Astronomy Archives

October 7, 2009December 24, 2015 by Fraser Cain

Why is the Sun Hot?

Plasma on the surface of the Sun. Image credit: Hinode

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The Sun is the hottest place in the Solar System. The surface of the Sun is a mere 5,800 Kelvin, but down at the core of the Sun, the temperatures reach 15 million Kelvin. What’s going on, why is the Sun hot?

The Sun is just a big plasma ball of hydrogen, held together by the mutual gravity of all its mass. This enormous mass pulls inward, trying to compress the Sun down. It’s the same reason why the Earth and the rest of the planets are spheres. As the pull of gravity compresses the gas inside the Sun together, it increases the temperature and pressure in the core.

If you could travel down into the Sun, you’d reach a point where the pressure and temperature are enough that nuclear fusion is able to take place. This is the process where protons are merged together into atoms of helium. It can only happen in hot temperatures, and under incredible pressures. But the process of fusion gives off more energy than it uses. So once it gets going, each fusion reaction gives off gamma radiation. It’s the radiation pressure of this light created in the core of the Sun that actually stops it from compressing any more.

The Sun is actually in perfect balance. Gravity is trying to squeeze it together into a little ball, but this creates the right conditions for fusion. The fusion releases radiation, and it’s this radiation that pushes back against the gravity, keeping the Sun as a sphere.

We have written many articles about the Sun for Universe Today. Here’s an article about how hot the surface of the Sun is, and here’s an article about the parts of the Sun.

If you’d like more information on the Sun, check out NASA’s Solar System Exploration Guide on the Sun, and here’s a link to the SOHO mission homepage, which has the latest images from the Sun.

We have also recorded an episode of Astronomy Cast about the Sun. Check it out, Episode 30: The Sun, Spots and All.

October 7, 2009December 24, 2015 by Fraser Cain

When Was the Sun Discovered?

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When was the Sun discovered? Obviously the Sun is such an important feature in our lives, and the absolute necessity to all life on Earth. It’s kind of impossible to say when the Sun was discovered, since the first life forms on Earth probably relied on its energy. Humans have been well aware of the Sun for tens of thousands of years, and before modern astronomy had no idea what it was.

So perhaps a better question might be, when did we realize that the Sun is a star?

The Sun is incredibly important to our lives. When the Sun is in the sky, we have day. And when the Sun is below the horizon, we have night. Our biological clocks are programmed on it, and we life our lives by this routine. Ancient peoples thought the Sun was some kind of deity, and many civilizations – like the Inca in South America – worshipped it.

The Greek philosopher Anaxagoras first proposed that the Sun was a burning ball of fire, larger than a Greek Island, and not the chariot of a god. And other astronomers were able to calculate the distance to the Sun with surprising accuracy. In the modern scientific era Lord Kelvin proposed that the Sun was ball of hot liquid that was slowly cooling. But it wasn’t until the early 20th century that scientists were finally able to figure out what the source of the Sun’s energy is.

Ernest Rutherford proposed that the Sun’s heat came from radioactive decay, and it was Albert Einstein who used his famous mass-energy equation (E=mc²) to suggest that the Sun was converting mass into energy. And finally, the theoretical concept of fusion was created in the 30s by Subrahmanyan Chandrasekhar and Hans Bethe. They were able to calculate the actual fusion reactions in the Sun that convert hydrogen into helium.

I would say then, that the Sun was really discovered in the 1930s, when astrophysicists finally understood the mechanisms working inside the Sun that gave off so much energy.

We have written many articles about the Sun for Universe Today. Here’s an article about how big the Sun is, and here’s an article about the Sun’s future.

If you’d like more information about the Sun, check out NASA’s website for the SOHO spacecraft mission.

And you should check out an episode of Astronomy Cast where we talk all about the Sun. Listen here, Episode 30: The Sun, Spots and All.

References:
NASA: The Sun, Our Nearest Star
NASA: A History of Our Understanding of the Sun – A Closer Look
NASA: The Life Cycles of Stars

October 6, 2009December 24, 2015 by Fraser Cain

Earth’s Layers For Kids

My son recently came back from a science day camp with one of the coolest things. It was a model of the Earth that he had created out of modeling clay. It showed the internal structure of the Earth, and because he built it, he was able to remember all of the layers of the Earth. Very cool. So here’s a good way to learn the Earth layers for kids.

To make your own, you need some modeling clay of different colors. You start by making a ball about 1.2 cm across. This represents the Earth’s inner core. Then you make a second ball about 3 cm across. This ball represents the Earth’s outer core. Then you make a third ball about 6 cm across. This ball represents the Earth’s mantle. And finally, you make some flattened pieces of clay that will be the Earth’s crust. To make it extra realistic, make some pieces blue and others green.

