Author: Fraser Cain

Question: What kind of star is our Sun?

Answer: As you probably know, our Sun is just a star. It’s our closest, most familiar star, but it’s still just a star. With a great big Universe out there, populated with countless stars, astronomers have been able to see examples of stars in all shapes, sizes, metal content and ages.

According to their system of classification, the Sun is known as a yellow dwarf star. This group of stars are relatively small, containing between 80% and 100% the mass of the Sun. So the Sun is at the higher end of this group. The official designation is as a G V star.

Stars in the this classification have a surface temperature between 5,300 and 6,000 K, and fuse hydrogen into helium to generate their light. They generally last for 10 billion years.

But there’s more to this question, because G V Stars can experience several different stages. Some are newly forming, others are in their middle ages, and others are nearing the end of their lives.

Our Sun is right in the middle ages, in a time known as the main sequence. It has already lived for 4.3 billion years, and will likely last another 7 billion years or so. At that point, it will balloon into a red giant star, and eventually collapse down into a white dwarf.

The Sun also belongs to the Population I group of stars, which contain relatively large amounts of heavier elements. The first ever stars, made from pure hydrogen and helium are Population III. These exploded as supernovae, producing fusing the lighter elements into heavier and heavier elements. Our Sun, then, contains the metal from previous generations of stars that went supernova.

Some other examples of the yellow dwarf star group include Alpha Centauri, Tau Ceti and 51 Pegasi.

For the quick answer, the Sun is a Population I yellow dwarf star, in the main sequence. Why is the Sun yellow? It’s actually because of the Earth’s atmosphere. If you saw it from space, it would actually look white.

Reference:
NASA Starchild: The Sun

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Ready…
1. How many planets are in the Solar System?

• a. 8
• b. 9
• c. 10
• d. 12

2. How old is the Solar System?

• a. 65 million years
• b. 1.2 billion years
• c. 4.6 billion years
• d. 13.7 billion years

3. What is the biggest moon in the Solar System?

• a. The Moon
• b. Ganymede
• c. Titan
• d. Triton

4. What is the least dense planet in the Solar System?

• a. Jupiter
• b. Saturn
• c. Uranus
• d. Neptune

5. What is the most dense planet in the Solar System?

• a. Mercury
• b. Venus
• c. Earth
• d. Mars

6. Where is the tallest mountain in the Solar System?

• a. Mercury
• b. Venus
• c. Earth
• d. Mars

7. How many planets are known to have life?

• a. 0
• b. 1
• c. 2
• d. 3

8. What is the most abundant element in the Solar System?

• a. oxygen
• b. helium
• c. carbon
• d. hydrogen

Answers: 1. a, 2. c, 3. b, 4. b, 5. c, 6. d, 7. b, 8. d

Well, how did you do with our Solar System quiz?

Here’s a link to a 3 D Solar System

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• Solar System Simulator – It’s not really a game, but the Solar System simulator from NASA is one of the coolest online tools you’ll find. It lets you simulate the entire Solar System, so you can see what things look like from any planet, moon or spaceship. Very cool.
• Solar System Jigsaw – This interactive tool from BBC lets you build jigsaw puzzles on the Internet of the Solar System. You can make them more difficult or easy.
• Solar System Games – Windows on the Universe has a whole system of Solar System games you can try out. Some are built in Java, and others are programmed in Macromedia Flash, so you might need to install plugins to make them work.
• Science@NASA – NASA’s science website for kids has a series of games you can play online. You can explore Mars, or compare the size of planets.
• NASA Space Place – NASA has many sites for kids, and most of these have online games you can play. This Solar System game lets you see how well you know your moons and planets.
• Surfing the Solar System – This game from the Astronomical Society of the Pacific lets you go on a treasure hunt through the Solar System.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

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The Solar System holds some big records. Want to know which are the largest in the Solar System?

Largest star
Well, there’s only one star in the Solar System: the Sun, so it’s the automatic winner here. The Sun measures 1.4 million km across. That’s so big, you could put 109 Earths side by side to match the size of the Sun. Astronomers have theorized that the Sun might have a companion star on a long orbit, but if was anywhere as large or bright as the Sun, we’d definitely see it. So this is a record that won’t fall.

Largest Planet
The largest planet in the Solar System is Jupiter, which measures 143,000 km across its equator. That’s the same as 11 Earths. In fact, Jupiter is so large that it has 2.5 times the mass of all the other planets in the Solar System… combined. One interesting note is the Jupiter actually can’t get any bigger. If you added more mass to Jupiter, the increased gravity would actually pull it together harder, and it would shrink.

Largest Moon
The largest moon in the Solar System is Jupiter’s moon Ganymede, which measures 5,268 km across. It’s actually larger than Mercury, as well as Pluto and the dwarf planets. If it orbited the Sun, it might be a planet in its own right. Astronomers used to think that Saturn’s moon Titan was the largest moon, but then they realized that Titan’s thick atmosphere made it just appear larger.

