Fraser Cain, Author at Universe Today

June 29, 2013March 16, 2017 by Fraser Cain

What is the Distance to the Moon?

The short answer is, the average distance to the Moon is 384,403 km (238,857 miles). But before you go thinking that this is the final answer, you need to consider a few things. For starters, note the use of the word “average”. This refers to the fact that the Moon orbits around the Earth in an elliptical pattern, which means that at certain times, it will be father away; while at others, it will be closer.

Hence, the number 384,403 km, is an average distance that astronomers call the semi-major axis. At its closest point (known as perigee) the Moon is only 363,104 km (225,622 miles) away. And at its most distant point (called apogee) the Moon gets to a distance of 406,696 km (252,088 miles).

This means that distance from the Earth to the Moon can vary by 43,592 km. That’s a pretty big difference, and it can make the Moon appear dramatically different in size depending on where it is in its orbit. For instance, the size of the Moon can vary by more than 15% from when it’s at its closest to when it’s at the most distant point.

It can also have a dramatic effect on how bright the moon appears when it is in its Full phase. As one might expect, the brightest full Moons occur when the Moon is at the closest, which are typically 30% brighter than when it’s fathest away. When it’s a Full Moon, and it’s a close Moon, it’s known as a Supermoon; which is also known by it technical name – perigee-syzygy.

To get an idea of what this all looks like, check out the animation above that was released by the Goddard Space Flight Center Scientific Visualization Studio in 2011. The animation shows the geocentric phase, libration, position angle of the axis, and apparent diameter of the Moon throughout the year, at hourly intervals.

At this point, a good question to ask would be: how do we know how far away the Moon is? Well, that depends on when we’re talking. In the days of ancient Greece, astronomers relied on simple geometry, the diameter of the Earth – which they had already calculated to be the equivalent of 12,875 km (or 8000 miles) – and the measurements of shadows to make the first (relatively) accurate estimates.

Having observed and recorded how shadows work over a long period of history, the ancient Greeks had determined that when an object is placed in front of the Sun, the length of a shadow this generates will always be 108 times the diameter of the object itself. So a ball measuring 2.5 cm (1 inch) across and placed on a stick between the Sun and the ground will create a triangular shadow that extends for 270 cm (108 inches).

This reasoning was then applied to the phenomena of Lunar and Solar Eclipses.

In the former, they found that the Moon was imperfectly blocked by the shadow of the Earth, and that the shadow was roughly 2.5 times the width of the Moon. In the latter, they noted that the Moon was of sufficient size and distance to block out the Sun. What’s more, the shadow it would create terminated at Earth, and would end in the same angle that the shadow of the Earth does – making them different-sized versions of the same triangle.

Using the calculations on the diameter of the Earth, the Greeks reasoned that the larger triangle would measure one Earth diameter at its base (12,875 km/8000 miles) and be 1,390,000 km (864,000 miles) long. The other triangle would be the equivalent of 2.5 Moon diameters wide and, since the triangles are proportionate, 2.5 Moon orbits tall.

Adding the two triangles together would yield the equivalent of 3.5 Moon orbits, which would create the largest triangle and gave the (again, relatively) accurate measurement of the distance between the Earth and the Moon. In other words, the distance is 1.39 million km (864,000 miles) divided by 3.5, which works out to around 397,500 km (247,000 miles). Not exactly bang on, but not bad for ancient peoples!

Lunar Laser Ranging Experiment. NASA — *Lunar Laser Ranging Experiment from the Apollo 11 mission. Credit: NASA*

Today, millimeter-precision measurements of the lunar distance are made by measuring the time it takes for light to travel between LIDAR stations here on the Earth and retroreflectors placed on the Moon. This process is known as the Lunar Laser Ranging experiment, a process that was made possible thanks to the efforts of the Apollo missions.

When astronauts visited the Moon more than forty years ago, they left a series of retroreflecting mirrors on the lunar surface. When scientists here on Earth shoot a laser at the Moon, the light from the laser is reflected right back at them from one of these devices. For every 100 quadrillion photons shot at the Moon, only a handful come back, but that’s enough to get an accurate appraisal.

Since light is moving at almost 300,000 kilometers (186,411 miles) per second, it takes a little more than a second to make the journey. And then it takes another second or so to return. By calculating the exact amount of time it takes for light to make the journey, astronomers are able to know exactly how far the Moon is at any time, down to millimeter accuracy.

From this technique, astronomers have also discovered that the Moon is slowly drifting away from us, at a glacial rate of 3.8 cm (1.5 inches) a year. Millions of years in the future, the Moon will appear smaller in the sky than it does today. And within a billion years or so, the Moon will be visually smaller than the Sun and we will no longer experience total solar eclipses.

We’ve written many articles about the Moon for Universe Today. Here’s an article about how LCROSS discovered buckets of water on the Moon, and here’s an article about how long it takes to get to the Moon.

If you’d like more info on the Moon, check out NASA’s Solar System Exploration Guide on the Moon, and here’s a link to NASA’s Lunar and Planetary Science page.

We have recorded several episodes of Astronomy Cast about the Moon. Here’s a good one, Episode 113: The Moon, Part 1.

June 20, 2013October 19, 2016 by Fraser Cain

Where Are All the Aliens? The Fermi Paradox

Consider this. The Universe is enormous.

