How Well Do You Know Your Moon?

Phil Plait, who writes the wonderful Bad Astronomy blog over on Slate, noticed something interesting in a recent episode of The Simpsons:

Photo by 20th Century Fox Film Corp.
Photo by 20th Century Fox Film Corp.

To the untrained eye, nothing about this cartoon image is likely to seem unusual. But if you spend a lot of time looking at the sky, and you have the additional context that this scene occurred in the evening, then the Moon is actually quite revealing.

(For those of you thinking “it’s just a cartoon, don’t expect it to be accurate”, I realise that. But if you decide to treat it as though it must be accurate then it can be interesting to think about so bear with me.)

To understand why that is and how we know, we have to have a think about how we look at the Moon.

The Moon orbits the Earth in a plane that’s pretty well aligned with the plane of the solar system. This means if you drawn a line in the sky tracing the path of the Moon, you’ll also find the Sun and the planets roughly on that line. This is why we experience solar and lunar eclipses, which happen when the Sun and Moon are lined up particularly well with the Earth. Because the line is where eclipses happen, it’s called the ecliptic by astronomers.

Earth’s axis is tilted by 23.5° relative to this plane, but if you’re not too close to the equator (for example, if you’re in New Zealand or the USA) then you can say that if you projected the equator into the sky it would be in roughly the same position as the ecliptic. If you’re in the southern hemisphere, that means it’s to the north, and if you’re in the northern hemisphere, it’s to your south.

So, if you’re looking at the Moon from New Zealand, you must be looking roughly to the north. If you’re looking at it from the USA, you must be looking roughly to the south. This also means the Sun and Moon, moving east to west across the sky as the Earth spins, appear to move right to left from the southern hemisphere and left to right from the northern hemisphere.

When we look at the Moon, we’re seeing the same thing no matter where we are on Earth except for one thing: which way is “down”. The “bottom” of the Moon in the part that’s closest to the horizon. If you travel to the other hemisphere, and you’re familiar enough with the Moon, you may notice that it appears upside down. That’s because the direction of “down” has swapped – from roughly north to roughly south (or vice versa if you’ve travelled from north to south). If you want to see what the Moon looks like from the other half of the world, you have to bend over backwards (or lie on the ground). This is also why the Moon will appear to have rotated if you compare it when it’s rising to when it’s setting.

One more thing: the Moon orbits us in the same direction as we’re spinning, which means it moves across the sky slightly slower than the Sun. Each day, the Moon rises roughly 50 minutes later than the day before, so that over its 28 day cycle of phases this sums to 24 hours.


Now, getting back to that image from the Simpsons episode. That scene was apparently in the evening, and the Moon is low on the horizon. That means the Moon must either be about to set or have just risen. If it had just risen after sunset, then it was recently full (because a full moon rises at sunset and the moon rises later each day), which means its phase would be a waning gibbous. Waning refers to the fact that it is on its way from being full to being new, and a gibbous is the shape made by a circle with a crescent cut out from it.

In the picture, the Moon is obviously a crescent, so it can’t have just risen. If it’s just about to set after sunset, then is must just have been a new moon (because a new moon sets at sunset and the moon rises later each day), which means its phase would be a waxing crescent. Waxing refers to the fact that it is on its way from being new to being full, and the crescent refers to its curved shape.

Another thing we know about the Moon is that its lit side always faces the Sun. For example, the lit side of a full moon points right back at us, because from its perspective the Sun shines on it from behind us. If the Sun has just set, and the Moon is just about to set as well, then the lit side of the Moon must be facing the Sun. As the Sun sets in the west, this means the lit side of the Moon should also be facing west if it is a waxing crescent.

In the picture from the Simpsons, which we’ve established should be a waxing crescent, the lit side of the Moon is facing to the left. But remember, if you look at the Moon from the northern hemisphere you must be looking to your south, so west should be on your right. So if the waxing crescent moon is lit on its left, then you must be looking north to see it, which means you’re in the southern hemisphere.


Unfortunately, a lot of pop culture doesn’t get the Moon and its phases right. I know it’s such a tiny thing, and typically when they don’t get it quite right I can’t say I mind too much (although I often can’t help but notice), but I really love it when they put in that extra bit of effort to get it correct.

Almost all video games with day/night cycles where you can see the sky have the Moon orbit in 24 hours. Some of them include phases, although technically if your Moon always rises at sunset then it should always be full. I can forgive video games fairly easily though, I’m probably the only person who cares and I understand it could take significant development time to get proper lunar phases in. The only example I can think of that gets it right is Kerbal Space Program, where accurate celestial mechanics is an important part of the game.

Some books have issues with the Moon as well. Last year I was reading the book Ship of Theseus, and one scene describes the protagonist seeing the crescent moon rise as it gets dark. But crescent moons never rise as the Sun sets, light simply doesn’t work that way.

Movies often have trouble with it as well. The worst offender I’ve seen is the final scene from the movie Cloud Atlas:

Final scene from the movie Cloud Atlas
Final scene from the movie Cloud Atlas

Remembering that the lit side of a moon points towards its sun, and this applies even with multiple moons, that image implies some very strange things about the nature of light.

