What Causes Tides?

Tides refer to the rise and fall of our oceans’ surfaces. It is caused by the attractive forces of the Moon and Sun’s gravitational fields as well as the centrifugal force due to the Earth’s spin. As the positions of these celestial bodies change, so do the surfaces’ heights. For example, when the Sun and Moon are aligned with the Earth, water levels in ocean surfaces fronting them are pulled and subsequently rise.

The Moon, although much smaller than the Sun, is much closer. Now, gravitational forces decrease rapidly as the distance between two masses widen. Thus, the Moon’s gravity has a larger effect on tides than the Sun. In fact, the Sun’s effect is only about half that of the Moon’s.

Since the total mass of the oceans does not change when this happens, part of it that was added to the high water regions must have come from somewhere. These mass-depleted regions then experience low water levels. Hence, if water on a beach near you is advancing, you can be sure that in other parts of the world, it is receding.

Most illustrations containing the Sun, Moon, Earth and tides depict tides to be most pronounced in regions near or at the equator. On the contrary, it is actually in these regions where the difference in high tide and low tide are not as great as those in other places in the world.

This is because the bulging of the oceans’ surface follows the Moon’s orbital plane. Now, this plane is not in line with the Earth’s equatorial plane. Instead, it actually makes a 23-degree angle relative to it. This essentially allows the water levels at the equator to seesaw within a relatively smaller range (compared to the ranges in other places) as the orbiting moon pulls the oceans’ water.

Not all tides are caused by the relative positions of these celestial bodies. Some bodies of water, like those that are relatively shallow compared to oceans, experience changing water levels because of variations in the surrounding atmospheric pressure. There are also other extreme situations wherein tides are manifested but have nothing to do with astronomical positioning.

A tidal wave or tsunami, for example, makes use of the word ‘tide’ and actually exhibits rise and fall of water levels (in fact, it is very noticeable). However, this phenomena is caused entirely by a displacement of a huge amount of water due to earthquakes, volcanic eruptions, underwater explosions, and others. All these causes take place on the Earth’s surface and have nothing to do with the Moon or Sun.

A thorough study of tides was conducted by Isaac Newton and included in his published work entitled Philosophiæ Naturalis Principia Mathematica.

We have some related articles here that may interest you:

There’s more about it at NASA. Here are a couple of sources there:

Here are two episodes at Astronomy Cast that you might want to check out as well:

Sources:
Princeton University
NASA
NOAA

After Loss of Lunar Orbiter, India Looks to Mars Mission

India Moon Mission

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After giving up on re-establishing contact with the Chandrayaan-1 lunar orbiter, Indian Space Research Organization (ISRO) Chairman G. Madhavan Nair announced the space agency hopes to launch its first mission to Mars sometime between 2013 and 2015. Nair said the termination of Chandrayaan-1, although sad, is not a setback and India will move ahead with its plans for the Chandrayaan-2 mission to land an unmanned rover on the moon’s surface to prospect for chemicals, and in four to six years launch a robotic mission to Mars.


“We have given a call for proposal to different scientific communities,” Nair told reporters. “Depending on the type of experiments they propose, we will be able to plan the mission. The mission is at conceptual stage and will be taken up after Chandrayaan-2.”

On the decision to quickly pull the plug on Chandrayaan-1, Nair said, “There was no possibility of retrieving it. (But) it was a great success. We could collect a large volume of data, including more than 70,000 images of the moon. In that sense, 95 percent of the objective was completed.”

Contact with Chandrayaan-1 may have been lost because its antenna rotated out of direct contact with Earth, ISRO officials said. Earlier this year, the spacecraft lost both its primary and back-up star sensors, which use the positions of stars to orient the spacecraft.

The loss of Chandrayaan-1 comes less than a week after the spacecraft’s orbit was adjusted to team up with NASA’s Lunar Reconnaissance Orbiter for a Bi-static radar experiment. During the maneuver, Chandrayaan-1 fired its radar beam into Erlanger Crater on the moon’s north pole. Both spacecraft listened for echoes that might indicate the presence of water ice – a precious resource for future lunar explorers. The results of that experiment have not yet been released.

