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When can I see an aurora?

The aurora can be seen best at magnetic midnight which only occurs when the magnetic pole, the observer and the Sun are all aligned.  It is best to view these displays in winter because nights tend to be clearer and the hours of darkness are longer.

Large magnetic storms mean that the aurorae can be seen at lower latitudes and these are most common during the solar maximum, which is the peak of the eleven-year sunspot cycle, and for three years after that peak.

Magnetic storms also happen more often during the months around an equinox. An equinox occurs in March and September, when day and night are of equal length.

In most cases the Northern and Southern Lights are mirror images of each other that occur at the same time and have similar colours and shapes.

The greatest aurora in history

In 1859 it is thought that the Sun released one of the biggest coronal mass ejections ever. This created a series of huge magnetic storms in August and September of that year.

The aurorae these storms produced were extremely bright and very widespread, being seen at much lower latitudes than normal. It is said that in Boston, USA it was so bright at 1am in the morning that you could read a newspaper.

The storms disrupted many telegraph lines but those that were in line with the magnetic field of the aurora on the night in question continued to work even when the batteries were turned off.

This helped scientists to understand the connection between aurorae and electricity.

Aurora in folklore

Many native people thought that the lights they saw were spirits of the animals that they hunted. Some believed that the lights were the spirits of their own people.  In medieval times it was thought that seeing an aurora meant that war or famine were just around the corner.

Aurorae on other planets

Of course, other planets have magnetic poles and so they also have aurorae. The Hubble Space Telescope has observed aurorae on Jupiter and Saturn.  Other instruments have recorded aurorae on Venus, Mars, Uranus and Neptune as well as Jupiter’s moons Io, Europa and Ganymede.

The Moon

The Moon
The Moon is a 4.5-billion-year-old ball of rock in space and is Earth’s only natural satellite. A satellite is something which revolves around a planet. This can be a natural satellite, such as the Moon, or a man-made satellite placed into orbit for research or communications.

How the Moon Formed
The most likely theory about how the Moon was formed is called the Giant Impact Hypothesis. It is thought that, 4.5 billion years ago, a planet the size of Mars collided with the Earth. This impact caused huge amounts of liquid rock to be thrown into space and this debris gathered together to form the Moon. The newly formed Moon settled into an orbit just 22,500km (14,000 miles) away from the Earth, which was the closest it could have been without Earth’s gravity pulling it back again.

Distance to the Moon

The Moon is now, on average, 384,467km (238,897 miles) away from Earth. It revolves around Earth on an elliptical or oval shaped orbit, so sometimes it is nearer to the Earth and sometimes farther away. We know the distance to the Moon exactly because special reflectors were left on the Moon’s surface by the astronauts of the Apollo missions. Astronomers bounce laser beams off these reflectors and, because they know the speed at which the light of these laser beams travels, they can calculate the distance by the length of time it takes for the beam to get to the Moon and back.

The Moon is slowly moving away from Earth at a rate of 3.78cm (1.5 inches) per year. If the Moon moved far enough away this would have a catastrophic effect on the Earth’s climate. However, the Moon is moving so slowly that it would be billions of years before this happened.

Size of the Moon

Size of the Moon
The Moon has a diameter of 3,476km (2,159 miles) which is about a quarter of the size of the Earth. The volume of the Moon is about 49 times less than Earth, which means you could fit 49 Moons inside the Earth.

Speed
The Moon orbits the Earth at a speed of 3,683km/h (2,288mph). In one complete orbit around the Earth it travels 2,290,000 km (1,423,000 miles).

Atmosphere
There is no air on the Moon as its gravity is too weak to have an atmosphere and because of this the sky always appears black. Sound travels through air, so as the Moon has no air, it is always silent. With no atmosphere to trap heat, the Moon’s temperature varies from very hot 123°C (253°F) to very cold -233°C (-387°F).

Tides
On Earth our oceans have tides and these occur because of the gravitational pull between the Earth and the Moon. The highest or Spring Tides occur during a Full or New Moon. The lowest or Neap Tides occur at the Quarter Moons.

The Far Side
From Earth we always see the same side of the Moon. This is because, as the Moon rotates around the Earth, it also rotates around its own axis at the same rate. The side that we do not see is called the Far Side or Dark Side of the Moon. It has more craters than the front of the Moon and does not have as many maria. The Far Side was first photographed by the Soviet spacecraft Luna 3.

Moon Light
The Moon does not make its own light but reflects the light from the Sun. When we see the Moon lit up in the sky it is actually the light from the Sun hitting the Moon and bouncing back to Earth. The Moon’s surface absorbs more than 90% of the Sun’s light, with only a small percentage reaching Earth.

The Moon’s Surface

A meteoroid is a small piece of debris in space. If a meteoroid enters Earth’s atmosphere it is called a meteor and if it reaches the ground it is called a meteorite. Most meteors burn up as they pass through Earth’s atmosphere and before they hit the ground. As the Moon has no atmosphere it is constantly bombarded by meteorites and so is covered in impact craters, some billions of years old. There is no wind or rain to wear away these craters, so the landscape does not change a great deal. The footprints of the astronauts who landed on the Moon in the 1960’s and 70’s are still there today.

One such impact crater is Tycho, named after the Danish astronomer Tycho Brahe. Tycho is a young crater, with an estimated age of only 108 million years. The crater is surrounded by distinctive long spokes that are up to 1,500km (932 miles) long and is visible from Earth.
The dark patches are plains formed by lava flows very early in the history of the Moon. They are called mare or plural maria, which is Latin for sea, because early astronomers thought these dark areas were filled with water.

Moon Phases

From Earth, we see the Moon appear to change shape throughout the month, from a crescent to a Full Moon and back again. What we are seeing is part of the Moon illuminated by the Sun, depending on the position of the Earth, Moon and Sun in the sky. This is called a phase of the Moon.

The Moon orbits the Earth near to the Equator, so people in different hemispheres see the moon from a different vantage point. People in the Northern Hemisphere are standing on the opposite side of the globe to the people in the Southern Hemisphere, so in effect we are upside down to each other! So, a person from one hemisphere will think the Moon looks upside down if they go to the other hemisphere. Likewise, the way we view the Moon phases is different in each hemisphere, as shown on the charts above.

When the Moon is between the Earth and the Sun the side of the Moon facing us is dark and this is called a New Moon. After the New Moon the Moon is said to be waxing, or gaining in strength or brightness. When the Moon is on the opposite side of the Earth to the Sun, the side of the Moon that we see is fully lit up and this is a Full Moon. After the Full Moon the Moon is said to be waning, or decreasing in strength or brightness. The time that the Moon takes to complete its full cycle from New Moon to New Moon is about 29.5 days or a lunar month.