I’d love to see more media put more effort into getting this right. I know that one author who paid particular attention to this detail was J.R.R. Tolkien, who tried hard to get the phases of the Moon consistent with his dates when writing The Lord of the Rings and apparently did a pretty good job of it too.

My favourite example of well-documented in-depth world building doesn’t involve the Moon but I’d like to share it here anyway. My brother Jeremy (who’s currently working as a concept artist at Weta Workshop, a job he got soon after leaving Uni) worked on creating a deep and internally consistent fictional history to earn his masters degree in 2013. He ended up creating a fake National Geographic article from 1932 recounting the reporter’s visit to the settlement of Elkwood. The article only scratched the surface of all the thought he put into the work, if you want to see what he came up with you can read both the article and his exegesis explaining his research methods here: Creating Elkwood: building an alternate history

When fictional worlds are deep and internally consistent they become that much more enriched. If you know of any that have represented lunar cycles particularly well (or particularly poorly) let me know in the comments.

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Irradiation of Food and Compulsory Labelling

Queensland Fruit Fly | Photo by James Niland
Queensland Fruit Fly | Photo by James Niland

Biosecurity is a big issue for New Zealand. Being a group of islands fairly isolated from all other landmasses and having quite a unique native ecosystem (many native birds with no native mammalian predators and few native land mammals), we have a lot to lose from introduced species. There are also biological threats to industry that we have to try really hard to keep out of the country, such as Queensland fruit fly. There’s good reason why the Ministry for Primary Industries (MPI, formerly MAF) reacted so strongly when one of these flies was found in Whangarei in April 2014. If enough of these flies made it into New Zealand to self perpetuate, they could cause massive damage to New Zealand’s $5 billion horticulture industry.

In order to kill off any biosecurity risks, including disease-causing organisms and foodborne pests, various treatments (also known as “phytosanitary actions” when used on plant products) can be used when importing products into New Zealand. Different products that can be imported each have an Import Health Standard (IHS) that documents the process of importing them.

For fruit and vegetables being imported, they need to come with a phytosanitary certificate from their country of origin, to say that either they have been inspected by someone from MPI and they couldn’t find any pests, they come from a certified pest free area, or they have been treated to kill any pests. A sample of the products is also inspected by MPI when arriving in New Zealand, and if any pests are found then the products will have to be treated if they are to enter New Zealand.

The treatment used depends on a few things, such as what pest was found that they’re trying to kill. For example, assuming I’m interpreting the IHS correctly, if Thrips palmi is found in a shipment of capsicum from Australia it would be fumigated with methyl bromide at 32 g/m3 for 2 hours. Whereas if Conogethes punctiferalis were found, then the capsicum would be irradiated with a minimum dose of 250 Gy (Grays; 1 Gray is equivalent to 1 Joule of energy absorbed per kg of food).

EDIT 2015/02/01:

The previous paragraph is incorrect. Those treatments are the ones that should appear on the phytosanitary certificate, having been performed in the country of origin. The treatments done if a pest is found when they arrive in New Zealand are determined in the Approved Biosecurity Treatments Standard. So for fresh fruit and vegetables (page 37), if insects except for fruit flies (not slugs and spiders) are found then they have to be fumigated with methyl bromide at a particular rate and temperature for a particular duration (presumably depending on the pest and the produce). Looking at this standard, it seems human food doesn’t get irradiated if pests are found when it arrives in New Zealand. According to MPI’s list of treatment providers (direct PDF download), there is only one facility in New Zealand able to provide food irradiation, which is in Wellington.


Methyl bromide is an insecticide, and it’s also recognised as an ozone-depleting substance. Because of this, its use is tightly controlled. It’s only allowed to be used for a few specific purposes, one of which is quarantine, and New Zealand has to provide statistical data to the Ozone Secretariat on the annual amount of methyl bromide that we use. It’s nasty stuff – even skin contact with high enough concentration of the gas can cause severe blistering – but after being used to fumigate food it apparently dissipates fairly rapidly. There are some objects that MPI won’t fumigate with methyl bromide for various reasons, which are described in their info sheet I linked to above.

Irradiation is quite different. Using either Cobalt 60, x-rays, or an electron beam food is blasted with a specific amount of ionising radiation. Cobalt 60 is a radioactive source of this radiation, but as it emits gamma rays instead of neutrons it doesn’t make anything else around it radioactive. Both x-rays and electron beams are created by non-radioactive sources and can be switched on and off.

When food is irradiated, the process kills any organisms that are living in the food, including disease-causing organisms and pests. The food does not become radioactive, instead it will just be slightly warmed from the energy it absorbs. Also, the radiation will trigger some chemical changes, but these occur only in amounts comparable to heat treatments. In this way it’s quite similar to the process of pasteurisation used to make milk safe to drink.

