Posted on by Fraser Cain

The Earth’s Cities at Night

You only have to walk outside at night, look up and not see the Milky Way to know that light pollution is a problem. And seen from space at night, the Earth’s surface glows with the light of millions of homes, buildings, cars and streetlights. Seen at night, our impact on the Earth is immediate and obvious.

A few years ago, NASA and NOAA compiled a complete world map of the nighttime Earth, using 9 months of data collected by satellites. This “Night Lights” image is pretty famous, and widely circulated around the Internet.

There’s a great article at NASA’s Earth Observatory that describes how they capture these night images of the Earth’s surface. You can also see many of the best images taken so far.

Click here to read the article.

Posted on by Fraser Cain

Discovery of Pluto

Once the planet Uranus was discovered, astronomers have suspected that there are probably more planets in the Solar System. Astronomers used Newtonian mechanics to predict Neptune from its perturbations of Uranus’ orbit. German astronomer Gottfried Galle found Neptune exactly where calculations predicted it should be.

Now that they knew the method worked, astronomers set about finding other planets beyond Neptune. In the late 19th century, astronomers were starting to suspect that another body was pulling on both Uranus and Neptune, and so they tried to calculate its position, and then go look for it.

Percival Lowell, a wealthy Bostonian who founded the Lowell observatory in Flagstaff, Arizona, took up that search. He searched from 1905 all the way up to his death in 1915, and he never found it.

The job then turned to a young astronomer named Clyde W. Tombaugh – a 22-year old Kansas farm boy. Tombaugh spent the better part of a year staring at two photographic plates capturing the same region of sky at two different points in time.

Using a tool called a blink comparator, Tombaugh finally turned up images of Pluto moving in 1930. It turns out there had been evidence of Pluto in earlier photographs, but nobody had noticed it yet.

As the discoverers, Tombaught and his team were given the honor of naming Pluto. In the end, they settled on the name Pluto, suggested by a British school girl.

Posted on by Fraser Cain

Pluto, Planet X

In the beginning of the 20th century, astronomers studied the orbit of Neptune and calculated that there must be another planet in the outer reaches of the Solar System that was pulling at the planet with its gravity. Percival Lowell, who was made famous by his “discovery” of canals on Mars, coined the term for this theoretical object: Planet X.

Lowell performed two searches for Planet X, but failed to turn up the object. He revised his predictions for the location of Planet X twice, and failed to find it. Ironically, two faint images had been recorded on photograph plates at the Lowell observatory, but Lowell didn’t recognize them.

Lowell’s observatory continued to search for Planet X up until his death in 1916. So the task fell to Clyde Tombaugh. Tombaugh’s job was to systematically observe pairs of photographs taken of the night sky. He used a machine called a blink comparator, which flashed two images of the same region of the sky. Any moving objects, like asteroids or undiscovered planets, would appear to change in position from one image to the next.

On February 18, 1930, Tombaugh finally turned up the object he was looking for, and announced that he had discovered Planet X, later renamed to Pluto.

Astronomers have been searching for additional planets beyond Pluto ever since, hoping to find the elusive Planet X. Japanese astronomers have predicted that an object between the size of Mars and Earth could be out at the end of the Kuiper Belt – a region known as the Kuiper Cliff, at 55 astronomical units from the Sun.

Posted on by Fraser Cain

Surface of Pluto

When you imagine cold, icy Pluto, orbiting in the distant regions of the Solar System, you imagine snowy white ball.

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But images of Pluto, captured by the Hubble Space Telescope have shown that Pluto’s surface isn’t just pure ice. Instead, it has a dirty yellow color, with darker and brighter regions across its surface. Hubble studied the entire surface of Pluto as it rotated through a 6.4 day period.

The images revealed almost a dozen distinctive features never before seen by astronomers. This included a “ragged” northern polar cap cut in half by a dark strip, a bright spot seen to rotate around the dwarf planet, and a cluster of dark spots. The images also confirmed the presence of icy-bright polar cap features.

