Astronomy

How can the author of this article conclude that earth-shine on the moon is 100 times brighter than moon-shine on earth?

How can the author of this article conclude that earth-shine on the moon is 100 times brighter than moon-shine on earth?


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I don't understand the reasoning of the author of this article, on page 26. How can he conclude that full earth-shine on the moon is 100 times brighter than full moon-shine on earth?


The author says that the difference between the factor of 100 and the geometric increase due to area and albedo is because of "atmospheric absorption and directional effects". The former is probably only about 20% or so (i.e. about 20% of moonlight is absorbed/scattered in the Earth's atmosphere). The latter effect could be quite big.

The reflectance of solar system objects shows an opposition surge at small phase angles.

It is difficult to see the full Moon at really small phase angles ($<2$ degrees) from Earth because you would get a lunar eclipse. However, it has been measured by spacecraft and according to Buratti et al. 1996, the brightness of the Moon increases by "more than 40%" between phase angles of just 4 degrees and zero.

When the Sun illuminates the Earth as seen from the Moon then it would be much easier to see at very small phase angles because the Moon's shadow is that much smaller.

I suspect this effect plus the ~20% absorption in the Earth's atmosphere is what the author of your reference is talking about.


Top 12 brightest objects in the solar system

South Carolina sunrise through a piece of beach glass. Image via Fran Aquino.

What are the brightest objects in our solar system that you can see in your sky? The sun is the very brightest, of course, but you might be surprised by some of the other objects that make the list. You can see the first seven objects on this list using just your eyes, even from cities and suburbs. The last items on the list are fainter and therefore more challenging, and likely require a dark-sky site and some optical aid.

In astronomy, the brightness of objects is measured by what’s called magnitude. The lower the number, the brighter the object. So, 1st-magnitude objects indicate the brightest stars in our sky, 2nd-magnitude fainter ones, 3rd-magnitude fainter still, and so on. Note that some objects, some planets for example, are even brighter than 1st magnitude, peaking in negative numbers at their brightest.

Without optical aid, the human eye can see objects to around 6th magnitude, in optimum conditions and under dark skies. There are about a dozen natural solar system objects that are, in theory, visible to the unaided eye. In practice, the fainter ones are very difficult to see with the eye alone, but perhaps possible for those keen vision and true darkness.

Transient objects, such as very bright meteors or comets, aren’t included in this list. Extraordinary meteors can turn the night sky as bright as day, and some comets reach stunning brightnesses, too, such as Ikeya-Seki in 1965, which reached a whopping -10 magnitude and could be seen at noon. But because they’re only in the sky on a temporary basis, and not something that can regularly or consistently be observed, these objects aren’t included here. We also don’t include manmade objects, such as satellites and the International Space Station. Try the Heavens-Above website, if you’re interested in observing human-made Earth-orbiting objects.

Here are the top 12 brightest natural solar system objects, in order from brightest to dimmest:

1. The sun. No surprise here. The sun shines at magnitude -26.7. Technically, the sun can’t even be looked at without special safety filters to protect your eyes. Gazing at the sun directly without special protective filters can cause blindness. That said, now would be a good time to equip yourself with filters for solar observing, and to begin a program of regular sun viewing. You might know that the sun increases and decreases in activity in a cycle lasting 11 years. The new cycle – Solar Cycle 25 – was officially announced in September 2020. At EarthSky Community Photos, we’re beginning to see more sunspots! And more are surely coming, increasing in number to a peak five or so years from now.

View at EarthSky Community Photos. | Victor C. Rogus wrote on January 20, 2021: “The sunspot formerly known as AR2797 has split in two: AR2797 and AR2798. Trailing sunspot AR2798 is crackling with C-class solar flares.” Thank you, Victor!

2. The moon. The moon varies in brightness depending on what phase it’s in. At its full phase when it’s the brightest, it tops out at magnitude -12.7. On the other hand, the moon in its crescent phase shines at only about magnitude -6. If you’re a deep-sky observer, the moon is bright enough to ruin your night vision, meaning it’ll prevent you from getting the best view of distant, faint star clusters, nebulae and galaxies. If you’re using a telescope, the moon should be your last stop during a night of observing. To the eye alone, though, there’s nothing more beautiful than a bright moon shining in the night sky, casting its light and creating moon shadows in the landscape all around you. Visit EarthSky’s moon phases page to learn the dates of major moon phases throughout 2020.

View at EarthSky Community Photos. | Kannan A in Singapore captured this image on January 26, 2021, and wrote: “The waxing gibbous moon rising from behind the apartment block. The moon was 94.1% illuminated and distance from Earth was 391,375 km [243,000 miles] away from Earth when this photo was taken. It was still very much a day moon, as the skies were still bright at this time.” Thank you, Kannan A!

3. Venus. The closest planet to Earth, one step inward in orbit around the sun, is also the brightest planet. It can shine as brightly as magnitude -4.7, bright enough to be seen in daylight if you know just where to look. The brightness of Venus is thanks in part to its proximity to Earth and also, largely, to its thick, reflective clouds. As with all the other solar system objects, Venus varies in brightness depending on a number of factors, including how close it is to Earth and what phase it’s in. Yes, as a planet orbiting inward from Earth, Venus shows phases! Venus was in our morning sky – in the east before sunrise – throughout late 2020. Soon, though, it’ll be gone from our skies for a few months, traveling behind the sun from Earth. Venus will return to our evening sky in May 2021. Find Venus’ location for each month in EarthSky’s planet guide.

View at EarthSky Community Photos. | Catherine Evans caught Venus near daybreak on January 17, 2021, from the Edna Valley in San Luis Obispo, California. She wrote: “Closer and closer to the sunrise, so it won’t be seen much longer.” So true, Catherine! Thank you. Even into early February 2021, if you have a clear sky to the eastern horizon, you might still be able to snag a last look at Venus. Look very low in the east before sunup. If you can’t see it, try sweeping with binoculars.

