Moon's Orbital Radius Increasing

In an unexpected and unprecented move, the European Space Agency announced this morning that their data shows that the Moon has started to increase its mean orbital radius at a rate considerably higher than previously believed.  It's been known for some time that the distance from the Earth to the Moon is increasing, but the rate of increase is worrying.  In other words, the Moon is moving further away from the Earth faster than we thought, and in a few year's time will leave the Earth's orbit completely.  

This finding comes after a series of measurements of the Earth-Moon distance (carried out using a more accurate process than this one), using a laser beam pointed at a network of mirrors which Neil Armstrong placed on the Moon's surface over 40 years ago, during the Apollo 11 mission.  By measuring how long it takes for a beam of light to travel to the Moon and back, ESA scientists have been able to determine that the distance from the Earth to the moon has, over the last three years, increased by an average of 140 metres per year.  

However, more alarming is the fact that the rate of increase is also going up - the Moon is, on average, moving further away at a faster rate with time.  The increase over the last six months is about 1.4% more than the average increase over the previous six months.
 

Exact forecasts vary, but ESA scientists are all agreed that within 14 years the Moon's orbit will have extended so far that it will leave the Earth's gravitational field completely, and head off into space.  The team of scientists have proposed various reasons for the Moon's recent moves, and the most common suggestions are related to the recent tectonic activity on Earth - the tsunami of 2004, the volcano in Iceland during 2009-10, and possibly the recent earthquakes near New Zealand, an in particular Japan, which has left to a shortening of the length of the Earth's day.  The recent earthquakes have coincided with the moon coming towards a particularly close approach (perigee) and the theory proposes that this has caused the moon to increase its speed while making this close approach, which will lead to it reaching a larger distance at its furthest point 14 days later.

Other scientists have yet to confirm the team's findings, which have sparked considerable controversy in astronomical circles.  Teams in the southern hemisphere have carried out measurements into the exact time for the moon's orbit and have not noticed a significant change in this - either an increase or a decrease, and therefore have concluded that the moon's orbital radius has not changed.  Other teams are preparing to carry out their own measurements using Armstrong's mirrors, and will be sharing their results later next week.

Other astronomy related articles you may find interesting:

Calculating the height of geostationary satellites
Calculating the angle of elevation of geostationary satellites
The Earth-Moon distance is increasing (published 1 April 2011)
What are constellations?

Calculating (and explaining) escape velocity

What are Constellations?

Astronomy 2:  Constellations

Constellations are man-made dot-to-dot pictures in the night sky, connecting the stars in the sky into pictures of people, animals and other objects.  The stars we see were grouped into constellations by the Greeks, who made up stories about their gods and then used the characters from these stories as the basis for grouping stars together.  For example, a group of stars might look like two people standing side by side, and so they'd be identified as twins.

The stars that we group into constellations are not always close together in space.  Although two stars might look close together, one could be considerably further away than the other, but might seem to be next to each other because we have no sense of perspective in space.  We can't tell if one star is closer to us than another - and brightness is no help either.  A star that looks bright might be close to us, but a star brighter might be an extremely bright star that's actually further away.

Anyway, treating the stars as points on a flat canvas, the ancient Greeks started to group stars together into pictures, characters, animals and so on.  They didn't have to contend with light pollution, and tended to have clearer skies than we do in Britain (I've missed a number of eclipses due to clouds) so they were able to see more stars at night.  This makes it easier to draw their imaginary dot-to-dot pictures in the sky.

The Greeks got to name the constellations that we talk about today, because they were the first to classify them.  However, there's nothing wrong with devising your own constellations, using the stars that you can see at night.  For example, here's a constellation called Ursa Major (Greek for the "Great Bear").  

This part of the constellation is also known as the Plough.  But they could just as easily be called the Saucepan or the Ladle.

The saucepan...

Or the ladle...

A few things to consider when looking for constellations:  they're not always the same way up.  The Earth is rotating all the time, and this means that the stars (and the constellations) rise in the east and set in the west, in the same way as the Sun (and the moon).  The Earth's axis is tilted - what this means is that the Earth doesn't spin with a vertical axis (like spinning a basketball on your finger), but it's tilted so that it spins with a tilt


The effect of this is that the constellations appear to rotate around a point in the sky - in fact, there's a star in the sky which doesn't rotate.  The earth's axis points directly at it, as it's above the North Pole, and the star is called Polaris.  The photo below was taken near the equator, and shows the stars rotating around the pole star (the dot near the centre of the horizon).

So, although pictures in a book or on a website might show an 'upright' version of a constellation, bear in mind that it might not always look like that in the sky.  It might be at a slightly different angle, and parts of it might be obscured by clouds, and may have fainter stars hidden by light pollution.  One very important consideration is the time of the year; some constellations are only visible at certain times of the year.  I'll explain this some time soon, but as an example, Orion is only visible during the autumn and winter months.

And in all honesty, constellation spotting is sometimes an exercise in imagination.  Some constellations look nothing like the objects or characters that they're meant to represent, and require a serious leap of faith to identify.

Other astronomy related articles you may find interesting:

Calculating the height of geostationary satellites
Calculating the angle of elevation of geostationary satellites
The Earth-Moon distance is increasing (published 1 April 2011)
What are constellations?

Calculating (and explaining) escape velocity

Astronomy 1: Stars, Planets and Moons

Following last night's visit to Keele Observatory, I thought it might be helpful to cover some of the basics of astronomy, and then move onto some more detailed topics.  Everybody's got to start somewhere, so I figure it's best to start with home, and move on from there.

