Pluto and Charon. Credit: Antonello Medugno and Daniele Gasparri
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This past summer, a group of seven amateur astronomers from Italy worked on an observation campaign of Pluto, with hopes of capturing an image of its moon, Charon. “Imaging Charon is very difficult and nobody has spotted it with amateur equipment, so far,” said Daniele Gasparri, one of the members of the group. The team made several attempts, and finally, one member of the group, Antonello Medugno, took this interesting image. “After many calculations,” said Gasparri, “we are sure that this image shows clearly Pluto and Charon, for the first time with amateur equipment.” Comparing the image to the graphic which shows the position of Pluto and Charon on the same date, it’s obvious, they nailed it! This is quite a feat considering their equipment was an “amateur” 14-inch telescope! Also, as The Bad Astronomers points out, Charon wasn’t discovered until 1978, and then a 61-inch telescope was used!
Compare their image to one taken by Hubble:
Hubble image of Pluto and Charon. Credit: NASA
Not bad!!
Gasparri is an astronomy student, and a contributor to the Italian astronomy magazine Coelum. With the support of the magazine, he coordinated the effort to image Charon. Medugno used an 14″ Schmidt-Cassegrain telescope, a Starlight Xpress SXV-H9 CCD camera and a R-IR passband filter.
The image was processed using the Lucy-Richardson Algorithm of the RAW image, composed of 21 frames of 6 seconds of exposure each, with a focal of 8900mm. “All data confirm the image: the magnitude, separation, and position angle,” said Gasparri. Nice work! Check out Gasparri’s website of more astronomical images he has taken.
Astronaut Eugene Cernan from Apollo 17, the last mission to the Moon (NASA)
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Your weight on the Moon is 16.5% what you would experience on Earth. In other words, if you weighed 100 kg on Earth, you would weigh a mere 16.5 kg on the Moon. For you imperial folks, imagine you tipped the scales at 200 pounds. Your weight on the Moon would only be 33 pounds.
Why is your weight on the Moon so much less than your weight on the Earth? It’s because of the lower gravity on the Moon. Objects on the surface of the Moon experience only 16.5% of the gravity they would experience on Earth. And why does the Moon have such a lower gravity? Gravity comes from mass. The more stuff you have, the more you’ll pull with gravity.
The mass of the Moon is only 1.2% the mass of the Earth, so you might expect it to have only 1.2% of the gravity. But it’s only 27% of the size of the Earth, so when you’re standing on the surface of the Moon, you’re much closer to its center of gravity.
Because your weight on the Moon is about 1/6th your weight on Earth, but your muscles are still as strong, you could do some amazing things. You would be able to jump 6 times higher, or jump off the roof of a house and be unharmed. And here’s the coolest thing. Strap on a pair of wings inside an air-filled dome on the Moon, and you would be able to fly around with just your own muscle power.
A lunar month takes 29.53 days. This is the amount of time it takes for the Moon to complete a cycle through all the phases, from new moon to full moon and then back to new moon again. This is very close to the length of a month in the Western calendar, which usually have 30 or 31 days. Every month usually has one of each of the phases. So a typical month will have a new moon, first quarter, full moon and last quarter moon. But every now and then, a month will have two of the same phases. When a month has two full moons, the second one is called a “blue moon”.
Blue moons are rare, and that’s where the phrase comes from, “once in a blue moon”. How rare? They always happen once every 2-3 years (2.72 years, to be exact). It’s this second moon in the month that’s considered the blue moon.
Does the blue moon actually turn blue? No. A blue moon is exactly the same color as a regular full moon – yellow.
The Moon can turn blue when there’s a certain amount of dust or pollution in the air. The extra dust scatters blue light, making the Moon appear more blue. For example, the Moon appeared blue across the entire Earth for about 2 years after the eruption of Krakatoa in 1883.
Here is a list of upcoming blue moons:
2018: January 2, January 31st
2018: March 2, March 31st
2020: October 1, October 31st
We have an article here on Universe Today about all the phases of the Moon.
