Skip to content

AGT 100 Greenwich EarthCache

This cache has been locked, but it is available for viewing.
Hidden : 09/25/2018
3 out of 5
1 out of 5

Size: Size:   other (other)

Join now to view geocache location details. It's free!


How Geocaching Works

Please note Use of services is subject to the terms and conditions in our disclaimer.

Geocache Description:

Greenwich in Meteorite Royal Observatory 100

And here it is. Jubilee 100 cache geological series AGT ... Alke's GeoEarthCache tour. For a long time, I've been wondering what kind of place is appropriate for this event. In the end, I chose the place that gave the world the coordinates - the Greenwich Observatory. Welcome to 100 consecutive AGT series.

Touch a 4.5 billion-year-old meteorite

Would you like to touch something that is as old as the Earth and the Sun itself? Come to the Astronomy Centre at the Royal Observatory.

4.5 billion-year-old meteorite

This meteorite is a large hunk of mostly iron with just under 10% of nickel. It was formed around the same time as our Sun and the Earth and after a leisurely tour of the Solar System as the centre of an asteroid, it came crashing down into southern Africa as the Gibeon Meteorite.

The Nama people used smaller bits of the meteorite for tools and countless chunks remained scattered over a large area. In 1836 Englishman J. E. Alexander collected samples and sent them to London. John Herschel confirmed they were indeed not of this planet.

People in observatory sliced away one side of the meteorite so that visit can see what it looks like inside and it has this beautiful pattern of metal crystals inside - those crystals only form if the metal has cooled over millions of years, just a few degrees every million years.


and Alke04's touch :-)

This remarkable object is in the Royal Observatory in the Astronomy Centre - entry is free.

What is a meteor?

What we are witnessing when we see a shooting star is a small piece of interplanetary matter, called a meteor, entering the Earth's atmosphere and 'burning up' at a height of about 100 km.

These small particles are moving very fast relative to the Earth and when they enter the Earth's atmosphere, they are completely evaporated and the air in the path of the meteor is ionized. We see light from the emission of radiation from the ionized gas and from the white-hot evaporating particle. The trail is the hot gas gradually cooling down.

Next meteorite in Observatory

What is a meteor shower?

Every meteor shower has a progenitor Comet. Comets which live a long way from the Sun sometimes tumble in towards the Sun and start to have a short periodic orbits of less than 200 years.

A good example is Halley’s Comet which orbits the Sun every 76 years and is the progenitor of the Orionids. As the Comet gets close to the Sun it heats up, and being a ball of mostly ice it starts to evaporate. Rather becoming a liquid it literally turns straight into a cloud of particles, just sublimes – a big cloud of debris.

As the comet goes around the Sun it is constantly filling its orbit with debris, and if its orbit coincides with the Earth’s orbit then every year you’ll go through that cloud of debris. Those little pieces then burn up in the Earth’s atmosphere as we smash into them and create shooting stars. Showers occur when we go through specific clouds of debris and then throughout the year we experience sporadic meteors which are just little pieces that are everywhere.

What is a meteor storm?

A meteor storm occurs when you go through a really unusually dense part of a comet’s debris cloud. It’s very unpredictable - you can’t really tell when it’s going to happen but when it does happen it’s possible to see thousands of meteors per hour for one or two hours.

I saw a meteor storm a number of years ago. It was extraordinary – I was seeing about 300 meteors in the space of about 20 minutes. And you could really see where the radiant was because the meteors were so regular that your eye could trace them all back to a common point where the radiant was.

What are meteorites?

When larger chunks of interplanetary matter enter the atmosphere it is unlikely that all of each one will be evaporated. The outer layers will disappear but the centre is likely to survive and will hit the ground as a meteorite. The speed with which small meteorites hit the ground can be around 500 km/h.

More than 2000 meteorites have been recovered. They are of different types, Stony meteorites, iron meteorites and the rare carbonaceous chondrites. The largest meteorite that has been found is the 60 tonne Hoba iron meteorite; the largest stony meteorite weighs about a tonne and the Allende carbonaceous chondrite was a series of chunks that totalled about 5 tonnes.

One of the best-known impact craters is the Arizona crater in the USA, which is 1280 metres across and 180 metres deep. It was formed several thousand years ago by a 250,000 tonne meteorite with a diameter of 70 metres hitting the Earth at a speed of nearly 60,000 km/h!

The Perseids

The Perseids are one of the best-known meteor showers and can be seen in August around 12 August. The radiant is in the constellation Perseus, just below the familiar 'W' of the constellation of Cassiopeia. At this time of year this can be seen reasonably high in the north-eastern sky at nightfall.

Sporadic meteors

If no prominent shower is active then most of the meteors that are seen will come from random directions in space. These meteors are called sporadic meteors and about one every ten minutes is the normal rate for them to be seen.

Most fire-balls and meteorites are sporadic meteors. The material in these meteors is associated with the material in the asteroids and it is likely that they represent material that has come from fragmented asteroids.



Questions and tasks:

1) Touch and meteorite and describe what the surface is (smooth or rough) and why is it so?

2) Find out where it came from on the meteorite information board. You can find the information sign directly below the meteorite.

3) Attach the magnet to the meteorite. Is it magnetic or not? Explain.

4) What is the width of the meteorite in the largest place? Do not reveal, please measure accurately.

5) Attach a photo of you or your GPS device with a meteorite to your log. This condition is mandatory as of June 2019.

Send your answers via the profile and log.

If your answers are wrong - I will contact you. If you do not send any answers, or your log will not contain the photo (s) specified - the log will not be recognized and will be deleted.

Information Sources:
Publikace: Geologické rozhledy

Publikace: Geologické zajímavosti
Geologická mapa ČR AVČR rok vydání 2012



Additional Hints (No hints available.)