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Learning objectives

By the end of this section, you will be able to:

  • Discuss what has been learned from both manned and robotic lunar exploration
  • Describe the composition and structure of the Moon

The Moon has only one-eightieth the mass of Earth and about one-sixth Earth’s surface gravity—too low to retain an atmosphere ( [link] ). Moving molecules of a gas can escape from a planet just the way a rocket does, and the lower the gravity, the easier it is for the gas to leak away into space. While the Moon can acquire a temporary atmosphere from impacting comets, this atmosphere is quickly lost by freezing onto the surface or by escape to surrounding space. The Moon today is dramatically deficient in a wide range of volatiles , those elements and compounds that evaporate at relatively low temperatures. Some of the Moon’s properties are summarized in [link] , along with comparative values for Mercury .

Two sides of the moon.

The Two Sides of the Moon. The left image shows part of the Moon’s hemisphere that faces Earth; several dark maria and rayed craters are visible. The right image shows part of the Moon that faces away from Earth; it is dominated by highlands and is more heavily cratered.
The left image shows part of the hemisphere that faces Earth; several dark maria are visible. The right image shows part of the hemisphere that faces away from Earth; it is dominated by highlands. The resolution of this image is several kilometers, similar to that of high-powered binoculars or a small telescope. (credit: modification of work by NASA/GSFC/Arizona State University)
Properties of the Moon and Mercury
Property Moon Mercury
Mass (Earth = 1) 0.0123 0.055
Diameter (km) 3476 4878
Density (g/cm 3 ) 3.3 5.4
Surface gravity (Earth = 1) 0.17 0.38
Escape velocity (km/s) 2.4 4.3
Rotation period (days) 27.3 58.65
Surface area (Earth = 1) 0.27 0.38

Exploration of the moon

Most of what we know about the Moon today derives from the US Apollo program , which sent nine piloted spacecraft to our satellite between 1968 and 1972, landing 12 astronauts on its surface ( [link] ). Before the era of spacecraft studies, astronomers had mapped the side of the Moon that faces Earth with telescopic resolution of about 1 kilometer, but lunar geology hardly existed as a scientific subject. All that changed beginning in the early 1960s. Initially, Russia took the lead in lunar exploration with Luna 3, which returned the first photos of the lunar far side in 1959, and then with Luna 9, which landed on the surface in 1966 and transmitted pictures and other data to Earth. However, these efforts were overshadowed on July 20, 1969, when the first American astronaut set foot on the Moon.

[link] summarizes the nine Apollo flights: six that landed and three others that circled the Moon but did not land. The initial landings were on flat plains selected for safety reasons. But with increasing experience and confidence, NASA targeted the last three missions to more geologically interesting locales. The level of scientific exploration also increased with each mission, as the astronauts spent longer times on the Moon and carried more elaborate equipment. Finally, on the last Apollo landing, NASA included one scientist, geologist Jack Schmitt, among the astronauts ( [link] ).

Apollo Flights to the Moon
Flight Date Landing Site Main Accomplishment
Apollo 8 Dec. 1968 First humans to fly around the Moon
Apollo 10 May 1969 First spacecraft rendezvous in lunar orbit
Apollo 11 July 1969 Mare Tranquillitatis First human landing on the Moon; 22 kilograms of samples returned
Apollo 12 Nov. 1969 Oceanus Procellarum First Apollo Lunar Surface Experiment Package (ALSEP); visit to Surveyor 3 lander
Apollo 13 Apr. 1970 Landing aborted due to explosion in command module
Apollo 14 Jan. 1971 Mare Nubium First “rickshaw” on the Moon
Apollo 15 July 1971 Mare Imbrium/Hadley First “rover;” visit to Hadley Rille; astronauts traveled 24 kilometers
Apollo 16 Apr. 1972 Descartes First landing in highlands; 95 kilograms of samples returned
Apollo 17 Dec. 1972 Taurus-Littrow highlands Geologist among the crew; 111 kilograms of samples returned