Largest Mountain
The largest mountain in the Solar System is Olympus Mons on Mars. This ancient shield volcano measures 27 km tall. That makes it 3 times the elevation of Mount Everest on Earth, and 2.6 times the height of Mauna Kea from its base below the ocean. Astronomers think that Olympus Mons got so big because Mars never developed plate tectonics. A hotspot opened up to the surface of Mars, and just stayed there for billions of years, pouring out lava and building up the mountain. Olympus Mons is also the largest volcano in the Solar System.

Largest Asteroid
The largest object in the asteroid belt is Ceres, measuring 974 km across. But there’s a problem, Ceres has been upgraded to the status of a dwarf planet, like Pluto. This means that the largest actual asteroid is Vesta, also located in the asteroid belt. Vesta measures 530 km across, and contains about 9% of the mass of the asteroid belt.

Largest Crater
The largest crater in the Solar System is on the Moon. It’s called the South Pole-Aitken Basin, and measures about 2,500 km across. Astronomers on Earth didn’t realize it was a huge crater until the first spacecraft orbited the Moon. That’s because we can’t see the crater itself from our vantage point, just a huge rim of mountains. South Pole-Aitken Basin might actually be the second biggest crater in the Solar System. That’s because new research indicates that a much larger impact site might be on Mars, called the Borealis Basin – measuring 8,500 km across, but more proof needs to be gathered.

Here’s an article about the largest planet, and the largest moon in the Solar System.

Here’s an article about that recent news on Borealis Basin.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

Reference:
NASA Solar System Exploration Guide
NASA SOHO: Our Star, The Sun
NASA: Moon’s Largest Impact Basin
NASA Photo Journal: Olympus Mons

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This is a a diagram of the Solar System. It was released shortly before the International Astronomical Union made its final decision about whether Pluto should be a planet or not. In the end, they decided that Pluto is not a planet. But for a few days, it was possible that there would be 11 planets in the Solar System, including Pluto, Eris and the asteroid Ceres. This image of the Solar System shows them all with the Sun.

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This is a montage photo of the Solar System, with a picture of a Sun and all the planets, as well as all the moons in the Solar System. This lets you see just how many objects there really are in the Solar System.

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This is another montage of the planets, dwarf planets, comets and asteroids in the Solar System. It’s one of the older Solar System pictures that we’ve seen.

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Here’s a Solar System image with all the planets correctly categorized. In this, we can see a picture of Pluto, Ceres and Eris are correctly designated as dwarf planets.

Want more images of planets? Here are some pictures of Mars, pictures of Venus, pictures of Saturn, pictures of Pluto, and pictures of Jupiter. Here’s an article about a 3D Solar System.

One of the best resources for photographs of the Solar System is NASA’s Planetary Photojournal. You can also check out Hubble’s photographs of the Solar System.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

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This image contains all of the largest objects in the Solar System. You can print this diagram of the Solar System, as well as this handy list of all the planets.

The Sun – The central star in the Solar System

Mercury – The first planet in the Solar System. It’s also the smallest planet in the Solar System. Mercury takes just 88 days to complete an orbit around the Sun.

Venus – The second planet from the Sun. In many ways, Venus is a twin to our own Earth. It has nearly the same size and mass as Earth, but the thick atmosphere on Venus makes surface temperatures hot enough to melt lead. Venus is also unusual because it rotates backwards to all the other planets.

Earth – Our home planet, the third planet from the Sun. Earth is the only planet in the Solar System known to support life. This is because we are at just the right distance from the Sun so that our planet doesn’t get too hot or too cold. We also have one moon – the Moon.

Mars – Mars is the fourth planet from the Sun, and is much smaller and colder than the Earth. Temperatures on Mars can rise to 20-degrees C, but dip down to -140-degrees C in the northern winters. Mars is thought to be the best candidate for life elsewhere in the Solar System. Mars has two small, asteroid-shaped moons: Phobos and Deimos.

Ceres – Ceres is the first dwarf planet in the Solar System, and the largest member of the asteroid belt.

Jupiter – Jupiter is the 5th planet from the Sun, and the largest planet in the Solar System. Jupiter has as much mass as 2.5 times all the rest of the planets combined – almost all of this mass is hydrogen and helium; although, scientists think it has a solid core. Jupiter has at least 63 moons.

Saturn – Saturn is the 6th planet from the Sun, and is well known for its beautiful system of icy rings. Saturn is almost as large as Jupiter, but it has a fraction of Jupiter’s mass, so it has a very low density. Saturn would float if you could find a tub of water large enough. Saturn has 60 moons at last count.

Uranus – Uranus is the 7th planet from the Sun, and the first planet discovered in modern times; although, it’s just possible to see with the unaided eye. Uranus has a total of 27 named moons.

Neptune – Neptune is the 8th and final planet in the Solar System. Neptune was only discovered in 1846. It has a total of 13 known moons.

Pluto – Pluto isn’t a planet any more. Now it’s just a dwarf planet. Pluto has one large moon, called Charon, and then two smaller moons.

Eris – The next dwarf planet in the Solar System is Eris, which was only discovered back in 2003. In fact, it was because of Eris that astronomers decided to reclassify Pluto as a dwarf planet.

I hope you find this diagram of the Solar System helpful.

Reference:
NASA Solar System Exploration Guide