Author: Fraser Cain

The color of Neptune is a bright azure blue. During its flyby in 1989, NASA’s Voyager 2 revealed the bright blue color, different from the pale blue color of Uranus. So why does Neptune have this color?

The answer to Neptune’s color comes from its cloud tops. The upper atmosphere of Neptune is made up of 80% hydrogen, 19% helium with a trace 1% amount of methane and other ices, like ammonia and water. Methane absorbs light at 600 nm, which is the red end of the spectrum of visible light.

Like all the planets in the Solar System, the light we see coming from Neptune is actually reflected light from the Sun. These methane clouds absorb the red end of the spectrum, and allow the blue end of the spectrum to bounce back out. So when you see the color of Neptune, you’re seeing reflected sunlight with the red light stripped out.

From a distance, Neptune looks just like a blue ball, but as you get closer you can see variations in its clouds. Lighter clouds of methane hang above the lower cloud deck. Powerful storms whip across the surface of Neptune; the fastest storms in the Solar System are on Neptune, with winds exceeding 2,400 km/hour. Neptune has a large dark storm, similar to the Great Red Spot on Jupiter.

We have written many articles about Neptune on Universe Today. Here’s an article about “movies” of Neptune captured by Hubble. And some additional images captured by Hubble that really show the color of Neptune.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

The atmosphere of Neptune is similar to all the large planets in the Solar System; it mostly consists of hydrogen and helium, with trace amounts of methane, water, ammonia and other ices. But unlike the other gas planets in the Solar System, Neptune’s atmosphere has a larger proportion of the ices. It’s the methane in the planet’s upper atmosphere that give it its bright blue color.

At the highest altitudes, where the Neptune’s atmosphere touches space, it consists of about 80% hydrogen and 19% helium. There’s also a trace amount of methane. The light we see from Neptune is actually the reflected light from the Sun. Although the entire spectrum of light hits Neptune. This trace amount of methane absorbs light from the red end of the spectrum, while allowing the blue light to bounce back out. The color of Neptune’s atmosphere is brighter than Uranus, which has a similar atmosphere; astronomers aren’t sure why there’s such a dramatic color difference.

The upper level clouds on Neptune occur at the point where pressures are low enough for methane to condense. Astronomers have photographed these high altitude clouds forming shadows onto the lower cloud deck below. Deeper down inside Neptune, temperatures should get up to 0 C, where clouds of water might form.

As with the other planets, the atmosphere of Neptune is broken up into distinct bands of storms. In fact, the fastest moving winds in the Solar System occur at Neptune – winds have been clocked at 2,400 km/h (1,500 miles per hour). Some storms can grow large and remain for long periods of time. Neptune has its own Great Dark Spot, similar to the Great Red Spot on Jupiter.

We have written many articles on Universe Today about the atmosphere of Neptune and its storms. Here’s an article about the weather in springtime on Neptune, and how Neptune’s south pole might be the warmest place on the planet.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

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When we look at the Moon, we see a landscape shaped by impact craters. But scientists only discovered the true cause of crater in the last hundred years. Before that, they believed that there were many volcanoes on the Moon, and this is what caused the craters we see today.

Now we know that craters come from meteorite impacts, that still doesn’t answer the question: are there volcanoes on the Moon?

There used to be volcanoes on the Moon. The Moon is much smaller than the Earth. Although it was molten after its formation, it cooled down relatively rapidly. Scientists think that the Moon’s interior remained hot enough to produce magma for about a billion years after the Moon formed. The lava that came out of the Moon cooled quickly, and formed fine-grain, dark rocks called basalt. The Apollo astronauts sampled this material when they landed on the Moon.

When you look at the Moon, you see lighter and darker regions. The lighter regions are the mountainous highlands. The darker regions are vast “seas” of basalt lava that erupted out of the Moon billions of years ago.

Are there volcanoes on the Moon today?

There is recent evidence that there were volcanoes on the far side of the Moon much longer than on the near side. While the near side of the Moon shut down more than 3 billion years ago, there seems to be evidence that there were volcanoes on the surface of the Moon as recent as about a billion years ago.

Some researchers believe there are still vents that blast out volcanic gasses, but there are no longer active volcanoes on the Moon.

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

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A lunar year or lunar calendar is one that is based on the cycles of the moon phases. The problem with a lunar calendar is that it drifts away from the seasons. Each year, the start and end dates of each month drift by 11 days. In order to stay correct, every lunar calendar has to deal with this drift away from the calendar year.

Let’s examine a year. A lunar month lasts 29.53 days. So after 12 lunar months, you’re about about 354 days. This is short of the 365 days that it takes the Earth to orbit the Sun. This is a problem since after about 3 years, the lunar months are out of cycle with the solar year by about a month. And this problem would just continue.

To make the lunar calendar work in China, farmers would add in a leap month every 3 years. This would mostly get the lunar month to line up with the solar year, but they still drifted apart somewhat. For some calendars used for religious purposes, such as the Islamic Hirji calendar, they never bothered to sync up the calendars and let them drift. It takes 33 years for the cycle of lunar years to get back to the original position.

