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Orbit: Episode Two

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Aira Idris Aira Idris | 21:30 UK time, Sunday, 11 March 2012

The second instalment of the series follows the Earth's journey from the start of January to the Spring Equinox in March. Available on iplayer. What did you think?

Kate begins the film on a day with a very significant point in our Earth's journey - Perihelion. Kate climbs Aonach Mor mountain, one of the highest mountains in Scotland, which brings her as close to the Sun as she'll ever be for the entire year.

This however is not because of where she is but because of the point the Earth has reached in its orbit around the Sun. In fact we kick started our blog on this day just over a year ago, when we explored the elliptical shape of our planet's orbit and how significant this was to our understanding of Earth's climate.

Later in the film Helen explains how the proximity of the Earth to the Sun doesn't guarantee warmth - which brings us to the tilt of the Earth (23.4 degrees) - a theme we explore in further detail in episode three.

Throughout this episode Kate and Helen explore the increase in solar radiation and how land and ocean respond to it.

Kate drives over a frozen lake in Canada with an ice road trucker in one of the coldest places in that region and learns how important this ice formation is to connecting communities.

In this film we also tackle ice ages and how over time, as Earth has repeated it's annual journey, it's climate has changed.

Helen dives under water in Belize to discover how sea levels have risen and fallen over time due to ice age - and explores the three cycles that need to be right in order for another ice age to exist.

What did you think of episode two?

(There are a total of three episodes in this series)


  • Comment number 1.

    Congratulations on a superb programme. Two things: First, if I'd known how good it was going to be I'd have recorded it (we can't use the iplayer here in Dublin). Will it be repeated any time soon on and of BBC 1,2, 3 or 4 as I intend reviewing it on my blog [Broken URL removed by Moderator] https://anthonyokeeffe.com/ ?
    And second, you summarized very succinctly why none of us will ever see another ice age; 1) where we are on the perihelion cycle, 2) the Earth's tilt and 3? Could you drop me a line with that succinct summary again please? Thanks! Anthony.

  • Comment number 2.

    Where did 60,000 years until the next ice age come from? Your Mr.Black indicates 1,500 years...

    see https://www.bbc.co.uk/news/science-environment-16439807

  • Comment number 3.

    also I think you forgot to mention the wobble of the earths axis as another contibuting factor to the cycle to the ice age

  • Comment number 4.

    Kate Humble climbed a mountain in Scotland at perihelion to get closer to the Sun. Instead, she should have got on a plane and gone to anywhere near the Tropic of Capricorn and then at midday she would have been something like 2000 miles closer to the Sun. Even London would have been closer! Dumb TV science again...

  • Comment number 5.

    Actually, I think it would have been more like 3900 miles closer to the Sun at the Tropic of Capricorn not 2000 miles, but you get the idea. Should've done my sums before commenting...

  • Comment number 6.

    Why did you spoil an otherwise excellent and scientifically sound programme by ending it with the blaming of thinning arctic ice on human activity?
    There is absolutely no scientific evidence for this - instead you pandered to the BBC's bias and the errors perpetrated by the IPCC.
    Explain please why :
    - no discernible global temperature change since 1998 (despite CO2 rising)
    - though Artic ice may be thinning, Antarctic ice is increasing
    - sea levels are not rising (despite the protestations of the Maldivan government)

  • Comment number 7.

    Was this a science programme or a travelogue? I'm struggling to tell the difference nowadays.

  • Comment number 8.

    Next week: Kate visits Copacabana beach to pick up a handful of sand, while Helen goes skiing in Klosters to show us what snow looks like in winter.

  • Comment number 9.

    Kate Humble states that the Aurora Borealis is caused by 'radioactive particles' hitting the top of the Earth's atmosphere. I have always thought that the particles involved were mainly electrons and protons. Neither of these undergo radioactive decay. Has she other information?

  • Comment number 10.