There are as many as four-hundred billion stars in our galaxy: the Milky Way. And there are more than one-hundred-and-seventy billion galaxies in the observable Universe. Most of those stars have planets, and many of those planets have got to contain useful minerals and fall within their star’s habitable zone where liquid water is present.

The conditions for life are probably everywhere.

But where are all the aliens?

And think about this.

The Universe has been around for 13.8 billion years. Human beings originated 200,000 years ago, so we’ve only been around for 0.01% of the age of the Universe. An intelligent species could arise on any one of those countless worlds, and broadcast their existence to the entire galaxy.

Once a species developed interstellar travel, they could completely colonize our galaxy within a few tens of millions of years; just a heartbeat in the age of the Universe.

So where are they?

As far as we know, Earth is the only place in the Universe where life has arisen, let alone developed an intelligent civilization.

This baffling contradiction is known as the Fermi Paradox, first described in 1950 by the physicist Enrico Fermi.

Scientists have been trying to resolve this mystery for decades, listening for radio signals from other worlds. We’ve only sampled a fraction of the radio spectrum, and so far, we haven’t detected anything that could be a signal from an intelligent species.

How can we explain this?

Maybe we really are the only planet in the entire Universe to develop life. Maybe we’re the first civilization to reach this level of advancement in the entire galaxy. But with so many worlds out there, that really seems unlikely.

Artist impression of an asteroid impact on early Earth (credit: NASA)

Maybe civilizations destroy themselves when they reach a certain point. Nuclear weapons, global warming, killer epidemics, and overpopulation could all end humanity. Asteroids could strike the planet and wipe us out. But would this happen to every single civilization? one-hundred-percent of them? Even if ninety-nine-percent of civilizations destroy themselves, we’d still have a couple that made it through and fully colonized the galaxy.

Maybe they’re just too far away, and our signals can’t reach each other. But then, self-replicating probes could traverse those distances and leave a local artifact in every single star system.

Maybe we can’t understand their signals or recognize their artifacts. Maybe, but if aliens constructed a series of artifacts on Earth, I think we’d notice them. The aliens would have experience creating obvious structures.

Maybe they’re just too alien and we just can’t understand them. Maybe we’re too insignificant, and they don’t think we’re even worth talking to. We don’t need to talk to them to know they exist. If they flew through our Solar System, ignoring us, we’d still know they’re around.

Maybe they’re not talking to us on purpose, and we’re really in some kind of galactic zoo. Or aliens have a Prime Directive, and they’re not allowed to talk to us. Again, all the aliens? Not a single one has gotten through and snuck us some evidence?

There are many other potential solutions to the Fermi Paradox, but I personally find them all insufficient. The Universe is big, and old, and if extraterrestrial life is anything like us, it wants to multiply and spread out.

Perhaps the most unsettling thought is that something happens to 100% of intelligent civilizations that prevents them from exploring and settling the galaxy. Maybe something good, like the discovery of a transportation system to another Universe. Or maybe something bad, like a destructive technology that has destroyed every single civilization before us.

How do you feel about the Fermi Paradox? How do you resolve the contradictions? Whatever the solution, it’s really fun to think about.

We’ve recorded a couple of episodes of Astronomy Cast about the Drake Equation and the Fermi Paradox, and we did a sequel episode called, Solutions to the Fermi Paradox.

June 17, 2013October 18, 2016 by Fraser Cain

What is the Hottest Planet in the Solar System?

Earth is the third planet from the Sun, and the climate here is just right for life. Here in our Solar System, there are planets both hotter and colder than Earth.

So… which one is the hottest?

You might think it’s Mercury, the planet closest to the Sun. Mercury orbits at a distance of only 58 million kilometers, travelling in a blast-furnace of scorching radiation. Its temperature can skyrocket to 700 Kelvin, or 426 degrees Celsius on the sunward side. In the shadows, temperatures plunge down to 80 Kelvin, which is -173 degrees Celsius

Mercury sure is hot, but Venus is hotter.

Venus imaged by Magellan Image Credit: NASA/JPL

Venus is much further from the Sun, orbiting at a distance of more than 108 million kilometers. Average temperature there is a hellish 735 Kelvin, or 462 degrees Celsius – hot enough to melt lead.

Venus remains that same temperature no matter where you go on the planet. At the North Pole? 735 Kelvin. At night? 735 Kelvin. Daytime at the equator? You get the point.

So, why is Venus so much hotter than Mercury, even though it’s further away from the Sun? It’s all about the atmosphere.

Mercury is an airless world, not unlike the Moon. Venus, has a very thick atmosphere of CO2, which adds incredible pressure, and traps in the heat.

Consider our own planet. When you stand at sea level on Earth, you’re experiencing one atmosphere of pressure. But if you could stand on the surface of Venus – and trust me, you don’t want to – you’d experience ninety-two times as much atmospheric pressure. This is the same kind of pressure as being a kilometer underneath the surface of the ocean.

Venus also shows us what happens when carbon dioxide levels just keep on rising. Radiation from the Sun is absorbed by the planet, and the infrared heat emitted is trapped by the carbon dioxide, which creates a runaway greenhouse effect.

You might think a planet this hot with such extreme temperature and pressure, would be impossible to explore.

And if you did, you’d be wrong.

