Carol-Irene Southworth, a student in Professor B’s Solar System class at the University of California at San Diego, wrote and recorded the following song describing the phases of the Moon. If you want to play along, the chords are just C and F, in this case played on the ukulele (according to Woody Guthrie, “if you play more than two chords, you’re showing off”).
Over the course of roughly a month, the part of the Moon that is illuminated goes through a regular cycle of phases. Starting from dark new moon phase, the Moon gradually brightens, or waxes, through waxing crescent, first quarter, waxing gibbous and finally to a bright full moon phase 14 days later. The Moon then dims, or wanes, over the next 14 days, going through waning gibbous, third quarter, waning crescent and finally dark new moon again. This cycle is due to the relative orientation of the Sun, Moon and Earth, and the dark portions of the Moon are always caused by its own shadow shielding the Sun’s rays. New moon phase happens when the Sun, the Moon and the Earth are in a line, so that the far side of the Moon we can’t see is lit up. Full moon phase happens when the Sun, the Earth and the Moon are in a line, so we see the sunlit side of the Moon. The other phases occur in between these two alignments, which are also called syzygy.
The earliest astronomers may have been women, who discovered that the cycle of the Moon was synchronized with their menstrual cycle. Having an external cue for this internal cycle would have allowed women to time the birth of their children and perhaps help regulate the population of their tribe or clan in an environment with limited resources.
Our earliest evidence of the connection between the Moon cycle and menstruation cycle – indeed, our earliest evidence of the practice of astronomy – is found on a reindeer bone over 20,000 years old, called the Ishango Bone. This bone is also believed to be early evidence of the beginning of mathematical thought. The Ishango bone is one of our first calendars (other ancient calendars also traced the cycles of the Moon).
Halfway through our lunar cycle, the Moon and the Sun are now on opposite sides of the Earth, so we see a fully sun-lit full Moon. At this time, the Moon rises as the Sun sets, and the Sun rises as the Moon sets. This alignment of Sun, Earth and Moon is called syzygy (pronounced “SI-zi-gee“) and occurs during both new and full moon. This alignment magnifies the ocean tides on Earth (both the Sun and the Moon cause tides through gravitational force), and the full moon is a time when lunar eclipses can occur, about once or twice a year. Imagine standing on the Moon at this moment; you would see a “new Earth”, or the dark side of the Earth, up in the sky. Similarly, you would see a “full Earth” during the period of new moon. In many ways, full moon is a period of opposition. It is also a period of celebration, with many holidays occurring during full moon in tradiational cultures, such as the Chinese Lantern Festival, the Hebrew Passover, and the Muslim Shab-e-Bara’at. The bright night also inspires full moon parties. Have fun celebrating our closest celestial neighbor!
This Astrofact is dedicated to Mahina, our four-legged full moon.
“A month is a Moonth, a Moonth is a moon.” For many traditional calendars – Hawaiian, Chinese, Hebrew, Islamic – this is still true, although our western calendar has been tweaked to fit the months into one year. The new moon is the start of the lunar month, and the time when the moon lies between the Sun and the Earth (this is called syzygy, a great Scrabble word). Imagine yourself floating out in space well above the Sun, Moon and Earth, and you will see these three bodies in a row, with the Sun-lit side of the Moon facing away from the Earth. So where is the new Moon in the sky? Directly in front the Sun!
Why doesn’t the Moon block, or eclipse, the Sun every time the new moon phase happens? It’s because the plane of the Moon’s orbit is actually inclined by about 5° relative to the plane of the Earth’s orbit (the ecliptic plane). So most of the time, the Sun, Moon and Earth are out of alignment during new moon. However, the Moon’s orbit actually rotates, or precesses, every 27.2 days. So perfect alignment at new moon occurs about once every 18 years, a period the Babylonians called a Saros cycle (a complete explanation can be found here). In fact, there are several Saros eclipse cycles because the Sun-Moon-Earth alignment doesn’t have to be perfect, so we get about two eclipses at new moon every year.
New moon is a great time for star-gazing as the Sun and the Moon will have both set in the evening. So be sure to enjoy the dark skies that accompany the new Moon!