Chandrayaan-1 craft was designed to orbit the moon for two years, but lasted 315 days. It will take about 1,000 days until it crashes to the lunar surface and is being tracked by the U.S. and Russia, ISRO said.

The Chandrayaan I had 11 payloads, including a terrain-mapping camera designed to create a three-dimensional atlas of the moon. It is also carrying mapping instruments for the European Space Agency, radiation-measuring equipment for the Bulgarian Academy of Sciences and two devices for NASA, including the radar instrument to assess mineral composition and look for ice deposits. India launched its first rocket in 1963 and first satellite in 1975. The country’s satellite program is one of the largest communication systems in the world.

Sources: New Scientist, Xinhuanet

LRO, Chandrayaan-1 Team Up For Unique Search for Water Ice

NASA’s Lunar Reconnaissance Orbiter and India’s Chandrayaan-1 will team up on August 20 to perform a Bi-Static radar experiment to search for water ice in a crater on the Moon’s north pole. Both spacecraft will be in close proximity approximately 200 km above the lunar surface, and both are equipped with radar instruments. The two instruments will look at the same location from different angles, with Chandrayaan-1’s radar transmitting a signal which will be reflected off the interior of Erlanger crater, and then be picked up by LRO. Scientists will compare the signal that bounces straight back to Chandrayaan with the signal that bounces at a slight angle to LRO to garner unique information, particularly about any water ice that may be present inside the crater.

Both spacecraft are equipped with a NASA Miniature Radio Frequency (RF) instrument that functions as a Synthetic Aperture Radar (SAR), known as Mini-SAR on Chandrayaan 1 and Mini-RF on LRO.

“The advantage of a Bi-Static experiment is that you’re looking at echoes that are being reflected off the Moon at an angle other than zero,” said Paul Spudis,principal investigator for Chandrayaan-1’s Mini-SAR,discussing the mission on The Space Show. “Mono-static radar sends a pulse, and you are looking in the same phase or incident angle. But with Bi-Static, you can look at it from a different angle. The significance of that is ice has a very unique bi-static response.”

Erlanger Crater from the Lunar Orbiter. Credit: NASA
Erlanger Crater from the Lunar Orbiter. Credit: NASA

Stewart Nozette, Mini-RF principal investigator from the Universities Space Research Association’s Lunar and Planetary Institute, said, “An extraordinary effort was made by the whole NASA team working with ISRO to make this happen”

While this coordination sounds easy, this experiment is extremely challenging because both spacecraft are traveling at about 1.6 km per second and will be looking at an area on the ground about 18 km across. Due to the extreme speeds and the small point of interest, NASA and ISRO need to obtain and share information about the location and pointing of both spacecraft. The Bi-Static experiment requires extensive tracking by ground stations of NASA’s Deep Space Network, the Applied Physics Laboratory, and ISRO.

Even with the considerable planning and coordination between the U.S. and India the two instrument beams may not overlap, or may miss the desired location. Even without hitting the exact location Scientists may still be able to use the Bi-Static information to further knowledge already received from both instruments.

“The international coordination and cooperation between the two agencies for this experiment is an excellent opportunity to demonstrate future cooperation between NASA and ISRO, “says Jason Crusan, program executive for the Mini-RF program, from NASA’s Space Operations Mission Directorate, Washington, D.C.

New Device Extracts Oxygen from Moon Rocks

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Are we perhaps one step closer to being able to live on the Moon? A new device developed by scientists in Cambridge, UK, can extract oxygen from Moon rock. This technology would be extremely important for creating a lunar bases for long term habitation, or using the Moon as a jump-off point to explore the deeper reaches of space.

The new device, a reactor developed by Derek Fray and his colleagues, was created from a modified electrochemical process the team invented in 2000 to get metals and alloys from metal oxides. The process uses the oxides — also found in Moon rocks — as a cathode, together with an anode made of carbon. To get the current flowing through the system, the electrodes sit in an electrolyte solution of molten calcium chloride (CaCl2), a common salt with a melting point of almost 800 °C.