In 2010, following an extensive literature search, the European Food Safety Authority (EFSA) published their Scientific Opinion on the Chemical Safety of Irradiation of Food. They found that the new evidence published since their previous decision in 2003 wasn’t enough to change their opinion that “there is not an immediate cause for concern” regarding the safety of irradiated food.

Irradiated Food symbol | FSANZ
Irradiated Food symbol | FSANZ

The strongest negative evidence they found seemed to be a case in which cats ate a diet consisting largely or entirely of highly irradiated (25.7 to 53.6 kGy, i.e. 100 to 200 times as much as in the capsicum example from earlier) cat food and subsequently suffered from leukoencephalomyelopathy (LEM). This evidence doesn’t necessarily have any relevance to humans though; in another report dogs ate the same pet food and didn’t exhibit LEM. Also, as the incident was only linked to one specific lot of one specific brand of pet food it’s unclear if irradiation was the culprit at all.

Even though irradiated food appears to be entirely safe to eat and not significantly different from food that hasn’t been irradiated, it is currently compulsory to label irradiated food in New Zealand under the Australia New Zealand Food Standards Code Standard 1.5.3.

MPI’s Food Smart website has an informative page on food irradiation. It’s quite clear on several important points (you can read their full answers on the page):

Does irradiation change food?

At the approved doses, changes to the nutritional value of the food caused by irradiation are insignificant and do not pose any public health and safety concerns.

Some treated foods may taste slightly different, just as pasteurized milk tastes slightly different from unpasteurized milk. There are no other significant changes to these foods.

Does irradiation make food radioactive?

No.

Is it safe to eat irradiated food?

Yes. Irradiation of food does not make the food unsafe to eat.

The World Health Organisation, the Food and Drug Administration in the US and the American Medical Association all agree that irradiated food products are safe to eat.

The FDA’s page on food irradition has an informative “Debunking Irradiation Myths” inset:

Irradiation does not make foods radioactive, compromise nutritional quality, or noticeably change the taste, texture, or appearance of food. In fact, any changes made by irradiation are so minimal that it is not easy to tell if a food has been irradiated.

FDA

It also states that:

FDA has evaluated the safety of irradiated food for more than thirty years and has found the process to be safe. The World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC) and the U.S. Department of Agriculture (USDA) have also endorsed the safety of irradiated food.

FDA


Earlier this week, the Herald published an article by Sue Kedgley on irradiated food. In my opinion that article is a load of unscientific scaremongering. Here are a few excerpts that appear clearly intended to be more emotive than informative:

But irradiated food is anything but fresh. It’s been exposed to radiation doses that are between three and 15 million times the strength of x-rays. The Brisbane radiation facility uses Cobalt 60 to irradiate food, a radioactive material that is manufactured in Canadian nuclear reactors, and shipped to Australia in special unbreakable steel canisters.

I visited the Brisbane irradiation facility in 2004. Boxes of food travel by conveyor belt into an irradiation “chamber”. The irradiation process breaks down the molecular structure of food; destroys vitamins in food, and creates free radicals and other “radiolytic compounds” that have never been found in nature, and whose effect on human health is not known.

Also of concern is the fact that in 2008 the Australian Government was forced to ban irradiated cat food after more than 80 cats died or became seriously ill after eating irradiated cat food.

This begs the question – if cats can die, or become ill from eating irradiated cat food, what could be the cumulative effect on humans of eating significant quantities of irradiated food? There’s no benefit to New Zealand consumers, and only risks to our growers, from imported irradiated produce.

Her comment that irradiation “breaks down the molecular structure of food [and] destroys vitamins in food” is quite at odds with the evidence that the nutritional content of irradiated foods are not changed significantly. This statement is entirely blown out of proportion, it’s like describing a papercut as having “ripped my flesh apart”.

She also doesn’t mention any of the details regarding the cat food incident, such as that their diet consisted largely or wholly of food irradiated 100-200 times as much as human food generally is, that the same food seemed to have no negative effects when eaten by dogs, or that the incident was only linked to one specific lot of one brand of cat food. How it relates to humans consuming irradiated food, if it has any implications on that at all, is not clear but her reaction is just scaremongering.

Her article appears to have been prompted by a couple of changes to the regulations that are being considered:

FSANZ is currently assessing Application A1092 seeking permission to irradiate twelve specific fruits and vegetables. A call for submissions on our assessment is expected to be released in the second half of 2014.

Food Standards Australia New Zealand | Food irradiation

FSANZ plans to start work on recommendation 34 (that the requirement for mandatory labelling of irradiated food be reviewed) later this year.

Food Standards Australia New Zealand | Labelling review

Here’s a link to Application A1092. That page specifies the 12 fruits and vegetables involved as apple, apricot, cherry, nectarine, peach, plum, honeydew, rockmelon, strawberry, table grape, zucchini, and scallopini (squash).

Ms Kedgley describes these potential changes as:

the Government is about to approve the importation of irradiated apples, peaches, apricots and nine other fruit and vegetables from fruit fly-infested Queensland.

If they succeed, retailers will be able to sneak irradiated produce into the food chain, and it will be sold, unlabelled, as if it was “fresh”.

