Space and astronomy news
“Once more into the breach, my dear friends…”
Such a quip may be deemed appropriate as we endured the media onslaught this past weekend for the third and final perigee Full Moon of 2013.
Tonight, on Monday, July 22nd, the Moon reaches Full at 18:15 Universal Time (UT)/4:15 PM EDT. This is only 21.9 hours after reaching perigee, or the closest point in its orbit at 358,401 kilometres from the Earth on the Sunday evening at 20:28 UT. Continue reading “Super-Moon Monday: The 3rd (& Final?) Act”
In a fitting testament to NASA’s momentous Apollo Moon Landing Program, NASA and billionaire Jeff Bezos confirmed today (July 19) the discovery of a powerful F-1 first stage engine component from the Saturn V moon rocket that launched three American astronauts on the historic journey of Apollo 11 to land the first two humans on the Moon on July 20, 1969.
“On the eve of the 44th moonwalk anniversary, the Bezos Expedition confirms an Apollo 11 Saturn V F1 engine find,” NASA officially announced on its websites just moments ago today, July 19.
Apollo 11 commander and NASA astronaut Neil Armstrong, was immortalized forever when he first set foot on the moon 44 years ago tomorrow (July 20, 1969), followed minutes later by the lunar module pilot, NASA astronaut Buzz Aldrin.
The Saturn V rockets first stage was powered by a cluster of five F-1 engines – a technological marvel and the most powerful single-nozzle, liquid-fueled rocket engine ever developed.
“44 years ago tomorrow Neil Armstrong stepped onto the moon, and now we have recovered a critical technological marvel that made it all possible,” says Bezos on his Expedition website today.
Bezos, founder and Chief Executive Officer of the aerospace company Blue Origin and Amazon.com, originally announced the discovery and recovery of significant components of two flown F-1 engines amongst a field of twisted wreckage from the floor of the Atlantic Ocean in March of this year, aboard the Seabed Worker at Port Canaveral, Florida, along with a treasure trove of other major Saturn V components hauled up from a depth of almost 3 miles.
“We brought back thrust chambers, gas generators, injectors, heat exchangers, turbines, fuel manifolds and dozens of other artifacts – all simply gorgeous and a striking testament to the Apollo program,” wrote Bezos in a update this morning, July 19.
But until today, the engines exact identification remained elusive because of decades of severe seabed corrosion and their fiery, destructive end upon plunging and smashing unimpeded onto the ocean’s surface.
Conservators from the Kansas Cosmosphere and Space Center in Hutchinson, Kansas worked painstakingly since March to identify the F-1 engine parts.
“Today, I’m thrilled to share some exciting news. One of the conservators who was scanning the objects with a black light and a special lens filter has made a breakthrough discovery – “2044” – stenciled in black paint on the side of one of the massive thrust chambers, says Bezos.
“2044 is the Rocketdyne serial number that correlates to NASA number 6044, which is the serial number for F-1 Engine #5 from Apollo 11. The intrepid conservator kept digging for more evidence, and after removing more corrosion at the base of the same thrust chamber, he found it – “Unit No 2044” – stamped into the metal surface.”
Apollo 11 launched to the Moon on July 16, 1969 from Launch Complex 39-A at the Kennedy Space Center in Florida.
Armstrong and Aldrin landed on the Sea of Tranquility inside the Lunar Module. They took a single lunar excursion and spent 2 hours and 11 minutes as the first two men to walk on the moon. They stayed on the moon for a total of 21 hours and 36 minutes before blasting off for the journey back home to Earth.
Armstrong suddenly passed away nearly a year ago on August 25, 2012 at age 82 – read my stories, here and here.
Aldrin is still active and strenuously advocating for starting human expeditions to the Red Planet.
He outlined his exploration concepts in a newly published book titled – “Mission to Mars.”
The five F-1 engines used in the 138-foot-tall Saturn V first stage known as the S-IC generated 7.5 million pounds of liftoff thrust, or some 1.5 million pounds each. They stand 19 feet tall by 12 feet wide. Each one weighs over 18,000 pounds and was manufactured by Rocketdyne.
The F-1 had more power than all three space shuttle main engines combined. They burned a mixture of liquid oxygen and kerosene fuel for two-and-one-half-minutes, carrying the Saturn V to an altitude of some 36 miles.
