Planetary Science

Planetary Science is the study of Planets and the Solar System, a combination of Astronomy and Earth Sciences. Find questions about the different planets and more.

84,154 Questions
Planetary Science

How bright would the sun appear to be to an observer on Earth if the Sun were four times farther from the Earth than it actually is?

The sun would be 4 times less bright than it is now. The brightness of the sun follows an inverse square law

Planet Jupiter
Planetary Science
The Moon

What is the closest planet near Earth's moon?

Well, it is obviously Earth. But if you meant the nearest planet (excluding Earth), it varies from time to time; at their closest approaches Venus is around 45,000,000 km away to the Earth and Mars is around 80,000,000 km away from the Earth. But they aren't always or even usually at their closest approach to Earth. Whether Earth and the Moon are closer to Venus or to Mars depends on the three planets' relative positions in their orbits. When Mars is at opposition it is only about 80 million km from Earth and the Moon (60 million km if the opposition occurs at Mars' perihelion), and when Venus Is at superior conjunction it is 225 million km away.

Religion & Spirituality
Planetary Science
Planet Earth

Does the discovery of life on other planets contradict with religions?

No, if life is discovered on other planets then it will not contradict with religions.

Below are opinions from view points of different religions:A. In the Islamic religion:
  • It is mentioned in Quran, Muslim's holy book, that God (the Creator) is the Lord of all worlds. God says in Quran that God is the Lord of what we know and what we don't. God says in Quran that we have known only little. Accordingly, nothing in Quran or Islam religions contradicts with the possibility of discovering life on other planets. God says in Quran (meaning English translation):
    • {In the name of Allah (God), the Entirely Merciful, the Especially Merciful. (1) [All] praise is [due] to Allah, Lord of the worlds...} [Quran, chapter 1, verse 1-2]
    • {To Him belongs what is in the heavens and what is on the earth and what is between them and what is under the soil. (6)} [Quran, chapter 20, verse 6]
    • {And they ask you, [O Muhammad], about the soul. Say, "The soul is of the affair of my Lord. And mankind have not been given of knowledge except a little." (85)} [Quran, chapter 17, verse 85]
    • {The seven heavens and the earth and whatever is in them exalt Him. And there is not a thing except that it exalts [Allah] by His praise, but you do not understand their [way of] exalting. Indeed, He is ever Forbearing and Forgiving. (44)} [Quran, chapter 17, verse 44]
    • There is a religious explanation, even before such discoveries, revise these verses:

      {28. And He it is Who sendeth down the saving rain after they have despaired, and spreadeth out His mercy. He is the Protecting Friend, the Praiseworthy. 29. And of His portents is the creation of the heaven and the earth, and of whatever beasts He hath dispersed therein. And He is Able to gather them when He will.}[quoted from, Meanings of the Golrious Quran, by Marmaduke Pickthall]

      Here the mention of Heavens and earth, meant the whole universe,

    • {12. Allah it is who hath created seven heavens, and of the earth the like thereof. The commandment cometh down among them slowly, that ye may know that Allah is Able to do all things, and that Allah surroundeth all things in knowledge.}So, for certain there is life on other parts of the universe, whether we discovered this or not.

The above Quran verses confirm that we still don't know except a little and that God is the Creator of all worlds what we know and what we don't. Accordingly, discovering life on other planets doesn't contradict with Quran or with Islam religion.

