## Orbit: Episode Two

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| 21:30 PM, 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)

## Can you calculate the tilt of the Earth?

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| 15:30 PM, Thursday, 16 June 2011

Distance travelled ~ 429'657'600 km: day 167

In this blog post we are going to show you how you can calculate the exact tilt of Planet Earth by using your shadow. You can only do this at a certain time of the year, the Summer Solstice, and that moment is fast approaching.

This year Summer solstice is on 21 June. This is the longest day of the year and also for us here in the northern hemisphere, the time when the Sun is highest in the sky. Astronomers regard it as the start of summer for the northern hemisphere winter for the southern.

So what's the Summer Solstice got to do with measuring the tilt of the Earth, I hear you ask. Well, the orientation of the Earth to the Sun is defined by angles, and on June 21 the physics align so that you can use the position of the Sun in the sky at 1pm BST to accurately measure the tilt of the Earth. It still works around 2 days before and 2 days after so you have a few days to try this out.

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Here's a tip - measure from the balls of your feet to the top of your shadow and remember be careful and don't look directly into the Sun.

The first important angle is Solar Zenith. This is the angle between the Sun and straight up and it's marked in green on the figure below. We can find this because the smaller this angle is - or the higher in the sky the Sun is - then the smaller your shadow. To work this out we use tan. If you know about tan, then your height is the adjacent side and your shadow is the opposite side of a square-angled triangle.

Figure 1.

Next we need latitude. This is essentially the angle between the equator and your position on the Earth. You can see from the figure above that if you take the green angles away from the pink angle then you get the yellow angle. This angle between the equator and the place on Earth where the Sun is straight above you is called the "solar declination". But on the solstice it's exactly the same as the tilt of the Earth - convenient.

There are loads of ways of getting your lattitude -a gps device maybe on your phone or satnav, or endless websites can provide you with this. Some are as simple as putting in your postcode.

Most importantly the 23 Degrees team would love to hear how you get on. Send us your calculations, photos or videos of you doing the challenge on the Solstice, or maybe a photo of your shadow. Shadows have long been a key indicator to our Earth's position in it's orbit around the Sun.

Continue the conversation and put #solstice in your tweets!

## What happens if you throw hot coffee into -37˚C temperatures?

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| 20:43 PM, Thursday, 27 January 2011

d ~ 69'465'600 km: day 27 of Earth's orbit

The 23 Degrees production team and I were in Yellowknife Canada last week one of the coldest cities in North America. Great opportunity to test for myself what would happen if you threw hot coffee into the air with a temperature of  -37˚C.

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