The moon in its waning gibbous phase on Sept. 12, 2014. Photo taken with a Canon 700D attached to a Maksutov 127mm telescope. Credit: Sarah&Simon Fisher
Human beings have been observing the Moon for as long as they have walked the Earth. Throughout recorded and pre-recorded history, they have paid close attention to its phases and accorded them particular significance. This has played a major role in shaping the mythological and astrological traditions of every known culture.
With the birth of astronomy as a scientific discipline, how the Moon appears in the night sky (and sometimes during the day) has also gone long way towards helping us to understand how our Solar System works. It all comes down to the Lunar Cycle, the two key parts of this cycle involve the “waxing and waning” of the Moon. But what exactly does this mean?-day
Lunar Cycle:
First, we need to consider the orbital parameters of the Earth’s only satellite. For starters, since the Moon orbits Earth, and Earth orbits the Sun, the Moon is always half illuminated by the latter. But from our perspective here on Earth, which part of the Moon is illuminated – and the amount to which it is illuminated – changes over time.
When the Sun, the Moon and Earth are perfectly lined up, the angle between the Sun and the Moon is 0-degrees. At this point, the side of the Moon facing the Sun is fully illuminated, and the side facing the Earth is enshrouded in darkness. We call this a New Moon.
After this, the phase of the Moon changes, because the angle between the Moon and the Sun is increasing from our perspective. A week after a New Moon, and the Moon and Sun are separated by 90-degrees, which effects what we will see. And then, when the Moon and Sun are on opposite sides of the Earth, they’re at 180-degrees – which corresponds to a Full Moon.
Waxing vs. Waning:
The period in which a Moon will go from a New Moon to a Full Moon and back again is known as “Lunar Month”. One of these lasts 28 days, and encompasses what are known as “waxing” and “waning” Moons. During the former period, the Moon brightens and its angle relative to the Sun and Earth increases.
Synthetic view of the waxing Moon as viewed from Earth on 2013-10-15 17:00:00 UTC. Credit: NASA/GSFC/Arizona State UniversityWhen the Moon starts to decrease its angle again, going from 180-degrees back down to 0-degrees, astronomers say that it’s a waning moon. In other words, when the Moon is waning, it will have less and less illumination every night until it’s a New Moon.
Waning Phases:
When the Moon is no longer full, but it hasn’t reached a quarter moon – i.e. when it’s half illuminated from our perspective – we say that it’s a Waning Gibbous Moon. This is the exact reverse of a Waxing Gibbous Moon, when the Moon is increasing in brightness from a New Moon to a Full Moon.
This is followed by a Third Quarter (or last quarter) Moon. During this period, 50% of the Moon’s disc will be illuminated (left side in the northern hemisphere, and the right in the southern), which is the opposite of how it would appear during a First Quarter. These phases are often referred to as a “Half Moon”, since half the disc is illuminated at the time.
The moon in its waning gibbous phase on Sept. 12, 2014. Photo taken with a Canon 700D attached to a Maksutov 127mm telescope. Credit: Sarah&Simon Fisher
Finally, a Waning Crescent is when the Moon appears as a sliver in the night sky, where between 49–1% of one side is illuminated after a Full Moon (again, left in the northern hemisphere, right in the southern). This is the opposite of a Waxing Crescent, when 1-49% of the other wide is illuminated before it reaches a Full Moon.
Even today, thousands of years later, human beings still look up at the Moon and are inspired by what they see. Not only have we explored Earth’s only satellite with robotic missions, but even crewed missions have been there and taken samples directly from the surface. And yet, it still possesses enough mystery to keep us inspired and guessing.
Quarter Moon, captured by NASA astronauts. Image credit: NASA
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A quarter moon occurs when we see the Moon half illuminated by the Sun, and half enshrouded in darkness. Since the illuminated side points towards the Sun, it tells astronomers that the Moon and the Sun are separated by 90-degrees from our perspective here on Earth.
