily an economic motive for departure may in reality also involve a political element, and it may be the political opinions of the individual that expose him to serious consequences, rather than his objections to the economic measures themselves”.
As signatories to the 1951 Refugee Convention, we have an obligation to hear – without prejudice – the testimony of each asylum seeker before presuming that their claim for refugee status is not valid because of their nationality or ethnic origin.
Based on the available information, the foreign minister’s statement is incorrect.
The author is correct that it is the political context surrounding current asylum debates that has prompted a shift in language, now likening asylum seekers to economic migrants. This shift in language heralds a potential future shift in asylum policies.
It is true that as the reference to UNHCR in this article notes, Convention-based persecution can lead to economic deprivation, and Australia should be wary of making blanket assessments of particular countries or groups. However on the matter of claims not being processed and the unavailability of data, there are a number of Sri Lankans in particular who have either returned voluntarily or involuntarily on the grounds that they have not invoked Australia’s protection obligations. It may be instances like this that Senator Carr is using to extrapolate to all boat arrivals. – Melissa Philips
The Conversation is fact checking political statements in the lead-up to this year’s Australian federal election. Statements are checked by an academic with expertise in the area. We then seek a second opinion from another academic expert, who gets an anonymous copy of the article to review for accuracy and fairness. Our Election FactCheck page launches on Monday 8 July.
The Conversation is fact checking political statements during the federal election period. Statements are checked by an academic with expertise in the area. We then seek a second opinion from another academic expert, who gets an anonymous copy of the article to review for accuracy and fairness. The author of this Election FactCheck, Sara Davies, receives funding from Australian Government (AusAID grant in partnership with University of Queensland) and has received funding from Australia Research Council.
The reviewer of this Election FactCheck, Melissa Phillips, has received funding from the Australia Research Council. She is also an individual member of the Refugee Council of Australian and Amnesty International.
New powers for health and safety representatives in all mines following the Pike River disaster are a “scary proposition” and should be limited to coal mines only, a gold mining company says.
Bernie O’Leary, who manages Oceana Gold’s Macraes Mine in Otago, on Thursday urged parliament’s industrial relations select committee to pare back the proposed new inspectors’ roles in the Health and Safety (Pike River Implementation) Bill.
The bill includes recommendations from the Royal Commission into the Pike River Coal Mine disaster in November 2010 which left 29 men dead following explosions in the mine.
Unions or groups of workers will be able to appoint health and safety representatives – similar to Australia’s mine check inspectors – who will be able to give notice of suspension of mining operations when there is a risk of serious harm, or to call a stop to operations if the risk of harm is imminent.
Oceana Gold – the country’s largest gold miner, and second largest mines operator after Solid Energy – objects to the suspension power, and wants it removed from the bill.
“It’s a pretty powerful part of the act, and quite frankly a scary proposition in the hands of an ill-informed or maybe overly eager representative,” Mr O’Leary said.
He says the royal commission made it clear health and safety representatives should only be able to halt operations when the risk is imminent, and in other cases, the representative should take their concerns to a mines inspector.
Mr O’Leary also warned unions might misuse the representatives’ powers for their own interests, and there were not adequate safeguards in the bill to prevent that.
Oceana Gold wants the representatives’ powers to apply only to coal mines, where methane is a major hazard, as is the case in Australia.
“For the non-coal part of the industry, check inspectors are neither necessary nor add any value, and in some cases, a wrongful stop-work notice could cost an operation,” he said
The bill will also require mining companies to pay a mines rescue levy to fund disaster teams, but Oceana Gold wants it funded on a user-pays basis.