A lunar calendar was used in England up until Tudor times.

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

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The density of the Moon is 3.346 g/cm³. The Moon is actually the second densest moon in the Solar System after Io.

Need some comparisons? The density of Earth is 5.52 g/cm³. This makes it the densest planet in the Solar System. The density of Io is 3.53 g/cm³.

Astronomers believe that the Moon formed when a Mars-sized object crashed into the Earth. The resulting debris from the collision collected into orbit around the Earth and became the Moon. The Moon’s relatively low density comes from the fact that it was mostly the Earth’s upper mantle and crust that was thrown up into space, and not very much of its core.

The low density of the Moon means that it has less mass, and less gravity. If you ever get a chance to stand on the Moon, you’ll see that its gravity is only 16.5% the gravity of Earth. In other words, if you weight 100 kg on Earth, you would only weigh 16.5 kg on the Moon.

Want to know the density of other objects in the Solar System? Here’s the density of Jupiter, the density of the Sun, and the density of Saturn (the least dense planet in the Solar System).

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

The composition of the Moon is a bit of a mystery. Although we know a lot about what the surface of the Moon is made of, scientists can only guess at what the internal composition of the Moon is. Here’s what we think the Moon is made of.

Like the Earth, the Moon has layers. The innermost layer is the lunar core. It only accounts for about 20% of the diameter of the Moon. Scientists think that the lunar core is made of metallic iron, with small amounts of sulfur and nickel. Astronomers know that the core of the Moon is probably at least partly molten.

Outside the core is the largest region of the Moon, called the mantle. The lunar mantle extends up to a distance of only 50 km below the surface of the Moon. Scientists believe that the mantle of the Moon is largely composed of the minerals olivine, orthopyroxene and clinopyroxene. It’s also believed to be more iron-rich than the Earth’s mantle.

The outermost layer of the Moon is called the crust, which extends down to a depth of 50 km. This is the layer of the Moon that scientists have gathered the most information about. The crust of the Moon is composed mostly of oxygen, silicon, magnesium, iron, calcium, and aluminum. There are also trace elements like titanium, uranium, thorium, potassium and hydrogen.

Want to compare the Moon to other objects in the Solar System? Here’s what the Earth is made of, and here’s what Mars is made of.

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

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Want to help your kids learn more about the Moon with some interesting activities? Here are some Moon activities that we can suggest:

• Learn the phases of the Moon – For this activity, you need a bright light to represent the Sun, and a ball that you can use as the Moon. Have your child sit on a chair away from the light. The child is the Earth. Then orbit the child in a counter-clockwise direction. The child should see the different amounts of illumination on the ball representing the Moon.
• Organize the phases of the Moon – Draw out all the Moon phases on pieces of paper and mix them all up. Let your children arrange them into the proper order, starting with the new moon going to the full moon, and then back again. You can refer to a calendar of Moon phases if you need to know if they’re right.
• Make craters – Drop marbles or ball bearings into a material that shows how craters can form. To make your lunar surface, put a layer of a white material, like flour in a pan to a depth of a few cm. Then cover it with a thin layer of something dark, like cocoa powder. When you drop the marbles into the material, it will create very familiar looking craters.
• Feel your weight on the Moon – Calculate your child’s weight on the Moon by multiplying their current weight by 0.165. For example, if they weigh 30 kg, they would only weigh 5 kg on the Moon. Have them stand on a bathroom scale and then support their weight until the scale shows their moon weight. Now let them walk around the room with you supporting the bulk of their weight. That’s what it would feel like to walk on the Moon.

Want more activities? NASA has a huge list of cool space activities on their website.

We also have instructions on how you can build a model of the Solar System.

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

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The Moon, on average, is about 150 million kilometers away from the Sun. That’s actually an interesting coincidence, since the Earth orbits about 150 million kilometers away from the Sun. What? Well, the Moon orbits the Earth, so it’s following the Earth around in its orbit around the Sun.

Now, we can actually get a little more precise here. The Earth actually takes an elliptical path around the Sun. It ranges in distance from 147 million km to 152 million km. So the Moon can actually range in this distance as well.

But wait, we can get even more precise. The Moon takes an elliptical orbit around the Earth. Sometimes it gets as close as 363,000 km, and other times it gets as far as 406,000 km.

So the closest point that the Moon can get to the Sun is when the Earth is at its closest point in orbit, and the Moon is most distant from the Earth. The closest point that the Moon can actually get to the Sun is 146,692,378 km.

The furthest that the Moon can get from the Sun is the opposite situation. The Earth is at its most distant from the Sun, and the Moon is furthest from the Earth. At that point, the Moon would be 152,503,397 km.

And that’s how far the Moon is from the Sun.

Here’s more information about how far the Moon is from Earth, and how far the Earth is from the Sun.

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?