B. In the Christian religion:
  • There is nothing in the Bible that says God created life only on this planet. Doesn't even rule out other intelligent life in the universe. But after seeing the mess we created in this world, He would probably not try again.
  • Most certainly. The Bible speaks nothing of life on other planets, though some may craft an explantion through through vague references and loose endings. However, the fact remains that would seriously hinder Christian credibility as an absolute religion whose implications are universal. What I think is more interesting is that this does not rule out the existence of God as creator, merely the existence of a God we thought we knew. This discovery would force us as an entire race to seriously question our faith - at least where we rest our faith - because a discovery like that would prove beyond doubt many religions false.
  • The original unadulterated idea of God transmitted to us by Adam through Noah is one of having no form, no physical or natural bounds, one beyond perception and even conception (the imagination). That theology is completely invulnerable and impervious to a discovery of life at another location. Only theologies which are self (human)-centric could be weakened by such a discovery.
  • Read the Scriptures as God speaks to Abraham. He says that he has created worlds without end. The Scriptures do not say that life and God's children are restricted to just this earth. If God would create one world where Billions have lived, why would He not create another place, where more of His children can be tested whether they will follow what is right or not. There are Christian churches that use other holy Christian writings as well as those gathered into 'The Bible'. Certain of those writings reveal that God has created "worlds without number" ... and "the inhabitants thereof are as numberless as the sands upon the seashore" [Moses 1:28] ... 'and the inhabitants thereof, are begotten sons and daughters unto God', ... "But only an account of this earth, and the inhabitants thereof, give I unto you ... For behold there are many worlds ..." [Moses 1:35] Here is also a scientific way to test the truthfulness of the Gospel. Put it to the test. Exercise a little faith, read the scriptures, pray about it and wait for answer. And when you receive the answer, feed it and let it grow. It's an experiment. Try it. (And to express an idea that God has killed millions is incorrect. We have the freedom to choose; it's a sacred right. We are judged by those choices. We are free to choose and those who have decided to murder suffer their choices.)
  • The simple answer is no. God has no limits, and the only limit in religion is the mind of man, who is unable to comprehend this. The real answer is: the Baha'i Faith teaches that there are an infinity of other planets out there, and each is alive with God's creatures. They may be very unlike us, but they exist.
  • For some religions, the answer would be "we already knew that". For most others, the answer would be "we already knew that, it's just that you misunderstood us before".
  • I do not think that it would debunk religion. Science and religion serve VERY different needs of humanity, religion is a matter of faith; faith is belief without proof. Science is a tool to understand our surroundings and has zero room for "faith". I do not think that religion and science are mutually exclusive.
  • Actually, the Bible itself says there is intelligent life other than man. There are intelligent beings called angels, cherubim, seraphim, there are the four beasts which stand before the throne of God. The Bible is full of "life on other planets." Also, Christian writers in the last century wrote many sci-fi stories about encountering life on other planets, etc. Some were better than others, but the concept is not foreign to Orthodox Christianity. And if you incorporate Christian fantasy writings such as The Chronicles of Narnia and Lord of the Rings, the treatment of the idea of intelligence other than man is even more fully developed. The "problem" posed by the possibility of life on other planets is mostly a moral question. If there are other beings, do they have to obey the same rules as we do? What if their religion were contradictory to ours? Would that challenge the truth of ours? If they experienced a "fall" as our first ancestors did, do they need redemption? In fact, I once heard about a sci-fi story written by a non-Christian author (I have not read it) in which humans land on a planet and Jesus is there getting ready to die on the cross. Several of the earthmen try to stop His execution but Jesus won't let them. He tells them it's necessary for Him to die there, just as He had to die on earth.
  • In every single religious book eg. "Bible" it doesn't say that life doesn't exist on other planets. But in most religious books it states that there are nine planets eg. Mercury, which have life on them... Life being some form eg. Bacteria, not necessarily "Aliens" and in my personal opinion UFO's are a load of CRAP, you can see in UFO sighting pics and videos that its all rubbish. But religions' explanation would be along the lines of what it says in their religious books.
  • The Bible does mention life in other planets that has not gotten corrupted by sin like in earth.
C. Other views
    • Who said God only created Planet Earth? God created the entire Universe and everything and everyone in it. Why would "religion" be debunked by discovery of life on another planet? Personally, I don't have "religion." I have a RELATIONSHIP with the God of this universe. To me, discovery of life on another planet would be quite exciting scientifically, and for me, it would strengthen and enhance my faith and beliefs. God is not a limited being.
    • To debunk a religion with such a discovery, you would have to first identify a particular sect that insists no alien life can exist. Not even all sects of Christianity make such a claim.
    • Rather than 'debunking' religion, I believe the opposite would hold least for a while. The discovery of life on other worlds - I'm assuming you mean sentient life? - would be a momentous thing, indeed. I think it would draw people to churches and religious communities in a way that only life-altering events can - for emotional and spiritual support and guidance, to pray for protection or to give thanks, for any number of personal and spiritual reasons. Once the discovery becomes 'old news' people will probably be drawn back to their old ways and habits, but, at first, there would be a huge revival of religion.
    • This is an interesting type of question that has no definite answer, and will not be known until it actually happens. Every person will be different if and when it happens, and of course by human nature there will be people who panic and be full of fear. However, I am sure most people who are religious will believe that instead of debunking God and religion, it would instead be a testament to his/her/its/their power. God is supposed to be diverse, with unlimited power and love. If you believe that, then it should be difficult to believe that he would create one single lonely planet in this huge, possibly infinite universe.
    • There is no direct contradiction between the Bible and the possibility of life on other planets.
    • many traditional Americans view the story of Genesis as describing a process of creating one unique place for life. They also point to John 3:16 (which describes God sending his only son to Earth) to show that Earth is the only place for life. Both of these interpretations really stretch the text to say more than is on paper. Most religions based on the Pentatuch (Judaism, Catholicism, Protestantism, etc.) have traditions that intelligent life exists only here on Earth. Some Asian and African religions teach that the universe is full of life.
Planetary Science
The Moon
Sailor Moon