The Soviets sent a series of spacecraft called Venera, which parachuted down through the thick atmosphere and returned images from the surface of Venus. Although the first few missions were failures, this taught the Soviets just how hellish the Venusian environment really is.

Venera 13 made it down to the surface in nineteen-eighty-one and survived for one-hundred-and-twenty-seven minutes, sending back the first color pictures of Venus’ surface.

The hottest planet in our solar system is Venus,

When it comes to temperature, distance from the Sun matters, but it takes a backseat to wrapping a planet in a atmospheric blanket of carbon dioxide.

We release this explainer videos every Monday and Thursday from the Universe Today YouTube Channel. Click here to Subscribe to the channel.

June 14, 2013October 18, 2016 by Fraser Cain

Closest Star to the Sun

This is a classic trick question. Ask a friend, “what is the closest star?” and then watch as they try to recall some nearby stars. Sirius maybe? Alpha something or other? Betelgeuse?

The answer, obviously, is the Sun; that massive ball of plasma located a mere 150 million km from Earth.

Let’s be more precise; what’s the closest star to the Sun?

Closest Star

You might have heard that it’s Alpha Centauri, the third brightest star in the sky, just 4.37 light-years from Earth.

But Alpha Centauri isn’t one star, it’s a system of three stars. First, there’s a binary pair, orbiting a common center of gravity every 80 years. Alpha Centauri A is just a little more massive and brighter than the Sun, and Alpha Centauri B is slightly less massive than the Sun. Then there’s a third member of this system, the faint red dwarf star, Proxima Centauri.

It’s the closest star to our Sun, located just a short 4.24 light-years away.

Closest Star, Proxima Centauri — Proxima Centauri

Alpha Centauri is located in the Centaurus constellation, which is only visible in the Southern Hemisphere. Unfortunately, even if you can see the system, you can’t see Proxima Centauri. It’s so dim, you need a need a reasonably powerful telescope to resolve it.

Let’s get sense of scale for just how far away Proxima Centauri really is. Think about the distance from the Earth to Pluto. NASA’s New Horizons spacecraft travels at nearly 60,000 km/h, the fastest a spacecraft has ever traveled in the Solar System. It will have taken more than nine years to make this journey when it arrives in 2015. Travelling at this speed, to get to Proxima Centauri, it would take New Horizons 78,000 years.

Proxima Centauri has been the nearest star for about 32,000 years, and it will hold this record for another 33,000 years. It will make its closest approach to the Sun in about 26,700 years, getting to within 3.11 light-years of Earth. After 33,000 years from now, the nearest star will be Ross 248.

What About the Northern Hemisphere?

Bernard's Star, one of the closest stars to the Sun — Bernard’s Star

For those of us in the Northern Hemisphere, the closest visible star is Barnard’s Star, another red dwarf in the constellation Ophiuchus. Unfortunately, just like Proxima Centauri, it’s too dim to see with the unaided eye.

The closest star that you can see with the naked eye in the Northern Hemisphere is Sirius, the Dog Star. Sirius, has twice the mass and is almost twice the size of the Sun, and it’s the brightest star in the sky. Located 8.6 light-years away in the constellation Canis Major – it’s very familiar as the bright star chasing Orion across the night sky in Winter.

How do Astronomers Measure the Distance to Stars?

They use a technique called parallax. Do a little experiment here. Hold one of your arms out at length and put your thumb up so that it’s beside some distant reference object. Now take turns opening and closing each eye. Notice how your thumb seems to jump back and forth as you switch eyes? That’s the parallax method.

To measure the distance to stars, you measure the angle to a star when the Earth is one side of its orbit; say in the summer. Then you wait 6 month, until the Earth has moved to the opposite side of its orbit, and then measure the angle to the star compared to some distant reference object. If the star is close, the angle will be measurable, and the distance can be calculated.

You can only really measure the distance to the nearest stars this way, since it only works to about 100 light-years.

The 20 Closest Stars

Here is a list of the 20 closest star systems and their distance in light-years. Some of these have multiple stars, but they’re part of the same system.

Alpha Centauri – 4.2
Barnard’s Star – 5.9
Wolf 359 – 7.8
Lalande 21185 – 8.3
Sirius – 8.6
Luyten 726-8 – 8.7
Ross 154 – 9.7
Ross 248 – 10.3
Epsilon Eridani – 10.5
Lacaille 9352 – 10.7
Ross 128 – 10.9
EZ Aquarii – 11.3
Procyon – 11.4
61 Cygni – 11.4
Struve 2398 – 11.5
Groombridge 34 – 11.6
Epison Indi – 11.8
Dx Carncri – 11.8
Tau Ceti – 11.9
GJ 106 – 11.9

According to NASA data, there are 45 stars within 17 light years of the Sun. There are thought to be as many as 200 billion stars in our galaxy. Some are so faint that they are nearly impossible to detect. Maybe, with technological improvements, scientists will find even closer stars.

June 10, 2013June 5, 2017 by Fraser Cain

Ten Interesting Facts About Saturn

This article comes from our archive, but we updated it with this video.

Saturn is my absolute favorite object in the night sky. When I was a child, I had a dog-eared book on the Solar System, which I read over and over, stopping and staring with wonder at the section on Saturn. How could a planet have rings of ice? What would it be like to fly out and visit the planet, to see the rings with your own eyes. How did it get all those strange moons?