    I've just noticed that Malcolm Soo (above) has the same query as me. In this episode Kate Humble describes the solar wind as consisting of 'radioactive particles'. Also on a previous page titled: 'The Sun and the Solar Wind: Earth has been spared the fate of Mars' - Stephen Marsh: Series Producer, said: - "Every day we are hit by a blizzard of radioactive particles. It's called the solar wind". But are any of these particles heavy enough to be 'radioactive'? (i.e. subject to decay)? Is it correct to describe these particles as 'radioactive'?

  • Comment number 11.

    This is what happens when you throw technical terms around carelessly. Solar wind is plasma, that's all. Nothing to do with nuclear reactions, except its energy comes from the fusion reactions in the sun's core.
    (Since I'm here again, I'm going to revise my figure from before again to 3300 miles...)
    Can we have some care with scientific terms please...

  • Comment number 12.

    Great programme.

    Does anyone know when Episode 2 will be repeated as my Dad missed it and has no access to iPlayer.

  • Comment number 13.

    When will episode 2 be repeated on BBC HD? Last week Episode 1 was repeated on Tuesday at 2300 which was far too late. How are we supposed to know when these will be? Many people can now get Freeview HD and a programme like this looks much better in HD. I can't find an online searchable schedule of BBC programmes - is there one and if not why not?

  • Comment number 14.

    I have read of a condition called 'precession' which (long story short) means the tilt of the earth changes every 25800 years causing hitherto summer to be winter and vice versa. I have only ever seen or heard of one reference to this. Any comments please?

  • Comment number 15.

    One might be forgiven for expecting a programme devoted so much to the Earth's orbit and tilt to mention the precession to which Rob Brown refers. This effect is the result of an external torque on the Earth by the Sun's gravity. The Earth is not spherical, but 'squashed' at the poles due to its daily rotation. The equatorial bulge nearer the Sun experiences a force which is not exactly counteracted by the farther bulge, resulting in a torque, and this causes the rotational 'axis' to precess.

    If we are to be more scientific, then we need to recognise that in general, a free moving body does not 'rotate' about a fixed axis. It moves in a complicated rolling and tumbling fashion which is clearly seen in the motion of many asteroids. Often the motion can reasonably be approximated as mere rotation, as is usually the case with the Earth, but care must be taken here. There is a question posed on this site about whether or not the Earth's axis can be shifted by an Earthquake. Assuming that the Earth has a fixed rotational axis which is shifted by an Earthquake is wrong on both counts. If the Earth had a fixed rotational axis, then an external torque would be needed to shift it to a different rotational axis. As all of the forces in an Earthquake are internal, an Earthquake can't do this. The motion of a free moving rigid body can be described as having a precessing rotational axis, and the particulars of this precession can be altered by internal forces, but the body's angular momentum is conserved. The media appears to prefer ambiguous and simplistic arguments over accuracy however.

  • Comment number 16.

    Thanks for your comments

    @Gimlet and MrT_123 - You can keep up to date with all scheduling, including repeats and BBC HD transmissions via the programme page. We only know once it has been automated on that page... https://bbc.in/zx2F1r

    @Malcom Soo and Rob Clennell, I'm looking into that and will get back to you soon


  • Comment number 17.

    @Malcom Soo and Rob Clennell - You’re right, that was an error on our part, it should have been charged particles not radioactive...


  • Comment number 18.

    @David Ellis – Thanks for the comment – In response to your query on Arctic sea ice – It is accepted that it is getting warmer. Arctic sea ice extent over the modern satellite record (1979–present) shows down - ward trends in all months, smallest in winter and largest at the end of the summer melt season in September (Sea ice extent has decreased by 5.25% to 8.25% since 1979).

    Since about 2000, positive anomalies dominate all months. The period from 2002 onwards has seen a series of extreme September extent minima. A new record minimum was set in 2005, followed by some recovery in 2006. Then, in September 2007, Arctic sea ice extent fell to the lowest value ever recorded, 23% below the 2005 minimum. Including the last three Septembers (2008–2010), which ended up with the second, fourth and third lowest extents in the satellite record, respectively, the September linear trend stands at −12.4% per decade.

    This warmer Arctic climate *has* been linked to increased concentrations of atmospheric greenhouse gases.

