On April 20th (4/20) at midnight Earth’s horizon (in northern latitudes) lines up perfectly with the plane of the entire Milky Way galaxy. The galaxy “wraps around” our view of the sky and we can see into and through the plane of the galaxy.
At this moment when you look out around you at the horizon, you are looking into the plane of the Milky Way galaxy.
How to See the Milky Way Galaxy Plane
Look southward (and a little bit east) and you are looking toward the center of the galaxy. Look northward (and a little bit west) and you are looking toward the outer edges of the galaxy.
Why does the galaxy line up with the horizon?
Each year on 4/20 the galaxy lines up with the horizon – an “event” I call the Galaxy Horizon. In fact, this “event” occurs every day! It’s just an interesting coincidence that the alignment happens on 4/20 at midnight. Each day the galaxy lines up again with the horizon but it happens 4 minutes earlier.
Earth Map in the Sky – Landforms as Constellations
Learn how to see the map of Earth in the starry sky.
Stars help us find our way. Stars are like a giant map in the sky that tells us where we are on the surface of the Earth. Sailors use them as a “map” to navigate the world. For thousands of years, the stars were stationary markers of latitude and longitude.
We are going to learn to map something new onto the sky: locations on the Earth! We can create an exciting new set of “constellations” out of the shapes of the continents on the Earth.
We live on a sphere so we can see half of the sky (a hemisphere) at any one moment. It’s easy to imagine half the Earth mapped onto half the sky. Keep reading to learn how.
Wherever you are on the Earth, when you look straight up (toward your zenith), you might see one star, but there are a bunch of other stars within view. All of the stars you see in the sky are directly overhead some other place on the Earth. Every place on Earth has their own set of stars directly overhead – their “zenith stars.”
Look up at any star in the night sky; that star is directly over some place on Earth. There are hundreds of “faraway zeniths” up there.
World Zeniths – See the Map of the Earth in the Sky
Every star maps to a location on Earth and every location on Earth maps to a star.
If you live in the western hemisphere, you can learn to look up and “see” the land borders of the North American and South American continents visible, projected into the sky like a giant painting on a curved ceiling. You can learn to see even more landforms in the sky – you can learn to see the entire western half of the Earth projected in the sky.
Visualize Countries in the Sky
We can learn to see country outlines in the sky. The key is to imagine yourself at the center of the Earth looking out into space “through” a translucent Earth surface.
Here is a good way to visualize these countries-in-the-sky even when you are on the surface. Imagine that you can look up and see your location at the zenith.
When I do this, I see southern New York state, Long Island jutting out into the water like a long pier, and the wide Hudson River emptying past New York City. Eastward is the dark expanse of the Atlantic Ocean and low on the eastern horizon are the countries of Europe and West Africa.
Westward in the sky, I can see the outline of the west coast of the US. Then, there is a big blank space of the Pacific Ocean and a spot near the western horizon that is Hawaii.
The Map of the Earth in the Sky is Reversed
There is one odd thing about the map as you see it in the sky… it’s reversed – as if seen in a mirror! This happens because we project the map lines outward into space toward the stars. When we look at the map this way it’s as if we are “inside” the Earth looking outward.
The map of the USA covers about 58˚ of sky from east-to-west. 58˚ is about 2x pinky-to-thumb (spread out all your fingers of both hands and touch thumbs). Your left pinky tip should be on your zenith. If you are in New York or somewhere on the east coast, the right pinky tip will indicate the approximate western edge of the USA.
Physical Astronomy – Stars Map to Places on Earth
Learn to see the zenith map in your sky using this Physical Astronomy technique.
Exercise 1: face south and point high in the sky.
Face south. Then, reach both hands straight up over your head and point above your head with both pointer fingers. You are pointing at your zenith. Now, bring both arms down until they are pointing one due east and one due west. You are pointing at two points in the sky that are zeniths for someone else.
Secret! You Can See a Star That Another Person Can’t
If you do this physical astronomy exercise right after sunset, the eastern and southern zenith locations are in night, but the western and northern sky points are over Earth locations that still have daytime.