You can have a first quarter moon, when the Moon is halfway between a new moon and full moon. A new moon occurs when the Moon is directly in between the Sun and the Earth. From that perspective, the illuminated Moon is facing away from the Earth. A full moon happens when the Moon and the Sun are on opposite sides of the Earth. At that point, we see the Moon fully illuminated by light from the Sun.
When we see the first quarter of the Moon, that means the amount of the Moon that’s illuminated is increasing. Astronomers call an increasingly illuminated moon: “waxing”.
You can also get a last quarter moon, when the Moon is half illuminated, but the opposite side is illuminated. This is the halfway point between a full moon and a new moon. When the amount of the Moon that’s illuminated is decreasing, astronomers call this “waning”.
Want to know when the next quarter moons are going to happen? Here’s a chart from NASA that calculates the phases of the Moon over a 6000 year period. And here’s a cool calculator that shows you what the Moon is doing right now.
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Hey, here’s a question: does the Moon orbit the Sun? Of course not, it’s a silly question. Of course the Moon orbits the Earth.
But wait a second and think. The Moon follows the Earth around the Sun in its orbit, and if you didn’t have the Earth, the Moon would really be orbiting the Sun. So can we say that the Moon is really orbiting the Sun?
No. But the case is pretty compelling.
First, take a look at the orbital velocity of the Moon. The Moon’s velocity around the Moon is a mere 1 km/second. But the Moon’s velocity around the Sun is 30 km/sec; same as the Earth.
And here’s something stranger. the Moon doesn’t follow a spiral pattern around the Sun, as you would think, but it always follows a convex path compared to the Sun. It’s not exactly a circle, but it looks like a 12-sided object with rounded corners. Check out this page to see what the Moon’s path around the Sun actually looks like.
Furthermore, the Moon experiences twice the pull of gravity from the Sun than it does from the Earth. So, does the Moon really orbit the Sun?
To figure out what orbits what, you need to know a term called the “Hill sphere” (named after the American astronomer George William Hill). This is the volume of space around an object where its gravity dominates the influence of gravity from a more distant object. If an object is orbiting within this Hill sphere, it’s a moon of the larger object.
You have to calculate the gravity from the primary body (the Earth), the gravity from the secondary body (the Moon) as well as the centrifugal force experienced by a particle moving around the Sun at the same orbit as the Earth. If the sum of those three forces is pointed towards Earth, the Moon is held in orbit. If they didn’t point towards Earth, the Moon would drift away from the Earth and orbit the Sun directly instead.
In other words, because the Moon actually orbits around the Earth; it’s orbiting the Earth. I know that sounds like circular logic, but stay with me. If the Moon wasn’t orbiting Earth, it would go into a smooth orbit around the Sun, and have no regular gravitational interaction with the Earth.
Of course, my good friend Phil Plait over at Bad Astronomy has a great explainer for this puzzler.
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A new moon occurs when the Earth, Sun and Moon are lined up so that the Moon is directly in between the Earth and the Sun. From this perspective, the side of the Moon covered in sunlight is turned away from the Earth, and the face we see is in shadow. The Moon takes approximately 29 days to complete the cycle from new moon to full moon and then back to new moon again. During a new moon, the Moon is in conjunction with the Sun, as seen from Earth.
Astronomers call it a “new moon”, because shortly after the Moon is completely shadowed, a think crescent peeks out from one side. This is the beginning of the Moon’s rise to brightness over the next 2 weeks. The exact time this occurs depends on your geography on Earth, but it will always occur in the Western horizon between sunset and moonset.
The orbit of the Moon isn’t exactly lined up the the orbital plane of the Sun and the planets, so it doesn’t actually get exactly between the Earth and the Sun. When this exact line does happen, the new moon is seen as a solar eclipse, darkening the Sun by various amounts depending on your position on the Earth.
We’ve got a list of all the new moons for the next few years. Here’s a list for 2008, 2009, 2010, 2011 and 2012.
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The full moon occurs when the Sun and Moon are located on opposite sides of the Earth. In this situation, the face of the Moon visible from the Earth is completely illuminated by the Sun. More specifically, the full moon occurs when the geocentric apparent longitudes of the Sun and the Moon are 180 degrees apart. This is a fancy way of saying that the Sun and the Moon are on opposite sides of the sky.
