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Moon Phases (CosWatch Blog 4)23/06/2020

Welcome to the second of Fun Science‘s CosWatch blog posts, which you can read through with your young scientist and learn the phases of the Moon.

What is CosWatch?

There’s so much to see in the night sky! You may have seen Brian Cox on TV describing the “wonders of the universe”, or Carl Sagan talking about the “awesome machinery of nature”, and they’re absolutely right. But while huge rockets and observatories can help, space isn’t just for people with expensive equipment. You can see amazing things from millions of miles away from your very own back garden. Each week, I’m going to talk about one of these incredible objects, and how you can find them.

This time, we’re going to be talking about the Moon, and why it changes shape!

This amazing shot from NASA shows the Moon creeping up behind some trees at the US National Arboretum in 2018. A large number of the Earth’s beings would have looked upon sights like this all through their evolution.

Tell me about the Moon

The Moon is the Earth’s only natural satellite. Satellites in nature are objects that orbit planets and minor planets. The Earth is a planet, which makes the Moon, which goes around the Earth, a natural satellite! It takes just under a month to orbit around the Earth, and it takes about 1.28 seconds for light reflected off of it to reach our planet.

It’s a solid, rocky mass, like the first four planets (Mercury, Venus, Earth and Mars). It does technically have an extremely thin atmosphere, but nothing substantial. Scientists believe the Moon may exist because an early version of Earth collided with a planet the size of Mars, and the remaining rocks formed into the Earth and the Moon. This is called the “Giant-impact hypothesis”, and has a fair bit of evidence. Scientists really developed results that suggests that the Moon may be much older than this, but this doesn’t necessarily contradict the “giant impact” idea.

This graph shows us roughly what scientists imagine might have happened.

Because The Moon is visible from Earth, it has been an object of fascination for human cultures since the dawn of civilization. The Moon has been described by various peoples and races as a female God, a male God, a rabbit, a Buffalo, and countless other unusual and interesting interpretations. This is probably because of the different colours of the Moon; the darker parts, or “Maria”, look like shapes compared to the brighter “Highland” parts. These areas aren’t actually any particularly different; “Maria” simply reflect a few percent less light, which makes them appear darker.

This lovely art from Matthew Meyer demonstrates how people – or rabbits! – may have seen likenesses of themselves or stories they’d heard in the Moon.

It is the only celestial body other than Earth that humans have  visited; between 1969 and 1972, twelve astronauts have walked on the moon, collecting samples and enjoying the reduced gravity; anything on the Moon weighs about six times less than on Earth. This is because the Moon is roughly six times smaller than the Earth.

[youtube https://www.youtube.com/watch?v=az9nFrnCK60&w=560&h=315]

Why does the Moon change shape?

The Moon is tidally locked with the Earth, which also means it is in “synchronous rotation”. What that means, simply, is it moves around the Earth just as fast as it turns on its axis. Or, even more simply, the same side is always facing the Earth.

However, the Moon also doesn’t produce its own light, and only reflects that of the Sun. That means that as it moves around the planet, the half of it that is lit by the Sun moves around but the actual Moon doesn’t. This is difficult to visualise, but this image shows it quite well.

There are eight “phases” of the Moon. They are either “waxing” phases, when it appears to be getting bigger, or “waning” ones, where it appears to be getting smaller.

Waxing or waning? Shape Appearance
New Moon This phase is barely visible, because no light can reach it!
Waxing Crescent

More about this image…

Quarter

(or “first quarter”)

More about this image…

Gibbous

More about this image…

Full Moon

More about this image…

Waning Gibbous

More about this image…

Quarter

(or “third quarter”)

More about this image…

Crescent

More about this image…

The Moon’s visibility, age, and regular changes make it one of the earliest clocks in the world. Early human beings would use it to keep track of time, just like the seasons of the Earth.

How can I see the Moon?

As you might imagine, it isn’t too difficult to spot the Moon when it isn’t in its “New Moon” phase. It is the brightest object in the night sky; in fact, it reflects so much of the Sun’s light it can be seen quite often in the day.

The speed of the Earth’s rotation relative to the Moon’s orbit means that it rises about fifty minutes later every evening.  Like the Sun, it rises in the East. As with Jupiter, your best course of action for working out when it will appear is using the National School Observatory‘s website; unlike Jupiter, you’re unlikely to mistake it for anything else!

In conclusion:

  • The Moon is Earth’s only large, long-term natural satellite.
  • It has been observed by humans since time immemorial, and the different-coloured areas (“Maria” and “Highlands”) look like shapes.
  • The Moon moves around the Earth as fast as it turns around, meaning the same “face” is always looking at us, and light moves around it, causing the different phases.
  • It can be seen easily with the naked eye, except during “New Moon” phases.

What’s next on CosWatch?

Next time, I’ll be talking about Uranus, the third gas giant, and the seventh planet in our Solar System. Somerset residents will be particularly interested in this one!