How was the moon created?

Theories of the Origin of the Moon

After years of research, studying gamma rays and rock samples from the Earth and the Moon, it is generally accepted that the ages of the Earth and the Moon are the same. There are several theories on its formation.

  • IMPACT : One theory is that it was formed from the Earth's crust, following the impact of a large (Mars-sized) asteroid. A long string of rocky fragments were blown out from the Earth in the form of a trail, which coalesced into the Moon. Supporting this, the Earth has a large iron core but the Moon does not : the Earth's iron would have already sunken into the core by the time the giant impact happened.
  • COACCRETION : Another theory, advocated by Edward Roche, is known as coaccretion. It proposes the concurrent information of both the Earth and the Moon from clouds of space material. As a result the new Moon gets spun by the Earth's gravity field and starts to circle the Earth. The fact is that all smaller solar bodies appear to be irregularly shaped, but larger ones are nearly spherical.
  • FISSION : The fission theory states that the Moon long ago split off from a fast-rotating Earth, like mud flung from a spinning bicycle wheel. The present Pacific Ocean basin is the most popular site for the part of the Earth from which the Moon may have come. This is not supported by evidence of higher rotational speed in the past.
  • CAPTURE : If the Moon formed separately, it could have come close enough to the Earth's gravitational field to be trapped. The angle of orbital approach would have to be within narrow parameters in relationship to the moving centre of the orbiting Earth. The chance of this occurrence is very low without some other gravitational interaction.

The prevailing theory at present is some form of early impact, possibly by a co-orbiting object that fused with the Earth after the collision, but that blasted loose the material which later formed the Moon.

Most widely accepted scientific explanation

It is believed that the moon formed around 4.5 billion years ago and only a few hundred million years after the Earth.

Today, based on the evidence, the most widely accepted scientific explanation for the formation of the Moon is called the Giant Impact Hypothesis. According to this model, the Moon formed from debris that was the result of a huge collision. Not long after Earth formed, a proto-planet about the size of Mars (often called Theia) smashed into it at a low angle and relatively low speed. The cataclysmic impact rendered the entire Earth molten, and caused significant amounts of its mantle and crust to be blown into space. The metallic core of the impactor sunk through the Earth's mantle to fuse with Earth's core, thereby depleting the Moon of metallic material and explaining its unusual composition. The force of the collision is also believed to have been responsible for tilting the Earth at angle of 23.5 degrees, allowing for seasons.

The debris from the collision began orbiting the Earth and gathered together through gravity to form a sphere: the Moon. The Moon formed surprisingly quickly, possibly in less than a month but no more than a century. It started out closer to the Earth than it is today, and must have caused massive tides. Slowly, due to conservation fo angular momentum, it moved further and further out until it got to the familiar orbit it is now. Even today, the Moon is receding from Earth by an inch and a half every year, but it will take billions of years for the Moon to escape from Earth's gravity altogether.

There are still some problems with the Giant Impact hypothesis that need to be overcome. For example, the ratios of the Moon's volatile elements (such as water) are not explained by this model. Also, the moon's oxygen isotopic ratios are essentially identical to Earth's when they should be different. Regardless, the Giant Impact model is currently the best explanation scientists have based on the evidence that has been gathered, and holds more weight than the other theories for the Moon's formation.