The waxing crescent is the first phase in the new Moon to new Moon lunar cycle. You can catch it by looking toward the western sky early in the evening; there you will see a bowl-shaped sliver pointing toward the setting Sun, following it down to the horizon. The opposite side is darker but not completely dark – it is faintly lit up by sunlight reflected from the Earth’s surface, called Earthshine. The origin of Earthshine was first figured out by Leonardo Da Vinci in the 1500s; scientists now use Earthshine to track global cloud coverage and variations in the Earth’s climate. The waxing and waning crescent phases are the best time to observe Earthshine, so enjoy our spotlight on the Moon!
The waning crescent, or “old moon”, can be seen shortly before dawn, a thin sliver that rises ahead of the Sun. You have a short period to catch it; after the Sun rises, the thin crescent is hard to see in the bright glare of day. The waning crescent occurs toward the end of the new Moon to new Moon cycle, a siderial period of 27 1/2 days if you measure the Moon’s position relative to the stars, or a synodic period of 29 1/2 days if you measure relative to Sun. The difference is due to the Earth’s motion around the Sun. During a “moonth” the Earth has traveled about 1/13th of its yearly orbit (at a rate of 1.3 million miles per day). So from our point of view, the Sun has moved to a different part of the sky relative to the stars – by about 28 degrees – over the lunar cycle. Every month brings a new perspective!
Charae & Bryce have put together a song that’s rich in astrofacts. Let’s break down the lyrics to see what they will encounter on their trip into spacetime.
Lyrics:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune, Uranus, Plut-
Whao! Hold up. Not Pluto.
What?!? Not Pluto?
Yeah, Not Pluto.
I’m goin’ crazy now
To the moon in this ship,
We’re gonna get it started,
Fuel tanks filled to the rim,
Discover the uncharted,
Breaking through atmospheres,
It’s not for the fainthearted,
We’re gonna go into space, yeah
Want to go into space? Be prepared for an explosive ride! You only need enough force to overcome Earth’s gravitational pull to go toward space – which you can do briefly by jumping! But to sustain the upward trajectory requires lots of fuel and thrust. The rockets that carry the Space Shuttle have a combined thrust of 13 million Newtons – 20,000 times the force you exert when jumping – to lift the 4.5 million pounds (2 million kg) that hold 7 lucky astronauts!
It’s real hot on the Sun,
Forgot my sunscreen,
It’s definitely hot on the Sun – 9,800 degrees Farenheit! That’s so hot that everything is essentially evaporized on the surface, and atoms are even stripped of their electrons to form a 4th state of matter called plasma.
The day’s long here on Mars,
I need some caffeine,
A day on Mars take 24 hours, 39 minutes, and 35 seconds – about 3% longer than that of Earth. So it’ a little longer, but you’ll adjust.
2.9 times 10 to the 13
Miles a minute, I’m carsick.
That’s a pretty big number, and one would hazard to guess that it’s the speed of light. However, the speed of light is only about 11 million miles per minute. 290,000,000,000,000 miles is about 5 light-years, a little further than the nearest star to the Sun, Alpha Centauri. If you could do that in a minute, you would certainly be carsick!
We’re in great heights,
In one of Saturn’s rings, yeah
You ain’t go bling like mine,
Meteors made for kings,
We watch the stars shine,
From Polaris to Betelgeuse,
The universe is mine.
Some of the most beautiful things in our Universe! Saturn’s rings are definite bling, comprised of small particles of water ice and dust that are extremely reflective – that’s why Saturn it so bright despite being further from the Sun than Jupiter. Meteors are of course another dazzling night sky event, while Polaris (the North Star, in the constellation Ursa Minor, or Little Bear) and Betelgeuse (in Orion’s armpit!) are two of the brightest stars in the sky.
We’re all in Space-time,
Two words in one continuum,
Space-time,
1, 2, 3, 4 Dimensions,
Your mind’s in Space-time
Beyond comprehension,
Space-time, Space-time.
Space-time is that idea of three-dimensional space (length, width and height) combined with one-dimensional time as the “framework” of the Universe. You probably already think this way, as in “I need to get to the third floor of the building on the corner of Main and 1st Avenue at 3pm”. These dimensions appear to be completely separate in our slow, small-scale world, but when you travel close to the speed of light, or near a massive object like a black hole, Einstein’s theory of general relativity tells us that the continuum of space and time can get mixed up, resulting in some bizarre effects!