Questions & Answers

another theory of universe except big ban
Albash Reply
how was universe born
Asmit Reply
there many theory to born universe but what is the reality of big bang theory to born universe
Asmit
what is the exact value of π?
Nagalakshmi
by big bang
universal
from where on earth could u observe all the stars during the during the course of an year
Karuna Reply
I think it couldn't possible on earth
Nagalakshmi
in this time i don't Know
Michele
is that so. the question was in the end of this chapter
Karuna
in theory, you could see them all from the equator (though over the course of a year, not at pne time). stars are measured in "declination", which is how far N or S of the equator (90* to -90*). Polaris is the North star, and is ALMOST 90* (+89*). So it would just barely creep over the horizon.
Christopher
is time travel possible?. Practically?!!
Elisha Reply
There are some theories of the great Scientist Nikola Tesla. According to his theories time travel is possible!
puvananathan
I think it is possible
Asmit
no it is not possible practically with current technology but there are theorys we can travel to future with help of time dilation we can go to past with help of worm Holes
universal
of course it is. you are constantly moving forward in time. you're time-traveling while you read this.
Christopher
what is latitudes
SOURAV Reply
latitudes are the measurement of distance north or south of the Equator . It is measured with 180 imaginary lines that form circles around the earth east - west , parallel to the Equator . These lines are known as parallels.
Saumya
hi
Rehmtullah
Yeah. Simply the Imaginary Vertical measurements.
puvananathan
does universe has a limit
THE Reply
no
Vinisha
dear Vinisha, will you please tell me what is 4 dimension?
THE
no its unlimited
SOURAV
no
Saumya
with current technology we estimated the age of universe so we can't say that universe is infinite universe has a limit and there are many universes in multiverse
universal
is their life on mars
Darius Reply
yes, as of now..
Rosselle
alien?
THE
Mars does not have either a magnetic field or an ozone layer to protect it's surface from the harmful u.v rays. so there is no way life can be possible on mars.
Elisha
but can't live in that planet due to lack of oxygen at the rate of 13 % That we considered as dengouros of 16 %
SOURAV
I don't think so .
Saumya
Experiments are still go in on..... Soon there will be lives as on our Earth. (Experiments by NASA) (Experiments by Space X) and many more.
puvananathan
currently we can't live on mars but in future life is possible in mars
universal
what is the origin of the universe
Ummisalmah Reply
Big Bang
Michele
what is it first cause
Ummisalmah
is its existence necessary
Ummisalmah
from where the first energy came during big bang?
Bysali
the steady state theory may be true too
Shaunak
from big bang
SOURAV
it all began with the singularity...
Elisha
a single atom i.e singularity
Saumya
no...singularity means infinitely small, which mathematically is 1/♾ single atom is way to large as compared to a singularity
Shaunak
oh thanks for correcting me
Saumya
Did there is any life probability on titan (largest moon of saturn)
sanjay Reply
Yes, there could be a possibility of existance of life because Titan is full icy mountains which are one form of water and. could assist in microbial growth
Astronomy
although life is not yet detected on it, it is theorized that when the sun starts its red giant phase, the temperatures on titan,enceladus,etc will become suitable for life and they may develop an atmosphere too
Shaunak
it is theorized that a life form could be there, but due to titans long distance from sun, it has to be near its core
Sun
What is 5 dimension
Sourav Reply
hi
Danbirnianz
yo!!!
Bennett
5 dimension is truth
Bennett
form - order - structure - society - TRUTH
Bennett
nice topic! i reread this.
TPonder
why not string theory called a theory of everything
Harsh Reply
Perhaps because string theory is useless when discussing "things" like music theory, or morality and justice. Therefore cannot be a theory of "everything."
Bennett
why the energy cost
MASTER Reply
most energy is still sourced from fossil fuels, specifically petroleum, coal and natural gas. ... This has made energy more expensive to produce
puvananathan
what is sagittarius
Noorzad Reply
what is gimine
Noorzad
Black hole of Milky way galaxy
deepanshu
thanks a lot for your sympath and information
Noorzad
thanks a lot for your sympath and information Deepanshu
Noorzad
Hello: My friends, How do you do?
zin
(Sagittarius A) is a name of black hole ,present center of Milky Way
Harsh
No dude, Sagittarius is a constellation in the milky way galaxy. There is another name too. It is tea pot constellation. reason for the name Tea pot constellation is: In the star map if you find the Sagittarius, the middle part of the constellation consist of a roughly drawn tea pot shape.
puvananathan
also the milky way galaxy is the steam comes from the tea pot constellation.
puvananathan
It's a natural space co-incident.
puvananathan
this question is for atheists what created humans , how did they evolve
ilyes Reply
not entirely sure what this question has to do with Atheism but, firstly, there is no "who", life evolved in multiple paths, humans are simply one of those paths. The process of how life evolves is a very complicated but very well researched field of biology, so it would be worth doing research...