Surely consumers have a right to know whether the apples they are buying are fresh, or have been imported from Queensland and exposed to high doses of radiation to sterilise them and kill off potential fruit fly lava?

Red apple
Red apple | Photo by Abhijit Tembhekar

Looking at the IHS for fresh fruit and vegetables (direct PDF download), you can see that honeydew, rockmelon, strawberry, grape, zucchini, and scallopini are already included, they just aren’t yet allowed to be treated via irradiation. As far as I can tell the others – apple, apricot, cherry, nectarine, peach, and plum – can’t currently be imported from Australia.

Given that the entire function of irradiating food is to kill unwanted organisms such as Queensland fruit fly larva, I think it seems disingenuous of Ms Kedgley to repeatedly refer to it as though allowing these products in will bring Queensland fruit fly to New Zealand. The reason why we can’t currently import these products is because of that fly, but allowing them to be treated by irradiation would let us safely import them.

On the issue of labelling, this seems to be a very similar issue to compulsory labelling of genetically modified foods and foods containing genetically modified ingredients (this is currently mostly compulsory in New Zealand). In that case, as with food irradiation, opposition generally seems to be driven by idealogical issues with the technology used or misinformed beliefs that it’s somehow unsafe, even though it’s entirely safe. It’s effectively a lose/lose situation – if labelling isn’t mandatory then “What are they trying to hide?” but if it is mandatory then “They wouldn’t have to put it on the label if it wasn’t bad for you”.

If you want to oppose the addition of those 6 new fruits to the list of foods that can be imported from Australia on the basis of supporting New Zealand farmers then okay, that’s a different argument altogether that has nothing to do with irradiation. There doesn’t seem to be much reason to oppose this on grounds that irradiated food may be unsafe to eat though.

Foods are not allowed to be irradiated unless they have been through a pre-market safety assessment process conducted by FSANZ

http://www.foodsmart.govt.nz/elibrary/food_irradiation_.htm

Given that irradiated food doesn’t appear to be unsafe, is there really any reason to keep labelling of irradiated food compulsory? If anything, isn’t compulsory labelling most likely to make people think that means it’s bad or unsafe when it isn’t? If it’s all about allowing consumers to make informed decisions, that would be rather counterproductive.


I’m lucky enough to know someone who’s a food scientist. Claire Suen has an MSc in Food Science from the University of Auckland, and I contacted her to ask for her thoughts on the process of food irradiation. Here are some of the things she had to say in response to some of the common arguments opposing food irradiation:

[Irradiation] changes the nature of food: carcinogenic, loss of nutrients etc.

So does cooking, burning toast, deep frying, etc. Irradiation causes minute changes to the food and some loss of nutrients such as vitamins, but these have all been thoroughly researched and the results are readily available. In short, no significant changes to the food have been found.

Regarding the lost of nutrients, I usually point out to people that this is negligible considering the nature of the food.

FSANZ have published some comprehensive risk assessment reports in the past, and using the latest report on tomato as an example:

Nevertheless, even assuming an upper estimate of vitamin A and C loss of 15% following irradiation from all fresh tomatoes, capsicums and tropical fruits (with existing irradiation permissions), estimated mean dietary intakes of these vitamins would decrease by 2% or less and remain above Estimated Average Requirements following irradiation at doses up to 1 kGy, with dietary intake typically derived from a wide range of foods.

The impact of cooking and storage time on nutrients in food is far more severe than the effects of irradiation.

Here’s a link to that FSANZ report on Irradiation of Tomatoes & Capsicums (direct DOC download)

There are better alternatives

Irradiated food saves cost for the manufacturers/importers/supermarkets because it eliminates otherwise costly alternatives.

Methyl bromide for example, is not 100% effective against insect eggs and larva, particularly if they are buried inside the fruit or seed. Storage pest such as beetles and weevils are extremely difficult to control and often need a combination of methods such as heat treatment, and fumigation. For herbs and spices, irradiation can be used to control pathogens such as salmonella and E. coli. No other method is as effective. But because consumers in NZ are against it, we have to use methods such as steam sterilisation and heat treatment, which impacts on the flavour and quality of the product. Consumers sometimes do not understand the amount of work MPI and the importers have to do to make sure foreign organisms do not get in the country. All it will take is a slack importer, a missed check, or an incomplete fumigation. What of the products that have to be destroyed due to microorganism contamination, or spoilage? If they had been irradiated, this wastage wouldn’t happen.

We don’t need irradiation since we can just buy local products

Unfortunately NZ is a small country and we have limited produce. I’m not saying we can’t get by without EVER importing anything, but, it seems to me that these people don’t realise just what the consequences are. Sure, we don’t have to import apples, or nectarines, but what about the tropical fruits not grown locally? Or spices? Let’s not eat fresh mango again, or curries, since pepper used to be worth its weight in gold because it’s not grown in Europe. We can’t get away from importing and by not using irradiation, NZ business have to use more costly, and less effective alternatives, which means all these cost are passed ultimately onto the consumers. I understand people’s concern that this will hurt local producers, but that is a question of economy and has nothing to do with the safety of irradiated food.