This means that you can see the star that is at their zenith, but they cannot see that star. For example, Seattle still has 3 hours of sunlight left in their day so stars are invisible behind blue sky. The city of Yekaterinburg is on the opposite side of the world and just after sunset in New York it faces the Sun and has a bright daytime sky!
We are on the night time side of the Earth and we can see the current zenith stars of Seattle and Yekaterinburg – but people who live in these cities cannot see them! They have to wait to rotate to the night time side of the Earth to see stars.
The Math – How High Up is the Zenith Map?
Project an imaginary map of the Earth into the sky. The map has to be the correct size so that when it is viewed from a distance it “covers” the same distances.
If a map is too close, it is just the same size as the territory. So, we have to choose the correct distance to project the zeniths. As the zenith map “projector screen” moves away from the Earth we see more of the borders of the Earth. But, at some point the distance of the map corresponds exactly to the faraway zeniths.
Our question is: “How far away from the Earth do you have to be so the landforms (like the continents) have an angular diameter that is equivalent to their “actual size” in the sky?” How far away does our imaginary zenith map USA (about 3000 miles wide) image have to be to cover 58 degrees of arc in the sky?
To answer this we need math.
The Zenith Map Distance from Earth
The Earth is approximately 24,901 miles in circumference at the equator. If we can see half the sky from any point on the Earth, then we can “see” half the Earth projected onto the sky by the zenith map. That means that for 180˚ of sky we can “see” about 12,450 miles of the Earth’s surface projected into space. 12,450/180 = 69 miles. When 1 degree of arc spans 69 equatorial miles the image is “at” the correct distance.
1 Degree of Sky equals 69 Miles
So, at the equator every degree of sky covers about 69 miles in every direction. As you go towards the poles the longitude degrees (east and west) cover less and less zenith map distance, but the latitude degrees (north and south) always stretch 69 miles. Every 15˚ of sky equals about 1035 (69*15) miles.
The distance between your pointer finger and your pinky (when you hold your arm and hand stretched out in front of you) is 15˚ – so you are measuring about 1035 miles on Earth with that sky measurement. One pinky width is equal to 1˚, which is 69 miles of zenith map!
The Math – Inverse Tangent and Angular Diameter
There is a simple calculation that helps us determine how far away something needs to be to fill just 1˚ of the sky. Here we use just a tiny drop of trigonometry to discover the “tangent of 1 degree.”
The tangent of 1˚ is 0.017455. The inverse of something is when you divide 1 by the number you want to invert. So, the inverse of 0.017455 (1/0.017455) is 57.29. The inverse of the tangent of 1˚ helps us figure out the distance something has to be to appear to be 1 degree angular diameter.
So, 57.29 * 69 miles = 3,953 miles away! This is how far away the “map” has to be to show you your hemisphere of the Earth map. 3,953 miles is higher than low Earth orbit (LEO) satellites (lower than 1200 miles); it’s closer than geosynchronous satellites (at about 23,000 miles); and it’s about 1/60 the way to the Moon.
So, imagine that the Earth map is projected onto a screen – an imaginary celestial sphere, shell-shaped – that is quite close to the Earth and encircles us. It shows us our Earthen landforms and the oceans beside, superimposed in the sky.
We live on a sphere. When we look at out night sky we are able to see stars low on our horizon that are visible directly above someone else – one-quarter the way around the around the world in all directions.
If you live within 6 time zones of someone that means that you share some “simultaneous sky.” Anyone living further than 6 time zones away sees a completely different sky – unless you can see circumpolar stars that dip under the North Star. That means that you can see countries past the North Pole and down the other side of the globe.
Your zenith is yours – it is unique and changing all the time. Not even someone standing right beside you shares your zenith. You can use this idea of the zenith stars to comprehend the vast and mysterious experience of life on a sphere.
Before that year there were wild places in between constellations where stars could exist. After 1930 all of the stars had been pinned down – like rows of dead butterflies. Every star is now “inside” a constellation boundary.