ben
...into that field, evolution isnt disputed. However, the direct path from the common ancestor (that we share with chimps) has not yet been completed. But know for sure that humans didn't just magically appear one day, it was over millions of years of evolution
ben
(I must ask though, what has this got to do with Atheism?)
ben
idk i thought believers will say god created us
ilyes
there are many types of believers one say that god created consciousness, one say we just magically appeared out of nowhere, and one say universe was created by God(all based on people I have met so far)
Tanmay
Hey
Asim
Tanmay!
Asim
Hello
Asim
hello Asim
Tanmay
hi my friends asim and tqnmay we hhave lern okay
Eyiba
did u forget me!!
Amit
Could God have created evolution? Nope, no way, too complicated.
Bennett
yes god can do that in theory
Tanmay
@Eyiba hello
Tanmay
@Amit seems like that XD
Tanmay
haha🤣🤣
Amit
This question is for theists, what created God?
Anthony
hi
UFOLIENS
God was begotten, not made. More of a concept than an entity.
Bennett
hello
Stuart
Hi🙂🙂
Harsh
Hi🙂🙂
Harsh
Hi🙂🙂
Harsh
Hi🙂🙂
Harsh
we came by God not real old stinky water
Bryant
Here people don't have a goal to become astronomers ,rather they want to become astrologers,with this mindset,there won't be any progress in this void earth as Feynman says in his book "if I could explain it to the average person (like how astrologers do) I wouldn't have been worth the nobel price".
Akshar
God did not create the universe.. Humans created god, possibly to fill in an unwanted reality no1 wants to believe because life can be a struggle for most.
Collins
astronomy and astrology diverged from the same concept, to deny either one is to deny them both.
Bennett
God created the universe ofcourse
Khairat
GOD CREATED THE UNIVERSE
Susanna
Some will use the Big Bang Theory, which even if statistically plausible, falls flat on it's face when you apply the law of angular momentum... If the universe evolved from a spinning dot-like singularity, why are some moons, planets, galaxies spinning backwards?
Taj
collisions with other planetary bodies can cause planets and other objects to rotate backwards. Venus and Uranus both have a retrograde rotation.
Eva
Also, we now know that we live in a digital universe, how can the origin of information be explained? Aliens from another galaxy? From an astrophysics standpoint that's not plausible unless their technology is so advanced that they can manipulate wormholes, intergalactic travel is HIGHL speculative
Taj
aliens could have unknown tecnologies! in theory aliens could control universe in many different ways! but it Is only a theory! humans(we all) don't Know aliens ufficially, aliens could not exist, so in this time we Can do only theories fantastic and not scientific! w umanity!w astronomy!
Michele
So if aliens exist, does that negate the possibility of their being an all-powerful God? Because you still must account for the actual ORIGIN of information...
Taj
@bennet God was not made nor begotten
Khairat
"..we must, of course ask next where God comes from. And if we decide this to be unanswerable, why not save a step and decide that the origin of the universe is an unanswerable question? Or, if we say that God has always existed, why not save a step an conclude that the universe has always existed?
Eva
-Carl Sagan
Eva
questing for God is unnecessary because you get "who created god" and then "who created the one that created god" endlessly
Eva
Certain entropic laws prove that the universe is NOT infinite.. It had a beginning... Also to say that God didn't have a beginning would imply an infinite regression of events...
Taj
If an all-powerful God exists then He created space-time itself... Time is a physical property that can be manipulated via gravity and velocity... E=mc2 AND experimental data confirms this... Time is NOT a set constant. The Universe had a beginning, then who set time in motion?
Taj
Einstein even came to believe in God because of the mathematics.. Also if someone can give a logical explanation as to why entire moons, planets, and entire galaxies are spinning backwards, then I'd love to hear it..
Taj
there is a person up there controlling everything, creater of our world- is a very childish concept. the theists and atheists are essentially the different sides of the same coin, they both believe in something about which they do not have a proof.
Shaunak
we should focus on science and seek answers to our questions instead of wasting our time debating about stupid things like God, about which we don't know a thing
Shaunak
there are various hypothesis regarding the origin of life like the abiogenesis and panspermia. as for the evolution, the gentleman named Charles Darwin has already answered that question
Shaunak
yes I agree with you all but then some of us do not believe in the big bang,so there must be a controller of our universe indeed and that is God
Khairat
well
Tao
what is FACt is
Tao
The big is not the only theory regarding the origin of the universe out there. There is the steady state theory which was popular before hawking popularized the big bang theory. Also, Sir Roger Penrose has his own different theory.
Shaunak
if you research then you will find that although we do not know a lot of things, there is no need for a "God"
Shaunak