  • The Fission Theory: This theory proposes that the Moon was once part of the Earth and somehow separated from the Earth early in the history of the solar system. The present Pacific Ocean basin is the most popular site for the part of the Earth from which the Moon came. This theory was thought possible since the Moon's composition resembles that of the Earth's mantle and a rapidly spinning Earth could have cast off the Moon from its outer layers. However, the present-day Earth-Moon system should contain "fossil evidence" of this rapid spin and it does not. Also, this hypothesis does not have a natural explanation for the extra baking the lunar material has received.
  • The Capture Theory: This theory proposes that the Moon was formed somewhere else in the solar system, and was later captured by the gravitational field of the Earth. The Moon's different chemical composition could be explained if it formed elsewhere in the solar system, however, capture into the Moon's present orbit is very improbable. Something would have to slow it down by just the right amount at just the right time, and scientists are reluctant to believe in such "fine tuning". Also, this hypothesis does not have a natural explanation for the extra baking the lunar material has received.
  • The Condensation Theory: This theory proposes that the Moon and the Earth condensed individually from the nebula that formed the solar system, with the Moon formed in orbit around the Earth. However, if the Moon formed in the vicinity of the Earth it should have nearly the same composition. Specifically, it should possess a significant iron core, and it does not. Also, this hypothesis does not have a natural explanation for the extra baking the lunar material has received.
Planetary Science

Dusty and gaseous material orbiting a star is called what?

It is most likely to be the stars jet trail of burned out gas which then began to orbit the star itself because of its immense mass.

Planetary Science

What degree is the earth's tilt?

Earth spins around on an imaginary line called an axis that runs from the north pole, through the center of the Earth, and on to the south pole. When we say that "Earth has an axial tilt of 23.5 degrees," we are comparing the direction of the axis to another imaginary line that is perpendicular to--or, at a right angle to--the ecliptic plane. The ecliptic plane is an imaginary disc that extends from the equator of the Sun, out to the edge of the solar system. It is on this disc that the 8 major planets circle the Sun; looking down from above the solar system, each planet's orbit would be a circle that was drawn on the ecliptic plane.

The earth is tilted at about 23.45 degree as compared to the ecliptic, the plane of the Earth's orbit around the Sun.

Planetary Science
Planet Mars
Planet Mercury

List the planets in order from the sun?

These are the 8 planets listed in order from the sun are,

1) Mercury

2) Venus

3) Earth

4) Mars

5) Jupiter

6) Saturn

7) Uranus

8) Neptune

Pluto is no longer a planet, it is a dwarf planet.

Planetary Science
Planet Mars

How long does it take to get to Mars from Earth?

Unmanned probes from Earth can take from 7 months to two years to reach Mars, depending on when they are launched and how fast they can travel. The direct distance can vary from about 58 million kilometers to more than 400 million kilometers.

The distance is at least 36 million miles (58 million km).

So the minimum time would be:

At 70 MPH -- 56 years

At 500 MPH -- 8 years

At Mach 1 (0.34 km/sec) -- 5.4 years (5 years, 5 months)

At 40,000 MPH (fastest Voyager speed) -- 38 days

Manned Missions

The most commonly offered figure is "Six months there, and six months back". That is based on current (2012) technology, and there are currently no solid plans for a manned flight to Mars. By the time man does inevitably make a manned flight to Mars, there may be newer technologies in space travel that shorten the travel time.
The travel time to Mars would depend on the relative position of the planets in their orbits. The shortest time at closest approach, given current rocket propulsion, is about 7 to 8 months. This is the estimated transit time for the Mars probe of December, 2011.

It is possible to get there faster using more powerful rockets, but this would only reduce the time to 2 months at best (48 days at 30,000 mph). The round trip time could be 6 months or more, unless the mission waited for the next close alignment of the planets, which occurs every 26 months.
Travelling to mars can take anything form 3 to 9 months based upon 2 aspects. Firstly, it depends how far away Mars is away from Earth because as you already know, an obit is not completely circular, ; the pathway is more of an elliptical shape and the second point is how fast your space craft is going; the average speed a rocket or space shuttle can go is 7 miles per second.
Unmanned probes from Earth can take from 7 months to two years to reach Mars, depending on when they are launched and how fast they can travel. The direct distance can vary from about 58 million kilometers to more than 400 million kilometers.