We don’t need this word sporades any more; all the stars have been captured.
It’s a skeleton key to the sky. It’s a poster. It’s a tome.
Guy Ottewell’s Zodiac Wavy chart poster.
This poster is HUGE. 24 inches wide x 36 inches tall. Also, it’s glossy and beautiful and full of engrossing details. You will return to this poster month after month and dwell on the intricate and scientifically-accurate renderings.
It is like a Moon Calendar but it shows the actual Moon position as well as its phase and date – plus it includes everything else in the sky. Best of all, it adds the “backdrop” of the zodiac constellations so you can see how everything moves among the stars.
The Zodiac Wavy Charts poster portrays the wildness of the Moon and its dynamic motion through the sky – all in a beautiful, informative, and rewarding wall hanging.
Guy Ottewell’s Zodiac Wavy Charts is a snapshot of the calendar month. Every day’s events are “layered” onto a wavy band. Think of those wavy charts in 3-dimensions: You can pluck one off the page, stitch it together into a ring, enlarge it, and step inside it and you’ve got a view of the most interesting and active sky chart you’ve ever seen!
It’s Better than a Moon Calendar
In a standard Moon Calendar the day squares contain the Moon phase images. The Moon images can be arranged artfully, but mostly they are placed to make the Moon conform to the month; the Moon gets “captured” into our cultural calendar. You can see the phase and the day the Moon phase will happen. This is good as far as it goes… but the Zodiac Wavy Charts poster is 100x better!
Guy Ottewell’s Zodiac Wavy Charts can tell you the day the Moon phase will happen. Also, it shows exactly where in the sky, and in which part of the Moon’s orbit it will happen. It tells you which part of the Moon is titled toward you, if it’s in an ascending or descending part of its orbit, and what constellation it is in.
This yearly calendar packs information that will teach you how to observe and will help you make sense of the sky. It’s like having an expert astronomer on-call all year long.
If you don’t have a Zodiac Wavy charts poster yet – you can order it here at Universal Workshop. The rest of this article will help people use the deep details on the poster to understand the motions of sky objects.
Quickstart Guide – Using the ZOD poster
Note: the Zodiac Wavy charts poster shows a northern hemisphere viewpoint. All writing here assumes you are in a northern hemisphere location.
Before you read this guide, please read Guy Ottewell’s text at the bottom of the poster. It explains many of the key items visible in the chart and serves as a legend. Guy’s writing provides a wonderful tour of the deep information revealed by these charts.
Unique Design Elements Tell the Story
Guy uses clever graphic design techniques to communicate how things move in the sky. For instance, to indicate how far the Sun moves in a month he expands the Sun with concentric rings. This clearly shows the sky location on the 1st of the month (the right edge of the outer yellow ring), the 16th of the month (the central Sun image), and the last day of the month (the left edge of the yellow ring).
Another unique design element (a variable-size red triangle) indicates the Moon’s current libration – tilt – towards or away from the Earth. Knowledge of the Moon’s libration helps observers see hidden Moon formations.
Guy also has prepared a detailed list of celestial events throughout the year that you can use to pinpoint on the Zodiac Wavy Charts. The Astronomical Calendar Any Year (or ACAY for short) has a FREE listing of celestial events. You can download the year’s worth of observing data in a PDF file from Guy’s website Universal Workshop.
Read the Charts from Right to Left
The Sun, Moon, and planets move (in general) from right to left across the sky. So too the Zodiac Wavy chart should be read from right to left. You can see the Moon phase images (and day numbers) grow from right-to-left. You can observe that the Sun moves from right-to-left over the month.
Sometimes when the Moon “overlaps” itself during a calendar month, the numbering looks a little funny – this happens because the calendar month is not the same as the Moon phase month (except February) the calendar month is always longer. This article about Blue Moons shows what happens when we try to squeeze the Moon into our monthly boxes.
