APOD: Moon Phases in 2021 (2021 Jan 11)

[APOD Robot]

Moon Phases in 2021

Explanation: What will the Moon phase be on your birthday this year? It is hard to predict because the Moon's appearance changes nightly. As the Moon orbits the Earth, the half illuminated by the Sun first becomes increasingly visible, then decreasingly visible. The featured video animates images taken by NASA's Moon-orbiting Lunar Reconnaissance Orbiter to show all 12 lunations that appear this year, 2021. A single lunation describes one full cycle of our Moon, including all of its phases. A full lunation takes about 29.5 days, just under a month (moon-th). As each lunation progresses, sunlight reflects from the Moon at different angles, and so illuminates different features differently. During all of this, of course, the Moon always keeps the same face toward the Earth. What is less apparent night-to-night is that the Moon's apparent size changes slightly, and that a slight wobble called a libration occurs as the Moon progresses along its elliptical orbit.

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[iv_s]

Hi! Does Aries sign at the right of the Earth have any astrology meaning? And if it's so, why it doesn't change?
Thanks for the great video!

[De58te]

Question, if the Moon's phases for the year are hard to predict for professional APOD astronomers, then how can my "Farmer's Almanac" get the Moon's phases correct right down to the hour and minutes, Greenwich Time, when they already published on 1st December of the previous year. [I bought my copy on 2nd December.]

[Tszabeau]

Watching that makes me feel like I’ve had a little too much libration.

[orin stepanek]

I loved it! Very mesmerizing; the music made it more so! I'm gonna watch it again sometime!

[neufer]

Hi! Does Aries sign at the right of the Earth have any astrology meaning? And if it's so, why it doesn't change?

<<The First Point of Aries, also known as the Cusp of Aries, is the location of the vernal equinox, used as a reference point in celestial coordinate systems. In diagrams using such coordinate systems, it is often indicated with the symbol ♈︎. Named for the constellation of Aries, it is one of the two points on the celestial sphere at which the celestial equator crosses the ecliptic, the other being the First Point of Libra, located exactly 180° from it. Due to precession of the equinoxes since the position was originally named in antiquity, the position of the Sun on the March equinox is now in Pisces, while that on the September equinox is in Virgo (as of J2000).>>

[neufer]

Lincoln in 1857

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Question, if the Moon's phases for the year are hard to predict for professional APOD astronomers, then how can my "Farmer's Almanac" get the Moon's phases correct right down to the hour and minutes, Greenwich Time, when they already published on 1st December of the previous year. [I bought my copy on 2nd December.]

<<Abraham Lincoln (February 12, 1809 – April 15, 1865) argued in an 1858 criminal trial, defending William "Duff" Armstrong, who was on trial for the murder of James Preston Metzker. The case is famous for Lincoln's use of a fact established by judicial notice to challenge the credibility of an eyewitness. After an opposing witness testified to seeing the crime in the moonlight, Lincoln produced a Farmers' Almanac showing the moon was at a low angle, drastically reducing visibility. Armstrong was acquitted.>>

[MarkBour]

Question, if the Moon's phases for the year are hard to predict for professional APOD astronomers, then how can my "Farmer's Almanac" get the Moon's phases correct right down to the hour and minutes, Greenwich Time, when they already published on 1st December of the previous year. [I bought my copy on 2nd December.]

No, it's not hard for professional APOD astronomers. The caption is phrased as an educator would phrase it: "This is not easy, young pupil, but I'm going to show it to you." Your Farmer's Almanac probably got its information from an astronomer.

I really loved this APOD, I could stare at it for a very long time noticing more details. It is incredibly precise, way beyond a simple listing of phases: From it I can tell that on the night of my birthday this year, which is a full 10 months away, the Moon will progress downward from 69% illuminated to about 65% illuminated over the course of the night (more exact than "waning gibbous"). Early in the evening, the craters DesCartes, Aristoteles, Sacrobosco and Maurolycus will be right on the terminator. But then, during the evening, the terminator will move past the site of Apollo 16's lander, and reach the craters Boscovich, Geber, Gemma Frisius, and Jacobi. The Moon's apparent diameter that evening will be 1782.7 arcseconds. Its position angle will be 7.971 degrees . It even tells me where to look for her in the sky, but I don't think I'll really need that help, she's kind of hard to miss.