Now coming to the question of labelling

Unfortunately, it’s a no-win situation. If we label then consumers will think something is wrong with it, if we don’t label it’s as if we are hiding something. There is simply no way to beat that logic. In my opinion, if we don’t label products which have been heat treated, or fumigated, then we shouldn’t need to label for irradiation. But because consumer backlash is so strong, I wouldn’t want to give haters a chance to play the “Ah ha you are hiding something” or “give me my freedom of choice” card.

I say let’s put irradiated fruits on the shelves and label it as such so I can chose to buy it because it will be cheaper and better!

I think that last point says it all really. As a food scientist, Claire is quite familiar with the topic of food irradiation, and she would choose to preferentially buy irradiated food because she understands the process to be safe, effective, and not detrimental to the food.

We Landed on a Comet

So, last night was exciting. The European Space Agency’s (ESA) robotic spaceship Rosetta arrived at the comet 67P/Churyumov-Gerasimenko in early August, after an amazing journey comprising of over 10 years and four gravity slingshots. Last night, it separated from its lander module, Philae, and sent it to touch down on the surface of the comet.

What I’ve been able to gather from watching the live stream last night and what I saw on Twitter when I woke up groggily for 2 minutes at 5:15 this morning is that not everything went to plan, but the landing seems to have been successful.

Philae (the lander) has several devices to make the landing easier. One of these is a “cold gas thruster”, a small engine to push it gently into the surface of the comet so it wouldn’t bounce off (remember the comet has extremely little gravity relative to something like the Earth or Moon). This engine failed to start working before the spacecraft separated, but the team decided to go ahead with the landing anyway.

Another device Philae has to help with the landing is a pair of harpoons to skewer the surface, but these also failed to fire. As far as I know they’re not sure yet why they failed, but Philae did make it to the surface, so the comet landing was a success.

The ESA be getting data back from Philae but I don’t think they know yet how it landed or where exactly it is relative to the landing site. There’s a danger it could be on its side, for example, which would prevent some of the experiments it’s carrying on board from going ahead. Time will tell, though.

A photo of the comet taken from Philae when it was only 3 km away has been posted to the official Twitter account:

Photo credit to European Space Agency, ROLIS camera on Philae

Photo credit to European Space Agency, ROLIS camera on Philae

UPDATE 2014/11/14

Since the landing a few other things have come to light. First, presumably because the harpoons failed to fire, Philae bounced of the surface twice. Although it bounced pretty much straight up, the comet was rotating beneath it so its final landing zone is a few hundred metres away.

Also, Philae has landed on its side. It’s still taking photographs and sending back data, so that’s good, but the fact that it’s on its side may mean that some of its experiments may not be able to go ahead. Phil Plait has a good write up explaining these updated on Bad Astronomy and Emily Lakdawalla has a more detailed one on her blog the Planetary Society.

Movement of the Moon

If you were up late last Wednesday, you’d have gotten the chance to watch the second total lunar eclipse this year. A lunar eclipse occurs when the Earth moves directly between the Moon and the Sun, therefore blocking the light to the Moon and making it turn dark.

This is very cool to watch, especially if you get a good look at the Moon during totality, when it is in the darkest part of the Earth’s shadow known as the umbra. At this point, the only sunlight reaching the Moon is that which is refracted through the Earth’s atmosphere. For the same reason as why sunrises and sunsets appear a lovely reddish colour, this light is also quite red, and as the Moon reflects some of this light back at us it appears a dim bronze colour.

This is one of my favourite space facts, and I find it quite poetic – you’re looking at the reflected light of all the sunrises and all the sunsets in the world, all at once. There are many spectacular photos of this effect online if you care to search for them too. But this is not what I want to write about in this article.

If you were watching Wednesday’s eclipse from Auckland, as I was, you’d probably have been disappointed to see that it was quite cloudy for the duration of totality. However, you were probably able to get a good view of the first part of the eclipse, when the Moon is moving into the outer part of the Earth’s shadow known as the penumbra.

Greg O’Beirne managed to put together a great compilation of this part of the eclipse:

Photo by Greg O'Bierne
Photo by Greg O’Beirne

As you can see, it looks rather like the Moon is having a bite taken out of it. In this compilation the position of the Moon is held roughly constant but in reality it’s the Moon that is moving here. During a lunar eclipse, we are given the rare opportunity to directly observe the Moon’s orbital motion.

Because the Earth is spinning, the Moon always appears to move across the sky from east to west (in the southern hemisphere, this effectively means it is moving right to left). The time it takes to move across the sky varies with the time of year, but it takes roughly 25 hours to do a full circuit.

Because of the Earth’s spinning, generally the only way we can usually observe the Moon’s orbital motion is by looking for it at the same time every day. If you do this, then instead of watching it migrate east to west over a day, you’ll see it move slowly from west to east over a couple of weeks.