The first and last wavy charts have lots of text indicating the constellation names, but the middle charts leave them out for clarity. If you want to find out which constellation a celestial object is “in” you can refer to the January or December charts.
Start with the Sun as the Anchor
Use the Sun as the anchor for understanding how to read the charts. Look to the left of the Sun image in each month. The space spanning 6 constellations to the left (east) of the Sun shows you the night sky at sunset. The space spanning 6 constellations to the right of the Sun shows you the pre-sunrise sky. The midnight sky is always centered about 6 constellations to the left of the Sun. You can imagine the whole of the night sky by centering your eye on the anti-Sun which shows the location of midnight on the 16th of the month.
The Sky at Midnight – Anti-Sun and the Full Moon
The anti-Sun indicates the meridian (the middle of the sky) at midnight. The anti-Sun also moves from right-to-left through the sky. It could be displayed with the same-sized concentric Sun rings. It marks midnight and you can see that the Full Moon is always close by.
Tilt the Poster to Line Up with the Sun
Here’s a fun idea: turn the poster sideways and place it on an east or west wall at sunset to “see” the star band lined up with the rising “anti-sun” (east wall) or the setting “sun” (west wall). Anchoring to the Sun or the Anti-Sun may help you visualize how the Zodiac Wavy Charts poster shows you the whole sky of Zodiac constellations all at the same time.
Why is it Wavy?
The meaning of the waves. It’s easier to imagine this if you think of the Equator as the horizontal and the plane of the solar system as tilted.
Eclipses – Every Six Months in the Same Sky
The location of eclipses = the location of node crossings = the location of the nodes = changes very, very slowly (18 years, 11 days, 8 hours to be exact).
Look at the eclipses – there are a few of them every year and 2019 is no exception! Notice that they all occur during the New Moon or the Full Moon and that they all occur in the constellations Gemini or Sagittarius. The reason the eclipses happen while the Moon or the Sun are in Gemini or Sagittarius is because of the Moon’s orbital nodes. These nodes are “in” these two constellations this year.
It’s not just the Moon that orbits the Earth, the Moon’s orbit nodes themselves actually orbit the Earth. This orbit of the nodes takes 18.6 years! The intersection with the lunar phase cycle and the orbit of the Moon’s apsides is the source of the famous Saros interval – where 2 similar eclipses occur.
So, if you buy the Zodiac Wavy Chart poster for the next 18 years, you’ll see the Moon’s orbital nodes – the location of eclipses – move through each of the fixed constellations!
Retrograde Motion – See it!
Planet motion is cool. Planets close to the Sun never cross the anti-sun, but outer planets do. This confused our ancient ancestors who did not realize that the planets were following an orbital path around the Sun at the same time that the Earth was following its own orbital path.
These two motions (the planet’s and the Earth’s) made it look like the planets sometimes moved backwards (retrograde)! You can find all of the retrograde motions easily and see exactly when and where they will happen.
Measurement – by Counting Constellations
Degree marking – the charts lack any of the standard degree measurements (Right Ascension/Declination or Altitude/Azimuth). This type of measurement is not really necessary for general use of these charts. This is because you can find these measurements in other places.
However, you may want to understand how big each section of the sky is compared to each section of the chart. You can think about it like this: there are 12 zodiac constellations (13 if you count Ophiuchus) and they span 360 degrees of the sky. We can see a bit less than 180 degrees of the sky at any one time so that’s about 6 visible constellations! Just count about 6 constellations and you’ll get about half the sky!
If you divide 360 degrees by 12, you get 30 degrees. So, an average constellation covers about 30 degrees of sky. And the sky moves at a rate of about 15 degrees per hour. That means it will take about 12 hours for the sky to completely change.
Want to figure out how big something is? Use your outstretched hand as a measuring tool. The distance from your thumb to your pinky (when your hand is fully-stretched out) is about 25 degrees – a little less than the average constellation width.
One interesting after-effect of rendering the Sun’s position in this “wavy” way is that you can see an aspect of the analemma. The slight movement in the Sun’s position month over month traces a very slim half-analemma shape across the poster. There is a very slight speed up and slow down that you can see if you look closely.