[johnnydeep]

Nice video, but I'm really confused. The text says the images were taken by the Lunar Reconnaissance Orbiter. Now, that is in orbit about the moon, so how are we supposed to end up with what purports to be the phases and librational motion of the moon as seen from the earth? Or am I misunderstanding what this is showing?

Also, though the date is obviously important in determining what the moon will look like as seen from earth, isn't the location on the earth also important, since exactly which hemispheric portion of the moon someone sees varies depending on where you are located? Granted, the difference will be small because the moon is roughly 30 earth diameters away, but still.

[Chris Peterson]

Nice video, but I'm really confused. The text says the images were taken by the Lunar Reconnaissance Orbiter. Now, that is in orbit about the moon, so how are we supposed to end up with what purports to be the phases and librational motion of the moon as seen from the earth? Or am I misunderstanding what this is showing?

Also, though the date is obviously important in determining what the moon will look like as seen from earth, isn't the location on the earth also important, since exactly which hemispheric portion of the moon someone sees varies depending on where you are located? Granted, the difference will be small because the moon is roughly 30 earth diameters away, but still.

The LRO records both optical data and also laser altimetry. The final output is a dataset that defines points on the Moon by reflectivity and height. From this, an image can be synthesized for any solar angle. The shadows are cast digitally. The landscape is created digitally. The frames in this video are synthesized, they are not made directly from images.

[johnnydeep]

Nice video, but I'm really confused. The text says the images were taken by the Lunar Reconnaissance Orbiter. Now, that is in orbit about the moon, so how are we supposed to end up with what purports to be the phases and librational motion of the moon as seen from the earth? Or am I misunderstanding what this is showing?

Also, though the date is obviously important in determining what the moon will look like as seen from earth, isn't the location on the earth also important, since exactly which hemispheric portion of the moon someone sees varies depending on where you are located? Granted, the difference will be small because the moon is roughly 30 earth diameters away, but still.

The LRO records both optical data and also laser altimetry. The final output is a dataset that defines points on the Moon by reflectivity and height. From this, an image can be synthesized for any solar angle. The shadows are cast digitally. The landscape is created digitally. The frames in this video are synthesized, they are not made directly from images.

So, the LRO only provided the exact mapping of the moon (presumably the entire sphere of the moon, even the "dark side" what we can't see from earth). And then "some software" just used that data to construct the image of the moon we would see at any particular time. And what about the position on the earth making a difference in the moon's appearance? An effect too small to notice?

[Chris Peterson]

Nice video, but I'm really confused. The text says the images were taken by the Lunar Reconnaissance Orbiter. Now, that is in orbit about the moon, so how are we supposed to end up with what purports to be the phases and librational motion of the moon as seen from the earth? Or am I misunderstanding what this is showing?

Also, though the date is obviously important in determining what the moon will look like as seen from earth, isn't the location on the earth also important, since exactly which hemispheric portion of the moon someone sees varies depending on where you are located? Granted, the difference will be small because the moon is roughly 30 earth diameters away, but still.

The LRO records both optical data and also laser altimetry. The final output is a dataset that defines points on the Moon by reflectivity and height. From this, an image can be synthesized for any solar angle. The shadows are cast digitally. The landscape is created digitally. The frames in this video are synthesized, they are not made directly from images.

So, the LRO only provided the exact mapping of the moon (presumably the entire sphere of the moon, even the "dark side" what we can't see from earth). And then "some software" just used that data to construct the image of the moon we would see at any particular time. And what about the position on the earth making a difference in the moon's appearance? An effect too small to notice?

Position on the Earth will produce enough difference to be noticable. But there's no way to capture that in a static video. So we have to live with a video synthesized from a single topocentric position (or maybe a geocentric view?). A version of this that ran as a real-time app could construct the image based on position, of course.

[neufer]

Question, if the Moon's phases for the year are hard to predict for professional APOD astronomers, then how can my "Farmer's Almanac" get the Moon's phases correct right down to the hour and minutes, Greenwich Time, when they already published on 1st December of the previous year. [I bought my copy on 2nd December.]