When I was 14, I purchased my first telescope, a 4-inch Newtonian from a local company in Vancouver. It was summer, and one of the first planets, appearing just after sunset was Saturn. And my telescope had just enough power and magnification to resolve the planet and its famous rings. In fact, when I first looked at Saturn through the eyepiece, I couldn’t believe that I was now seeing the planet with my own eyes. It didn’t look quite like the photographs, but my imagination could fill in the gaps.

From those first observations, my fascination with astronomy and Saturn only grew, leading me to a career in science journalism. It’s funny to think how far I’ve come, and how I can trace everything back to those warm summer nights, looking at Saturn.

Think you know everything about Saturn? Think again. Here are 10 facts about Saturn, some you may know, and some you probably didn’t know.

1. Saturn is the least dense planet in the Solar System

Saturn has a density of 0.687 grams/cubic centimeter. Just for comparison, water is 1 g/cm³ and the Earth is 5.52. Since Saturn is less dense than water, it would actually float like an apple if you could find a pool large enough. Of course, why you’d want to ruin a pool with all that hydrogen, helium and ices…

2. Saturn is a flattened ball

Saturn spins so quickly on its axis that the planet flattens itself out into an oblate spheroid. Seriously, you see this by eye when you look at a picture of Saturn; it looks like someone squished the planet a little. Of course, it’s the rapid spinning that’s squishing it, causing the equator to bulge out.

While the distance from the center to the poles is 54,000 km, the distance from the center to the equator is 60,300 km. In other words, locations on the equator are approximately 6,300 km more distant from the center than the poles.

We have a similar phenomenon here on Earth, where points on the equator are more distant from the center of the Earth, but on Saturn, it’s much more extreme.

Cassini's drawings of Saturn — Cassini’s drawings of Saturn

3. The first astronomers thought the rings were moons.

When Galileo first turned his rudimentary telescope on Saturn in 1610, he could see Saturn and its rings, but he didn’t know what he was looking at. He though that the rings might actually be two large moons stuck to either side of Saturn – ears maybe?

It wasn’t until 1655 that the Dutch astronomer Christian Huygens used a better telescope to observe Saturn. He had the resolution to realize that the moons on either side of Saturn were actually rings: “a thin, flat ring, nowhere touching, and inclined to the ecliptic.” Huygens was also the first person to discover Saturn’s largest moon, Titan.

4. Saturn has only been visited 4 times by spacecraft

Only 4 spacecraft sent from Earth have ever visited Saturn, and three of these were just brief flybys. The first was Pioneer 11, in 1979, which flew within 20,000 km of Saturn. Next came Voyager 1 in 1980, and then Voyager 2 in 1981. It wasn’t until Cassini’s arrival in 2004 that a spacecraft actually went into orbit around Saturn and captured photographs of the planet and its rings and moons.

Unfortunately, there are no future plans to send any more spacecraft to Saturn. A few missions have been proposed, including such radical concepts as a sailboat that could traverse the liquid methane lakes on Titan.

5. Saturn has 62 moons

Jupiter has 67 discovered moons, but Saturn is a close second with 62. Some of these are large, like Titan, the second largest moon in the Solar System. But most are tiny – just a few km across, and they have no official names. In fact, the last few were discovered by NASA’s Cassini orbiter just a few years ago. More will probably be discovered in the coming years.

6. The length of a day on Saturn was a mystery until recently

Determining the rotation speed of Saturn was actually very difficult to do, because the planet doesn’t have a solid surface. Unlike Mercury, you can’t just watch to see how long it takes for a specific crater to rotate back into view; astronomers needed to come up with a clever solution: the magnetic field.

To determine the rotational speed of Saturn, astronomers had to measure the rotation of the planet’s magnetic field. By one measurement, Saturn takes 10 hours and 14 minutes to turn on its orbit, but when Cassini approached Saturn, it clocked the rotation at 10 hours and 45 minutes. Astronomers now agree on an average day of 10 hours, 32 minutes and 35 seconds.

7. Saturn’s rings could be old, or they could be young.

It’s possible that Saturn’s rings have been around since the beginning of the Solar System – around 4.54 billion years ago. Or maybe they’re relatively brand new compared to the age of Saturn. Astronomers still don’t fully understand the origin of Saturn’s rings.

They might have formed recently, when a 300-km ice moon was torn apart by Saturn’s gravity, forming a ring around the planet.

It’s also possible that they’re the left over material when Saturn formed in the solar nebula. The material in the rings might have gotten jostled by Saturn’s gravity, and never could pull together into a cohesive Moon.

But astronomers have also found that the ring material looks just too clean to have formed so long ago, and could be as young as 100 million years old. It’s all just a big mystery.

Credit: NASA/JPL-Caltech/Space Science Institute

8. Sometimes the rings disappear

Well, they don’t actually disappear, but they look like they’re going away. Saturn’s axis is tilted, just like Earth. From our point of view, we see Saturn’s changing position as it takes its 30 year journey around the Sun. Sometimes, the rings are fully open, and we see them in all their glory, but other times we see the rings edge on – it looks like they’ve disappeared. This happened in 2008-2009, and will happen again in 2024-2025.

9. You can see Saturn with your own eyes

Saturn appears as one of the 5 planets visible with the unaided eye. If Saturn is in the sky at night, you can head outside and see it. To see the rings and the ball of the planet itself, you’ll want to peer through a telescope. But you can amaze your friends and family by pointing out that bright star in the sky, and let them know they’re looking at Saturn.