The Earth spins on its own axis, taking one day to complete one revolution (one full turn).  This gives us day and night.

The Earth orbits (goes around) the Sun, going around the Sun in one year.  One year is 365.25 days.

Stars:  Stars are huge (very, very big) balls of gas that are carrying out nuclear reactions.  It might be easier to think of a star as an enormous nuclear reactor, constantly going out of control.  The Sun is a star.

Planets:  Planets are smaller balls of rock or gas that go around stars.  There are nine planets that go around our star, the Sun.  The nine planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto (going in order from nearest to the Sun to furthest away).  

Moons:  Moons are smaller than planets, and go around planets in their own orbits.  Our Moon goes around the Earth in just under 28 days; some planets (such as Mercury and Venus) have no moons, while other planets (such as Jupiter and Saturn) have over 10 moons each.

One of the basic principles of astronomy is that smaller (lighter) objects go around larger (heavier) objects, and that's all due to gravity.  Galileo, who was one of the first people to make serious use of a telescope, saw Jupiter and four of its moons going around it, and started to wonder if the Earth goes around the Sun.  It wasn't a popular theory at the time, but a serious step forwards in our understanding of astronomy.

Our star, and its nine planets, are all part of a bigger group of stars (about 10 billion stars, roughly) that are all held together by gravity, in a group called a galaxy.  Our galaxy is called the Milky Way.  It's called the Milky Way because, if and when you can see the faint stars in our galaxy in the sky, they look like a milky cloud stretching across the sky.  Almost all of the stars that we can see in the night sky are in our galaxy.  Our nearest neighbouring galaxy is called Andromeda, and in the right conditions, it can be seen without a telescope or binoculars.

Why don't the planets crash into each other?
Because they're all going around the Sun at different distances.  Mercury is closest to the Sun, and completes one orbit in 88 Earth days, while Pluto, which is furthest away from the Sun, takes 220 times longer than the Earth to go around the Sun.

What is a light year?
A light year is a measurement of distance, and it's equal to the total distance that a ray of light would travel in a year.  The speed of light is 300,000,000 metres per second, or 186,000 miles per second, and there are 31 million seconds in a year (60 seconds in a minute, 60 minutes in an hour, 24 hours in a day, 365.25 days in a year).  This means that in 31 million seconds, light would travel 9,467,280,000,000,000 metres, or 9,467,280,000,000 kilometres, and this distance is called a light year.  The distances in space are so far, that we need a meaningful measurement that we can use to compare distances between objects.  

The Sun's nearest neighbour is called Proxima Centauri ("proxima" meaning "close") and that's 4.22 light years away.  This means that light shining from Proxima Centauri takes just over four years to reach us, and that means that we're seeing what it looks like four years ago.  This, it is true, is a very strange situation, and that's because we're used to looking at objects that are much closer, where we can assume that we're seeing things as they are now (because the speed of light is very, very fast, and it takes fractions of a second for the light to travel from the object to our eyes).

I should make it clear that a light year (despite its name) is not a measurement of time, it's a measurement of distance!

In my next post, I'll try and move onto some more specific details, and answer a few questions that I've heard or been asked about astronomy.
Other astronomy related articles you may find interesting:
Calculating the height of geostationary satellites
Calculating the angle of elevation of geostationary satellites
The Earth-Moon distance is increasing (published 1 April 2011)
What are constellations?
Calculating (and explaining) escape velocity

Travelling on the surface of a star

As a follow-up to my last post calculating the distance to the Moon I was asked to calculate the following:

"Here is a question for you Mr Science. How long would it take a plane flyng at approximately 900km per hour across the surface of the biggest known star in our galaxy to travel full circle?"

Good question.  Let's assume that the star is perfectly spherical, which seems reasonable enough.  Now, to find the largest known star in our galaxy.  According to Wikipedia, the largest star in our galaxy is VY Canis Majoris found in the constellation Canis Major (meaning 'large dog').  It's a particularly bright star, which appears faint in the night sky because it's so far away.

VY Canis Majoris has a radius of 1800~2100 solar radii (it's 1800-2100 times wider than the Sun) - the figure varies as the star is surrounded by a nebula, which also makes it difficult to get an exact figure.  Taking 1800 solar radii as a minimum figure, to give us an approximate idea, this means that the star has a radius of:

1 solar radius = 695,500 km
1800 solar radii = 1.251 billion kilometres

Now, the circumference (i.e. the distance around the edge of the star) is 2 π r which gives a circumference of 7.866 billion kilometres.

And that's just the distance around the star's equator...  it's enormous.

Travelling at 900 km per hour, this would take 7.866 billion / 900 = 8.74 million hours.
8.74 million hours = 364,163 Earth days = 997 Earth years (assuming 365.25 days per year).

The exact figure depends on the value of solar radius, the rest is maths, but a round figure would be 1000 years.  Having said that, 900 km/h is not that fast - the speed of sound (Mach 1) is 1193 km/h.  The land speed record is held by Thrust SSC which achieved 1240 km/h in 1997, while Concorde used to reach 2170 km/h.

Still, doubling the speed from 900 km/h to 2170 km/h is only going to reduce the journey time to 500 years... so perhaps the question of time should be put aside.   The real question should be, if you're going to fly or travel on the surface of a star with a temperature of 3000 K, how are you going to keep the pilot flying, and stop him from frying?