Posted on by Fraser Cain

When Was Venus Discovered?

Venus captured by Magellan.

Were you wondering when was Venus discovered? Actually, there’s no way to know. Venus is one of the 5 planets visible with the unaided eye. In fact, Venus is the brightest object in the night sky after the Sun and the Moon. When Venus is at its brightest, it even casts shadows. So even ancient people would have been aware of Venus, and so there’s no way to know who that first person was, and when it happened.

However, a better question might be to ask, when did we know that Venus was a planet? This happened about the same time that astronomers first realized the Earth was a planet too. In ancient times, astronomers used to think that the Earth was the center of the Universe, and everything orbited around it: the Sun, the Moon, the planets and the stars. One problem with this model was the strange behavior of the planets. Sometimes they would speed up, and then slow down, stop, and even go backwards in the sky.

But then in the 1500s, Nicolaus Copernicus developed his model of a Sun-centered Solar System. The Earth was just a planet, and all of the planets orbited around the Sun instead. This model explained how the planets could have such strange movements. Since the Earth is moving too, we’re really just seeing them from different perspective in they sky.

The first person to see Venus in a telescope was Galileo. Although he wasn’t able to resolve anything but a bright disk (astronomers can’t do any better today), he saw that Venus went through phases like the Moon. This was further evidence that Venus orbits around the Sun – closer than the Earth, and so we see it in various phases of illumination.

Because Venus is shrouded in clouds, astronomers weren’t able to get a better view of Venus until the first spacecraft arrived from Earth. The first spacecraft to visit Venus was NASA’s Mariner 2, which arrived at Venus in 1962. But even then the planet was still blocked by clouds. The Russian Venera landers were able to pierce through the clouds and landed on the surface to send back a few quick images of the planet’s surface. They showed a hellish world, with thick atmosphere, clogging clouds, and blasting heat, hot enough to melt lead. NASA’s Magellan spacecraft (launched in 1989) was equipped with a radar instrument that allowed it to pierce through the clouds on Venus and show the planet’s landscape, craters and volcanoes.

We’ve written many articles about the discovery of planets for Universe Today. Here’s an article about the discovery of Uranus, and here’s an article about the discovery of Neptune.

If you’d like more information on Venus, check out Hubblesite’s News Releases about Venus, and here’s a link to NASA’s Solar System Exploration Guide on Venus.

We’ve also recorded an entire episode of Astronomy Cast about Venus. Listen here, Episode 50: Venus.

Posted on by Fraser Cain

Who Discovered Pluto?

Clyde Tombaugh

Pluto is incredibly faint. You need a powerful backyard telescope to even see it as a dot, so it’s not surprising that Pluto wasn’t discovered until the modern age. Who discovered Pluto? That was the astronomer Clyde Tombaugh, who found Pluto on February 18, 1930.

Tombaugh worked as an astronomer at the Lowell Observatory in Flagstaff, Arizona. He was given the task of finding a trans-Neptunian object which was predicted by Percival Lowell and William Pickering – the search for Planet X. Tombaugh used a tool called a blink comparator to study two images of the same region of the sky taken several nights apart. He would display one image and then blink to the second image to see if any objects had moved from night to night.

And so on February 18, 1930, Tombaugh turned up just such an object moving at the right speed to be the unknown Planet X. The name “Pluto” was suggested by Venetia Burney, and 11-year old English school girl. Pluto was the name of the Roman god of the underworld, and Percival Lowell liked it because the first two letters started with PL, after his own initials.

Pluto was considered the 9th planet in the Solar System until 2006, when the International Astronomical Union reclassified Pluto as a dwarf planet, joining Eris and Ceres as the Solar System’s 3 dwarf planets. There are now only 8 planets in the Solar System.

We have written many articles about the discovery of planets in the Solar System. Here’s an article about who discovered Uranus, and here’s an article about who discovered Neptune.

If you’d like more info on Pluto, check out Hubblesite’s News Releases about Pluto, and here’s a link to NASA’s Solar System Exploration Guide to Pluto.