10. There could be life near Saturn

Not life on Saturn; the planet is way too hostile to support life. But there could be life on one of Saturn’s moons: Enceladus.

Water vapour geysers on Enceladus. Credit: NASA/JPL

NASA’s Cassini spacecraft recently discovered ice geysers blasting out of Enceladus’ southern pole. This means that some process is keep the moon warm enough that water can remain a liquid underneath the surface. And wherever we find liquid water on Earth, we find life.

Want to learn more about Saturn?

We’ve recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn’s Moons.

June 6, 2013October 16, 2016 by Fraser Cain

How Can You See a Satellite View of Your House?

This is an article from our archive, but we’ve updated it with this spiffy video.

Every now and then I go looking for a free aerial view of my home. It’s amazing what’s available through the internet now, totally free. Thanks to commercial Earth observation satellites, and internet tools that make these photos accessible through the internet, it’s easy to see your house from space.

In our modern space age, there are more than 8,000 satellites currently orbiting the Earth. The vast majority of these are relaying data to and from the Earth, and many are equipped with high power cameras. Just look up into the sky any night, and you’re sure to see satellite after satellite passing overhead. But what are some ways you can get access to these satellite and aerial images of your house?

Satellite Images of the Whole Earth
If you want to go way out and just see a satellite image of the entire planet, there are some solutions for you: weather satellites. For example, NOAA’s Geostationary Operational Environmental Satellites (GOES) release images of an entire hemisphere of planet Earth every 3 hours. From these images you can see major weather patterns affecting parts of the Earth. But you really can’t see any specific spot on Earth with any detail.

What is really cool about these satellite views is that they’re live. The weather systems you’re seeing in those images are happening on the planet right now.

If you don’t want a live view, and really just want to see a beautiful view of the Earth’s hemisphere, check out these images produced by NASA. Here’s a composite photograph that shows the Earth’s Western Hemisphere, and here’s a view of the Earth’s Eastern Hemisphere.

There were also some amazing new satellite images of the Earth released from the European Space Agency’s 3rd generation Meteosat spacecraft.

Zoom in. Let’s see Satellite Pictures of Houses
If those whole Earth pictures don’t give you enough detail, let’s zoom in, and see some pictures of houses from space. The best tool on the market, in my opinion, is the service from Google Maps. All you need is a web browser and a connection to the internet. When you first start up, Google Maps displays a satellite view of North America. You can then zoom in, or pan the camera around to see any location on Earth. You can also type in the address of the location that you want to see. Once you do that, you’ll get a free satellite view of your house. You can save the image or print it off.

View Larger Map

Another cool tool from Google is Google Earth. You can access by going to http://earth.google.com. The main difference between Google Maps and Google Earth is that you have to download and install Earth on your local computer (they have a version for PCs, Mac, Linux, and even the iPhone). Once you’ve downloaded and installed Google Earth, you can see a 3-dimensional view of Earth that you can zoom in and out and spin around. You can type in your address and get a view of your house from above. I actually like the printing function of Google Earth better, since it’s using your printer directly, and not going through the web browser.

And if you really hate using products from Google, no problem. There are similar services from Yahoo and Microsoft. Microsoft’s mapping service used to be called MSN Maps, and now it’s been changed to Bing Maps with their new identity. The Yahoo service is called Yahoo Maps, and it’s very similar to Google Maps. The two services do have some big differences, though, and there’s a cool application that lets you see the two of them side-by-side. I used it for my home and found that Google Maps has better resolution maps for my city.

Where Do All these Pictures Come From?
Google Maps and the other internet mapping services are really just customers for the satellite services that actually take these photographs from space. There are a few major services on the market, including GeoEye. GeoEye’s main competitors include DigitalGlobe and Spot Image.

Each company has a fleet of Earth observation satellites, with a capability of resolving features on the surface of the Earth as small as about 45 cm (18 inches). In other words, an object 45 centimeters across would appear as a single pixel in their photographs.

Private earth observation satellites:

GeoEye – 5 satellites: IKONOS, OrbView-2, OrbView-3, GeoEye-1, GeoEye-2 (in 2013).
DigitalGlobe – 4 satellites: Early Bird 1, Quickbird, WorldView-1, Worldview-2
Spot Image – 2 satellites: Spot 4, Spot 5

Each of these services allow customers to purchase satellite imagery directly, but I’ll warn you, the prices are extremely high: hundreds or even thousands of dollars for satellite imagery. You typically can’t buy directly from the satellite company itself, but through their international partners.It’s better to stick to the free sources.

Are These Live Satellite Views?
When you look at these amazing views of your house from space, you might wonder if this is live. If you walk outside and look up, will you be able to see yourself from space? Unfortunately, no. All of the free satellite images you’re accessing were captured by various spacecraft over the last couple of years.

You can actually get a pretty good sense of when the picture was taken by the image of your property. For example, in the photo of my house from space, I can see a car that I sold a couple of years ago. Obviously, this image isn’t live, it’s at least a couple of years old – even a decade old in some cases. A live satellite view of your house, is still a few years off.

There are some services which will give you a live view of Earth from space. For example, you can access a live broadcast from NASA’s International Space Station. About 40% of the time, if you follow this link you can see a live view of Earth from the space station. Another service called Urthecast will be attaching a high definition camera to the International Space Station in 2013 to broadcast a live view of Earth from space.