The current strips the metal oxide pellets of oxygen atoms, which are ionized and dissolve in the molten salt. The negatively charged oxygen ions move through the molten salt to the anode where they give up their extra electrons and react with the carbon to produce carbon dioxide — a process that erodes the anode. Meanwhile, pure metal is formed over at the cathode.
Moon
To make the system produce oxygen and not carbon dioxide, Fray had to make an unreactive anode. “Without those anodes, it doesn’t work,” said Fray. He discovered that calcium titanate, which is a poor electrical conductor on its own, became a much better conductor when he added some calcium ruthenate to it. This mixture produced an anode that barely erodes at all — after running the reactor for 150 hours, Fray calculated that the anode would wear away by roughly three centimeters a year.

To heat the reactor on the Moon would need just a small amount of power, Fray said, and the reactor itself can be thermally insulated to lock heat in. The three reactors would need about 4.5 kilowatts of power, which could be supplied by solar panels or even a small nuclear reactor placed on the Moon.

In their tests, Fray and his team used a simulated lunar rock called JSC-1, developed by NASA. Fray anticipates that three reactors, each a meter high, would be enough to generate a ton of oxygen per year on the Moon. Three tons of rock are needed to produce a ton of oxygen, and in tests the team saw almost 100% recovery of oxygen, he says. Fray presented the results last week at the Congress of the International Union of Pure and Applied Chemistry in Glasgow, UK.

Source: Nature

Gigapan the Apollo Landing Sites

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If you haven’t had enough Apollo yet, this is like a firehose of image goodness. Gigapan and NASA Ames have collaborated to make huge, zoomable, panable images from two of the Apollo missions to the Moon. Apollo 16 and 17 are the only missions where the astronauts took panoramic images, so these are the only landing sites available in Gigapan. And if you really want to blow your socks off, look at these images in Google Moon. Click your icon for Google Earth (you DO have it downloaded already, don’t you?? If not go to Google Earth and download it,) choose Moon under the little Saturn-like icon on top, zoom in and find the flags for the Apollo 16 and 17 landing sites. Then look for the “camera” icons and click on one, and then choose the option to “fly” into the images. I’m still gasping from doing this with Apollo 17! Once you recover from flying in, you can then pan around and feel like you are walking alongside Gene Cernan and Harrison Schmitt on the Moon. It really is amazing!

Here’s the Gigapan image site. Enjoy!

Company Looks to Etch Advertising on the Moon


A new company is looking to sell advertising on the Moon. No, not with giant billboards, but by a new technology called Shadow Shaping that can creates images with robots that carve small ridges in the lunar dust over large areas that capture shadows and shape them to form logos, domains names or memorials.

“Never in the history of advertising has the possibility of penetrating every market on Earth, reaching every person on the planet, and touching them at emotional level only possible with the beauty of the moon on a starlit night, been made available,” says the website for Moon Publicity. “Twelve billion eyeballs looking at your logo in the sky for several days every month for the next several thousand years.”

Bid now for this exclusive ad space, starting at $46,000 (USD).

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Isn’t this going a bit far, proposing to change the face of the Moon? The Moon Publicity people say they are doing this for the benefit of mankind.

“Advancements in space robotics as a result of Shadow Shaping, will aid in the colonization of outer space, helping preserve mankind from the inherent dangers of placing all of our species’ eggs in one basket, planet Earth. Any number of catastrophic events could end human life on Earth: Pandemics, collisions with comets or asteroids, weapons of mass destruction, supercollider accidents, environmental changes, hypernova radiation or the expansion of the Sun.”

“If shadows form a logo during a quarter moon, it will be a small price to pay for saving mankind.”

The website goes on to say that creating images on the Moon provides a commercial incentive for turbo charging space travel technology. “Shadows are only the beginning. These advancements will eventually place robots on other worlds building space stations and planting crops.”

Hmmm.

Source: Space Coalition Blog

Apollo Landing Sites Pose a Threat to LRO Instrument

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The recent images released by the Lunar Reconnaissance Orbiter of the Apollo landing sites are truly remarkable. But there is one instrument on board LRO that must avoid studying some of the the Apollo sites as well as other places where humans have placed spacecraft on the the lunar surface. The Lunar Orbiting Laser Altimeter (LOLA) pulses a single laser beam down to the surface to create a high-resolution global topographic map of the Moon. However, LOLA is turned off when it passes over the Apollo sites because bouncing the laser off any of the retro-reflective mirrors on experiments left by the astronauts might damage the instrument.