We’ve also recorded several episodes of Astronomy Cast about Pluto. Start here, Episode 64: Pluto and the Icy Outer Solar System.

Posted on by Fraser Cain

Who Discovered Mars?

Mars is one of the 5 planets visible with the unaided eye. On any dark night, when Mars is in the sky, it’s easy to see with your own eyes. Ancient people knew about Mars, and long ago discovered that it moves from night to night compared to the stars. So it’s impossible to know who discovered Mars. That would have been one of the first humans.

Perhaps a better question to ask is: who realized that Mars is a planet? And that discovery happened with the idea that the Earth is a planet.

In ancient times, astronomers thought that the Earth was the center of the Universe, and the Sun, Moon, planets and stars orbited around us in a set of crystalline spheres. But the motions of the planets were hard to explain; they would sometimes speed up, stop, and even reverse their direction in the sky.

But the astronomer Nicolaus Copernicus developed the view that it was the Sun that was at the center of the Solar System, and the planets orbited around it. This view neatly explained the strange motions of the planets, since the Earth was also moving around the Sun, and these quirks were really just changes in perception.

Galileo was the first person to view Mars in a telescope, and he saw not much more than a bright disk. He did take many observations over the course of the year and realized that Mars gets closer and more distant, and so larger and smaller in his telescope. As telescopes got bigger and better, astronomers were able to make out the polar ice caps on Mars, and some astronomers incorrectly thought they saw a system of canals crisscrossing the surface of the planet.

But the best views of Mars came with the first robotic exploration of Mars. The first spacecraft to arrive at Mars was NASA’s Mariner 4, launched in 1964. The first spacecraft to go into orbit around Mars was Mariner 9, in 1971. These spacecraft helped take high resolution images that revealed craters, mountains and chasms; the red landscape of Mars that we’re so familiar with today.

We’ve written many articles about the discovery of planets for Universe Today. Here’s an article about the discovery of Uranus, and another about the discovery of Neptune.

If you’d like more information on Mars, check out Hubblesite’s News Releases about Mars, and here’s a link to the NASA Mars Exploration home page.

We’ve also recorded several episodes of Astronomy Cast about Mars. Start here, Episode 52: Mars.

References:
NASA Mars Exploration
NASA: The Mariner Missions

Posted on by Fraser Cain

Google Satellite

If you’ve spent any time on the internet, you’ve probably had a chance to use either Google Earth or Google Maps. Both of these tools allow you to see a satellite view of the Earth, and zoom right in to see your home from space. But is there a Google satellite to take these photographs?

Google doesn’t actually have a satellite of their own. Instead, they use images from a variety of sources and store them on their servers. These images come from NASA satellites, USGS aerial surveys, and satellite photos from commercial operators. Google has an exclusive contract with a company called GeoEye, which recently launched their GeoEye-1 satellite. This commercial satellite blasted off on September 6, 2008, and is capable of resolving images on the Earth down to a size of 0.41 meters.

So how can you use these images? The easiest tool to use is Google Maps. This is a web-based tool that lets you browse around satellite photos of the Earth. You can zoom in and out, and type in a specific address anywhere on Earth to go right there. It also has driving directions, and all kinds of features that you can turn on and off to give you more information – like local sightseeing highlights.

The other tool that Google has created is called Google Earth. Unlike Google Maps, you actually need to download Google Earth to your local computer; PC, Mac, Linux, and even on your iPhone. Once you have the application installed, you see a 3-D version of the Earth that you can spin around, zoom in and out. You can zero in to any spot on Earth and see the highest resolution images they have available. There’s also a big community of developers who have created additional views that you can install. This lets you see additional photographs, contour maps, etc.

We have written many articles about Google satellite views. Here’s an article about how Google’s satellite had a bird’s eye view of the Obama Inauguration, and here’s a tool for Google Earth that lets you track satellite debris.

We’ve also recorded several episodes of Astronomy Cast about satellites. Listen here, Episode 100: Rockets.