Streaming video by Ustream

June 3, 2013October 16, 2016 by Fraser Cain

How Many Stars are There in the Universe?

When we look at the night sky, filled with stars, it’s hard to resist counting. Just with the unaided eye, in dark skies, you can see a few thousand.

How many stars are there in the entire Universe? Before we get to that massive number, let’s consider what you can count with the tools available to you.

Perfect vision in dark skies allows us to see stars down to about magnitude 6. But to really make an accurate census of the total number of stars, you’d need to travel to both the Northern and Southern Hemispheres, since only part of the sky is visible from each portion of the Earth. Furthermore, you’d need to make your count over several months, since a portion of the sky is obscured by the Sun. If you had perfect eyesight and traveled to completely dark skies in both the Northern and Southern Hemispheres, and there was no Moon, you might be able to get to count up almost 9,000 stars.

With a good pair of binoculars, that number jumps to about 200,000, since you can observe stars down to magnitude 9. A small telescope, capable of resolving magnitude 13 stars will let you count up to 15 million stars. Large observatories could resolve billions of stars.

But how many stars are out there? How many stars are there in the Milky Way?

According to astronomers, our Milky Way is an average-sized barred spiral galaxy measuring up to 120,000 light-years across. Our Sun is located about 27,000 light-years from the galactic core in the Orion arm. Astronomers estimate that the Milky Way contains up to 400 billion stars of various sizes and brightness.

A few are supergiants, like Betelgeuse or Rigel. Many more are average-sized stars like our Sun. The vast majority of stars in the Milky Way are red dwarf stars; dim, low mass, with a fraction of the brightness of our Sun.

As we peer through our telescopes, we can see fuzzy patches in the sky which astronomers now know are other galaxies like our Milky Way. These massive structures can contain more or less stars than our own Milky Way.

There are spiral galaxies out there with more than a trillion stars, and giant elliptical galaxies with 100 trillion stars.
And there are tiny dwarf galaxies with a fraction of our number of stars.

So how many galaxies are there?

According to astronomers, there are probably more than 170 billion galaxies in the observable Universe, stretching out into a region of space 13.8 billion light-years away from us in all directions.

And so, if you multiply the number of stars in our galaxy by the number of galaxies in the Universe, you get approximately 10²⁴ stars. That’s a 1 followed by twenty-four zeros.

That’s a septillion stars.

But there could be more than that.

It’s been calculated that the observable Universe is a bubble of space 47 billion years in all directions.

It defines the amount of the Universe that we can see, because that’s how long light has taken to reach us since the Big Bang.

This is a minimum value, the Universe could be much bigger – it’s just that we can’t ever detect those stars because they’re outside the observable Universe. It’s even possible that the Universe is infinite, stretching on forever, with an infinite amount of stars. So add a couple more zeros. Maybe an infinite number of zeroes.

That’s a lot of stars in the Universe.

Additional Resources:
How Many Stars Can you See?
Astronomy Cast: How Big is the Universe?
How Big is Our Observable Universe
Astronomy Cast: The Observable Universe
How Many Galaxies in the Universe?

May 30, 2013October 16, 2016 by Fraser Cain

How Old Is The Earth?

This article comes from the Universe Today archive, but was updated with this spiffy video.

How old is the Earth? Scientists think that the Earth is 4.54 billion years old. Coincidentally, this is the same age as the rest of the planets in the Solar System, as well as the Sun. Of course, it’s not a coincidence; the Sun and the planets all formed together from a diffuse cloud of hydrogen billions of years ago.

In the early Solar System, all of the planets formed in the solar nebula; the remnants left over from the formation of the Sun. Small particles of dust collected together into larger and larger objects – pebbles, rocks, boulders, etc – until there were many planetoids in the Solar System. These planetoids collided together and eventually enough came together to become Earth-sized.

At some point in the early history of Earth, a planetoid the size of Mars crashed into our planet. The resulting collision sent debris into orbit that eventually became the Moon.

How do scientists know Earth is 4.54 billion years old? It’s actually difficult to tell from the surface of the planet alone, since plate tectonics constantly reshape its surface. Older parts of the surface slide under newer plates to be recycled in the Earth’s core. The oldest rocks ever found on Earth are 4.0 – 4.2 billion years old.

Scientists assume that all the material in the Solar System formed at the same time. Various chemicals, and specifically radioactive isotopes were formed together. Since they decay in a very known rate, these isotopes can be measured to determine how long the elements have existed. And by studying different meteorites from different locations in the Solar System, scientists know that the different planets all formed at the same time.

Failed Methods for Calculating the Age of the Earth
Our current, accurate method of measuring the age of the Earth comes at the end of a long series of estimates made through history. Clever scientists discovered features about the Earth and the Sun that change over time, and then calculated how old the planet Earth is from that. Unfortunately, they were all flawed for various reasons.