Altogether, six Apollo Moon landing flights boosted by Saturn V’s sent a total of 12 humans on moon walking expeditions to Earth’s nearest neighbor during the 1960s and 1970s.
“This is a big milestone for the project and the whole team couldn’t be more excited to share it with you all,” Bezos wrote.
Bezos’ Blue Origin firm is also working to develop a commercial rocket and ‘space taxi’ to finally resume launching American astronauts back to low Earth orbit from American soil after a multi year gap.
More than four decades have passed since the last humans traversed the lunar surface in December 1972 during NASA’s Apollo 17 moon landing mission.
After all that time, the F-1 may yet live again.
NASA is now working on an upgraded F-1 to power a future variant of the new SLS heavy lift booster under development and intended to launch humans aboard the new Orion crew capsule back to the Moon and to deep space destinations including Asteroids and Mars.
NASA’s robotic exploration of the moon continues this year with the blastoff of the LADEE Lunar observatory on Sept. 6 from NASA’s Wallops Island facility in Virginia.
When I looked out my south-facing window last night, I saw a gorgeous quarter Moon high in the sky. Giuseppe Petricca from Marina di Pisa, Tuscany, Italy took a longer look and created this beautiful composition of five different shots of the Moon on July 15, 2013, revealing how the appearance of the Moon changes as it sinks lower in the sky.
“These are the colours that our natural satellite assumes thanks to the Rayleigh Scattering in Earth’s atmosphere,” Guiseppe said via email. He noted that in his image, colors of the single shots are not digitally altered (except with a light Sharpness Mask to enhance the surface details.)
Guiseppe used a Nikon P90 bridge digital camera, at ISO 100, and used various but limited exposition times (trying to maintain a short medium exposition range in seconds, he said. His mosaic composed with Photoshop.
Want to get your astrophoto featured on Universe Today? Join our Flickr group or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.
Have you ever noticed that the Moon always looks the same? Sure, the phase changes, but the actual features on the Moon always look the same from month to month.
Does the Moon rotate? What’s going on?
From our perspective here on Earth, the Moon always shows us the same face because it’s tidally locked to our planet. At some point in the distant past, the Moon did rotate from our perspective, but the Earth’s gravity kept pulling unevenly at the Moon, slowing its rotation. Eventually the Moon locked into place, always displaying the same side to us.
But if you looked down on the Earth-Moon system from the north celestial pole, from the perspective of Polaris, the North Star, you’d see that the Moon actually does rotate on its axis. In fact, as the Moon travels around the Earth in a counter-clockwise orbit every 27.5 days, it also completes one full rotation on its axis – also moving in a counter-clockwise direction.
If you look at a time lapse animation of the Moon moving entirely through its phases over the course of a month, you’ll notice a strange wobble, as if the Moon is rocking back and forth on its axis a bit.
This is known as libration.
On average, the Moon is tidally locked to the Earth’s surface. But its actual orbit is elliptical, it moves closer and then more distant from the Earth.
When the Moon is at its closest point, it’s rotation is slower than its orbital speed, so we see an additional 8 degrees on its eastern side. And then when the Moon is at the most distant point, the rotation is faster than its orbital speed, so we can see 8 degrees on the Western side.
Libration allowed astronomers to map out more of the Moon’s surface than we could if the Moon followed a circular orbit.
Until the space age, half the Moon was hidden from us, always facing away. This hemisphere of the Moon was finally first observed by the Soviet Luna 3 probe in 1959, followed by the first human eyes with Apollo 8 in 1968.
The two hemispheres of the Moon are very different.
While the near side is covered with large basaltic plains called maria, the far side is almost completely covered in craters. The reasons for this difference is still a mystery to planetary scientists, but it’s possible that a second Moon crashed into it, billions of years ago, creating the strange surface we see today.
So yes, the Moon does rotate.
But its rotation exactly matches its orbit around the Earth, which is why it looks like it never does.
You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?
NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) Observatory has arrived at the launch site on the Eastern Shore of Virginia at NASA’s Wallops Flight Facility on Wallops Island and is now in the midst of weeks of performance testing to ensure it is ready for liftoff in early September.
The LADEE lunar orbiting probe will be the first planetary science mission ever launched from NASA Wallops and the Mid-Atlantic Regional Spaceport (MARS). It will soar to space atop a solid fueled Minotaur V rocket on its maiden flight.