In order to watch the Moon move directly, it would be possible to watch it move relative to a stationary background object. The stars could serve this purpose while the Moon is up at night, although generally it’s bright enough that it’s very difficult to see any nearby stars. The occultation of Saturn earlier this year, which I watched from home through my telescope, gave me a chance to observe its movement against the relatively stationary planet. Like with the stars though, you simply wouldn’t be able to observe this with your naked eye.

A solar eclipse is also an opportunity to directly watch the Moon’s orbital motion, as we can compare it to the Sun, as its movement is fairly negligible for everyday purposes when compared with that of the Moon. The problem there, of course, is that you can’t look directly at it without damaging your eyes. A lunar eclipse gives you the same opportunity except, unlike a solar eclipse, you can watch it directly.

If we ignore the Earth’s spin, then both the Sun and the Earth’s shadow (which, of course, must always be directly opposite one another) each take one full year to move the whole way across the sky. Because the 365 1/4 days in a year is very close to the 360 degrees in a circle, we can say that they move roughly 1 degree every 24 hours, or half a degree every 12 hours. This sounds pretty slow, but half a degree is roughly the size of the full Moon so it isn’t entirely negligible.

It takes about an hour for the Moon to move fully into the outer part of the Earth’s shadow, so in this time it moves roughly 1/12th the diamater of the Moon. For the sake of simplicity, let’s ignore this motion as well. Below I’ve put together a (rather clumsy and very imprecise) animated gif, using the images from Greg O’Beirne’s great compilation as its frames, to show this motion of the Moon holding the position of the Earth’s shadow roughly constant:

Lunar Eclipse Oct 2014 Animation

If you want to view this for yourself, the next lunar eclipse visible from New Zealand isn’t too far away. You may have read that there won’t be another total eclipse visible from New Zealand until 2018, but on the 4th of April 2015 there will be a partial solar eclipse in the evening where you’ll be able to see this. In the meantime, have a look up at the sky occasionally and notice where the Moon is (using landmarks as a guide to remember its position will help). If you make it habitual to do this at a specific time (I do it every day when I leave for work, for example) then you’ll be able to watch the Moon’s slow movement backwards across the sky.

Poor Science Reporting on the Paleo Diet

This morning I saw an article in the NZ Herald on the “paleo diet” that rather frustrated me. It seems like a great example of poor science reporting, trying its hardest to turn a study into a story instead of doing any actual science reporting. The role of a science reporter is not to sensationalise, it’s to accurately report on science, and that includes making the drawbacks of a study clear and not exaggerating the conclusions.

In this case though, it looks like the author chose to omit half the results of the study, presumably so as not to pollute the narrative they had chosen. The take-home message of the article can be found in the first paragraph:

the best way to lose weight is by copying our ancient ancestors, a study suggests.

I’m not even going to get into the problems with characterising the so-called “paleo diet” as “copying our ancient ancestors”, that’s been adequately covered elsewhere. The information used to support this weight loss conclusion is that the study in question found that:

Women who adopted the so-called Palaeolithic diet lost twice as much weight within six months as those who followed a modern programme based on official health guidelines.

Wow, that sounds impressive. Case closed, right? Except, if you look at the actual study (not open access, unfortunately), which of course is not linked to from the online article, you’ll find another result that is curiously omitted from the Herald article:

Both groups significantly decreased total fat mass at 6 months (−6.5 and−2.6 kg) and 24 months (−4.6 and−2.9 kg), with a more pronounced fat loss in the PD [Paleolithic-type diet] group at 6 months (P<0.001) but not at 24 months (P=0.095).

So there was a statistically significant difference in fat loss after 6 months, as mentioned in the article, but after 24 months there was no statistically significant difference in fat loss between the groups. That is a negative result.

Although there was still an observed difference in fat loss between the groups at 24 months, it wasn’t big enough for the researchers to be reasonably confident that it wasn’t just due to random variation. That’s partly due to the size of the difference observed, and also because the study was so small. 70 people split into 2 groups is very small for this kind of study, whereas a good sample size would be hundreds or even thousands of participants, not just a few dozen. Of course, such large studies are much more difficult and expensive to undertake, so a lot of smaller studies like this do happen. Sample size is very important though – small studies like this are not nearly as reliable as the much larger ones – so it’s important to remember to take the sample size into account when evaluating a study’s conclusions.

The Herald article does mention, way down near the bottom, that all of the participants in the study were obese postmenopausal women. Everywhere else, however, it avoids that caveat and seems to imply that the conclusions should be applicable to everyone, or at least to all women.

It’s also rather frustrating that the article says that the study “found [the “caveman diet”] more effective than some modern diets”, and that this study suggests it is “the best way to lose weight”, even though the study didn’t compare it with “some modern diets”. It compared it with a single other diet, one based on the Nordic Nutritional Recommendations.

If the Herald wants some tips on how to report on science, a great place to start would be to take another look at the science itself. The conclusion in the abstract of the study they’re writing about seems much more appropriate, even if it does seem a bit dismissive of the negative 24 month results:

A PD [Paleolithic-type diet] has greater beneficial effects vs an NNR [Nordic Nutritional Recommendations] diet regarding fat mass, abdominal obesity and triglyceride levels in obese postmenopausal women; effects not sustained for anthropometric measurements at 24 months. Adherence to protein intake was poor in the PD group. The long-term consequences of these changes remain to be studied.