Declining Sea Levels – Benoit de Maillet, a French anthropologist who lived from 1656-1738 and guessed (incorrectly) that fossils at high elevations meant Earth was once covered by a large ocean. This ocean had taken 2 billion years to evaporate to current sea levels. Scientists abandoned this when they realized that sea levels naturally rise and fall.
Cooling of the Earth – William Thompson, later known as Lord Kelvin, assumed that the Earth was once a molten ball of rock with the same temperature of the Sun, and then has been cooling ever since. Based on these assumptions, Thompson calculated that the Earth took somewhere between 20 and 400 million years to cool to its current temperature. Of course, Thompson made several inaccurate assumptions, about the temperature of the Sun (it’s really 15 million degrees Kelvin at its core), the temperature of the Earth (with its molten core) and how the Sun is made of hydrogen and the Earth is made of rock and metal.
Cooling of the Sun – In 1856, the German physicist Hermann Ludwig Ferdinand von Helmholtz attempted to calculate the age of the Earth by the cooling of the Sun. He calculated that the Sun would have taken 22 million years to condense down to its current diameter and temperature from a diffuse cloud of gas and dust. Although this was inaccurate, Helmholtz correctly identified that the source of the Sun’s heat was driven by gravitational contraction.
Rock Erosion – In his book, The Origin of Species by Means of Natural Selection, Charles Darwin proposed that the erosion of chalk deposits might allow for a calculation of the minimum age of the planet. Darwin estimated that a chalk formation in the Weald region of England might have taken 300 million years to weather to its current form.

Orbit of the Moon – George Darwin, the son of Charles Darwin, guessed that the Moon might have been formed out of the Earth, and drifted out to its current location. The fission theory proposed that the Earth’s rapid rotation caused a chunk of the planet to spin off into space. Darwin calculated that it had taken the Moon at least 56 million years to reach its current distance from Earth. We now know the Moon was probably formed when a Mars-sized object smashed into the Earth billions of years ago.
Salinity of the Ocean – In 1715, the famous astronomer Edmund Halley proposed that the salinity of the oceans could be used to estimate the age of the planet. Halley observed that oceans and lakes fed by streams were constantly receiving more salt, which then stuck around as the water evaporated. Over time, the water would be come saltier and saltier, allowing an estimate of how long this process has been going on. Various geologists used this method to guess that the Earth was between 80 and 150 million years old. This method was flawed because scientists didn’t realize that geologic processes are extracting salt out of the water as well.

Radiometric Dating Provides an Accurate Method to Know the Age of the Earth
In 1896, the French chemist A. Henri Becquerel discovered radioactivity, the process where materials decay into other materials, releasing energy. Geologists realized that the interior of the Earth contained a large amount of radioactive material, and this would be throwing off their calculations for the age of the Earth. Although this discovery revealed flaws in the previous methods of calculating the age of the Earth, it provided a new method: radiometric dating.

Geologists discovered that radioactive materials decay into other elements at a very predictable rate. Some materials decay quickly, while others can take millions or even billions of years to fully decay. Ernest Rutherford and Frederick Soddy, working at McGill University, determined that half of any isotope of a radioactive element decays into another isotope at a set rate. For example, if you have a set amount of Thorium-232, half of it will decay over a billion years, and then half of that amount will decay in another billion years. This is the source of the term “half life”.

By measuring the half lives of radioactive isotopes, geologists were able to build a measurement ladder that let them accurately calculate the age of geologic formations, including the Earth. They used the decay of uranium into various isotopes of lead. By measuring the amount of three different isotopes of lead (Pb-206, Pb-207, and Pb-208 or Pb-204), geologists can calculate how much Uranium was originally in a sample of material.

If the Solar System formed from a common pool of matter, with uniformly distributed Pb isotopes, then all objects from that pool of matter should show similar amounts of the isotopes. Also, over time, the amounts of Pb-206 and Pb-207 will change because as these isotopes are end-products of uranium decay. This makes the amount of lead and uranium change. The higher the uranium-to-lead ratio of a rock, the more the Pb-206/Pb-204 and Pb-207/Pb-204 values will change with time. Now, supposing that the source of the Solar system was also uniformly distributed with uranium isotopes, then you can draw a data line showing a lead-to-uranium plot and, from the slope of the line, the amount of time which has passed since the pool of matter became separated into individual objects can be computed.

Bertram Boltwood applied this method of dating to 26 different samples of rocks, and discovered that they had been formed between 92 and 570 million years old, and further refinements to the technique gave ages between 250 million to 1.3 billion years.

Geologists set about exploring the Earth, seeking the oldest rock formations on the planet. The oldest surface rock is found in Canada, Australia and Africa, with ages ranging from 2.5 to 3.8 billion years. The very oldest rock was discovered in Canada in 1999, and estimated to be just over 4 billion years old.

This set a minimum age for the Earth, but thanks to geologic processes like weathering and plate tectonics, it could still be older.

Meteorites as the Final Answer to the Age of the Earth
The problem with measuring the age of rocks on Earth is that the planet is under constant geological change. Plate tectonics constantly recycle portions of the Earth, blending it up and forever hiding the oldest regions of the planet. But assuming that everything in the Solar System formed at the same time, meteorites in space have been unaffected by weathering and plate tectonics here on Earth.

Geologists used these pristine objects, such as the Canyon Diablo meteorite (the fragments of the asteroid that impacted at Barringer Crater) as a way to get at the true age of the Solar System, and therefore the Earth. By using the radiometric dating system on these meteorites, geologists have been able to determine that the Earth is 4.54 billion years old within a margin of error of about 1%.