4. Mars. The red planet is the second-closest planet to Earth after Venus, and it doesn’t often reach its maximum magnitude of -2.9. But when it does … wow! What a sight to behold. Just like other planets outside Earth’s orbit, when Mars is brightest around the time of its opposition, when it’s opposite the sun from Earth, rising in the east as the sun sets in the west. Mars’ oppositions come when our faster Earth moves between Mars and the sun. That happens about every two years. Some Mars oppositions are better than others. Mars was particularly bright in 2018, and its last opposition – around mid-October 2020 – was a good one, too. For about a month around the 2020 opposition, Mars was brighter than Jupiter. At other times (in fact, most of the time), Mars is relatively faint. Sometimes it’s very faint indeed, when it’s on the far side of the solar system from us, shining across its nearly-maximum distance from Earth (about 250 million miles, or 400 million km). After all, Mars is just a little planet, littler than Earth. So its brightness waxes and wanes dramatically as we and Mars move around the sun. Find Mars’ location for each month in EarthSky’s planet guide.

View at EarthSky Community Photos. | Niko Powe in Kiwonee, Illinois, captured Mars next to the Harvest Moon on October 2, 2020. Niko said: “There was a layer of clouds but these two’s appearance would not be denied.”

5. Jupiter. Because Jupiter is the largest planet in the solar system, some mistakenly believe it’s the brightest planet. But not so. Jupiter’s greater distance from us lets Venus and Mars, our neighbors, shine more brightly. Jupiter is nearly always brighter than Mars, though (except when Mars is at its best). At its maximum, Jupiter shines at magnitude -2.8, nearly as bright as Mars’s peak of -2.9, and brighter than Sirius, the sky’s brightest star, which shines at magnitude -1.4. Jupiter was named for the ancient king of the gods. And it has a king-like aspect, always shining at the same dazzling brightness, not changing in brightness like Mars. Plus Jupiter moves in a stately way around the sky it isn’t tied to the sunrise or sunset like Venus. Come to know Jupiter, and you’ll enjoy spotting in your sky for much of every year. Find Jupiter’s location for each month in EarthSky’s planet guide.

6. Mercury. Surprise! The rarely-seen planet Mercury shines more brightly than Saturn at its best. Mercury can reach -1.9 magnitude. That’s brighter than Sirius, the sky’s brightest star. But – because Mercury is our solar system’s innermost planet – this world, more than any other in our solar system, is tied to the sun in our sky. It’s always seen shortly before sunrise, or shortly after sunset, and never gets very high in the night sky. Therefore its brightness is often offset by the fact that you’re viewing the planet in twilight and not in a nice dark sky. Still, Mercury’s brightness will surprise you!

7. Saturn. The ringed planet Saturn is stunning in a telescope, and it’s also an easy catch without optical aid. With the eye alone, you won’t see its rings, but you will see Saturn’s golden color and steady light. At magnitude +0.7, Saturn outshines most stars and is on a par with most of the brightest stars. Plus – because it orbits our sun beyond Earth’s orbit – it’s seen more often than Mercury by casual observers. Saturn is often around deep into the night, when its brightness contrasts with the depths of a dark night sky.

View at EarthSky Community Photos. | Dan Wyman in Oceanside, California, captured Mercury, Jupiter, Saturn and a flock of birds on January 11, 2021. Thank you, Dan! Find Jupiter, Saturn and Mercury each month in EarthSky’s planet guide.

8. Ganymede. If you’re a sky-watcher, you’ve probably seen all the objects mentioned so far without optical aid, knowingly or not. But have you seen Jupiter’s largest moon, Ganymede? Binoculars will let you spot Ganymede circling Jupiter when the satellite is at its brightest, approximately 4.6 magnitude. Ganymede takes about seven Earth-days to complete an orbit around Jupiter, and the other Galilean moons take varying amounts of time (Io nearly two days, Europa about four days, Callisto 17 days). So on any given night, you’ll find the moons in ever-shifting locations with respect to Jupiter. They look like little “stars” strung out in a line that bisects Jupiter. Thus you’ll want to use software, for example SkyandTelescope.com’s interactive Jupiter moon page, to let you know which dot circling Jupiter is Ganymede, from the location, date and time at which you’re looking. Which leads us to …

9. Io. The next item on the solar system brightness list is Jupiter’s volcanic satellite, Io. At a little larger than our moon, Io is the innermost Galilean satellite and shines at magnitude 5.0 when it’s at its best. Can you see Io – or Ganymede – with the eye alone? In theory, you should be able to. But in practice they’re not that easy to see in the glare from Jupiter itself. Some observers with renowned vision (for example, Steven James O’Meara) have claimed to have seen Ganymede with the unaided eye. But such claims are rare. You’ll likely need binoculars for Ganymede or Io, or Europa (see below). Small telescopes show all four Galilean moons in their never-ending dance around Jupiter.

View at EarthSky Community Photos. | John Nelson was at Puget Sound, Washington, on September 24, 2020, when he captured this image. See Jupiter and its moons in the upper left? You might need to view this photo larger to see Jupiter’s moons. John wrote: “All four Galilean moons were visible. I brightened them up just a bit in Photoshop Elements so they would be easier to see in a photo that you can’t zoom in on. From left to right, the moons are Callisto, Ganymede, Europa and just to Jupiter’s right is Io.” Thank you, John.

10. Vesta. The fourth asteroid to be discovered, Vesta, is the only asteroid to make our list of brightest solar system objects. Vesta is the second-largest asteroid, after Ceres. Vesta can reach magnitude 5.1 at its closest approach to Earth. Its opposition – a highlight of the year for asteroid observers – is coming up on March 4, 2021. This is when Earth will sweep more or less between Vesta and the sun, bringing the asteroid closest to us for this year. Because it doesn’t have a bright nearby locator, as Ganymede and Io have with Jupiter, it’s best to watch for Vesta for a couple of nights in a row to see which dim “star” in the area appears to move slowly in front of the fixed star background. Try TheSkyLive for charts and other information on how to observe Vesta.