There’s a guy in the sky,
His names Orion,
Not a man, he’s made of stars,
Emitting carbon.
This refers to the massive giant star Betelgeuse in Orion, which is currently losing mass and size as it sheds its outer atmospheric layers. It will eventually supernova, releasing many elements such as carbon into space. It is all part of the cycle of life in the Universe, as the elements shed from stars like Betelgeuse when they die make their way to form other stars, planets and even people!
Acid rain falls,
It burns my eyeballs.
Venus lighting strobe light.
Remember our weather report from Venus? Acid rain doesn’t quite make it the surface of the planet, but there are plenty of lightning strikes that might make the surface of Venus feel like a disco!
Lots of holes out in space,
They try to grab you,
They can creep up behind you and consume you,
Not even light can escape,
Nothing can breakthrough,
Spa-ghe-tti-fi-ca-tion.
Black holes are the massive remnants of stars that are so dense that nothing, not even light, can escape being swallowed up. If you’re not careful you’ll get pulled into it and never come out again. And on the way in you’ll get stretched out long and slender, like spaghetti. That’s called spaghettification!
We’re in great heights,
In on of Saturn’s rings, yeah
You ain’t go bling like mine,
Meteors made for kings,
We watch the stars shine,
From Polaris to Betelgeuse,
The universe is mine.
We’re all in Space-time,
Two words in one continuum,
Space-time,
1, 2, 3, 4 Dimensions,
Your mind’s in Space-time,
Beyond comprehension,
Space-time, Space-time.
Pluto, the second-largest known dwarf planet in the Solar System (after Eris), and its largest moon, Charon, are sometimes treated as a binary system, because the center of their orbit does not lie within either body (Charon is about half as big and 1/7th as massive as Pluto). Indeed, before its re-classification, Pluto and Charon were the closest thing to a double planet known. The orbit of Pluto and Charon is also special in that it is nearly perpendicular to the plane of their mutual orbit around the Sun, like a record rolling on its side (Uranus and its moons are tilted over in a similar way). As such, the Pluto-Charon orbit can be seen either face-on – like a clock – or edge-on – like a thrown frisbee – during its 248-year trek around the Sun. Between 1985 and 1990 the orbit was aligned edge-on so that the two bodies repeatedly passed in front of each other, or eclipsed. These eclipses allowed astronomers to measure both the sizes of Pluto and Charon as well as make a rough map of Pluto’s surface features. Finally, Pluto and Charon are the only planet-moon pair whose orbit and rotations are mutual synchronized; that is, they both face the same face to each other all the time. This makes Pluto and Charon excellent partners as the dance their way through space!
Progressing from the first quarter, the Moon enters its waxing gibbous phase, on the way to full bright moon. The Moon is showing more of its sunny side to us on Earth, and is taking on an egg-like shape. That’s why Hawaiians call the gibbous phase (gibbous is derived from the latin word “gibbus”, or “hump”) the “hua” or “egg” phase.
Intergalactic Weather Channel’s cub reporter Timmy Cratchit reports from both the cold icy surface of Europa and its (relatively) warm subterranean sea. Look out for that crevasse Timmy!
Europa is Jupiter’s 4th largest moon and the smallest of the Galilean satellites (discovered by Galileo Galilei in 1610), all of which are visible with the aid of a small telescope or binoculars. One of the smoothest and shiniest objects in the Solar System (it reflects 64% of the light striking it), Europa has a surface that is made up mostly of water ice and is essentially free of craters, indicating that it is continually refreshed. It even has a thin atmosphere of oxygen, formed from sputtering of ice from its surface. But the most intriguing part of Europa may be underground, where a deep ocean is believed to exist, heated internally by gravitational tidal forces from Jupiter (the Moon induces similar forces on Earth that give rise to ocean tides). Water breaking through Europa’s surface may explain its overall smoothness and some low-lying features, including “chaos” regions such as Conamara Chaos. Liquid water may be one of the ingredients necessary for life, mitigating the chemical reactions that spawned life on Earth – the only planet with surface water known. Hence, the presence of water in Europa implies life may exist there, perhaps in the form of extremophiles that don’t need sunlight to derive energy. Hopefully Timmy has found a nice extremophile to play with!
Astrofacts! 