Then again, perhaps I should be glad the Herald didn’t reprint the original headline from the Daily Telegraph:

Caveman diet twice as effective as modern diets

I’m not sure I could come up with a more misleading headline if I tried.

Despite the horrific headline, the original article does have a bit more information in its second half from the study’s primary author that was truncated from the Herald’s reprint.

Telescopes Are for Everyone

UPDATE 2014/17/01 1:54pm NZDT:

The content of the page has now been updated for the better, although its title still says “Telescopes for astronomy or land viewing; a great gift for him”.


Over the summer holidays, for the first time ever I took some binoculars outside on a clear night and looked up at the sky. I had some idea of what I could expect to see, but still the number of stars I could see surprised me. It was marvellous and elating, and settled my resolve to (finally) take up amateur astronomy as a hobby instead of just an idle interest. As a first step, I plan to buy a telescope. Earlier today, I searched online to see what was available and was very disappointed by something that I found.

The New Zealand website telescopes.net.nz sells telescopes, which is all well and good, but they have decided to market them as a “gift for him”. The title of the page is “Telescopes for astronomy or land viewing; a great gift for him.”, and the content advertises them like this:

A telescope makes the perfect Christmas gift for him and we have picked the best brands available in the market today. Whether you want a gift for your Dad, the man in your life or you just want to indulge yourself, you will find it here.

I was thoroughly disappointed and, horribly, not particularly shocked to see such sexism regarding this. As a white straight male, I have tremendous privilege; my male privilege would let me simply ignore this if I wanted to, as it’s not an affront to me. However, I follow various fantastic (I cannot stress that enough) female astronomers, astrophysicists, and astronauts through Twitter and blogs, and have long been aware of the existence of sexism in STEM fields. In fields such as astronomy, there is a large gender gap – these fields are dominated (in terms of numbers) by men – and this is only made worse by commonplace sexist attitudes. Even if some of this behaviour is entirely innocent, it still does active harm by excluding women and girls from astronomy. Although my privilege gives me the option to ignore this, I consciously choose to be a feminist and fight these attitudes. Telescopes are for everyone.

I shared this page on Twitter, and the great Katie Mack (@AstroKatie) sent them an email. Seeing this, I also sent an email to telescopes.net.nz, which I include in full below, urging them to change the content of their website and the attitude from which it sprang. If you would like to do the same, you can contact them at staff@telescopes.net.nz. Here is the email I sent them:

Dear Telescopes New Zealand,

I’m interested in amateur astronomy, having for the first time viewed the night sky through binoculars over the summer holidays and marvelled at how many stars I could see. I decided that in the new year, I would like to buy a telescope and take up amateur astronomy as a hobby. I found your website when searching for a telescope online.

However, when I came upon your telescopes page I was very disappointed to see it advertised telescopes as a “gift for him”, casually excluding all the women and girls that are interested in astronomy. Unfortunately, women already face significant sexism in STEM fields, including astronomy. Attitudes such as the one shown on your website only encourage this hostile environment, and harm astronomy as a whole.

I hope that you will revise the content of your website. I’m sure you can see that its current content, however innocent your intentions may have been, contributes to a harmful atmosphere of exclusion. Taking a more positive attitude toward women in astronomy will only benefit yourselves, amateur astronomers, and the field of astronomy itself.

Sincerely,
Mark Hanna

I’ve set up a change detection service monitoring the page, and hope to see it change for the better soon. If it doesn’t then, needless to say, I certainly won’t be buying my telescope from telescopes.net.nz.

Why Testimonials Aren’t Enough

The business of “natural health” rests heavily on the use of testimonials. They are used in advertisements by people selling therapeutic products and services, and you’ll hear them as anecdotes from people that you know telling you what worked for them. Intuitively, it makes sense to trust in this sort of experience, but unfortunately testimonials and personal experience are not good ways of evaluating a treatment option.

I don’t expect you to take my word for this. Maybe you were told by a doctor that you’d need an operation, then you had reiki therapy and after that your doctor said the problem was no longer there. Perhaps your first child had terrible teething troubles, but on your second child you used a Baltic amber teething necklace and they didn’t have the same problems, but you swear if you forget to put it on them they become agitated. Or maybe you’ve been spraying a colloidal silver solution onto the back of your throat whenever you feel a cold coming on and you haven’t been sick in years. Who am I to doubt or deny your experience?

These are all testimonials that I have heard personally, not from advertisements but from individual people relating their own experiences to me. But still, I remain unconvinced that reiki is any more than an exotic twist on faith healing (that is just as ineffective), that Baltic amber teething necklaces are anything but expensive yet inert jewellery, and that colloidal silver is much good for anything other than causing argyria.