11. Europa. We bounce back out to Jupiter for the next item on the list, Europa, another of Jupiter’s four large Galilean moons. Europa is a great object to attempt to view and ruminate on, because it may harbor an ocean – and possibly life – beneath its icy crust. Europa just makes our list of the brightest objects in the solar system at magnitude 5.2. Again, we recommend using observing software, such as SkyandTelescope.com’s interactive Jupiter moon page, to know which Galilean moon is which.

12. Uranus, finally. Many know that planet Uranus is theoretically visible to the unaided eye. The seventh planet from the sun appears at magnitude 5.6 at its best. Uranus is most easily picked up with the unaided eye after first pinning down its location with binoculars or a telescope. It has a disk instead of a pinpoint image through an optical device and may even appear faintly bluish green. It is particularly easy to find on the occasions that it pairs up closely with objects easier to locate, such as Mars.

View at EarthSky Community Photos. | Victor C. Rogus in Sedona, Arizona, captured this image of Uranus and Mars through his telescope on January 20, 2021. He wrote: “The sky this evening was fair at best, but I was able to capture this image of an over-exposed Mars and the planet Uranus through thin clouds. Light takes 2 hours, 43 minutes and 27 seconds to travel from Uranus and arrive to us.” Thank you, Victor!

Bottom line: Here are the top 12 brightest natural solar system objects, in order from brightest to dimmest. If you’ve seen every one of these objects, with or without optical aid, congrats!


Mars Getting Closer to Earth

The mysterious Red Planet is going to put on a show this month. It has been getting progressively closer to Earth each night and will continue to grow larger and brighter. By late August it will be about 191 million miles closer, and the reddish point of light will appear six times larger and shine some 85 times brighter than it normally does.

At 5:51 a.m. EDT on August 27, 2003, Mars will be within 34,646,418 miles of Earth, closer than it has been since the days of Hezekiah. (By some calculations, it will be closer than it has been in 73,000 years, but these are based on some commonly held assumptions that are suspect. It may have been closer on several occasions in the more recent past, as will be discussed below.)

On August 28, 2003, Mars will be at "opposition," the moment that the Sun, Earth, and Mars will form a straight line. Mars comes to opposition every 26 months. This time, the opposition will be superior to others because Mars will be at perihelion, its closest point to the Sun. Perihelic oppositions of Mars are rather infrequent, occurring about every 15-17 years. The last opposition, in 2001, involved a separation of more than 41 million miles. In 1995 the distance between the two planets was nearly double what it will be this month.

Though Mars' opposition will come on August 28, it will be closest to Earth on August 27. At the close approach, the Red Planet will be brighter than Jupiter and all the stars in the night sky, outshone only by Venus and the Moon.

Most scientists take for granted that the movements of the planets and other objects in our solar system manifest an unchanging uniformity through time. These movements, however, also manifest minute variations that have, so far, eluded any consistent conjectures.

Furthermore, careful observations of the objects in our solar system indicate that it has been-at least at times-a rather rough neighborhood. Take a look at the Moon through binoculars and you will see a lot of bruises. Or examine any of the photographs from our space probes. You see craters and other evidences of collisions and catastrophes.

There is evidence that the present orbits were not always so. And some of the changes appear to have occurred during the memory of mankind.

Why did so many of the early cultures worship the Planet Mars? They were terrified of this strange planet. It was called the "God of War." Why? (The term "martial arts" is still in our working vocabulary.) And there are other mysteries that seem to be associated with this strange planet.

All early calendars appear to be based on a 360-day calendar: the Assyrians, Chaldeans, Egyptians, Hebrews, Persians, Greeks, Phoenicians, Chinese, Mayans, Hindus, Carthaginians, Etruscans, and Teutons all had calendars based on a 360-day year typically, twelve 30-day months.

In ancient Chaldea, the calendar was based on a 360-day year. It is from this Babylonian tradition that we have 360 degrees in a circle, 60 minutes to an hour, 60 seconds in each minute, etc.

The Biblical Year Is 360 Days

It is also significant that the Biblical year is also based on a 360-day year reckoning. 1 This critical insight unlocks several incredible prophecies which the reader is urged to discover-- in particular, the remarkable "70 Weeks" prophecy of Daniel 9, which is undoubtedly the most amazing passage in the Bible. 2

All Calendars Change in 701 B.C.

In 701 B.C., Numa Pompilius, the second King of Rome, reorganized the original calendar of 360 days per year by adding five days per year. King Hezekiah, Numa's contemporary, reorganized his Jewish calendar by adding a month each Jewish leap year (on a cycle of seven every 19 years). 3

The Roman year began with March, the month named after Mars. (They later reorganized their calendar in 364 B.C. to begin on January 1st.) Most of the early cultures organized their calendars around either March or October. Why? Why was any change necessary after 701 B.C.? What happened to affect all the calendars after that year?

The recent space age discovery of "orbital resonance"-the tendency of orbits to synchronize on a multiple of one another--has led to a fascinating conjecture that the orbits of the Earth and the Planet Mars were once on resonant orbits of 360 days and 720 days, respectively. A computer analysis has suggested that this could yield orbital interactions that would include a near pass-by on a multiple of 54 years, and this would occur on either March 25 or October 25. Such near pass-bys would transfer energy, altering the orbits of each. 4

In near proximity, such pass-bys would be accompanied by meteors, severe land tides, earthquakes, etc., and this would help explain why all the ancient cultures were so terrified by the Planet Mars 5 and why calendars tended to reflect either March or October. 6 A series of such pass-bys could also explain a number of the "catastrophes" of ancient history, including the famous "long day of Joshua" and several other Biblical episodes. 7

Stability appears to have been attained during the last near pass-by in 701 B.C., resulting in Earth's and Mars' present orbits of 365 1/4 days and 687 days, respectively. Provocative, but where's the evidence?