Sources:
Understanding Science – Lord Kelvin
USGS Age of the Earth
Lord Kelvin’s Failed Scientific Clock
The Role of Radioactive Decay
Astronomy Cast Episode 51: Earth
Oldest Rock Formations Found

May 27, 2013October 16, 2016 by Fraser Cain

How Many Planets are in the Solar System?

I’m just going to warn you, this is a controversial topic. Some people get pretty grumpy when you ask: how many planets are in the Solar System? Is it eight, ten, or more?

I promise you this, though, we’re never going back to nine planets… ever.

When many of us grew up, there were nine planets in the Solar System. It was like a fixed point in our brains.

As kids, memorizing this list was an early right of passage of nerd pride: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

But then in 2005, Mike Brown discovered Eris, an icy object thought to be about the same size as Pluto, out beyond its orbit.

That would bring the total number of planets to ten. Right? There’s no turning back, textbooks would need to be changed.
In order to settle the dispute, the International Astronomical Union met in 2006, and argued for, and against Pluto’s planethood. Some astronomers advocated widening the number of planets to twelve, including Pluto, its moon Charon, the Asteroid Ceres, and the newly discovered Eris.

In the end, they changed the definition of what makes a planet, and sadly, Pluto doesn’t make the cut:

Here are the new requirements of planethood status:

A planet has to orbit the Sun. Okay fine, Pluto does that.
A planet needs enough gravity to pull itself into a sphere. Okay, spherical. Pluto’s fine there too.
A planet needs to have cleared out its orbit of other objects. Uh oh, Pluto hasn’t done that.

For example, planet Earth accounts for a million times the rest of the material in its orbit, while Pluto is just a fraction of the icy objects in its realm.

The final decision was to demote Pluto from planet to dwarf planet.

But don’t despair, Pluto is in good company.

There’s Ceres, the first asteroid ever discovered, and the smallest of the dwarf planets. The surface of Ceres is made of ice and rock, and it might even have a liquid ocean under its surface. NASA’s Dawn mission is flying there right now to give us close up pictures for the first time.

Haumea, named after the Hawaiian goddess of fertility, is about a third the mass of Pluto, and has just enough gravity to pull itself into an ellipsoid, or egg shape. Even though it’s smaller, it’s got moons of its own.

Makemake, a much larger Kuiper belt object, has a diameter about two-thirds the size of Pluto. It was discovered in 2005 by Mike Brown and his team. So far, Makemake doesn’t seem to have any moons.

Eris is the most massive known dwarf planet, and the one that helped turn our definition of a planet upside-down. It’s 27% more massive than Pluto and the ninth most massive body that orbits the Sun. It even has a moon: Dysnomia.

And of course, Pluto. The founding member of the dwarf family.

Want an easy way to remember the eight planets, in order? Just remember this mnemonic: my very excellent mother just served us noodles.

For all you currently writing angry tweets to Mike Brown, hold on a sec. Changing Pluto’s categorization is an important step that really needed to happen.

The more we discover about our Universe, the more we realize just how strange and wonderful it is. When Pluto was discovered 80 years ago, we never could have expected the variety of objects in the Solar System. Categorizing Pluto as a dwarf planet helps us better describe our celestial home.

So, our Solar System now has eight planets, and five dwarf planets.

May 23, 2013October 16, 2016 by Fraser Cain

How to See the International Space Station

The International Space Station is one of the most complicated machines ever built and the largest object ever assembled in space.

At any time there are up to six astronauts on board, each originating from one of fifteen different nations on Earth. It orbits at an altitude of approximately four-hundred kilometers, and completes an orbit around the Earth every ninety-two minutes and fifty seconds. The station has a mass of four-hundred-and-twenty metric tonnes, and contains a dozen pressurized modules, and many more unpressurized modules, trusses and solar panels.

It truly is a feat of human ingenuity.

But did you know that the International Space Station is one of the brightest objects in the night sky? And it’s easy to see if you know when, and where, to look.

In fact, with your ability to find the station you can amaze your friends and neighbours.

The best place to start is NASA’s Spot the Station website. Enter your Country, Region, City along with an email address or mobile phone number. Then give your preference for notifications in the evening, morning or both and that’s it.

About twelve hours before the station is due to fly overhead, you’ll get a notification from NASA. Depending on your location, you might get notified a couple of times a week, or as rarely as once a month. As soon as you get the notification, create an alarm on your phone for about a minute before the flyover.

When the alarm goes off, take your friends outside and look to the West.

Station's path across the sky — Station’s path across the sky

The station orbits the Earth from West to East, so you’ll see it appear on the Western horizon as a very bright star, moving rapidly across the sky. It will take only few minutes to cross the entire sky.

The station moves so quickly if you’re using a telescope you will have a tough time tracking its movement. A nice pair of binoculars will make it look a lot brighter, and even let you see the H-shape of its solar panels. But even viewing it with the naked eye is a great experience.

NASA’s website is just one of the many ways you can get notifications.

If you use Twitter, follow @twisst. They can figure out your location and then send you a notification when the station is about to fly overhead via Twitter.

There are also dozens of Android and iPhone apps that will perform this function; many of which are free to use.

If you’ve never seen the station, head on over to NASA and set up a notification right away.

Then kick back and let orbital mechanics bring the station to your backyard at a time that’s convenient for you.

Want more details? We’ve got a detailed guide on how to View the International Space Station for Beginners, and How to Photograph the International Space Station.