The proposed NASA manned mission estimates about 200 days to reach Mars and 200 days to return. But one trip would take much longer unless the mission stayed on Mars for a year until the planets were again lined up in relation to their orbits. The actual yearly minimum distance is from 60 to 100 million kilometers.
Unmanned probes from Earth can take from 7 months to two years to reach Mars, depending on when they are launched and how fast they can travel. The direct distance can vary from about 58 million kilometers to more than 400 million kilometers.
The space probes launched to Mars take about 260 days (8 to 9 months) to reach Mars. Some high-speed transfer orbits could make the trip in as little as 130 days using current propulsion technology.
Depends on the propulsion. Under typical rocket power, upwards of 4 months if launched at the right time. With ion propulsion, it could take as little as 38 days to reach Mars.
It could take as little as 6 months or so. The most recent spacecraft to be sent there took 10 months (Pheonix), so its likely that a spacecraft carrying humans may go a little faster to limit the amount of time in space.
7 months if travelled by a satellite/space probe. But 3 years if done with someone actually in the rocket. .
Approximately 2 years one way.

Planetary Science
The Moon

What is the circle of light around the sun called?

The circle of light around the sun is called a Corona. The corona can usually only be seen during a total solar eclipse. When this happens it can be seen as an irregularly shaped glow surrounding the moon.

Earth Sciences
Planetary Science
Planet Mars

What is Mars made of?

Mars is made of rock and iron oxides. It's surface is covered in mountains, volcanoes, valleys, ice caps and dried up river beds. Mars is also very dry like a desert. It is also red because of the iron oxide in the pulverized rock dust.
Mars is a planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the volcanoes, deserts and polar ice caps of Earth.

Planetary Science
The Solar System

What are the names of the planets in our solar system?

Names of the Planets

  1. Mercury - named after the Roman mythological counterpart of Hermes, the Greek god of messengers, commerce, thieves, and sports. Named as such because of the speed at which it revolves around the Sun.
  2. Venus - named after the Roman mythological counterpart of Aphrodite, the Greek goddess of love and beauty.
  3. Earth (also known by its Latin name, "Terra") - named after the titan of the Earth from Greek mythology.
  4. Mars - named after the Roman mythological counterpart of Ares, the Greek god of war.
  5. Jupiter - named after the Roman mythological counterpart of Zeus, the Greek king of the gods.
  6. Saturn - named after the Roman god of agriculture and harvest, Saturn. He is the Roman mythological counterpart of Cronus (Kronos), the Greek titan who fathered Zeus.
  7. Uranus - named after the Greek mythological Father of the Sky, Ouranos. "Uranus" is the Latin translation of "Ouranos".
  8. Neptune - named after the Roman mythological counterpart of Poseidon, the Greek god of the seas.

Jupiter, Saturn, Uranus, and Neptune are all made primarily of gas and are very large. Mercury, Venus, Earth and Mars are small and made of rock.

My Very eager Mother Just Served Us Noodles

Pluto was considered a planet from 1930 to 2006, but was reclassified as a "dwarf planet", because many Pluto-like bodies were discovered in orbits past Neptune.

The dwarf planets are Ceres, Pluto, Haumea, Eris, and Makemake.

The names of our planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto. Pluto isn't really classified as a planet anymore, (which I hate) but it is now a Dwarf Planet.

Another way to remember the planets names is to make a cool rhyme or little

poem. Like this one:

My Very Eager Mother Just Sold Us Notebooks
According to the 2006 definition by the IAU, there are 8 "planets" in our solar system:

  1. Mercury
  2. Venus
  3. Earth
  4. Mars
  5. Jupiter
  6. Saturn
  7. Uranus
  8. Neptune

Furthermore, there are a number of large moons orbiting the gas giant planets, and there are several dwarf planets including the former "planet" Pluto (reclassified in 2006). Many new candidates for the dwarf category have been found past the orbit of Neptune.
venus, mercury, saturn, earth, mars,jupiter,uranus,neptune and the sun
The planets in our solar system are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. In 2006 the IAU redefined planets and reclassified Pluto, demoting it from planet to minor or dwarf planet - so now we are considered to have only eight. If there is a ninth, it would have to 1) be in hydrostatic equilibrium, 2) be in orbit around the sun, and 3) to have cleared its orbit.
With the reclassification of the term "planet" in 2006, there are only eight planets in the solar system, and Pluto is considered a "dwarf planet".

The remaining 8 planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

(see the related question)

1. Mercury

2. Venus

3. Earth

4. Mars


5. Jupiter

6. Saturn

7. Uranus (pronounced "you're-on-us")

8. Neptune

*Dwarf Planet: Pluto
In order from the sun









mars, venus, earth, mercury, jupiter, saturn, uranus, neptune
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
Mercury, Venus, Mars, Earth, Jupiter, Saturn, Uranus, Neptune. Pluto used to be listed as the ninth planet, but has since been demoted to a Dwarf Planet [See Link].