This remarkable conjecture, that Mars made pass-bys near the Earth, would seem to be corroborated by Jonathan Swift (1667-1745) in his famous fantasy known as Gulliver's Travels. In his third voyage, Gulliver visits the land of Laputa, where the astronomers brag that they know all about the two moons of Mars. 8 Their highly detailed description includes the size, the rotation, the revolutions, etc., of each of the two moons.

What makes this particular allusion so provocative is that the two moons of Mars were not discovered by astronomers until 151 years after Swift's publication of Gulliver's Travels in 1726. It was in 1877 that Asaph Hall, using a new telescope at the U.S. Naval Observatory, shocked the astronomical world by discovering the two moons of Mars.

What makes the two moons so difficult to see is that they are only about 8 miles in diameter and have an albedo (reflectivity) of only 3%. They are the darkest objects in the solar system: they are almost black. The two moons are also unique in their rotations and one of them is the only object in the solar system that orbits in reverse. 9 For Swift to have "guessed" these correctly is absurd.

Yet the telescopes of his day were inadequate to have actually seen these objects. But then how could he have known what the astronomers of his day did not? Swift, in order to embroider his satirical fiction, undoubtedly drew upon ancient records he probably assumed were simply legends, not realizing that they were actually eye witness accounts of ancient sightings when Mars was close enough for the two moons of Mars to be viewed with the naked eye!

The possibility that the Planet Mars interacted with the Planet Earth may have implications beyond simply ancient perturbations of our calendar and the subsequent veneration of October 31 as Halloween. It has been widely noted that the ancient Stonehenge monument in England and the Great Pyramid at Cairo have astronomical implications. 10 The geometric and mathematical mysteries of these fabled monuments have been the subject of much conjecture. Cairo was founded on August 5, A.D. 969 by conquering Fatimid armies and named, "Al Kahira," after Mars. Why?

And there are other enigmas.

Most of us have been taught that the planets of our solar system came out of the sun. It may come as a surprise that there are serious scientific difficulties with this presumption. In fact, a careful analysis of existing evidence suggests some surprising alternative possibilities.

Immanuel Kant, in his General History of Nature and Theory of the Heavens, in 1755 in Germany, theorized that some four billion years ago, the sun had ejected a tail, or a filament, of material that cooled and collected and thus formed the planets. Kant is generally credited as the originator of what is commonly called the "Nebular Hypothesis," but the originator was actually Emanuel Swedenborg (1688-1772).

Swedenborg wrote his treatise on cosmology in 1734, in Latin: Prodromus Philosophiae Retiocinantis de Infinito et Cause Creationis. Some 21 years before Kant's publication, Swedenborg proposed that the planets were the result of condensations of a gauze or filament ejected out of the sun. Swedenborg was a mining engineer with a wide range of interests and also claimed to have psychic powers. Historians and biographers seem to take him quite seriously and a number of public incidents caused his fellow Swedes of Stockholm to regard him as irrefutable. He claimed confirmation of his nebular hypothesis from sances with men on Jupiter, Saturn and other places more distant.

(Some 20 years earlier, in 1712, when Swedenborg was 24 years old, he had the opportunity to visit with Edmund Halley at Cambridge, who described to him the various aspects of comets and their tails. Halley had made a study of the reports of various medieval comets, their orbital trajectories, dates, and descriptions, and, of course, is famous for his predictions regarding the comet that still bears his name.)

The famous mathematician Pierre Simon Laplace (1749-1827) lent his endorsement to Kant's theory, but without checking the mathematical validations he was capable of providing. Thus, the nebular hypothesis gained widespread respectability despite serious mathematical flaws. Subsequent writers have continued to develop variations of this view even though increasing difficulties render it increasingly doubtful.

The sun contains 99.86% of all the mass of the solar system. Yet the sun contains only 1.9% of the angular momentum. The nine planets contain 98.1%. There is no plausible explanation that would support a solar origin of the planets.

James Jeans (1877-1946) pointed out that the outer planets are far larger than the inner ones. (Jupiter is 5,750 times as massive as mercury, 2,958 times as massive as Mars, etc.)

Other observations seem to raise even more provocative enigmas concerning our planetary history:

    There are three pairs of rapid-spin rates among our planets: Mars and Earth, Jupiter and Saturn, and Neptune and Uranus, are each within 3% of each other. Why?

(From angular momentum and orbital calculations, it would seem that these three pairs of planets may have been brought here from elsewhere.)

There are other mysteries and we certainly must take most of the conjectures in the field of cosmology as simply what they are: conjectures. But the more we learn, the more we have come to take the Word of God more seriously. After all, He made them all and ought to know! But He has left the thrill of discovery to us all if we will but trust Him:

It is the glory of God to conceal a thing: but the honor of kings is to search out a matter. - Proverbs 25:2

The secret things belong unto the LORD our God: but those things which are revealed belong unto us and to our children for ever, that we may do all the words of this law. -Deuteronomy 29:29

We hope that this brief article will provide some conversation for a warm summer evening.

  1. Genesis 7:24 8:3,4, etc. In Revelation, 42 months = 3 1/2 years = 1260 days, etc. We are indebted to Sir Robert Anderson's classic work, The Coming Prince , (Hodder & Stoughton, London, 1894).
  2. This foundational passage is explained in detail in Daniel's 70 Weeks, a briefing package.
  3. The 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years are leap years, where Adar II is added. Arthur Spier, The Comprehensive Hebrew Calendar , Feldheim Publishers, Jerusalem, 1986.
  4. Detailed in our briefing pack, Signs in the Heavens.
  5. 2 Kings 17:16 21:3-5.
  6. Note also Isaiah 24:1, 19, 20.
  7. Donald W. Patten, Ronald R. Hatch, and Loren C. Steinhauer, The Long Day of Joshua , Pacific Meridian Publishing Co., Seattle, WA, 1973. See also our Expositional Commentary on Joshua.
  8. Jonathan Swift, Gulliver's Travels , 1726, Part III, Chapter 3.
  9. Deimos and Phobos = "Panic" and "fear" in Greek. Phobos is 1/100 width of our moon (8 miles diameter) rotates 7h39m appears to rise in W: unique in our solar system. Deimos (30h18m) appears almost synchronous: 24h37m.
  10. Detailed in Monuments: Sacred or Profane?