I myself do not believe in anything. if someone shows me God I will start believing. if someone proves me that God does not exist, I will become an atheist
Shaunak
why
Tao
fact is
Tao
what is is
Tao
deitys are were mere beings
Tao
so
Tao
BTW do u know about the anunaki
Tao
so
Tao
@shaunak Sean Carroll calls himself a "naturalist" because he does not believe in God but he will change his mind upon evidence. that's pretty much an atheist but he says the term naturalist is more fitting. he believes in the physics and nature of the universe!
Eva
some evolved some not. like mythology has talk of outer earthly coming on earth
Tao
the San bush people the Hopi natives the Tibetan saying about beings making them
Tao
hello everyone
Dark
anyone can explain black hole
Dark
well I am not denying that there were some great people in very very ancient times, that we worship as gods and divine entities. I am just saying that they also were human beings like us, just extra ordinary.
Shaunak
also, we are not doing something wrong when we worship them today, for example, Jesus, Ram, Krishna,etc. I am just saying we should not misunderstand the worshipping by believing that they are indeed gods who created us and the whole universe.
Shaunak
for example the great Indian cricketer Sachin Tendulkar is known as the God of cricket in India. but that is just because what he did in his career was extraordinary. that doesn't mean he literally is a God
Shaunak
not the whole universe no. and yes worshipping is not needed. all in the all are equal . just another bitpart in the all
Tao
@Eva , I did not know that term before, but now that I know it, that may be a fitting term for me. I think everyone should be that way, not believing something without evidence or proof
Shaunak
@Tao Zen, yes. worshipping Is not needed at all.
Shaunak
what is is and what is not is not. factuality. so the paranormal is a fact too. like nde experiences account for other realms. light dark will always be a part. all are a part in the all . nothing more nothing less
Tao
I was just saying that it is not a problem if someone does worship
Shaunak
paranormal is fact? bruh srsly? although I do not deny the evidence for it, it is very vague, based upon personal experiences of people and highly doubtful. Also no serious research has been carried out in this area and it is not experimentally verified.
Shaunak
esp parapsychology telekenises telepathy . Tibetan monks thetha waves. you just check. NDE experience YouTube . reincarnation YouTube. enough material to go through
Tao
if you wanna know seriously how the universe came to be ask me. I ll hook you up with the info
Tao
let me known if you really wanna know seriously how the universe came to be
Tao
for actual scienze humanity was created for casual events and not by aliens! but some scientist says humanity was created by aliens! in this time it is not exact for actual scienze (but it is not impossibile).........
Michele
check accounts of the tribes of how they were made san bush people Hopi natives Tibetan creation myths
Tao
"myths" is the keyword here
Shaunak
its information about ' makers'
Tao
homo erectus to homo sapiens has a missing link
Tao
that is due to lack of research not due to a miracle
Shaunak
the San bush people have information about being made by praying mantis type of aliens/ makers. so do the tibetans information goes they were made out of makaks
Tao
there is evidence of outer earthly forces . alien lifeforms. the myths . happenings are all over the world. the dogon tribe in mali
Tao
etc.
Tao
we being made by aliens is a valid hypothesis, very interesting to think indeed...
Shaunak
its maybe us on earth but not every planet has the same history. according to some information . some reptoid intelligent species evolved here before us.
Tao
@Tao Zen, hey, I am curious, how come you claim to know about the origin of the universe? because even scientists haven't figured that out...
Shaunak
I can otherwise send you the YouTube link with the information
Tao
let's wassap
Tao
yes pls. do send the link
Shaunak
i Will do tomorrow now no possible
Tao
but if you type . Linda Moulton howe and jerry wills. yu ll get a video. are we living in a simulation. 1/2 hour vid. yull get the info
Tao
ok
Shaunak
tell me if you found it
Tao
well I'll just recommend u to talk to any Muslim friends and you will get for understand I am a Muslim and I believe in the supreme being because he caused u to live and u go back to where u come from when the time comes....
Khairat
and if u read the Qur'an u will discover that the new discoveries that we are having now has been in the Qur'an for a very longtime so I don't want u to go astray,change ur ways and go for the right path🙏🙏
Khairat
the theory of single cell organism were transported to earth due to meterorites where they evolved to multicell organisms and then animals
Sun
Khairat Abdulrasheed i think asking what is what and just believing our research is not in any way going in wrong direction believing if god is there or not is not in our hand but believing
Sun
may i ask a question
Raluca Reply
yes why not you don't need to ask anyone for permission
Tanmay
sure, why not?
ca

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Source:  OpenStax, Astronomy. OpenStax CNX. Apr 12, 2017 Download for free at http://cnx.org/content/col11992/1.13
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