  1. Mercury
  2. Venus
  3. Earth
  4. Mars
  5. Jupiter
  6. Saturn
  7. Uranus
  8. Neptune
  9. Pluto (no longer considered a planet)

Also a way to remember that is: MVEMJSUNP = My Very Elegant Mom Just Served Us Nine Pizzas = Mercury, (and all the other planets)

Planetary Science

What does the earth's gravitational attraction prevent gases from doing?

The Earth's gravitational attraction prevents gasses from escaping into outer space.

Space Travel and Exploration
Planetary Science

What are uses of constellation?

Constellations are used as a way of mapping surrounding space so that's its easier for us to find certain planets/stars alot easier. Also in history these constellations have being used for astrology which is suposerly a way of reading ones future, hope this helps

Planetary Science

How do crater counts tell us the age of a surface?

The more craters a surface in space has (e.g. moon's surface), the older it is likely to be. A surface which has been around longer will have been exposed to more impacts from objects such as meteorites.

In addition, if you are able to get figures for the rate of crater production, it is possible to use the number of craters to give an quantitative estimate of the age of the surface.

Planetary Science

What are the four orbital shapes?

We can come up with only three:

-- hyperbolic

-- parabolic

-- elliptical (including circular, a special case of elliptical)

Circles, ellipses, parabolas and hyperbolas are all conic sections, the intersection of a plane with a right-circular cone.

Orbitals in quantum chemistry have shapes that are spheres for s-orbitals, dumbbells for p-orbitals, and different types of d-orbital are either pairs of crossed dumbbells, or a dumbbell with a central collar. f-orbitals have yet more complex shapes, but they are not usually considered in textbooks.

In physics, p and d orbitals have rather different shapes. A s-orbital is still a sphere, but p-orbitals are either dumbbells or tyres, and d-orbitals are collared dumbbells, double (point to point) cones, or tyres.

Planetary Science
The Solar System

How many planets are there in our solar system?

There are a total of 13 known planets in our solar system:

There are 8 major planets in our solar system. Since the recent re-definition of 'planet', Pluto is a dwarf planet (along with 4 others in that classification).

The 8 major planets in the solar system:

1. Mercury

2. Venus

3. Earth

4. Mars

5. Jupiter

6. Saturn

7. Uranus

8. Neptune

The 5 dwarf planets:

1. Ceres (a large asteroid)

2. Pluto

3. Haumea (Kuiper Belt Object)

4. Makemake (Kuiper Belt Object)

5. Eris (Kuiper Belt Object)

Pluto was designated a dwarf planet when it became obvious that there were several other objects of its size within the outer regions of the solar system. Three of them are now also dwarf planets: Eris, Haumea, and Makemake, and others (Quaoar, Sedna) are candidates to be named dwarf planets.

There were 9 planets following the discovery of Pluto in 1930. But with the improvements in telescopes in the 21st century, a surprising number of sizable planetoids found past Neptune, and astronomers realized that there could be dozens of objects being called planets. So in 2006, Pluto was reclassified as a "dwarf planet" by the International Astronomical Union. The asteroid Ceres and 3 other trans-Neptunian objects (Haumea, Makemake and Eris) were also classified as dwarf planets and there are several other pending candidates.
There were nine planets in our solar system, but in 2005, the International Astronomical Union finally devised some criteria for determining what astronomical bodies can be called a "planet". (There had never been an official definition for "planet".

The planet Pluto was demoted from "planet" to "dwarf planet", because Pluto had not "cleared its orbit" of other objects, which left only eight official planets. Pluto became a "dwarf planet", as did the asteroid Ceres, and three trans-Plutonian objects Makemake, Haumea, and Eris.
There were eight... Mercury, Venus, Earth,Mars, Jupiter Saturn, Neptune, Uranus & Pluto. However - recently, Pluto has been 'downgraded' to a 'minor planet' - since it's distance from the sun places it closer to the Kuiper belt.

Planetary Science
The Solar System

How many Planets are there?

There are 8 major planets, and 5 dwarf planets, in our solar system. There are also about a half dozen bodies that may be dwarf planets, though this status has not yet been confirmed. and more than a hundred more that may be considered in the future.