This article was originally published in the
August 2003 Personal Update News Journal.


Is the Faint Young Sun Problem for Earth Solved?

Stellar evolution models predict that the solar luminosity was lower in the past, typically 20-25% lower during the Archean (3.8-2.5 Ga). Despite the fainter Sun, there is strong evidence for the presence of liquid water on Earth’s surface at that time. This “faint young Sun problem” is a fundamental question in paleoclimatology, with important implications for the habitability of the early Earth, early Mars and exoplanets. Many solutions have been proposed based on the effects of greenhouse gases, atmospheric pressure, clouds, land distribution and Earth’s rotation rate. Here we review the faint young Sun problem for Earth, highlighting the latest geological and geochemical constraints on the early Earth’s atmosphere, and recent results from 3D global climate models and carbon cycle models. Based on these works, we argue that the faint young Sun problem for Earth has essentially been solved. Unfrozen Archean oceans were likely maintained by higher concentrations of CO2, consistent with the latest geological proxies, potentially helped by additional warming processes. This reinforces the expected key role of the carbon cycle for maintaining the habitability of terrestrial planets. Additional constraints on the Archean atmosphere and 3D fully coupled atmosphere-ocean models are required to validate this conclusion.

This is a preview of subscription content, access via your institution.


It is commonly known that the moon is responsible for disturbances in sleep patterns, and one study carried out by the Psychiatric University Hospital (UPK) at the University of Basel in Switzerland found that around the full moon there was a decrease by 30 percent in electroencephalogram (EEG) delta activity during NREM sleep, which is an indicator of deep sleep. The study also showed an increase of five minutes in the time it took the subjects to fall asleep during a full moon, and a decrease in the quality of sleep.

The researchers also discovered that melatonin levels were lower for up to four days around the full moon, compared to the other lunar phases, suggesting the moon could affect our sleep four days before and four days after the moon is at its brightest stage. Overall, the people who were studied slept around 19 minutes less during the full moon than they did on a new moon, when the sky is at its darkest.

The study mentions the fact that there is more evening light during the full moon, suggesting that lower melatonin levels, due to the absence of darkness, could be a main indicator. This is because our circadian (daily) and circannual (seasonal) rhythms keep close track of subtle changes, so when the world we live in alters, our body patterns alter with it.

The majority of people who are affected by the full moon seem to sleep fine during other evenings in the summer months, when the moon is not full but the sky is still brightly lit at night due to later sunsets. Therefore, it appears that sleep disturbance is not so much to do with the evenings being lighter, but more likely to be correlated to a peak in light during the month, which temporarily disturbs our circadian rhythm.

The study also stated that the moon’s connection to sleep is “mysterious,” explaining that: “there are probably large individual differences that underlie the contradictory evidence for their existence—some people may be exquisitely sensitive to moon.”

Being unable to sleep deeply during a full moon isn’t simply due to knowing the moon is full, as there are many people who claim not to follow moon cycles, but when they find themselves unable to sleep, they research and discover that yet again the moon is shining full in the sky.

I, along with many others, can tell when the moon is full simply by paying attention to sensory information. One of the main things I notice is that I don’t sleep well during a full moon. Even with blackout curtains, I still don’t feel tired at night, and it is normally around 4:00 am before I finally fall asleep, if at all. I experience sleep deprivation just before, during, and after the moon is at its fullest.

Full moons rise at around the same time as the sun sets, which means that during this lunar phase the sky appears far lighter and brighter than normal throughout the night. On a full moon, the sun and moon are opposite one another, with the earth in the middle, and the sun’s rays shine directly on the moon. The glow reflecting off the moon can be so intense that at times it can feel as though there is no definitive break between day and night, so our body and mind may not receive a clear message to signal when it is time to deeply rest.

Some ocean life, including crabs, lay their eggs and mate in alignment with the full moon’s intense light. Coral is also light sensitive, and over 130 species simultaneously spawn in Australia’s Great Barrier Reef on each full moon, providing the clouds do not obscure it.

Although the bright summer nights have some influence over our sleep patterns, I believe the reason some people are so highly affected is that they have heightened sensitivity to energy—which includes light frequencies. Therefore, whenever the moon radiates powerful energy, those who are “light sensitive” would be far more likely to be adversely affected by the moon’s glow.

Human retinas have high sensitivity to blue light—and during the full moon, it is believed that people who have hypersensitive cones in their eyes are able to detect blue tones. This is a surprising phenomenon, known as blueshift, and the reason it is somewhat of a mystery is that the light intensity at moonlight is below the human cone cell’s detection threshold, so our visual perception is monochromatic. (In simple terms, it is thought that humans are unable to see colour when it is dark.)

The blue-light input, which is more intense during full moons, is thought to affect our suprachiasmatic nucleus, responsible for controlling our circadian rhythm. Our circadian rhythm releases melatonin that helps us sleep, and is also connected to physical activity, alertness, hormone levels, body temperature, immune function, and digestive activity. Therefore, it seems highly probable that the blue moonlight tones that light-sensitive people are able to perceive have a direct impact on our energy levels and sleeping patterns.

It is important to note that moonlight is a reflection of sunlight, and it is not blue—it is thought that only people whose eyes have light-sensitive cones are able to detect and perceive the bluish light. Even though it is widely believed that it is not possible to see color at moonlight, you can discover if you are one of the minority with light-sensitive cones by heading outdoors on the next full moon, as far from artificial light as possible, and stare out at the landscape. When you look out at specific areas and tune your focus, you may notice a blue tint to the scenery, and the atmosphere around you might have a blueish colour to it.