LADEE will blaze a brilliant trail to the Moon during a spectacular nighttime blastoff slated for Sept. 6, 2013 at 11:27 PM from Launch Pad 0B.
LADEE is equipped with three science instruments to gather detailed information about the lunar atmosphere, conditions near the surface and environmental influences on lunar dust.
“LADEE will investigate the moons tenuous exosphere, trace outgases like the sodium halo and lofted dust at the terminator,” said Jim Green, Planetary Science Division Director at NASA HQ, in an exclusive interview with Universe Today.
“The spacecraft has a mass spectrometer to identify the gases, a physical dust detector and an imager to look at scattered light from the dust. These processes also occur at asteroids.”
“And it will also test a laser communications system that is a technology demonstrator for future planetary science missions. It communicates at 650 megabits per second,” Green explained to me.
The couch sized 844 pound (383 kg) robotic explorer was assembled at NASA’s Ames Research Center, Moffett Field Calif., and is a cooperative project with NASA Goddard Spaceflight Center in Maryland.
The spacecraft was then shipped cross country by a dedicated truck inside a specially-designed shipping container – blanketed with protective nitrogen – which insulated the spacecraft from temperature, moisture, bumps in the road and more than a few crazy drivers.
The first leg of LADEE’s trip to the Moon took 5 days. The trans lunar leg will take 30 days.
It’s standard practice that whenever space probes are moved by ground transportation that they are accompanied by a caravan that includes a lead scout vehicle to ensure safe road conditions and followed by engineers monitoring the health and environmental storage conditions.
Technicians are now engaged in a lengthy series of performance tests to confirm that LADEE was not damaged during the road trip and that all spacecraft systems are functioning properly.
“One important preparation about to begin is spin-balancing LADEE,” says Butler Hine, LADEE Project Manager. “During this procedure, the spacecraft is mounted to a spin table and rotated at a high-speed to make sure it is perfectly balanced for launch.”
After all spacecraft systems pass the performance tests, LADEE will be fueled, encapsulated and moved to the Wallops Island launch pad later this summer for mating with the five stage Minotaur V booster stack.
“I’m excited about the night launch because people up and down the Atlantic seacoast will be able to see it,” Green told me.
Sierra Nevada Corporation’s Dream Chaser successfully rolls through two tow tests at NASA’s Dryden Flight Research Center in California in preparation for future flight testing later this year.
Watch way cool Dream Chaser assembly video below![/caption]
Sierra Nevada Corporation’s winged Dream Chaser engineering test article is moving forward with a series of ground tests at NASA’s Dryden Flight Research Center in California that will soon lead to dramatic aerial flight tests throughout 2013.
Pathfinding tow tests on Dryden’s concrete runway aim to validate the performance of the vehicles’ nose skid, brakes, tires and other systems to prove that it can safely land an astronaut crew after surviving the searing re-entry from Earth orbit.
The Dream Chaser is one of the three types of private sector ‘space taxis’ being developed with NASA seed money to restore America’s capability to blast humans to Earth orbit from American soil – a capability which was totally lost following the forced shutdown of NASA’s Space Shuttle program in 2011.
For the initial ground tests, the engineering test article was pulled by a tow truck at 10 and 20 MPH. Later this month tow speeds will be ramped up to 40 to 60 MPH.
Final assembly of the Dream Chaser test vehicle was completed at Dryden with installation of the wings and tail, following shipment from SNC’s Space Systems headquarters in Louisville, Colo.
Watch this exciting minute-long, time-lapse video showing attachment of the wings and tail:
In the next phase later this year, Sierra Nevada will conduct airborne captive carry tests using an Erickson Skycrane helicopter.
Atmospheric drop tests of the engineering test article in an autonomous free flight mode for Approach and Landing Tests (ALT) will follow to check the aerodynamic handling.
The engineering test article is a full sized vehicle.
Dream Chaser is a reusable mini shuttle that launches from the Florida Space Coast atop a United Launch Alliance Atlas V rocket and lands on the shuttle landing facility (SLF) runway at the Kennedy Space Center, like the Space Shuttle.
“It’s not outfitted for orbital flight. It is outfitted for atmospheric flight tests,” said Marc Sirangelo, Sierra Nevada Corp. vice president and SNC Space Systems chairman, to Universe Today.
“The best analogy is it’s very similar to what NASA did in the shuttle program with the Enterprise, creating a vehicle that would allow it to do significant flights whose design then would filter into the final vehicle for orbital flight,” Sirangelo told me.