Posted on by Fraser Cain

How Far Away is Pluto From the Sun?

The Pluto system seen from the surface of Hydra. Credit: NASA

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How far away is Pluto from the Sun? Pluto’s average distance from the Sun is 5.9 billion km or 3.7 billion miles.

But Pluto actually follows an elliptical orbit around the Sun. Sometimes it’s much closer to the Sun, and other times it’s further away. At its closest point, Pluto measures only 4.4 billion km from the Sun. This is close enough that a thin layer of frost evaporates from its surface, becoming a thin atmosphere around the planet. And then as it continues its journey around the Sun, Pluto gets colder again and this atmosphere refreezes onto the planet. It continues to travel out to a distance of 7.4 billion km from the Sun.

Astronomers use another method of measuring distances in the Solar System called the astronomical unit. 1 astronomical unit or AU is the average distance from the Earth to the Sun; approximately 150 million km. So we can use this to describe Pluto’s distance from the Sun. At its closest point, Pluto measures 29.7 AU. And then at its furthest point, Pluto is 49.3 AU.

We have written many articles about Pluto for Universe Today. Here’s an article about why Pluto isn’t a planet any more, and here are some pictures of Pluto.

If you’d like more info on Pluto, check out Hubblesite’s News Releases about Pluto, and here’s a link to NASA’s Solar System Exploration Guide to Pluto.

We’ve also recorded several episodes of Astronomy Cast about Pluto. Listen here, Episode 64: Pluto and the Icy Outer Solar System.

Posted on by Fraser Cain

How Far is a Light Year?

X-Ray image of Proxima Centauri. Image credit: Chandra

A light year is a standard of measurement used by astronomers to describe huge distances in the Universe. The nearest star is 4.22 light years away. The center of the Milky Way is about 26,000 light years away. But how far is 1 light year? A light year is the distance that light travels in a single year. And light travels fast.

1 lightyear is 9,460,730,472,580.8 kilometers.

Need some other measurements? A light year is 5,878,625,373,183.6 miles. And a light year is 63,241 astronomical units (1 astronomical unit, or AU is the average distance from the Earth to the Sun).

But a light year isn’t the largest measurement tool astronomers have. That’s a parsec. 1 parsec = 3.26156 light years.

We have written several articles about measuring distance for Universe Today. Here’s an article about the speed of light, and an article about a device that makes radio waves go faster than the speed of light.

If you’d like more information on light years, here’s an article about what a light year is and how it’s used, and here’s a cool video that shows you how far a light year is.

We’ve also recorded an episode of Astronomy Cast about different tools for measuring distance in the Universe. Listen here, Episode 10: Measuring Distance in the Universe.

Posted on by Fraser Cain

How Far is Jupiter from the Sun?

Jupiter's Red Spot

The distance from the Sun to Jupiter is approximately 779 million km, or 484 million miles. The exact number is 778,547,200 km.

This number is an average because Jupiter and the rest of the Solar System follows an elliptical orbit around the Sun. Sometimes it’s closer than 779 million km, and other times it’s more distant. When Jupiter is at its closest point in its orbit, astronomers call this perihelion; for Jupiter, this is 741 million km. At its most distant point, called aphelion, Jupiter gets out to 817 million km.

Astronomers use the term “astronomical unit” as another method for measuring distances in the Solar System. An astronomical unit, or AU, is the average distance from the Sun to the Earth – 150 million km. Jupiter’s average distance from the Sun is 5.2 AU. Its closest point is 4.95 AU, and its most distant point is 5.46 AU.

We have written many articles about Jupiter for Universe Today. Here’s an article about how Jupiter might be able to wreck the Solar System, and here’s an article about Jupiter’s Great Red Spot.

If you’d like more info on Jupiter, check out Hubblesite’s News Releases about Jupiter, and here’s a link to NASA’s Solar System Exploration Guide to Jupiter.

We’ve also recorded an entire episode of Astronomy Cast just about Jupiter. Listen here, Episode 56: Jupiter.