Part of the reason that humans now have out-of-sync circadian clocks and disrupted sleep patterns is due to the invention of electricity and the use of artificial light, which can confuse our natural rhythm if we are also absorbing the energy emanating from the moon. Cavemen, for example, would have worked with the moon phases and used the extra night light as an opportunity to hunt later in the evening, and the extra surge in energy would have been welcomed. Whereas, nowadays many people become frustrated with the sudden energy boost and inability to fully relax and deeply sleep on full moon nights. Instead of allowing nature and modern life to mix as one and understand that at certain stages of the month our need for sleep will likely be reduced, it is common for people to feel perplexed and irritable.

Some people use full moons as a chance to sleep out underneath the moon and stars to recharge and rejuvenate their bodies and minds, as even if they do not sleep for long or as deeply as normal, they still wake feeling refreshed and revitalised.

During a full moon, our planet is situated between the sun and the moon—and as we are in the middle of these two extremely powerful forces, we are subjected to a gravitational pull from both directions. This is why many who are ultra sensitive to incoming energy from the universe feel conflicted and possibly even a little out of control when the moon is full, as our energetic field is being pulled in opposite directions.

Therefore, it is highly recommended to keep our energy grounded during a full moon which means that for the few days before, during, and after, we should be drinking plenty of filtered water, abstaining from alcohol and caffeine, minimising the use of technology, taking salt baths, meditating or practicing yoga, and spending time in natural environments.

Not only do many people report that they find it difficult to fall (and remain) asleep during the full moon, the following symptoms are also frequently noted:

>> Vivid and intense dreams and nightmares.

>> Feeling impatient, easily triggered, and argumentative.

>> A vibratory sensation throughout the physical body.

>> Enhanced perception, intuition, and having premonitions.

>> Dramatically increased or decreased energy levels.

>> Difficulty focusing and poor concentration.

>> Prefer to spend time alone.

Disclaimer: If you experience any of the symptoms listed here, please also seek the advice of a medical professional. The above symptoms are commonly noted during major cosmic events, however, there may be other medically related causes.


[edit] Outer belt

The large outer radiation belt extends from an altitude of about three to ten Earth radii (RE) above the Earth's surface. Its greatest intensity is usually around 4𔃃 RE. The outer electron radiation belt is mostly produced by the inward radial diffusion [ 4 ] [ 5 ] and local acceleration [ 6 ] due to transfer of energy from whistler mode plasma waves to radiation belt electrons. Radiation belt electrons are also constantly removed by collisions with atmospheric neutrals, [ 6 ] losses to magnetopause, and the outward radial diffusion. The outer belt consists mainly of high energy (0.1󈝶 MeV) electrons trapped by the Earth's magnetosphere. The gyroradii for energetic protons would be large enough to bring them into contact with the Earth's atmosphere. The electrons here have a high flux and at the outer edge (close to the magnetopause), where geomagnetic field lines open into the geomagnetic "tail", fluxes of energetic electrons can drop to the low interplanetary levels within about 100 km (a decrease by a factor of 1,000).

The trapped particle population of the outer belt is varied, containing electrons and various ions. Most of the ions are in the form of energetic protons, but a certain percentage are alpha particles and O + oxygen ions, similar to those in the ionosphere but much more energetic. This mixture of ions suggests that ring current particles probably come from more than one source.

The outer belt is larger than the inner belt and its particle population fluctuates widely. Energetic (radiation) particle fluxes can increase and decrease dramatically as a consequence of geomagnetic storms, which are themselves triggered by magnetic field and plasma disturbances produced by the Sun. The increases are due to storm-related injections and acceleration of particles from the tail of the magnetosphere.

There is debate as to whether the outer belt was discovered by the U.S. Explorer 4 or the USSR Sputnik 2/3. [citation needed]


Contents

Because the moon is round, half of it is lit up by the sun. As it goes around (or orbits) the Earth, sometimes the side that people on Earth can see is all lit brightly. Other times only a small part of the side we see is lit. This is because the Moon does not send out its own light. People only see the parts that are being lit by sunlight. These different stages are called Phases of the Moon.

It takes the Moon about 29.53 days (29 days, 12 hours, 44 minutes) to complete the cycle, from big and bright to small and dim and back to big and bright. The phase when the Moon passes between the Earth and Sun is called the new moon. The next phase of the moon is called the "waxing crescent", followed by the "first quarter", "waxing gibbous", then to a full moon. A full Moon occurs when the moon and sun are on opposite sides of the Earth. As the Moon continues its orbit it becomes a "waning gibbous", "third quarter", "waning crescent", and finally back to a new moon. People used the moon to measure time. A month is approximately equal in time to a lunar cycle.

The moon always shows the same side to Earth. Astronomers call this phenomenon tidal locking. This means that half of it can never be seen from Earth. The side facing away from Earth is called the far side or dark side of the Moon even though the sun does shine on it—we just never see it lit.

Before people stood on the Moon, the United States and the USSR sent robots to the Moon. These robots would orbit the Moon or land on its surface. The robots were the first man-made objects to touch the Moon.

Humans finally landed on the Moon on July 21, 1969. [9] Astronauts Neil Armstrong and Buzz Aldrin landed their lunar ship (the Eagle) on the surface of the moon. Then, as half the world watched him on television, Armstrong climbed down the ladder of the Eagle and was the first human to touch the Moon as he said, "That's one small step for a man, one giant leap for mankind."

Even though their footprints were left on the moon a long time ago, it is likely that they are still there, as there is no wind or rain, making erosion extremely slow. The footprints do not get filled in or smoothed out.

More people landed on the moon between 1969 and 1972, when the last spaceship, Apollo 17 visited. Eugene Cernan of Apollo 17 was the last person to touch the moon.