Take inner core and surround it with the outer core, and then surround that by the mantle. Cover the entire mantle with a thin layer of blue, and then put on some green continents on top of the blue.

If you’ve been really careful, you should be able to take a sharp knife and slice your Earth ball in half. You should be able to see the Earth’s layers inside, just like you’d see the real Earth’s layers. And you can see that the mantle is thicker underneath the Earth’s continents than it is under the oceans.

Here’s a link with more information from Purdue University so you can do the experiment yourself.

If you’re interested in teaching your children Earth science, here’s lots of information about volcanoes for kids.

We have also recorded a whole episode of Astronomy Cast just about Earth. Listen here, Episode 51: Earth.

October 6, 2009December 24, 2015 by Fraser Cain

How Big is Earth?

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Here’s a question: how big is Earth? Let’s take a look at how big our planet is.

First, the equatorial diameter of Earth is 12,756 km. In other words, if you dug a tunnel on the equator that went straight down and went right through the center of the Earth, it would be about 12,756 km long. Just for comparison, that’s about 1.9 times the diameter of Mars. And only .09% the diameter of Jupiter.

The volume of Earth is 1.08 x 10¹² km³. Written another way, that’s 1.08 trillion cubic kilometers of rock and metal. Again, it’s about 6.6 times more volume than Mars.

The surface area of Earth is 510,072,000 square kilometers. Of that, 29.2% is covered by land and 70.8% is covered by water. Just for comparison, that’s 3.5 times as much surface area as Mars.

The mass of Earth is 5.97 x 10²⁴ kg. Here that is written out: 5,970,000,000,000,000,000,000,000 kg. Yeah, that’s a really big number. And yet, it’s only 0.3% the mass of Jupiter (and Jupiter is mostly lightweight hydrogen).

We have written many articles about Earth for Universe Today. Here’s an article about how fast Earth rotates, and here’s an article about Earth’s magnetic field.

You can learn more about Earth from NASA’s Earth Observatory, as well as NASA’s Solar System Exploration Guide.

We have also recorded an entire episode of Astronomy Cast that’s just about Earth. Listen here, Episode 51: Earth.

October 2, 2009December 24, 2015 by Fraser Cain

Nebula Pictures

Here are some cool nebula pictures taken by the Hubble Space Telescope.

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This is a cool picture of the Omega Nebula, which is also known as the Swan Nebula, or M 17. It’s located in the constellation Sagittarius, located about 5,000 light-years from Earth.

This is picture of the Cat’s Eye Nebula, a planetary nebula in the constellation Draco. This used to be a star similar to our Sun, but then it died and became a white dwarf, puffing off its outer layers into space.

This is the Carina Nebula, a star forming nebula in the Carina Constellation. It holds Eta Carinae, one of the most massive stars ever discovered, which is expected to detonate as a supernova in the next few hundred thousand years.

This is the Bubble Nebula, also known as NGC 7635. This nebula glows because of a hot central star that’s providing radiation and exciting the nebula atoms.

Full view of the Trifid Nebula. Credit: ESO

This is a picture of the Trifid Nebula taken by the European Southern Observatory. This nebula was cataloged M 20 by Charles Messier as part of his famous catalog. It’s called the “Trifid Nebula”, because it appears to be broken up into three parts.

We have written many stories about nebulae for Universe Today. Here’s an article with more details about the Trifid Nebula, and here’s an article about planetary nebulae found around heavy stars.

If you want more cool pictures of nebula, you should check out the source. Go to the Hubble Space Telescope page on nebulae.

We have recorded an entire episode of Astronomy Cast that’s just about nebulae. Listen here, Episode 111: Nebulae.

October 2, 2009April 26, 2016 by Fraser Cain

International Space Station Viewing

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Now that it’s mostly complete, the International Space Station is the brightest human-built object in space. It’s easy to see with your own eyes, the trick is knowing when to step outside and look up to see the station go overhead. If you do get your timing right, you’ll see the station as a bright star moving quickly in the sky. It only take a couple of minutes to pass through the sky above your house. Want to see the station for yourself? Here are some resources for International Space Station viewing.

The best place to go is NASA’s Human Spaceflight tracking page. This shows you the current location of the International Space Station, the Hubble Space Telescope, and any space shuttles currently in orbit.

So that shows you where the space station and shuttles are right now, but how will you know when they’re going to be passing over your part of the Earth?

NASA has a page for sighting opportunities. You can either choose your location from a list of common locations around the world, or you download an application that lets you pick your specific spot on Earth. It will then tell you the exact times ISS will be passing overhead.