Sierra Nevada Corp, along with Boeing and SpaceX are working with NASA in a public-private partnership using a combination of NASA seed money and company funds.
Each company was awarded contracts under NASA’s Commercial Crew Integrated Capability Initiative, or CCiCap, program, the third in a series of contracts aimed at kick starting the development of the private sector ‘space taxis’ to fly US and partner astronauts to and from low Earth orbit (LEO) and the International Space Station (ISS).
“We are the emotional successors to the shuttle,” says Sirangelo. “Our target was to repatriate that industry back to the United States, and that’s what we’re doing.”
The combined value of NASA’s Phase 1 CCiCap contracts is about $1.1 Billion and runs through March 2014.
Phase 2 contract awards will eventually lead to actual flight units after a down selection to one or more of the companies.
Everything depends on NASA’s approved budget, which seems headed for steep cuts in excess of a billion dollars if the Republican dominated US House has its way.
The Commercial Crew program’s goal is to ensure the nation has safe, reliable and affordable crew transportation systems to space.
“Unique public-private partnerships like the one between NASA and Sierra Nevada Corporation are creating an industry capable of building the next generation of rockets and spacecraft that will carry U.S. astronauts to the scientific proving ground of low-Earth orbit,” said William Gerstenmaier, NASA’s associate administrator for human exploration and operations in Washington, in a statement.
“NASA centers around the country paved the way for 50 years of American human spaceflight, and they’re actively working with our partners to test innovative commercial space systems that will continue to ensure American leadership in exploration and discovery.”
All three commercial vehicles – the Boeing CST-100; SpaceX Dragon and Sierra Nevada Dream Chaser – are designed to carry a crew of up to 7 astronauts and remain docked at the ISS for more than 6 months.
The first orbital flight test of the Dream Chaser is not expected before 2016 and could be further delayed if NASA’s commercial crew budget is again slashed by the Congress – as was done the past few years.
In the meantime, US astronauts are totally dependent on Russia’s Soyuz capsule for rides to the ISS. NASA must pay Russia upwards of $70 million per seat until the space taxis are ready for liftoff – perhaps in 2017.
“We have got to get Commercial Crew funded, or we’re going to be paying the Russians forever,” said NASA Administrator Charles Bolden at Dryden. “Without Commercial Crew, we probably won’t have exploration.”
Concurrently, NASA is developing the Orion Crew capsule for missions to the Moon, Asteroids and beyond to Mars and other destinations in our Solar System -details here.
NASA Orion spacecraft blasts off atop 1st Space Launch System rocket in 2017 – attached to European provided service module – on an ambitious mission to explore Deep Space some 40,000 miles beyond the Moon, where an asteroid could be relocated as early as 2021. Credit: NASA
Story updated with further details[/caption]
NASA managers have announced a bold new plan to significantly alter and upgrade the goals and complexity of the 1st mission of the integrated Orion/Space Launch System (SLS) human exploration architecture – planned for blastoff in late 2017.
The ambitious first flight, called Exploration Mission 1 (EM-1), would be targeted to send an unpiloted Orion spacecraft to a point more than 40,000 miles (70,000 kilometers) beyond the Moon as a forerunner supporting NASA’s new Asteroid Redirect Initiative – recently approved by the Obama Administration.
The EM-1 flight will now serve as an elaborate harbinger to NASA’s likewise enhanced EM-2 mission, which would dispatch a crew of astronauts for up close investigation of a small Near Earth Asteroid relocated to the Moon’s vicinity.
Until recently NASA’s plan had been to launch the first crewed Orion atop the 2nd SLS rocket in 2021 to a high orbit around the moon on the EM-2 mission, said NASA Associate Administrator Lori Garver in an prior interview with me at the Kennedy Space Center.
The enhanced EM-1 flight would involve launching an unmanned Orion, fully integrated with the Block 1 SLS to a Deep Retrograde Orbit (DRO) near the moon, a stable orbit in the Earth-moon system where an asteroid could be moved to as early as 2021.
Orion’s mission duration would be nearly tripled to 25 days from the original 10 days.
“The EM-1 mission with include approximately nine days outbound, three to six days in deep retrograde orbit and nine days back,” Brandi Dean, NASA Johnson Space Center spokeswoman told Universe Today exclusively.
