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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

I l don't understand questions
Nkateko Reply
which quesrions?
Ankit
How to make a telescope
Amit Reply
***youtube.com/channel/UClBN_RpR5X8IdrARwnaL3fg
Steve
***wikihow.com/Make-a-Telescope
Jennifer
optical mechanics
Astro
aptical
Nkateko
Which one has the ring
Isaac Reply
Saturn venue and even Jupiter all have rings the rings on Jupiter, however, aren't so easily noticed due to them only being viable through infrared
Hunter
visible *
Hunter
they each have three rings but not as you might think just think of them all as one big ring because that's basically what they are but they are desperate individual rings
Hunter
separate*
Hunter
can you tell me what is a quantam elighment? Lets see how many people give write answers
gdjm Reply
can you tell me what is a fomalhaut?
gdjm
Fomalhaut Is The Brightest Star In The Constalellation Of Piscis Austrinus.....
Adam
joe.
Tracy
Do You Mean Quantum Entanglement?
Adam
yes
gdjm
No Adam fomalhaut mean eye of universe
gdjm
quantum entanglement is when a husband has been married so long to his wife that he is directly influenced by her action usually in an opposite way. 🤣
Jocofranc
It Is Also The Brightest Star Of The The Constalellation Of Piscis Austrinus.....
Adam
who was the first person to get to the planet
Isaac
can anyone tell me daily rotation of the sun in tokyo
Liridona Reply
tokyo has it's own personal sun
Tracy
can you send me any pictures of the tokyo sun
Liridona
sure! ig?
Tracy
here can u?
Liridona
no it wont let me sadly
Tracy
or
Liridona
snapchat
Liridona
i dont have snapchat 😰
Tracy
okay ig
Liridona
my ig is fatwigga37 if you'd like to see :)
Tracy
Can we use SI units in the equation of Kepler's third law?
Naiyu Reply
can u tell the equation pls
sasmita
how does religion enters to this topic when god created this world
Sakira
How Do You Know A God Created Our Planet?
Adam
you must read bible
Sakira
u must the bible
Sakira
How Do You That Book Is Authentic? And I Have Read The Bible, The Koran, The Torah And The Urantia.....
Adam
The law is T^2 is proportional to R^3 where t is planet's time period and r is average of semi major axis and semi minor axis. Also,don't turn this place into a religious warzone. We already have idiots fighting about religion.
priyanshu
If I Had A Book That Said Insects Created The Universe, Would That Make It Fact?
Adam
Have You Ever Heard Of The Council Of Nicaea?
Adam
Through Out History Mankind Has Worshipped Over 5000 Different Gods, How Do You Know Christ Is The True God?
Adam
God Is A Hypothesis..... The Definition Of Faith Is Belief Without Proof.....
Adam
Thank You Prianshu Roy, This Is A Forum For Science Not Archaic Stories Written By Sheep Herders, Well Said.....
Adam
Hebrew 13:1
onome
P2 = a3
Adam
So You Quote A Bible Verse, Now What?
Adam
Science Discourse Nothing Else.....
Adam
god is real he's not just a wise guess
Sakira
god bless you
Sakira
u know what,u are not here if god werent there!
Sakira
Science Discourse, Nothing Else.....
Adam
Thier Are Many Religious Sites You Can Go To, To Discuss God.....
Adam
hahahaha
Sakira
Have A Great Day.....
Adam
night time here
Sakira
Look Up The Definition Of Day, Instead Of Trying To Look Witty, Again Have A Great Day.....
Adam
😈😈😈
Sakira
such an socratic person?
Sakira
What Was Your Intention In Stating "Night Time Here" ?
Adam
please don't fight over silly stuffs!
Romancho
tangina mo
Sakira
No I Don't Believe A God Exist, But I Will Fight For Your Right To Worship Any God You Wish.....
Adam
no fighting
Sakira
But This Venue Is For Science Discourse.....
Adam
i know!
Sakira
No Fighting, Just Discussion.....
Adam
yes Naiyu, we have to use SI unit in the equation for the Kepler's every laws
Madhav
Thanks.
Naiyu
wow
Kenneth
what's the scene of voyager 1,did we get any information through it
Aarushi Reply
we are getting a lot of info yet more to be received check official mission report from the officials site ....
Ganeshan
what are the best astronomy books?
neehar Reply
what is the parallel space?
neehar
how to measure the brightness of a star in w\m^2
Aarushi Reply
it's based on the percentage of helium I think
neehar
ok TQ😊
Aarushi
it's based planet colour and brightness which called lumiosity
gdjm
Are there planets that has the same characteristics as earth.
Nito Reply
yes ofcourse there are earth like planets but they aren't completely like earth.still scientists have a hope of life existence in there.
Aarushi
yeah of course example is Mars but they only discover water at mars
neehar
there's a much possibility of presence of earth like planets in the universe if they were present at goldilock zones
Jashwanth
what are goldilock zones?
Aarushi
why yes there are planets just like earth out there somewhere we know that much for sure given the number of planets in the galaxy, as a matter of fact, one of Jupiter moons officially named "gamamede" is very much like earth in size and characteristics
Hunter
How to become an astronomy
Aakarsh Reply
astronomer*
Emilya
Yes
Aakarsh
Astronomer
Aakarsh
yes i Also want to know the answer
Mehar
How to become?