No, it's not hard for professional APOD astronomers. The caption is phrased as an educator would phrase it: "This is not easy, young pupil, but I'm going to show it to you." Your Farmer's Almanac probably got its information from an astronomer.

• After astronomer/editor David Young’s death in 1852 the Farmers’ Almanac got it Wright:

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<<Founded in 1818, the Farmers’ Almanac mixes a blend of long-range weather predictions, humor, fun facts, and advice on gardening, cooking, fishing, conservation, and other topics [much like the Asterisk*]. The Farmers’ Almanac has had seven editors. Poet, astronomer, and teacher David Young held the post for 34 years starting from when he and publisher Jacob Mann first founded The Almanac Publishing Company in Morristown, New Jersey. Following Young’s death in 1852, astronomer Samuel Hart Wright became editor.

Each new year’s edition is released at the end of August of the previous year and contains 16 months of weather predictions broken into 7 zones for the continental US as well as seasonal weather maps for the winter and summer ahead. Predictions for each edition are made as far as two years in advance. The U.S. retail edition of the Farmers' Almanac contains weather predictions for 7 U.S. climatic zones, defined by the publishers, in the continental United States, broken into 3-day intervals. Seasonal maps and summaries for each season are also shared in each new edition, as are forecasts for annual sporting events.

The Farmers' Almanac will only state publicly that their method is an “exclusive mathematical and astronomical formula, that relies on sunspot activity, tidal action, planetary position (astrology) and many other factors." The Almanac's forecaster is referred to by the pseudonym Caleb Weatherbee. According to the publishers, the true identity of the forecaster is kept secret to prevent them from being "badgered."

The Farmers’ Almanac's forecaster: Mr. Weatherbee

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Publishers point to the fact that "many longtime Almanac followers claim that their forecasts are 80% to 85% accurate" on their website. Their website also contains a list of the many more "famous" weather predictions they have accurately forewarned of and like to point out that they’ve been predicting the weather longer than the National Weather Service. Most scientific analyses of the accuracy of Farmers' Almanac forecasts have shown a 50% rate of accuracy, no greater than random chance, but higher than that of groundhog prognostication, another folklore method of forecasting.>>

Art Neuendorffer (whose APOD posts are 80% to 85% accurate )

[johnnydeep]

The LRO records both optical data and also laser altimetry. The final output is a dataset that defines points on the Moon by reflectivity and height. From this, an image can be synthesized for any solar angle. The shadows are cast digitally. The landscape is created digitally. The frames in this video are synthesized, they are not made directly from images.

So, the LRO only provided the exact mapping of the moon (presumably the entire sphere of the moon, even the "dark side" what we can't see from earth). And then "some software" just used that data to construct the image of the moon we would see at any particular time. And what about the position on the earth making a difference in the moon's appearance? An effect too small to notice?

Position on the Earth will produce enough difference to be noticable. But there's no way to capture that in a static video. So we have to live with a video synthesized from a single topocentric position (or maybe a geocentric view?). A version of this that ran as a real-time app could construct the image based on position, of course.

Thanks. Do we know what position on earth was used for this? I suppose it doesn't have anything to do with the Position, Subsolar, Sub-Earth and Pos. Angle values, but I don't understand those anyway.

[Chris Peterson]

So, the LRO only provided the exact mapping of the moon (presumably the entire sphere of the moon, even the "dark side" what we can't see from earth). And then "some software" just used that data to construct the image of the moon we would see at any particular time. And what about the position on the earth making a difference in the moon's appearance? An effect too small to notice?

Position on the Earth will produce enough difference to be noticable. But there's no way to capture that in a static video. So we have to live with a video synthesized from a single topocentric position (or maybe a geocentric view?). A version of this that ran as a real-time app could construct the image based on position, of course.

Thanks. Do we know what position on earth was used for this? I suppose it doesn't have anything to do with the Position, Subsolar, Sub-Earth and Pos. Angle values, but I don't understand those anyway.

I didn't see anything on the source page where the video is presented and discussed.

[alter-ego]

featured video

The animation archived on this page shows the geocentric phase, libration, position angle of the axis, and apparent diameter of the Moon throughout the year 2021, at hourly intervals.

Geocentric - The logical coordinate center.