Don Mitchell, who owns a software consulting company and is writing a book on the Soviet Exploration of Venus, wrote about this problem on his blog, saying that if LOLA’s beam did strike the retro reflector experiment, “the light bounced back would be 1,000 times the detector damage threshold.”

LOLA Engineering model. Credit: Goddard Space Flight Center
LOLA Engineering model. Credit: Goddard Space Flight Center

The LOLA instrument is based on Mars Orbiter Laser Altimeter (MOLA), flown on Mars Global Surveyor and the Mercury Laser Altimeter (MLA), currently on MESSENGER. LOLA will perform the same type of work as these previous instruments, but with 3-5 times greater vertical accuracy and 14 times more measurements along the spacecraft ground track.

The Laser Ranging Retroreflector experiment was deployed on Apollo 11, 14, and 15. It consists of a series of corner-cube reflectors, which reflects an incoming light beam back in the direction it came from.

Ever since the experiments were deployed, the McDonald Observatory in Texas has beamed a laser at these mirrors and measured the round-trip of the beam. This provides accurate data on the Moon’s orbit, the rate at which the Moon is receding from Earth (currently 3.8 centimeters per year) and variations in the rotation of the Moon. These are the only Apollo experiments that are still returning data. A similar device was also included on the Soviet Union’s Lunakhod spacecraft.

David E. Smith, LOLA principal investigator confirmed that, indeed, LOLA is switched off over the Apollo and Lunakhod sites, to avoid damaging the instrument. He said the Russians have been very helpful in in providing the LOLA team the best known locations for the two Lunokhod landers. Lunokhod-2 has been located precisely and is routinely probed by lasers from Earth. Lunokhod-1 has never been found by laser, and it is not known for certain if its reflector is deployed. Smith said he and co-PI Maria Zuber have visited Moscow to consult with Russian scientists, who have shared their knowledge of the locations of their landers.

As Mitchell wrote, “While conspiracy nuts debate the reality of the Apollo landings, scientists must deal with some practical consequences of what astronauts put on the Moon.”

Sources: Don Mitchell’s Blog, email exchange with David E. Smith

Hat tip to Emily Lakdawalla on Twitter!

Weight on Other Planets

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Many children, and even adults, dream of visiting other planets and wonder what it would be like to stand on another planet. For one thing, your weight would be different on another planet, depending on a number of factors including the mass of the planet and how far you are away from the center of the planet.

Before we start, it’s important to understand that the kilogram is actually a measurement of your mass. And your mass doesn’t change when you go anywhere in the Universe and experience different amounts of gravity. Your weight is best measured in newtons. But since your bathroom doesn’t measure your weight in newtons, we’ll use kilograms. This is what your bathroom scale would say if you stepped on another world.

Mercury is the smallest planet in our Solar System, but it is dense. Because Mercury is so small, it has very little gravity. If you weighed 68 kg on Earth, you would only weigh 25.7 kg on Mercury. 

Venus is very close to Earth in size and mass. Venus’ mass is roughly 90% of the mass of the Earth. Thus, it is no surprise that someone would weigh a similar amount on Venus. Someone who weighed 68 kg on Earth would weigh 61.6 kg on Venus.

Mars is quite a bit smaller than Earth with only 11% of our planet’s mass. Mars is larger than Mercury, but it is not as dense as the smaller planet. If you weighed 68 kg on Earth then you would weigh 25.6 kg on Mars. Since Pluto was demoted to a dwarf planet, Mars became the planet where you would weigh the least.

Jupiter is the largest planet in our Solar System with the most mass. Because of Jupiter’s mass, you would weigh more on that planet than on any other one in our Solar System. If you weighed 68 kg on Earth then you would weigh 160.7 kg on Jupiter, over twice your normal weight. That is if you could actually stand on Jupiter’s surface, which is impossible because it is a gas giant, and gas giants do not have solid surfaces.

Saturn is a gas giant best known for its planetary rings system. It is also the second biggest planet in our Solar System. Despite its mass though, the planet has a very low density and a lower gravity than Earth. If you weighed 68 kg on Earth, you would weigh 72.3 kg on Saturn.