Here is an image of the poster showing the slight but noticeable curve that the Sun makes.
Sidereal Map – the Stars Stand Still
These Zodiac Wavy Charts create a sidereal map of the sky. Sidereal refers to the fact that the background of stars remains fixed through every chart while all the other objects move through them.
What do you see?
There are hidden treasures all through this gorgeous image. Share them with us when you find them!
Frequently Asked Questions
Why is the Zodiac Wavy Chart wavy? The charts are wavy because Guy wanted to show what was happening at the ecliptic. The ecliptic is tilted at 23.4˚ from Earth’s pole (90˚ from the equator). So, sometimes objects in the ecliptic are below the equator and sometimes they are above it.
What is the Zodiac? The zodiac is the collection of constellations that define the ecliptic. The zodiac constellations define a band of sky where the Sun, Moon, and planets can always be found. Fun fact: Zodiac comes from the same root word that Zoo does – and it’s called that because many of the constellations are animals.
Is this an astrology tool? No, this is a visual astronomy tool. Astrologers will certainly find this a useful poster to refer to, but it is designed for visual astronomy observation assistance.
What can I use this for? This astronomy poster is useful for many things! Mostly, it’s a beautiful wall hanging that will draw your eye and reveal the deep celestial mechanics behind our Earth’s motion through the solar system each year. It’s also a wonderful conversation piece. Try telling people “It’s like a Moon Calendar, but it works for everything else in the sky too!”
Can I order this Zodiac poster internationally? Yes – you may have to pay a little extra shipping and sometimes customs duties, but the poster can be shipped almost anywhere.
Does the site accept purchase orders? No, Universal Workshop does not accept purchase orders. You can pay by credit, debit, or paypal.
Can I order a 2020 poster now? Yes! Please contact Guy [at] Universal Workshop [daht] com or visit UniversalWorkshop.com and make a comment on one of the recent blog posts.
Can I order in bulk? Yes! Contact Guy Ottewell for details.
The Moon Hat keeps your head warm – yes! And, every day it gently reminds you to be curious about the Moon. It reminds you to observe what usually stays hidden. It reminds you to #doscienceeveryday.
There are many ways to wear a Moon Hat. You can wear the Moon Hat in at least 10 different ways. The Moon Hat is made of soft stretchy fleece with small embroidered Moon phase images placed all around the brim.
The Moon Hat fabric is flexible and foldable.
10 ways to wear the Moon Hat
Moon Finder – where is the Moon right now
Phase Reminder – what is the Moon phase right now
Hidden Moon outside – hide the moons outside
Hidden Moon inside – hide the moons inside
Tidal Shores no tag – longshoreman style
Tidal Shores show tag – longshoreman style
Moon Slouch – Moon Finder, pull the fleece backward
Moon Beret – Moon Finder, pull the fleece forward
Moon Disk – Hidden Moon inside, show one embroidered disk
Moon Peeker – Hidden Moon inside, peek one embroidered disk
Halfsies (Bonus #11) – Hide half the phases, wear the hat straight
#1 – The Moon Finder
The standard way to wear the Moon Hat with the new Moon image in front. This creates the model of the Moon, Earth, Sun relationship and helps you understand how the motions of the Moon create the phases that we see from Earth.
Get the current Moon phase. Put the hat on with the New Moon image on your forehead. Face the Sun. Now, all of the Moon phase images point to where the Moon is in the sky. Amazing!
#2 – The Phase Reminder
This everyday style is for people who want to remind themselves of the phases of the Moon and how they change over the 29 and a half days of the cycle. Just choose a Moon phase and put it at the front.
This is a subtle way to keep track of the Moon phases and learn their sky location. Before you put on the hat, pause for a second and consider which phase to wear. And, it doesn’t feel like a Moon phase quiz – it’s fun to put your thinking cap on!
#3 – Hidden Moon outside
Don’t want any Moon phases to show? Just fold up the brim toward the outside of the hat and all of the Moon phase images disappear.