Outside of our Solar System, there are billions. These are called exoplanets.
In addition to the eight planets in our solar system, due to new equipment and new techniques, new planets are being found in other solar systems every week.

Planetary Science
The Solar System

How many moons are there in the solar system?

There are 178 known moons in the Solar System. The planet which has the most natural satellites is Jupiter with 66. There are also 104 asteroid moons and as many as 58 satellites of potential dwarf planet candidates.

Major Planets (171)

  • Mercury does not have any natural satellites (moons)
  • Venus does not have any natural satellites (moons).
  • Earth has 1 natural satellite (moon) called 'The Moon' or Luna (asteroid Cruithne orbits the Sun in a 1:1 orbital resonance with Earth)
  • Mars has 2 natural satellites (moons)
  • Jupiter has 66 natural satellites (moons)
  • Saturn has 62 (+1 unconfirmed) natural satellites (moons) and over 150 moonlets
  • Uranus has 27 natural satellites (moons)
  • Neptune has 13 natural satellites (moons)

Dwarf Planets (7)

  • Pluto has 4
  • Eris has 1
  • Haumea has 2
  • Ceres has none
  • Makemake has none

*For a complete list, see the related link below. There is also a link to more information at the Nine Planets website.
Planet/# of moons







Uranus- 27


Planetary Science
The Moon

Why does the moon look orange when it rises?

The Moon appears orange-ish when it rises for the same reason the Sun looks redder at sunset -- the Earth's atmosphere scatters the shorter, bluer wavelengths of light and more of the reddish light makes it to your eye. At moonrise, you are seeing the moon through more of the Earth's atmosphere than when the moon is overhead, and more of the light at red wavelengths makes it through the atmosphere to your eye.

Planetary Science

How far from earth to betelgeuse in miles?

Betelgeuse is 640 light-years away from the Earth.

1 light-year is the distance traveled by light in 1 year.

speed of light = 3 x 108 meters per second

So, 1 ly = 3 x 108 x 365 x 24 x 60 x 60 = 9.46 x 1015 meters

640 light-years = 640 x 9.46 x 1015 = 6.05 x 1018 meters

1 meter = 0.621 x 10-3 miles

640 light-years = 6.05 x 1018 x 0.621 x 10-3 = 3.76 x 1015 miles

That is 3,760,000,000,000,000 miles.

Planetary Science
Planet Mars

What are two reasons why mars is a cold planet?

1. Mars is considerably farther from the Sun than Earth and therefore receives less sunlight to warm it.

2. It's atmosphere is very thin, so it cannot produce a substantial greenhouse effect and quickly loses the heat it gains in the daytime at night becaus the atmosphere is too thin to hold onto it.

Planetary Science
The Moon

What it the distance from the earth to the Sun?

Average distance is about 150 million kilometers. Keep in mind, though, earth is continuously moving around the sun so this measurement in sure to change at any point in time. Earth has and oval- shaped orbit around the sun- not a perfect circle so there could be a point that the earth is at its minimal distance from the sun or at its maximum. No one knows exactly.

Planetary Science

What angular resolution would you need to see the Sun and Jupiter as distinct points of light if you were looking at it from 15 light years away?

Great question to chew on ! And I think I can work it out, at least

to an order-of-magnitude approximation.

Radius of Jupiter's orbit is around 5 AU = 5 x 93 million = 465,000,000 miles.

15 light years = 15 x 5.8787 x 1012 = 8.818 x 1013 miles

(Tangent)-1 of (5 AU / 15 LY) = 0.000302 degree = roughly like 1.09 arc-second.

There's a rule for the resolution you need in order to completely resolve two sources

that subtend a given angle, and I don,t remember what it is. But the order of magnitude

for this particular case is about 1 arc-second ... with one bright object and a dim one.

That calculation looks right and the separation can theoretically be resolved by a telescope with a 4½" aperture. But there is a big difference in brightness because the Sun would be a star of magnitude 3.2 while Jupiter's magnitude would be about 21. So a considerably bigger telescope would be needed because to see something that dim needs a big aperture, round about 100".

Planetary Science

Find the change in the force of gravity between two planets when the distance between them is increased by a factor of five?

The force of gravity varies as the inverse square of the distance, so if the distance were increased by a factor of five, the force between them would decrease by a factor of five squared, or 25.

So the new force would be 4% of the original force.


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