Because it is smaller, the Moon has less gravity than Earth (only 1/6 of the amount on Earth). So if a person weighs 120 kg on Earth, the person would only weigh 20 kg on the moon. But even though the Moon's gravity is weaker than the Earth's gravity, it is still there. If person dropped a ball while standing on the moon, it would still fall down. However, it would fall much more slowly. A person who jumped as high as possible on the moon would jump higher than on Earth, but still fall back to the ground. Because the Moon has no atmosphere, there is no air resistance, so a feather will fall as fast as a hammer. [10]

Without an atmosphere, the environment is not protected from heat or cold. Astronauts wore spacesuits, and carried oxygen to breathe. The suit weighed about as much as the astronaut. The Moon's gravity is weak, so it was not as heavy as on Earth.

In the Earth, the sky is blue because the blue rays of the sun bounce off the gases in the atmosphere, making it look like blue light is coming from the sky. But on the moon, because there is no atmosphere, the sky looks black, even in the daytime. There is no atmosphere to protect the moon from the rocks that fall from outer space, and these meteorites crash right into the moon and make wide, shallow holes called craters. The moon has thousands of them. Newer craters gradually wear away the older ones.

The giant impact hypothesis is that the Moon was created out of the debris from a collision between the young Earth and a Mars-sized protoplanet. This is the favored scientific hypothesis for the formation of the Moon. [11]

In 2009 NASA said that they had found a lot of water on the moon. [12] The water is not liquid but is in the form of hydrates and hydroxides. Liquid water cannot exist on the Moon because photodissociation quickly breaks down the molecules. However, from the image NASA received, there is a history of water existence.

During the Cold War, the United States Army thought about making a military post on the Moon, able to attack targets on Earth. They also considered conducting a nuclear weapon test on the Moon. [13] The United States Air Force had similar plans. [14] [15] However, both plans were brushed-off as NASA moved from a military to a civilian-based agency.


How Far Can Laser Light Travel?

(Inside Science) -- Have you ever played with a pocket-sized laser, wondering how far its light would travel? Could you, a naughty student inside a classroom on Earth, annoy a poor substitute teacher on Mars by waggling your laser pointer at him?​

The math:

One only needs three rather simple equations for all the calculations done in this article. First, if we assume the laser is optimized so that its spreading angle is at its theoretical minimum, then we can calculate its beam divergence (in radians) using this equation.

(The laser's wavelength)/(π × The laser's aperture)

Then a little bit of geometry will give us the size of the final lit spot at the destination.

π × (Beam divergence in radians × Distance) 2

Finally, the brightness at the destination is given by dividing the output power of the laser over the area of the spot.

(The laser's power)/(Size of the spot)

If you didn’t make a mistake in your calculations and kept everything in radians, watts and meters, the final number should be in watts per square meter.

The dimmest light visible to the naked eye in perfect darkness is around one ten-billionth of a watt per square meter. However, with the presence of urban light pollution, one usually can’t see stars much dimmer than the North Star, which has an intensity of around four-billionths of a watt per square meter. For comparison, the full moon is almost a million times brighter at one-thousandth of a watt per square meter. Finally, the midday sun is at a whopping 1,000 watts per square meter, about half a million times brighter than the moon.

In this article, we will be using these numbers as references.

T​he short answer: no. By the time the light finally reached Mars, the glint would be a million times dimmer than the faintest light visible to the human eye.

But you don’t need to take our word for it. The math needed to calculate the answer is surprisingly simple.

Partly inspired by a talk at a recent astronomy meeting that explored whether we could detect photons from potential exoplanet-dwelling aliens, Inside Science performed some of our own calculations to see if a hypothetical alien Galileo could observe photons coming from Earth.

All we need is an equation for calculating how quickly a laser beam spreads out as it travels through space. From that we can use straightforward geometry to derive the diameter of the beam when it hits its target. Finally, we divide the power output of the laser by the area of the final lit spot and voila! -- that's how intense the laser is at the destination. While the way humans, or aliens, perceive the brightness of this light is much less straightforward, for the purpose of this exercise we treat brightness and light intensity as the same thing.

Your pocket laser pointer

The power for an average laser pointer is a measly 0.005 watts. However, because of the narrow path of the laser beam, if you pointed it directly at your eye from an arm's length away, the little illuminated dot on your eyeball would be 30 times brighter than the midday sun. So, don't do this at home, or anywhere.

Still, the narrow beam will spread out over long distances. Around 100 meters away from a red laser pointer, its beam is about 100 times wider and looks as bright as a 100-watt light bulb from 3 feet away. Viewed from an airplane 40,000 feet in the air -- assuming there’s no clouds or smog -- the pointer would be as bright as a quarter moon. From the International Space Station, it would fade to roughly as bright as the brightest star in the night sky -- Sirius.

Credit: Abigail Malate, Staff Illustrator, Copyright: American Institute of Physics

For Starman, the dummy driving the Tesla car that Elon Musk's company Space X recently launched into space, your little red laser pointer would be too dim to notice. If you want to get his attention, you'll need something brighter.

The Navy's missile-killer

The U.S. Navy might have what we need. According to recent reports, their current goal is to develop a laser that is both logistically practical and powerful enough to destroy incoming cruise missiles. A laser like that would need to put out about 500,000 watts of power -- 100 million times more powerful than your pocket laser pointer. These lasers typically operate in the infrared spectrum, which is invisible to humans. But for the sake of this exercise we'll assume that both Starman and the Martians can see in the infrared.

More Light and Laser Insight from Inside Science:

Could Nobel-Winning Laser Tech Make Sci-Fi 'Tractor Beams' a Reality?

Liquid Crystals Could Protect Pilots Against Laser Pointer Attacks

How Much Starlight has the Universe Produced?

Weapons-grade lasers also tend to have a much larger opening, or aperture, which counterintuitively causes the laser beam to spread out less, thus enhancing the beam’s ability to maintain its intensity over longer distances.

Because of the larger aperture, if the missile-killer laser beam is aimed at the moon, the infrared spot it would make on the surface would only be about 1.5 miles across. For comparison, the incredibly dim red dot from your pocket laser pointer would be 8 miles wide once it reached the moon.