Aakarsh
Me too
Romancho
By hard study
Zulker
Try to keep all the basics of science subjects and also English
Zulker
Ya i know that I will do hard work but
Aakarsh
I have always found astronomy fascinating, but my first love is philosophy.
GARY
I wanna become astromer as neel armstrang
Aakarsh
that's an astronaut
Emilya
Neil Armstrong
antman
what is your name who are you where are you why are you there
GARY
Neil Armstrong was an astronaut. You first work is to know the meaning of astrophysicist, astronomer, astronaut, astrologer and to find the work of the individual. And the most important thing is to be good in English. Because u have done some mistakes while doing chat with me like :an astronomer
Zulker
sorry I'm talking to somebody else someplace else on the internet
GARY
The heading will be "How to become an astronomer"
Zulker
jus be yourself and follow your passion and I think there is no need to copy anyone
Aarushi
hey it's simple yaar, it's based on your curiosity
neehar
what is the length of Earth
comedy Reply
The Earth is not a perfect sphere, however it's roughly 25,000 miles, or 131.5 million feet, or 1.6 Billion inches. In the Metric system its HUGE!
Jocofranc
Thank for your knowledge.Sr
nyo
But can I also know and calculate the whole weight of earth includeing flora, funa,water on earth even air's weight.Depending on super compruter, I think it can be.For the very detail in the Metric System.Such as kilogram and pound.
nyo
Earth is about 6 Sextillion metric tons check out formula at ***science.howstuffworks.com/environmental/earth/geophysics/planet-earth-weigh.htm
Jocofranc
thank again Sr.I wanna ask another question if you don't mind.The earth had 4.5billion years age old.My question is from fire ball to today more and more stable geology was how happen.Please answer me starting of life on this planet and how many era are there and the earth history.
nyo
My friend you have asked a question(s) that scientists struggle with. There is no short cut...the information is lenghty. Here is an additional site for you. It is a good place to start. ***newscientist.com/article/dn17453-timeline-the-evolution-of-life/
Jocofranc
Sr,your web site is very useful to me.And another question is how gene or DNA transfer from parent to sibling.how we know the first DNA of our first human from arfarica.
nyo
Good morning Nyo; ur question is out of my league, although fascinating. Maybe you'll find this page helpful: ***genetics.thetech.org/ask/ask445
Jocofranc
If speed is so many thousand time of light and start to travel from one point,how speed will return to it starting point even in straight line back.Will time and energy be limit it?Can it be posible.Please let me explain Sr.
nyo
hey neo ur curiosity is great, where r u from?
neehar
in physics actully no but thory make possible
gdjm
earth is about 13,000 kilometers across
Hunter
there is aliens or parallel universe
Chithra Reply
There may be both who knows
Debabrata
It would be quite surprising to me to learn that there is no aliens in our very own galaxy. The size of our galaxy alone seems to favour life. There's so many reasons why we haven't made contact but as our technology grows we will undoubtedly find answers. I also think that it's possible that ...
Jocofranc
But I don't think that that alien species might be developed.... Because if they were developed or advanced than us then they must have located us first and might have even contacted us
Debabrata
many other universes exist. I don't think that they would be parallel universes in the purest sense of the word. Only speculations on my part. We simply dont know with certainty.
Jocofranc
Hi Debabrata; You may be right. It's hard to say with certainty. An ugly truth (guess really) is that Tellurian are simply not interesting. We are not all that!
Jocofranc
Yeah Jocofranc you are also right about parallel universe. Who knows what lies ahead.
Debabrata
the parallel universe theory is something secondary but first let's focus on the nearby objects like titan which shows great hope
Aarushi
I read it before about aliens, but I have to research on it
neehar
yeah of course
neehar
What about XTs... Exo-Tellurians. Ancient people who could have obtain a spurt of technology and left home. Progression of men r not always linear but sometime cyclic. Civilization comes and goes. Geo-upheaval can easily erase any evidence. Our bros r out there. (have fun 😁)
Jocofranc
sir jocofranc I think u didn't listen about aliens who send a message to our space research organization.
neehar
what is inside Jupiter how it will rain there
Chithra Reply
interesting question!
Mahesh
would love to learn about it 😃
Morrie
jupiter is a gas gaint so you can't walk on the surface like here on earth, but there is a solid core.
Yannick
The latest term being used is a 'fuzzy core'. An inbetween of solid and liquid. Check ***sciencemag.org/news/2019/08
Jocofranc
I think it based on the nature of the source in Jupiter
neehar
Scientists believe that onJupiter and Saturn, it rains diamonds. New atmospheric data for the gas giants indicates that carbon is abundant in its dazzling crystal form, the BBC reports. Lightning storms turn methane into soot which hardens into chunks of graphite and then diamond as it falls.
gdjm
Where is a moon HOW MANY KILLOMETER FAR FROM EARTH
Guddi Reply
On Average 383,000 Kilometers, Between Perigee And Apogee.....
Adam
386,000 km
neehar
3.6×10^5 km
gdjm

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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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