Some of the variations seen on Pluto’s surface could be topographic features, like basins and fresh impact craters. But most of them are probably caused by the complex distribution of frosts that move across Pluto’s surface during its orbital and seasonal cycles.

The surface area of Pluto is 1.795 x 107 square kilometers; about 0.033% the surface area of Earth.

When Pluto is furthest away from the Sun, gases like nitrogen, carbon monoxide and methane partially freeze onto its surface.

All will be revealed when NASA’s New Horizons spacecraft finally arrives at Pluto in 2015, finally capturing close-up pictures of Pluto and its moon Charon.

Posted on by Fraser Cain

Who Was Pluto Named After?

You’re thinking about a certain Disney dog, aren’t you? Goofy’s pet dog? Nope, it was actually named after Pluto, the Roman god of the underworld.

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When Pluto was first discovered by Clyde Tombaugh in 1930, he was given the honor of giving it a name. Although they were calling it Planet X informally, they needed something that matched the rest of the planets in the Solar System.

The name Pluto was suggested by Venetia Burney, an 11-year old school girl in England. She was interested in ancient mythology, and thought that Hades, the Greek god of the underworld, made a good name. She suggested Pluto, to match the Roman god names given to the other planets.

Each astronomer in the Lowell Observatory was allowed to vote on a short list of names: Minerva, Cronus, and Pluto. Every one of them voted for Pluto. Venetia was given a 5-pound reward for providing the name.

In other languages, the name has been translated to names that match underworld god mythology, such as Yama, the Guardian of Hell in Buddhist mythology.

Posted on by Fraser Cain

Mass of Pluto

In everything but the largest telescopes, Pluto appears as a tiny dot. And determining mass from so little information is incredibly hard to do.

Astronomers could only try and work out its mass by knowing how bright it was – its albedo. They could detect that it had large quantities of methane ice on its surface, and so astronomers knew that it had to be very bright. But there were sure about Pluto’s size, or even if it was larger than Mercury or Earth’s moon.

But astronomers lucked out in 1978 when James Christy discovered Pluto’s moon Charon. Once you get a system where two objects are orbiting one another, such as in the case of Pluto and Charon, you can use Newton’s formulation of Kepler’s Law to work out the mass very precisely.

Plugging in the orbital information for Pluto and its moon Charon, astronomers calculated its mass to be 1.31 x 1022 kg – less than 0.24% the mass of Earth. Followup observations were able to determine its size very accurately as 2,390 km across.You can also look through these books from Amazon.com if you want more information about Pluto.

Posted on by Fraser Cain

Temperature of Pluto

Pluto's temperature makes it one of the coldest places in the Solar System.

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With such a large distance from the Sun, Pluto is incredibly cold. But this temperature can vary enough to change the dwarf planet significantly. At its closest point, it warms up enough so that Pluto’s nitrogen atmosphere sublimates and forms a diffuse cloud around it. As Pluto gets further away from the Sun; however its this atmosphere freezes out, and falls to the surface of Pluto like snow.

First, let’s define some measurements. Room temperature is considered 21-degrees Celsius or 70-degrees Fahrenheit. The freezing point of water is 0-degrees Celsius or 32-degrees Fahrenheit. But when you’re measuring temperatures on Pluto, you really want to use Kelvin.

Zero Kelvin is the absolute zero temperature; a theoretical maximum point where no more energy can be extracted from a system. 0-degrees Kelvin corresponds to -273-degrees Celsius.

The surface of Pluto, in comparison, can range from a low temperature of 33 Kelvin (-240 degrees Celsius or -400 degrees Fahrenheit) and 55 Kelvin (-218 degrees Celsius or -360 degrees Fahrenheit). The average surface temperature on Pluto is 44 Kelvin (-229 Celsius or -380 Fahrenheit).