In this series of blog posts, I intend to explain to you why I don’t consider anecdotes like these to be useful in drawing any conclusions about therapeutic interventions. But first, I’d like to point out that I am not trying to be dismissive of personal experience. I don’t think anecdotes are all lies, or anything of that nature, and personal experience can certainly be useful in drawing all sorts of conclusions in everyday life. The only conclusion I am arguing for here is that anecdotes are not useful for evaluating the efficacy of therapeutic interventions.


In searching for any truth, we have to be very careful not to jump to conclusions. There will always be a vast number of potential explanations for any observation, and if we really care about the truth then we can’t just pick the explanation that we like the most, or even the one that we think is most likely. Some possible explanations can be ruled out right from the start, if they’re impossible to test, but the explanations that can be tested are known as hypotheses. If we want to determine whether or not one particular hypothesis is correct, we should design and carry out a test that will rule out every other potential cause of our observation.

Note that this method of testing does not prove anything. Instead, it focuses on ruling out everything else, until only one idea is left standing. The key to designing a good test of an intervention is to make sure anything you observe is as unlikely as possible to be due to anything other than the intervention. This means that, in order to design a good test of an intervention, it is important to have a good understanding of what these other potential causes are.


After This, Therefore Because of This

There’s a formal logical fallacy that’s usually known by its latin name post hoc ergo propter hoc, which translates to “After this, therefore because of this”. The fallacy is of the form:

  1. A happened, then B happened
  2. Therefore A caused B

Of course, the reason why this is a logical fallacy is that it’s entirely possible that something other than A was the cause of B. This doesn’t mean that the conclusion is false, but it does mean that it is not necessarily true.

Anecdotes take the same form as the above example: “I tried treatment X and I got better”. Although experiences like this can result in strong beliefs, the fact that the improvement happened after the treatment does not mean the treatment necessarily helped at all. Instead, the improvement could have been due to a few different things.

Self-Limiting Conditions

Many common health conditions are self-limiting. This means that, left to their own devices, they will almost always go away in time. The common cold is an example of a self-limiting illness. Unless you are seriously immunocompromised, if you catch a cold you will be fine again after a few days. This includes things like the flu, teething, colic, and acne. Pretty much everything that isn’t a chronic illness and won’t kill you is self-limiting.

Regression to the Mean

Even when nothing external seems to be changing, your health is not constant. Instead, it fluctuates over time around a baseline level of health that itself changes over longer amounts of time. This baseline is basically your average health over a certain period of time; the mean. The tendency for your wellbeing to return to this mean after a fluctuation is known as regression to the mean.

This is a picture of 300 random data points generated in Microsoft Excel. Starting with 0, I added a random number between -0.5 and 0.5 to the running total 310 times, and then took a 10 point running average to smooth the resulting curve.

Regression to the mean

As you can see, even though the changes are all random, trends do form and the data oscillate around a particular mean. Especially over longer periods of time, the data will tend to return to that mean.

I’ve indicated the 2 most prominent downward trends with arrows. As you might imagine, such low points in a person’s health could motivate a person to take a therapeutic intervention in order to reverse this trend. After the intervention, they’ll likely start to feel better, but as you can see by this graph such variations can happen randomly, and it can be very hard to say whether an improvement was caused by something in particular or if it was just the result of regression to the mean.

For example, I get frequent headaches. However, the frequency and intensity of those headaches varies from day to day, just due to random chance. I’d be more likely to decide to seek a therapeutic intervention on a particularly bad day. However, considering that my wellbeing is fluctuating around a mean value I’d expect my headaches to return to their “normal” level, unless of course something has changed to make them worse on average. If I take an intervention and then the next day my headaches are better, how can I know whether it’s due to the intervention or regression to the mean?

Spontaneous Remission

Even with illnesses that are not self-limiting, spontaneous remission that has no obvious cause is something that does happen occasionally. I’m not familiar with the data on this, so I won’t go into it in too much depth, but it is worth knowing that even some serious illnesses can get better on their own, so even some sudden recoveries from serious illnesses can happen on their own, whether an intervention has recently been used or not.


As you may have noticed, these things all have a common theme. They describe ways in which health can improve on its own, which make it difficult to tell whether a particular improvement is due to an intervention or if it would have happened anyway. Ideally, in order to tell the difference, we’d travel back in time in order to try without the intervention and see what would have happened in that case, but unfortunately that’s not an option. The next best method is to have what is known as a control that has the same problem but doesn’t get the treatment.

However, as I discussed earlier, health fluctuates on its own. If the person receiving the intervention improves and the person acting as the control stays the same or gets worse, we still can’t be too sure that the intervention was helping. Variations between different people can make outcomes difficult to interpret as well. Like how random fluctuations will tend to return to the mean over longer periods of time, testing more people will smooth over these random variations. The more people we include in both the treatment group and the control group, the better, as having more observations will help us to tell whether any effect we observe is due to random variation or due to the intervention itself.

Having a control group and a large sample size are 2 aspects of a good test of a therapeutic intervention, but that’s not all there is to it. In my next post, I’ll discuss some other potential confounding factors, and how we can modify our test in order to account for them.