If you could see in the infrared and stood on the moon underneath the military laser’s beam, it would appear roughly 30 times brighter than the full Earth. That’s quite bright, but not blindingly so. It’s still only one-thousandth the brightness of the midday sun on Earth.

By the time the beam reached the Martians -- if we assume the shortest possible distance between Earth and the red planet, which is about 34 million miles -- the spotlight would be about 200 miles across. Its light should still be noticeable -- about half as bright as the brightest star in the sky sans the sun -- but not exactly attention grabbing.

Looks like we need more power.

Credit: Abigail Malate, Staff Illustrator, Copyright American Institute of Physics

The most powerful laser ever built

Several scientific facilities around the world have huge lasers that operate at more than a thousand trillion watts. In other words, these lasers have as much power as a million trillion pocket laser pointers -- that’s almost a billion laser pointers for every person on the planet!

If run continuously, these lasers would use up the entire world's electricity supply in seconds. Luckily, the only reason these lasers can put out such intense power is that they concentrate the release over an extremely short period of time -- usually less than a trillionth of a second. The extremely short laser pulse is then focused down to a point a few thousandths of a millimeter across, and can be 10 trillion trillion times brighter than the surface of our sun. It's so powerful that scientists are using them to rip apart empty space itself in a quest to learn more about the fundamental laws of our universe.

What if we just want to use this for fun and shoot it at space invaders? One major drawback is that these lasers usually produce ultraviolet light, which is mostly absorbed by the Earth’s atmosphere. If we don’t want to turn our air into plasma, we’d have to construct our building-sized super laser cannon in space instead.

Credit: Abigail Malate, Staff Illustrator, Copyright American Institute of Physics

For the extremely brief time we could afford to fire the laser at Mars, it would cast UV light a thousand times more intense than the midday sun on Earth over an area 150 miles across. Let’s hope that the Martians have some SPF-1,000 sunblock handy.

Sadly, as we know by now, there are no little green men on Mars, or most likely anywhere else in our solar system. However, there are thousands of discovered exoplanets -- planets that orbit around stars outside our solar system -- many of which have the possibility to contain life. What if we try to get their attention?

Credit: Abigail Malate, Staff Illustrator, Copyright American Institute of Physics

Proxima Centauri, located roughly four light-years away, is the closest star to us and is orbited by several exoplanets. If we aimed our most powerful laser there, by the time the light reached it, it would appear brighter than the brightest star looks to us in a clear night sky. So, four years after we’ve fired our laser, if there's any alien astronomer looking at the right spot in their night sky, they may notice a nanosecond flash of ultraviolet light and go, "What was that?"

Yuen would like to thank Eric Korpela, an astronomer from the Berkeley SETI Research Center for the insightful conversation that led to this exercise. This article is partly inspired by a presentation by Barry Welsh, an astronomer from the University of California, Berkeley, during the 231st meeting of the American Astronomical Society, and also this blog post from “What If?” by Randall Munroe.

Editor’s Note: This article has been updated to correct a previous inaccuracy concerning the distance between Proxima Centauri and Earth. We regret the error.


The lunar atmosphere

Optical and radio estimates of the upper limit of density of the lunar atmosphere are reviewed. Properties of the lunar ionosphere in contact with the surface are analyzed theoretically and applied to an estimate of its composition and density. Considering the balance between injection and escape, the daytime average probable number density at the surface is rated at 3 to 5 × 10 5 cm −3 , with an uncertainty ratio of about 2 and with 50–70 per cent CO2, 45-27 per cent H2O anf 4-2 per cent H2. The electron density, in equilibrium with contact recombination at the surface, is then 200–300 cm −3 . The sources of the atmosphere are solar wind, its interaction with, and sputtering of, the surface, meteor impact degassing, and somewhat dubious “volcanic” sources. The surface electric charge is slightly negative or neutral only when the total density falls below 3 × 10 5 , and the electron density below 200, will there be a positive charge.

The photoelectric efficiency of silicates is estimated to be of the order of 1 80 , and the electron emission as depending on surface potential is estimated accordingly from the solar ultraviolet emission. Mechanisms of escape—thermal, collisional with solar wind, and ionic—are evaluated quantitatively. Thermal escape prevails for hydrogen the other two processes for the heavier molecules. The longest escape time scale is about 2 years for xenon, provided the layer is thin (exospheric). No permanent atmosphere can exist on the moon.

The conditions of static and escaping plasma equilibrium are reviewed. Conservation of space charge in an escaping plasma stream requires the establishment of turbulent electric fields which force the electrons to oscillate with thermal velocities around the mean motion determined by the momentum of the ions. The fields prevent direct escape of the photo-electrons from the lunar surface, and play a decisive role in the structure of the lunar ionosphere.

From cometary phenomena and optical data for the zodiacal light the persistent and principal component of solar wind is estimated to correspond to N 6 = 50 cm −3 , v = 200 km sec , a relative electron temperature of about 400–500°K at the earth's orbit, and a translational energy of 210 eV for the protons and ∼1000°K for the electrons.

Whereas other constituents of the lunar atmosphere are escaping to space, water molecules created chemically by solar wind chiefly sublimate into the cold spots of permanent shadow where lunar glaciers up to 100 meters equivalent thickness may have accumulated over the ages.


Cosmic tumbleweeds

These dusty hazards are a bit like cosmic tumbleweeds and may end up having quite a bit of relevance for future space exploration.

For instance, certain space missions involve parking satellites at the Lagrange points, where they consume minimal fuel to stay in orbit. That includes the upcoming James Webb Space Telescope, which is due to unfurl at the Lagrange point L2 sometime in the 2020s. Space agencies have also come up with plans to use Lagrange points as transfer stations on a so-called interplanetary superhighway for missions to Mars, Horváth says.

“The investigation of the dynamics of Kordylewski clouds may very well end up being most important from the point of view of space navigation safety,” he adds.

And if Horváth amd Slíz-Balogh’s hypotheses are right, there may be more of these roving clouds of dust chasing Earth, just waiting to be discovered in neighboring Lagrange points.