The proposed much more technologically difficult EM-1 mission would allow for an exceptionally more vigorous work out and evaluation of the design of all flight systems for both Orion and SLS before risking a flight with humans aboard.
A slew of additional thruster firings would exercise the engines to change orbital parameters outbound, around the moon and inbound for reentry.
The current Deep Retrograde Orbit (DRO) plan includes several thruster firings from the Orion service module, including a powered lunar flyby, an insertion at DRO, an extraction maneuver from the DRO and a powered flyby on return to Earth.
Orion would be outfitted with sensors to collect a wide variety of measurements to evaluate its operation in the harsh space environment.
“EM-1 will have a compliment of both operational flight instrumentation and development flight instrumentation. This instrumentation suite gives us the ability to measure many attributes of system functionality and performance, including thermal, stress, displacement, acceleration, pressure and radiation,” Dean told me.
The EM-1 flight has many years of planning and development ahead and further revisions prior to the 2017 liftoff are likely.
“Final flight test objectives and the exact set of instrumentation required to meet those objectives is currently under development,” Dean explained.
Orion is NASA’s next generation manned space vehicle following the retirement of NASA’s trio of Space Shuttles in 2011.
The SLS launcher will be the most powerful and capable rocket ever built by humans – exceeding the liftoff thrust of the Apollo era Moon landing booster, the mighty Saturn V.
“We sent Apollo around the moon before we landed on it and tested the space shuttle’s landing performance before it ever returned from space.” said Dan Dumbacher, NASA’s deputy associate administrator for exploration systems development, in a statement.
“We’ve always planned for EM-1 to serve as the first test of SLS and Orion together and as a critical step in preparing for crewed flights. This change still gives us that opportunity and also gives us a chance to test operations planning ahead of our mission to a relocated asteroid.”
Both Orion and SLS are under active and accelerating development by NASA and its industrial partners.
The 1st Orion capsule is slated to blast off on the unpiloted EFT-1 test flight in September 2014 atop a Delta IV Heavy rocket on a two orbit test flight to an altitude of 3,600 miles above Earth’s surface.
It will then reenter Earth’s atmosphere at speeds of about 20,000 MPH (11 km/sec) and endure temperatures of 4,000 degrees Fahrenheit in a critical test designed to evaluate the performance of Orion’s heatshield and numerous spacecraft systems.
Orion EFT-1 is already under construction at the Kennedy Space Center (KSC) by prime contractor Lockheed Martin – read my earlier story here.
Integration and stacking tests with Orion’s emergency Launch Abort System are also in progress at KSC – details here.
NASA says the SLS is also in the midst of a extensive review process called the Preliminary Design Review (PDR) to ensure that all launch vehicle components and systems will achieve the specified performance targets and be completed in time to meet the 2017 launch date. The PDR will be completed later this summer.
NASA’s goal with Orion/SLS is to send humans to the Moon and other Deep Space destinations like Asteroids and Mars for the first time in over forty years since the final manned lunar landing by Apollo 17 back in 1972.
NASA Headquarters will make a final decision on upgrading the EM-1 mission after extensive technical reviews this summer.
It’s always striking to see a tiny sliver of the New Moon. But you’ve probably never seen a sliver this tiny or a Moon this “new” before. This brand new image by astrophotographer extraordinaire Thierry Legault was taken this morning and is the youngest possible lunar crescent, with the “age” of the Moon at this instant being exactly zero — at the precise moment of the New Moon. The image was taken in full daylight at 07:14 UTC on July 8, 2013.
Normally it is just about impossible (and dangerous) to see this, as when the Moon is this “new,” the Moon is between the Earth and the Sun and it is so close to the Sun in our sky that it can’t be seen because of the Sun’s glare. Plus, the New Moon appears as an extremely thin crescent which is barely brighter than the blue sky. But Thierry has designed a special sunshade to prevent sunlight from entering the telescope (see it below).
Thierry says the irregularities and discontinuities seen in the edge of the crescent are caused by the relief at the edge of the lunar disk; i.e. mountains and craters on the Moon. Very cool!
The “New Moon” is defined as the instant when the Moon is at the same ecliptic longitude as the Sun. When we refer to the “age” of the Moon, it is the number of hours (or days) since New Moon.
From Thierry’s shooting site in Elancourt, France (a suburb of Paris), the angular separation between the Moon and the Sun was only 4.4° (nine solar diameters).