If you’ve got an iPhone, check out the ISS Visibility App. This tool will calculate the next times you’ll be able to see the ISS pass overhead.

You can also use a great service called Heavens Above. This will also show you the current location of satellites, as give you times when ISS will be passing overhead.

We have written many articles about the International Space Station for Universe Today. Here’s an article about how ISS is now visible in the daytime.

We have recorded an episode of Astronomy Cast about the space shuttle. Listen to it here, Episode 127: The US Space Shuttle.

October 2, 2009December 24, 2015 by Fraser Cain

1 AU in KM

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1 AU in KM = 149,598,000 kilometers

An astronomical unit is a method that astronomers use to measure large distances in the Solar System. 1 astronomical unit, or 1 au, is the average distance from the Sun to the Earth.

The Earth’s orbit around the Sun is actually elliptical. It varies from 147 million km to 152 million km. So the measurement of an astronomical unit is just the Earth’s average distance from the Sun. That’s where the more precise measurement of 1 AU to KM (149,598,000 km) comes from.

Here are some other distances in the Solar System:
Mercury: 0.39 AU
Venus: 0.72 AU
Mars: 1.5 AU
Jupiter: 5.2 AU
Saturn: 9.6 AU
Uranus: 19.2 AU
Neptune: 30.1 AU
Pluto: 39.5 AU
Eris: 67.7 AU
Oort Cloud: 50,000 AU
Alpha Centauri: 275,000 AU

We have written many articles about large distances in space. Here’s an article that explains how far space is, and here’s an article about the distance to stars.

You can also check out this cool calculator that lets you convert astronomical units into any other distance.

We have also recorded an episode of Astronomy Cast detailing how astronomers measure distance in the Universe. Check out Episode 10: Measuring Distance in the Universe.

October 1, 2009October 31, 2016 by Tega Jessa

What are Cumulonimbus Clouds?

Cumulonimbus clouds are a type of cumulus cloud associated with thunder storms and heavy precipitation. They are also a variation of nimbus or precipitation bearing clouds. They are formed beneath 20,000 ft. and are relatively close to the ground. This is why they have so much moisture. Cumulonimbus clouds are also known as thunderheads due to their unique mushroom shape.

These clouds often produce lightning in their heart. This is caused by ionized droplets in the clouds rubbing against each other. The static charge built up create lightning. Cumulonimbus clouds need warm and humid conditions to form. This gives them the moist warm updrafts needed to produce them. In some instances a Thunderhead with enough energy can develop into a supercell which can produce strong winds, flash floods, and a lot of lightning. Some can even become tornadoes given the right conditions.

Despite the heavy rainfall these clouds produce, the precipitation normally just lasts for around 20 minutes. This is because the clouds require not only a lot of energy to form but also expend a lot energy. However, there are exceptions to the rule. There are also dry thunderstorms which are cumulonimbus clouds whose precipitation does not touch the ground. This type is common in the Western United States where the land is more arid. It is often cited as a cause of wild fires.

An overlooked result of Cumulonimbus clouds are flash floods. This was proven recently in Atlanta, Georgia area of the United States. The state had gone through a two year drought and water supplies such as creeks and rivers were low. However the fall season brought with it the end of the drought and a lot of Thunderstorms. Even though Atlanta is not near any major waterways, the resulting flash floods were on a scale seen only with areas near major rivers with wide flood plains. This demonstrates how much precipitation that Cumulonimbus clouds can produce even in a short amount of time.

Cumulonimbus clouds are a perfect example of how difference in altitude can affect the formation of clouds. Cumulonimbus clouds form in the lower part of the troposphere, the layer of the atmosphere closest to the surface of the Earth. This region due to evaporation and the greenhouse effect produces alot of the warm updrafts that make creation of cumulus and cumulonimbus clouds possible. The turbulence created by the friction between air and the surface of the Earth combined with stored heat from the sun helps to drive the majority of weather.

If you enjoyed this article there are others on Universe Today that you will be sure to enjoy. There is a great article on cloud types and another on the composition of the Earth’s atmosphere.

There are also great resources online. USA today has a great article on cloud types. You can also check out the cloud types website for the University of Illinois.

You can also check out Astronomy Cast. Episode 151 is about atmospheres.

October 1, 2009December 24, 2015 by Nicholos Wethington

Who Invented the Telescope

Galileo Galilei's telescope with his handwritten note specifying the magnifying power of the lens, at an exhibition at The Franklin Institute in Philadelphia. Credit: AP Photo/Matt Rourke

The history of the telescope dates back to the early 1600s. Galileo Galilei is commonly credited for inventing the telescope, but this is not accurate. Galileo was the first to use a telescope for the purpose of astronomy in 1609 (400 years ago in 2009, which is currently being celebrated as the International Year of Astronomy). Hans Lipperhey, a German spectacle maker, is generally credited as the inventor of the telescope, as his patent application is dated the earliest, on the 25th of September 1608.