    The reports by the IPCC highlight that annual average Arctic temperatures over the last 100 years has increased - in fact by almost twice as much as the global mean temperature has. Furthermore Climate models predict that over the next century this Arctic temperature increase will continue to about twice the global average temperature.

  • Comment number 19.

    Good to see that episode 2 will be on HD on Fri23Mar12. I feared that the BBC would be unable to find space on the HD channel for this as there was no indication of the HD broadcast on the episode 2 page for a long time. It amazed me that BBC go to the effort and expense of producing HD programmes, but can not find the space for them! This adds to my frustration of the reduced quality of HD picture on BBC due to over-compression of the broadcast. I am reduced to being thankful for what I get1

  • Comment number 20.

    When will episode 3 be broadcast in HD?

  • Comment number 21.

    To Aira Idris
    Thanks for your response to my comment.
    However you haven't dealt with the point I made which agreed that whilst Arctic ice cover is declining, Antarctic ice is increasing.
    Also that average global temperatures have been static for the last 14 years whereas CO2 has continued to rise.
    Therefore the Climate models you mention, and upon which the IPCC rely, are incorrectly programmed and useless.
    Apart from these incorrect computerised climate models, there is absolutely no empirical evidence that man's activity (additional CO2) has any effect at all on climate.

  • Comment number 22.

    The explanation given for ice ages and warm periods was naive and wrong since it ignored feedback effects which are chiefly responsible for the changes. What happens is this. Ice ages and warm periods form an oscillating system. The ice recedes Northwards (warm periods) then something - orbit change, volcanic dust causing cooling etc - starts the ice sweeping S (this takes thousands of years but in geological timescales this is rapid). As it sweeps S it engulfs vegetation, this traps carbon under the ice and removes CO2 from the atmosphere reducing global warming also the increased reflection of the increasing ice gives another feedback. The ice sweeps S until it reaches its southern limit, where the suns radiation keeps it warm enough for the ice to extend no further. It pauses here (ice age) until some unusual warming - orbit change or possibly a belch of CO2 - causes the ice to start melting. But by this time the vegetation under the ice will have turned to methane, a strong GHG this combined with the reduced reflexivity of the melted ice provide the opposite feedbacks causing the ice to sweep back northwards giving us a warm period.
    Now man-made global warming is causing the ice to recede further than normal and threatening a drastic further methane release and catastrophic global warming.

  • Comment number 23.


    @David Ellis - the global warming debate is an interesting one, and one that I doubt will be resolved on this blog.

    I didn't mention Antarctic sea ice as even if wintertime Antarctic sea ice were to increase or decrease significantly in the future, it would not have a huge impact on the climate system. This is because during the Antarctic winter energy from the Sun is at its weakest point; its ability or inability to reflect the Sun's energy back into space has little affect on regulating the planet's temperature.

    Besides the lack of a downward trend in Antarctic sea ice is linked to the ozone hole, see https://nsidc.org/asina/faq.html. The basic issue is that because of the ozone hole, we get a persistent pattern of winds that, except around the Antarctic peninsula, favours having lots of sea ice. Regarding global temperatures it goes without saying that the "El Nino of the Century" (1997 - 1998) had a lot to do with maximising the 1998 global temperature. See here for more on global temperature. https://data.giss.nasa.gov/gistemp/2011/

    @BahHumbug - I can see your point about the 'closest point to the Sun' segment, however the aim of that film was to highlight the significance of *when* Kate was making the climb not where. Filming in the snowy mountains of Scotland was for illustrative purposes - where better to show that proximity to the Sun does not guarantee warmth than on a Snowy mountain on the day of Perihelion...


  • Comment number 24.

    Thanks for responding. I'm not totally convinced your explanantion isn't just some post-realisation rationalisation however. I can see that some of my comments have been quite negative, and that you've had plenty of others posting positive comments, so your program appears to have been popular. I just ask that so as to avoid turning off viewers like me, and misinforming others, you take care with the 'sciencey bits'. Thanks.


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