Back in the days when Pluto was still a planet, it was the coldest planet in the Solar System. But now it’s just a regular temperature dwarf plant – poor Pluto. Neptune is now the coldest planet.

Posted on by Fraser Cain

Distance to Pluto

Pluto has the most elliptical orbit of all the planets and dwarf planets. In addition to this widely varying orbital distance, Pluto is also highly inclined, orbiting above and below the planet of the ecliptic that the rest of the planets follow.

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Pluto Distance from the Sun
Since Pluto orbits the Sun, like the rest of the planets and dwarf planets, astronomers typically measure the distance of Pluto in terms of Astronomical Units (AU). 1 AU measures the distance of the Earth to the Sun.

At its closest point, Pluto is only 29 astronomical units from the Sun (4.4 billion km or 2.75 billion miles). And at its most distant, it can be 49 AU (7.29 billion km, or 4.53 billion miles) from the Sun. In addition to being highly elliptical however, Pluto’s orbit is also inclined at an angle of over 17-degrees. At some points along its orbit, Pluto is above the plane of the ecliptic that the planets follow, and at other times, it’s below.

Pluto’s average distance from the Sun is 40 astronomical units (5.91 billion km or 3.67 billion miles).

Distance From Earth to Pluto
The Earth is only 1 AU from the Sun. When the Earth and Pluto are perfectly lined up with the Sun, their closest point is approximately 28 astronomical units. And at their furthest point, when Earth is on the opposite side of the Sun, Pluto can be 50 astronomical units.

Posted on by Fraser Cain

Trailer for the International Year of Astronomy 2009

Okay, now I’m getting excited. As I’ve mentioned in the past, and will bring up again and again, the UN has designated 2009 as the International Year of Astronomy. There are some really great projects planned that will try to get as many people as possible interested in astronomy. The IYA has released a cool trailer to get us all inspired. It’s working for me.

Posted on by Fraser Cain

What is Pluto Made Up Of

No longer a planet, Pluto is just a member of the Kuiper Belt; a collection of icy objects that extend out past the orbit of Neptune. If you brought Pluto into the inner Solar System, it would start to act like a comet – blasting out gas and particles from the solar wind. It’s a good thing Pluto is in the cold, dark outer Solar System, far away from the Sun.

So, if it would act like a comet, what is Pluto built of, and how do we even know? Pluto is so small and dim that only the largest telescopes can see it. To even see with your own eyes, you want a 30 cm (12 inch) telescope – and then you’ll only see a dot.

Astronomers using the world’s biggest telescopes, including the Hubble Space Telescope see a much better view. By using a technique called spectroscopy, astronomers can analyze the details about Pluto’s surface. The current thinking is that it’s composed of more than 98% nitrogen ice, with traces of methane and carbon monoxide.

The limits of telescope technology mean that we can’t get a better view of Pluto’s surface. But NASA’s New Horizons spacecraft is making the journey to Pluto, and will make a flyby in 2015. At that point, it will fly within 10,000 km of Pluto’s surface and send back images that show features as small as 1.6 km across. This will be a tremendous improvement over our current understanding of Pluto.

But what’s inside?

Planetary scientists have calculated Pluto’s density at between 1.8 and 2.1 g/cm3. From this density, they have calculated that its interior is probably 50-70% rock and 30-50% ice. Decaying radioactive elements inside Pluto would heat the interior of the dwarf planet, allowing the rock and ice to move around. At this point, the interior of Pluto is probably a rocky core surrounded by a shell of ice. If the radioactive elements are still decaying today, they could heat Pluto up enough that it has an interior liquid ocean, like Jupiter’s moon Europa.

The surface of Pluto is a thin layer of nitrogen, methane and carbon monoxide. When Pluto is at its closest to the Sun, this material evaporates, and forms an atmosphere around the dwarf planet. And then, when it’s further from the Sun, and cooler, this atmosphere freezes back down onto the surface.

Here are some nice Pluto images.

Source: NASA