Uranus is a gas giant without a solid surface. Although Uranus is larger in size than Neptune, it has less mass and therefore less gravity. You would only weigh 60.4 kg on Uranus, if you weighed 68 kg on Earth.

Neptune, the last planet in our Solar System, is a gas giant. If you weighed 68 kg on Earth, then you would weigh 76.5 kg on Neptune if you could stand on the planet’s surface.

Although the Moon is not a planet, it is one of the few objects that astronauts have actually visited. Because the Moon is so small, it has a low density and low gravity. If you weighed 68 kg on Earth, then you would only weigh 11.2 kg on the Moon.

Universe Today has a number of articles to check out including weight on the moon and mass of the planets.

If you are looking for more information then determine your weight on other planets and facts about the planets.

Astronomy Cast has an episode on gravity.

Land on the Moon in Google Earth


To celebrate the 40th anniversary of the Apollo 11 Moon landing, Google has launched a new feature: the Moon in Google Earth. You can now use Google Earth to explore, fly around and search the Moon. Google was able to get several astronauts to participate in this new feature, and you can get tours of landing sites, narrated by Apollo astronauts, view 3D models of landed spacecraft, zoom into 360-degree photos to see astronauts’ footprints and watch rare TV footage of the Apollo missions. The hi-resolution views of the Moon were developed in collaboration with NASA Ames Research and JAXA. It’s loads of fun and provides an historic perspective as well as a look to the future of lunar exploration. If you already have Google Earth 5.0 on your computer, just click on the tab on the top toolbar that has a picture of Saturn, and click on Moon. If you click on the Apollo 11 flag, you can zoom in on that location and take a tour of the first landing site on the Moon! What a great way celebrate the 40th anniversary. Enjoy!

Click here to go the the Moon in Google Earth.

Plane of the Ecliptic

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Plane of the ecliptic, also known as the ecliptic plane, is a phrase you will often hear in astronomy. A basic definition is that the plane of the ecliptic is the plane of the Earth’s orbit, but that does not mean much to most people. Space is a three-dimensional vacuum, which you can think of as a kind of pool with the planets suspended in it. The Earth orbits the Sun on a particular angle and its orbit is elliptical in shape. The orbit is often shown as an ellipse made of dotted lines with the Sun at its center. If you made this ellipse a solid surface and extended it infinitively, then you would have the plane of the ecliptic. Actually our entire Solar System can be thought of as flat because all of the planets’ orbits are near or on this plane.

The ecliptic plane is used as the main reference when describing the position of other celestial objects in our Solar System. The angle between the plane of the ecliptic and the plane of an orbit is called the inclination. Until it was stripped of its status as a planet, Pluto was the planet with the most extreme inclination – 17°. Mercury is the only other planet with a significant inclination of 7°. There is also a 7° inclination between the plane of the Sun’s equator and the ecliptic plane. There are other celestial bodies that have a much greater inclination than any of the planets, such as Eris with a 44° inclination or Pallas with a 34° inclination.

The ecliptic plane got its name from the fact that a solar eclipse can only happen when the Moon crosses this plane to block out the Sun. Our Moon crosses the ecliptic about twice a month. A solar eclipse occurs when a new Moon crosses the ecliptic, and a lunar eclipse occurs when a full Moon crosses it.

Seasons on Earth are caused by our planet’s axial tilt of 23.5°, which causes variations in the amount of sunlight different parts of the Earth receive. This goes for all the other planets too. For example, Uranus rotates on its side with an axial tilt of 97.8°, which results in extreme variations in its seasons. The eclipse is also home to the constellations of the zodiac. There are twelve constellations in the zodiac, which are important symbols in astrology and can also be found in the Chinese calendar.  Here’s a list of all the zodiac symbols.

Universe Today has a number of articles including Virgo one of the zodiac signs and axial tilt.

You should also check out these articles on the ecliptic plane and ecliptic facts for more information.

Do not forget to tune into Astronomy Cast’s episode about the planet’s orbits.

Reference:
NASA: The Path of the Sun, the Ecliptic