Notes:

Fun Science recently created a “Planets and Space” home kit, pre-orderable now for only £5.00. Check it out here!

See Jupiter (CosWatch Blog 2)08/06/2020

Welcome to the second of Fun Science‘s CosWatch blog posts, which you can read through with your young scientist and learn how to see Jupiter.

What is CosWatch?

There’s so much to see in the night sky! You may have seen Brian Cox on TV describing the “wonders of the universe”, or Carl Sagan talking about the “awesome machinery of nature”, and they’re absolutely right. But while huge rockets and observatories can help, space isn’t just for people with expensive equipment. You can see amazing things from millions of miles away from your very own back garden. Each week, I’m going to talk about one of these incredible objects, and how you can find them.

This amazing shot of Jupiter was taken with the Hubble Space Telescope that orbits the Earth.

This time, we’re going to be talking about how to see Jupiter, the largest planet in the solar system!

Tell me about Jupiter

Jupiter is the fifth planet from the Sun, and takes just under twelve years to go around it. It is a gas giant; unlike our planet, which has a solid surface and a relatively small atmosphere, Jupiter is almost nothing else but atmosphere. Like all the gas giants, it has rings, though unlike Saturn’s, they’re very faint.

This amazing image from the spacecraft Juno is useful for two reasons; we can see the swirls of Jupiter’s atmosphere, and we can also see the shadow of one its moons!

Jupiter is a powerful planet; it is the third-brightest thing in the night sky after the Moon and Venus, and, despite being so large, it is the fastest-spinning planet, with its days only ten hours long. It also has a huge magnetic field, fifteen times bigger than the Sun’s! You may have heard of the great red spot, which is a storm in Jupiter’s atmosphere that has been raging for four centuries, and is very slowly diminishing. You could fit three Earths inside it, such is its size.

There are many, many moons of Jupiter. The human race has confirmed at least 79, but there could be quite a few more. The most famous are the four “Galilean” moons: Callisto, Europa, Ganymede, and Io. These are much larger than Earth’s moon, and are named after the Astronomer who first spotted them, Galileo Galilei. They have many interesting qualities; Io is teeming with volcanoes because its surface is torn apart by the gravity of the other planets, while Europa may hold life in its Icy oceans, twice the volume of Earth’s!

The Jupiter mystery

A photo from NASA of the four Galilean moons, edited so they sit together. From top to bottom: Io, Europa, Ganymede, and Callisto.

When scientists look at planets that go around stars that aren’t our sun, the largest gas giants – that is to say, the ones like Jupiter – tend to orbit very close to their star. They aren’t quite sure, then, why Jupiter orbits from so far away, past four solid planets. They think a young Jupiter may have collided with several other early planets, then been catapulted back to where it is now – this theory is called the “Grand Tack”.

The eight planets that make up our solar system. What this graph from NASA doesn’t show is at least five dwarf planets and thousands and thousands of other objects, including satellites we’ve made outselves. To get a model of the Solar System, check out the link to Fun Science’s home kit in the notes at the bottom of this CosWatch!

How can I see Jupiter?

As I mentioned, Jupiter is at times the third brightest object in the night sky. This means that, like the ISS, it can be observed with the naked eye, and indeed it has been; people as far back as the Ancient Egyptians tracked its movements across the sky.

However, unlike the ISS, which is simply too fast to catch with most equipment, you can see Jupiter with any telescope or pair of binoculars if you’d like to. You don’t necessarily need any special filters or lenses, and you may be able to see the Galilean moons in your device!

A handy graph from SchoolsObservatory.Org shows UK stargazers how to spot Jupiter, next to Saturn, Mars and the Moon, in the south this month.

You can try to memorise the movements of all the planets, but given that this is quite complicated, I like to use the National Schools’ Observatory, which provides a daily forecast for the UK sky at night. To see Jupiter at the moment you’d need to be up at 2-6am – but there are plenty of times in the year where it is visible much earlier, so don’t be disheartened!

In conclusion:

  • Jupiter is the powerful fifth planet from the Sun, with a huge magnetic field and a fast spin.
  • A gas giant, very little of Jupiter is solid, instead mostly being liquid and gas.
  • Jupiter has at least seventy-nine moons, of which four are very famous. One of these may hold life!
  • Jupiter is in an unusual place for a planet of its size, and scientists still aren’t certain why.
  • You can see it with the naked eye, but get an extra-special view through equipment.

What’s next on CosWatch?

Next time, I’ll be talking about Orion’s Belt. See you soon!

Notes:

Fun Science recently created a “Planets and Space” home kit, pre-orderable now for only £5.00. Check it out here!

Younger scientists, or older ones with good taste, may want to check out The Magic School Bus Lost in the Solar System in Joanna Cole’s Magic School Bus series to help them remember and learn about the different planets – though note that this book has Pluto classified as a planet, which is of course out of date..