Tag Archives: space

The Milky Way is shaped like a CD

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The Earth orbits just one of the 200-400 billion stars that make up the Milky Way. This star, the Sun, orbits at a distance of about 27000 light years from the Galactic Centre, travelling at 220 km/s (one mile every seven thousandths of a second).

The Milky Way is about 100000 light years across, but only about 1000 light years in height, making it about one hundred times wider than it is tall. To scale, viewed from side on, it would look like the line below:

With a thickness of 1.2 millimetres and a diameter of 120 millimetres a standard CD or DVD has exactly the same thickness:width ratio as the Milky Way; you could correctly describe our galaxy as “CD-shaped”.

Update: I’m reliably informed that a thickness of 1000 light years is incorrect, and that the true thickness is probably somewhere around 2000-3000 light years, and could be as large as 6000 ly. (It also depends very heavily on your definition of the “edge” of the Universe.)

Star traveller etymology

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The term astronaut comes from the two Greek words: ástron (star) and nautes (traveller), making an astronaut a “star traveller”. In Russia astronauts have always been known as cosmonauts, an anglicised version of the Russian word kosmonavt (originally from the Greek kosmos meaning “universe”) and the difference between the two terms used seems to have encouraged other nations.

Officially the Chinese use “astronaut” when writing in English and “cosmonaut” when writing in Russian but the term taikonaut (from the Chinese taikong for “space”) has often been used by non-Chinese media.  The French have used spationaut, from the Latin word for space spatium and some have suggested that the Indian space program should use anthanaut from the Hindi anthariksh, also meaning “space”.

Looking at constellations from a different angle

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You are probably familiar with the constellation of Orion (The Hunter), in particular with the asterism that makes up Orion’s Belt.

Because of the way the right ascension data is plotted the images shown here are how they would appear to a distant observer looking at Orion towards Earth.

Because stars are so far away we tend to think of them as being painted onto a surface at a fixed distance – “like a huge picture painted on the sphere of the sky”. But if you look at the stars in three dimensions then Orion looks very different.

From above it’s difficult to recognise Orion’s shape as the lines connecting the two rightmost stars (Betelgeuse and Saiph) to the rightmost star of Orion’s belt (Alnitak) overlap:

From the side the shape is more obvious. Alnilam, the middle star of Orion’s belt is by far the furthest star, more than 1300 light years away from Earth:

This post was inspired by an arXiv paper* by Dr Daniel Brown from the School of Science and Technology at Nottingham Trent University. You can download the data I used as an Excel spreadsheet (.XLS, 29 kB).

* Daniel Brown (2011) “The Orion constellation becomes installation: An innovative three dimensional teaching and learning environment”, arXiv:1110.3469v1 [physics.ed-ph].

Time on the Moon

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I was surprised to find that the amount of time spent on the Moon by Neil Armstrong and “Buzz” Aldrin on the Apollo 11 mission was really quite small when compared with the time spent by astronauts on subsequent Apollo missions.

Only 12 people (all men, unfortunately) have ever set foot on the Moon. The person to spend the most time on the Moon is Gene Cernan, the commander of the Apollo 17 mission. He left the Apollo lander before the Apollo 17 Lunar Module pilot, NASA geologist Harrison Schmitt, and re-entered the lander after Schmitt. He is therefore also the last person to set foot on the Moon, all the way back in 1972.

Gene Cernan cruising the lunar surface in the lunar rover

Cernan also co-holds (with Thomas Stafford and John Young) the record for the fastest speed achieved by a human being, as the Apollo 10 probe on which he was a passenger reached a speed of 11.1 kilometres per second (24 790 mph) on its return to Earth after orbiting the Moon. The Apollo 10 Command Module is now on display at the Science Museum in London.

Remembering Challenger

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(A guest post from Leila Johnston.)

It’s almost exactly 25 years since one of the most tragic incidents in the history of space flight. Mission STS-51-L was to be the 25th Space Shuttle mission, an event surrounded by tremendous excitement and optimism. Children around the world knew that a schoolteacher was on board – a thrilling prospect that made the whole thing so much more human. But Sharon Christa McAuliffe never made it into space. With the world watching, the craft disintegrated just 73 seconds after launch, and all seven crew members perished in a twist of smoke. The story of Challenger is so tragic that it still feels very difficult to even look at the pre-flight footage or publicity shots. It was also avoidable.

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