The Moon takes 27.3 days to orbit the Earth. But because the Moon is orbiting around the Earth in the same direction that the Earth is orbiting the Sun, the Moon takes an additional 2.2 days to return to the same position in the sky, where it’s perfectly lined up with the Sun. That’s why the amount of time it takes to go from a full moon to a full moon is 29.5 days long. Astronomers call this length of time a lunar month.
One interesting side note, the month of February only has 28 days. Since that’s less than the 29 day lunar month, there are some years where February doesn’t have a single full moon. The last time this happened was in 1999, and it’s expected to happen again in 2018.
When the Moon is full, it’s at its brightest. Astronomers measure the brightness of an object using a term called apparent magnitude. The apparent magnitude of the full Moon is -12.7. When the Moon is only at its first quarter, its brightness is -10.0, which is a reduction of 12x. Ancient peoples carefully recorded the times from full moon to full moon since those were some of the few times that they could actually see and get work done in the night – before we had artificial illumination.
A blue moon occurs when a single month has two full moons. The second full moon in a calendar month is known as a blue moon. Blue moons tend to occur every 2.7 years.
We have written several stories on Universe Today about the full moon. Here’s one about interesting things that might happen during a full moon. And here’s one about blue moons.
Want to know when the next full moon is going to happen? Here’s a calculator from the US Navy’s Observatory.
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A lunar month is the amount of time it takes for the Moon to pass through each of its phases (new moon, half, full moon), and then return back to its original position. It takes 29 days, 12 hours, 44 minutes and 3 seconds for the Moon to complete one lunar month.
You might have heard that the Moon only takes 27.3 days to complete one orbit around the Earth. So why is a lunar month more than 2 days longer than the orbit of the Moon?
A lunar month is the amount of time it takes for the Moon to get from a specific phase, like a new moon, back to the same phase. In other words, the Moon has to get back to the point in its orbit where the Sun is in the same position from our point of view. Since the Moon is going around the Sun with the Earth as part of its orbit, the Moon has to catch up a little bit on each orbit. It takes 2.2 additional days each orbit of the Moon to catch up.
This method of measuring a lunar month, from new moon to new moon, is known as a synodic month. A new moon is defined as when the Moon has the same ecliptic longitude as the Sun, as seen from the center of the Earth; when the Sun, Moon and Earth are perfectly lined up.
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The Moon takes about 27.3 days to complete one orbit around the Earth. That’s the simple answer to the orbit of the Moon, but there’s a lot more going on, so let’s take a look.
The first think that you have to understand is that that Earth and the Moon actually orbit a common center of gravity. This place is about 4,700 km from the center of the Earth. In other words, the Earth wobbles back and forth because of the orbit of the Moon. Some scientists have even proposed that the Earth and the Moon are actually a double planet because of their relationship, but this would only be the case if the common center of gravity was outside the surface of the Earth.
The orbit of the Moon is about 385,000 km from the Earth on average. Like the planets in the Solar System, the orbit of the Moon isn’t circular; it actually follows an elliptical path around the Earth. At its closest point, called perihelion, the Moon is 364 397 km from the Earth. And then at its most distant point, called aphelion, the Moon is 406 731 km.
You might have heard that the Moon is slowly drifting away from the Earth. Although the Moon is tidally locked to the Earth, presenting the same face to our planet, the Earth isn’t tidally locked. But in about 50 billion years from now, the Moon will complete an orbit once every 47 days, and it will remain in exactly the same place in the sky. One half of the Earth will be able to see the Moon, and it will be hidden from the other half. Of course, the Sun is expected to become a red giant in about 5 billion years and potentially destroy the Earth and Moon, so this time may never come.
![Synthetic view of the waxing Moon as viewed from Earth on 2013-10-15 17:00:00 UTC [NASA/GSFC/Arizona State University].](https://www.universetoday.com/wp-content/uploads/2013/10/tuesday_syntheticview_thumb.png)