Posted on by Fraser Cain

How Far is Neptune’s from the Sun?

Neptune

Neptune’s distance from the Sun is 4.5 billion km; more specifically, it’s 4,503,443,661 km. If you’re still using the Imperial system, that’s the same as 2.8 billion miles.

But this number is actually an average. Like all of the planets in the Solar System, Neptune follows an elliptical orbit around the Sun, so it’s sometimes closer and sometimes further than this average number. When Neptune is at its closest point to the Sun, called perihelion, it’s 4.45 billion km from the Sun. And then when it’s at its most distant point from the Sun, called aphelion, it’s 4.55 billion km from the Sun.

Astronomers also measure distance in the Solar System using a measuring tool called the “astronomical unit”. 1 astronomical unit, or AU, is the average distance from the Earth to the Sun; that’s about 150 million km. So, Neptune’s average distance from the Sun is 30.1 AU. Its perihelion is 29.8 AU, and it’s aphelion is 30.4 AU.

We have written many articles about Neptune for Universe Today. Here’s an article about Neptune’s moons, and here’s an article about how Neptune’s southern pole is the warmest place on the planet.

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

We’ve also recorded an episode of Astronomy Cast all about Neptune. Listen here, Episode 63: Neptune.

Posted on by Fraser Cain

Pluto’s Distance from the Sun

The Pluto system seen from the surface of Hydra. Credit: NASA

Pluto’s distance from the Sun is 5.9 billion km – the exact number is 5,906,376,272 km. Need that figure in miles? Pluto’s distance from the Sun is 3.67 billion miles.

Keep in mind that this distance is an average. Pluto follows a highly elliptical orbit around the Sun. At the closest point of its orbit, called perihelion, Pluto gets to within 4.44 billion km from the Sun. And then at its most distant point of its orbit, called aphelion, Pluto gets to within 7.38 billion km of the Sun.

Astronomers use another term to measure distance in the Solar System called “astronomical units”. 1 astronomical unit, or AU, is the average distance from the Earth to the Sun – about 150 million km. Pluto’s perihelion is 29.7 AU, and its aphelion is 49.3 AU. Pluto’s average distance, or semi-major axis, is 39.5 AU.

We have written many articles about Pluto for Universe Today. Here’s an article about why Pluto isn’t a planet any more, and here’s an article about methane in Pluto’s atmosphere.

Want more info on Pluto, check out Hubblesite’s News Releases about Pluto, and here’s a link to NASA’s Solar System Exploration Guide to Pluto.

We’ve recorded several episodes of Astronomy Cast about Pluto. Here’s one, Episode 64: Pluto and the Icy Outer Solar System.

Posted on by Fraser Cain

How Far is Uranus from the Sun?

Uranus, seen by Voyager 2. Image credit: NASA/JPL

Uranus’ distance from the Sun is 2.88 billion km. The exact number is 2,876,679,082 km. Want that number in miles? Uranus’ distance from the Sun is 1.79 billion miles.

This number is just an average, though. Uranus follows an elliptical orbit around the Sun. At its closest point, called perihelion, Uranus gets to within 2.75 billion km of the Sun. And then at its most distant point, called aphelion, Uranus gets to within 3 billion km from the Sun.

Astronomers use another term called “astronomical units” to measure distance within the Solar System. 1 astronomical unit, or AU, is the average distance from the Earth to the Sun – about 150 million km. So in astronomical units, Uranus is an average distance of 19.2 AU. Its perihelion is 18.4 AU, and its aphelion is 20.1 AU.

We have written many articles about Uranus for Universe Today. Here’s an article about how many rings Uranus has, and here are some interesting facts about Uranus.

If you’d like more information on Uranus, check out Hubblesite’s News Releases about Uranus. And here’s a link to the NASA’s Solar System Exploration Guide to Uranus.

We’ve also recorded an entire episode of Astronomy Cast all about Uranus. Listen here, Episode 62: Uranus.