Lipperhey combined curved lenses to magnify objects by up to 3 times, and eventually crafted sets of binocular telescopes for the Government of the Netherlands.

There exists some confusion as to who actually came up with the idea first. Lipperhey’s patent application is the earliest on record, so this is usually used to settle the debate, although another spectacle-maker, Jacob Metius of Alkmaar, a city in the northern part of the Netherlands, filed for a patent for the same device a few weeks after Lipperhey. Another spectacle-maker, Sacharias Janssen, also claimed to have invented the telescope decades after the initial claims by Lipperhey and Metius.

Regardless of the inventor, most of the earliest versions of the telescope used a curved lens made of polished glass at the end of a tube to magnify objects to a factor of 3x. To learn more about how a telescope lens works, read our article on the telescope lens in the Guide to Space.

Galileo heard news of the telescope, and constructed his own version of it without ever seeing one. Instead of the initial 3 power magnification, he crafted a series of lenses that in combination allowed him to magnify things by 8, 20 and eventually 30 times. You can obtain a version of Galileo’s original telescope today, at the Galileoscope web site.

The lens telescope is still in use today in smaller telescopes, but many larger and more powerful telescopes use a reflective mirror and eyepiece combination that was initially invented by Isaac Newton. Called a “Newtonian” telescope after its inventor, these types of telescopes have a polished mirror at the end of a tube, which reflects the image into an eyepiece at the top of the tube. More information about Newtonian telescopes can be found in our Guide to Space article here.

Here’s a few more links on the history of the telescope:

October 1, 2009April 26, 2016 by Jean Tate

What Is The Crab Nebula?

The Crab Nebula; at its core is a long dead star. Did early massive stars die in supernova explosions like this? Image credit: NASA, ESA, J. Hester and A. Loll (Arizona State University)

The Crab Nebula, or M1 (the first object in Messier’s famous catalog), is a supernova remnant and pulsar wind nebula. The name – Crab Nebula – is due to the Earl of Rosse, who thought it looked like a crab; it’s not in the constellation Cancer (the Crab), rather Taurus (the Bull).

The supernova which gave rise to the Crab Nebula was seen widely here on Earth in 1054 (and so it’s called SN 1054 by astronomers); it is perhaps the most famous of the historical supernovae. It is certainly one of the brightest (estimated to be –7 at peak), partly because it is so close (only 6,300 light-years away), and partly because it’s not hidden by dust clouds. The expansion of the nebula – as in seen-to-be-getting-bigger, rather than the-gas-is-moving-very-fast – was first confirmed in 1930.

As it was a core collapse supernova (a massive star which ran out of fuel), it left behind a neutron star; by chance, we are in line with its ‘lighthouse beam’, so we see it as a pulsar (all young neutron stars are pulsars, but not all of them have beams which point to us in one part of the cycle). It’s a pretty fast pulsar; the neutron star rotates once every 33 milliseconds. Because it’s so young and so close, the Crab Nebula pulsar was the first to be detected in the visual waveband, and also in x-rays and gamma rays. Being the source of the tremendous output of energy, from both the pulsar wind nebula and the pulsar itself, and as energy is conserved, the pulsar is slowing down, at a rate of 15 microseconds per year.

The inner part of the Crab Nebula, the pulsar wind nebula, contains lots of really hot (‘relativistic’) electrons spiraling around magnetic fields; this creates the eerie blue glow … synchrotron radiation. This makes the Crab Nebula one of the brightest objects in the x-ray and gamma ray region of the electromagnetic spectrum, and as it is a relatively steady source (unlike most high energy objects) it has given its name to a new astronomical unit, the Crab. For example, a new x-ray source may be 2 mCrab (milli-Crab), meaning 0.002 times as strong an x-ray source as the Crab Nebula.

This SEDS page has a lot more information on the Crab Nebula, both historical and contemporary.

Such an intensively studied object, no wonder there are lots of Universe Today stories on it; for example Nearly a Thousand Years After the Death of a Star, Giant Hubble Mosaic of the Crab Nebula, The Peculiar Pulsar in the Crab Nebula, Astronomers Locate High Energy Emissions from the Crab Nebula, and Evidence of Supernovae Found in Ice Core Sample.

Astronomy Cast’s Neutron Stars and Their Exotic Cousins has more on pulsars, and Nebulae more on nebulae.

Sources: Caltech Astronomy, SEDS, Stanford University SLAC