Sometimes a hat is just a hat.
#4 – Hidden Moon inside
Another way to hide the Moon phase images… tuck the brim of the Moon Hat towards the inside. All the Moon phase embroidery is now hidden and you have a sleek cap.
Looking for a unique style? The Moon Hat is flexible.
#5 – Tidal Shores no tag
This is the longshoreman style. Turn the Moon Hat inside out and then fold the brim outward. The brim should be wide enough to both show the Moon phase images and hide the instruction tag.
A close-fitting style that uncovers your ears.
#6 – Tidal Shores show tag
Just like the Tidal Shores no tag, but the brim of the hat is folded thinly so that the tag is revealed. You can wear the tag on the side, or the back, or if you are feeling daring, on the front!
This style makes a strong statement – show off the instruction tag.
#7 – Moon Slouch
This is the Moon Finder style, but pull the Moon Hat upwards to get some amount of fabric standing up away from your head and then pull it backward and flatten it for a sleek look
You can easily wear the Moon Hat pulled up above your ears.
#8 – Moon Beret
This is the Moon Finder style, but pull the Moon Hat upwards to get some amount of fabric standing up away from your head and then pull it forward and flatten it for an intense look.
Folding and bunching the fabric in the hat leads to a renaissance or jester look.
#9 – Moon Disk
The Moon Disk style starts with the Hidden Moon inside, but then you pull the embroidered disk of your favorite Moon phase and place it somewhere – it could be centered on your forehead or placed round the side of your head just behind the ear, or all the way at the back. It’s your choice.
This style lets you show an individual Moon image disk.
#10 – Moon Peeker
This style is the same as the Moon Disk, but pull the Moon phase under the fabric of the brim until it is just peeking out. This style looks particularly good when the disk is just in front of your left or right ear.
This look makes a sly statement.
#11 – Halfsies
Fold down half the Moon Hat brim to hide 4 of the phases, then adjust, and angle the hat so that it looks like it is sitting flat on your head.
An alternative way of hanging your hat.
Go out and play with the Moon Hat
This is a fun and flexible bit of fabric with lots of science and a mountain of style potential. Hide and show the Moon phase images, fold and flex the fabric. Get outside and get curious about the Moon and its motion.
This hilariously-headlined New York Times article describes the results of the observational experiment performed during the 1919 eclipse. It highlights that the expedition proved Einstein’s prediction. But the writer claims that only 12 men on Earth can really understand the result: that light’s path is curved by space time.
Assuming you are not above the Arctic circle and not too close to the equator… if you could look right at the Sun (when the night is exactly half over) – by looking through the Earth – which cardinal direction would you be facing? East, West, North, or South?
Physical Astronomy is a new way of teaching astronomy that emphasizes the human body and its relationship to other moving objects in space. The goal is to bring geometric and scientific awareness to a child’s everyday sky observations. Kids learn easily visible sky motions at a “kid’s eye level.”
The Sun does not move… we move
One of the first steps in Physical Astronomy is to forget you ever heard the words “Sunset” or “Sunrise.” These words (while rife with history, beautiful in their own right, and descriptive) are scientifically wrong. These words obscure the truth of our trip around the Sun. We are on the Earth, the Earth is spinning; the Sun appears to be moving, but it is us moving. Click here to continue reading…
Ptolemaeus, Alphonsus, and Arzachel… the names of three massive, interlocking craters on the Moon. These three craters tell the story of the ancient Moon’s creation and evolution. It’s a story of violent bombardments and oceans of lava. We can use light and shadows to reveal the shapes and deep history of these features.
Most people think of astronomy a science of light. But, light creates shadows when it hits things. Those features that lie in the shadows, the dark parts and seemingly just-in-the-way-of-the-light parts, are just as important as those that shine brightly. These dark shadows form most of the mass of all galaxies, house stellar nurseries, reveal old lava rivers on the Moon, and create curious plays of light and dark. These can play tricks on our eyes and make patterns appear.