“At this very small separation, the crescent is extremely thin (a few arc seconds at maximum) and, above all, it is drowned in the solar glare, the blue sky being about 400 times brighter than the crescent itself in infrared (and probably more than 1000 times in visible light),” Thierry writes on his website. “In order to reduce the glare, the images have been taken in close infrared and a pierced screen, placed just in front of the telescope, prevents the sunlight from entering directly in the telescope.”
Thierry cautions anyone trying to see this with the naked eye. Basically, don’t try it.
“The very thin crescent of the New Moon cannot be observed visually whatever the instrument (naked eye, binoculars, telescope, etc),” he said. “Moreover, pointing a celestial object that close to the Sun is dangerous for the observer and his equipment if it is not performed under the control of an experienced astronomer and with the proper equipment.”
See more information at Thierry’s website. He also took another image of the New Moon at the exact moment back in 2010.
If you want to keep track of what the Moon will look like each night (or day!), Universe Today has a great app for that, our Phases of the Moon app, available for iOS or Android.
If you’re like me, you don’t change your computer’s desktop background nearly often enough… especially not considering all the fantastic space images that get released on an almost daily basis. But this picture, shared a couple of weeks ago by NASA’s Marshall Space Flight Center on their Flickr stream, really should inspire you to fix that. (I know it did for me!)
Captured by an Expedition 28 crew member aboard the International Space Station, this beautiful image shows a crescent-lit Moon seen through the upper layers of Earth’s atmosphere.
As it circles the globe, the ISS travels an equivalent distance to the Moon and back in about a day, making an excellent platform for viewing the Earth and its atmosphere. This photo shows the limb of Earth near the bottom transitioning into the orange-colored troposphere, the lowest and most dense portion of the Earth’s atmosphere. The troposphere ends abruptly at the tropopause, which appears in the image as the sharp boundary between the orange- and blue- colored atmosphere. Silvery-blue noctilucent clouds extend far above the Earth’s troposphere.
Expedition 28 began on May 23, 2011, with a crew consisting of Andrey Borisenko, Ron Garan, Alexander Samokutyaev, Sergei Volkov, Mike Fossum, and Satoshi Furukawa.
Image credit: NASA (Source)
Look up into the night sky and count the moons. You can see only one moon, “the” Moon. But does the Earth have any other moons? Around the Solar System, multiple moons are the rule. Jupiter has 67 natural satellites, even Mars has two asteroid-like moons.
Could Earth have more than one?
Officially, the answer is no. The Earth has a single moon.
Today.
It’s possible Earth had more than one moon in the past, millions or even billions of years ago. Strange terrain on the far side of the Moon could be explained by a second moon crashing into it, depositing a layer of material tens of kilometers deep.
Moons could come and go over the billions of years of the Earth’s history.
For example, Mars has two Moons, but not for long. Phobos, the larger moon, is spiraling inward and expected to crash into the planet within the next 10 million years. And so, in the future, Mars will only have a single Moon, Deimos.
It’s also possible that the Earth might capture a Moon in the future. Neptune’s largest moon, Triton, orbits in the opposite direction from the rest of the moons around the planet. This suggests that Triton was actually a captured Kuiper Belt Object which strayed too close to the planet.
So we can assume events like this have happened in the past.
Additionally, we might have more moons, but they haven’t been discovered yet because they’re just too small. Researchers have calculated that there could be meter-sized asteroids in orbit around the Earth, remaining in orbit for hundreds of years before gravitational interactions push them out again.
And there are other objects that interact with Earth’s orbit in strange ways. Scientists don’t consider them moons, but they do stick around in our neighbourhood:
Asteroid 3753 Cruithne is in an orbital resonance with the Earth. It has a highly eccentric orbit, but takes exactly one year to orbit the Sun. From our perspective, it follows a slow, horse-shoe shaped path across the sky. Since the discovery of Cruithne in 1986, several other resonant near-Earth objects have been discovered.
So, the answer… Earth only has a single Moon. Today. We might have had more moons in the past, and we might capture more in the future, but for right now… enjoy the one we’ve got.
Want to learn more? Here are some articles on Universe Today we’ve written about this topic:
What are some objects known as Earth’s other moons?
Did Earth have more than one moon in the past?
Does Earth have many tiny moons?
You might also enjoy this episode of Astronomy Cast: Where did the Moon come from?