Scientists reveal secrets of lost continent Zealandia. In February, scientists were discussing whether a submerged realm called Zealandia should be recognized as a full-fledged Earth continent. In October, a team of researchers returned from an expedition to Zealandia and reported their results.
A rainbow seen from the research ship JOIDES Resolution, during the Zealandia expedition. Image by Tim Fulton via International Ocean Discovery Program/ JRSO/ NSF.
Close shave from an undetected asteroid. Whoosh! Astronomers discovered a small asteroid – now designated as asteroid 2017 OO1 – on July 23. That was 3 days after it passed 1/3 the moon’s distance from Earth. More.
Artist’s concept of an asteroid passing near Earth.
When’s the next U.S. total solar eclipse? After 2017’s awesome total solar eclipse on August 21, the next total solar eclipse visible from North America will be April 8, 2024. More.
Image via Fred Espenak at the NASA Eclipse Web Site.
Biblical signs in the sky on September 23, 2017? A mirror in the sky to “signs” from the Bible’s Book of Revelation? Possibly. But this same sky scene has been seen 4 other times in the past 1,000 years. An astronomer explains.
Green arrows show the “9” stars of Leo. Blue arrows show the planets Mercury, Venus, and Mars. Red arrow is Jupiter. Violet arrow is the moon (shown enlarged). The sun is at Virgo’s shoulder. Image via Christopher M. Graney.
Mysterious rock-comet 3200 Phaethon. This asteroid-comet hybrid was closest to Earth December 16. Its presence near Earth may be why the Geminid meteors put on a good show in 2017. Info and images of the rock-comet here.
History of global temperature 1880-2016. Take 14 seconds to watch the change in Earth’s surface temperature from 1880 through 2016. More.
And, lastly, the ever-popular … Betelgeuse will explode someday. Someday, the star Betelgeuse will run out of fuel, collapse under its own weight, and then rebound in a spectacular supernova explosion. Someday … but probably not soon. More.
Betelgeuse imaged in ultraviolet light by the Hubble Space Telescope and subsequently enhanced by NASA. The bright white spot is likely one of this star’s poles. Image via NASA/ESA.
Bottom line: EarthSky’s 7 most-viewed news and feature stories of 2017. Happy new year to our readers, and thank you for visiting EarthSky!
Scientists reveal secrets of lost continent Zealandia. In February, scientists were discussing whether a submerged realm called Zealandia should be recognized as a full-fledged Earth continent. In October, a team of researchers returned from an expedition to Zealandia and reported their results.
A rainbow seen from the research ship JOIDES Resolution, during the Zealandia expedition. Image by Tim Fulton via International Ocean Discovery Program/ JRSO/ NSF.
Close shave from an undetected asteroid. Whoosh! Astronomers discovered a small asteroid – now designated as asteroid 2017 OO1 – on July 23. That was 3 days after it passed 1/3 the moon’s distance from Earth. More.
Artist’s concept of an asteroid passing near Earth.
When’s the next U.S. total solar eclipse? After 2017’s awesome total solar eclipse on August 21, the next total solar eclipse visible from North America will be April 8, 2024. More.
Image via Fred Espenak at the NASA Eclipse Web Site.
Biblical signs in the sky on September 23, 2017? A mirror in the sky to “signs” from the Bible’s Book of Revelation? Possibly. But this same sky scene has been seen 4 other times in the past 1,000 years. An astronomer explains.
Green arrows show the “9” stars of Leo. Blue arrows show the planets Mercury, Venus, and Mars. Red arrow is Jupiter. Violet arrow is the moon (shown enlarged). The sun is at Virgo’s shoulder. Image via Christopher M. Graney.
Mysterious rock-comet 3200 Phaethon. This asteroid-comet hybrid was closest to Earth December 16. Its presence near Earth may be why the Geminid meteors put on a good show in 2017. Info and images of the rock-comet here.
History of global temperature 1880-2016. Take 14 seconds to watch the change in Earth’s surface temperature from 1880 through 2016. More.
And, lastly, the ever-popular … Betelgeuse will explode someday. Someday, the star Betelgeuse will run out of fuel, collapse under its own weight, and then rebound in a spectacular supernova explosion. Someday … but probably not soon. More.
Betelgeuse imaged in ultraviolet light by the Hubble Space Telescope and subsequently enhanced by NASA. The bright white spot is likely one of this star’s poles. Image via NASA/ESA.
Bottom line: EarthSky’s 7 most-viewed news and feature stories of 2017. Happy new year to our readers, and thank you for visiting EarthSky!
The star Mira has a comet-like tail, discovered in 2007. The tail stretches 13 light-years in space. Image via NASA’s Galaxy Evolution Explorer.
The star Omicron Ceti – proper name Mira and known to early astronomers as Mira the Wonderful – lies 420 light-years away in the constellation Cetus the Whale. It’s in an unremarkable patch of the night sky along the celestial equator, easily visible from the entire Earth, well to the west in our sky of the hard-to-miss constellation Orion the Hunter. Mira is visible to the unaided eye – except when it isn’t, which is most of the time. And that’s why it earned the name wonderful, in the sense of arousing wonder.
Today we know this star varies in brightness. Its changes happen on a regular schedule of about 11 months. Mira’s last brightness peak was in late January 2017. Its next brightness peak was scheduled for late December 2017, and indeed – according to recent observations from the American Association of Variable Star Observers (AAVSO) – Mira is now easily bright enough to be viewed with the eye alone.
At this writing, the estimates for Mira’s stellar magnitude, or brightness, are ranging up to about magnitude +3.6. That’s in contrast to Polaris, for example – the legendary North Star – whose magnitude holds steady at nearly +2. In other words, Mira isn’t as bright as Polaris now, but it’s easily visible to the eye.
Mira might get brighter in the coming days. How bright Mira will become at this current peak isn’t predictable!
You can spot Mira’s constellation, Cetus, during the evening hours. Even at its brightest, Mira isn’t one of our sky’s brightest stars. But it’s a super interesting star to come to know and to follow.
Throughout the centuries, Mira has sometimes been as bright as 2nd magnitude (approaching the noticeability of Polaris, say, or the stars of the Big Dipper), but it usually peaks at about magnitude +3.5. In other words, it might now be about as bright as it’ll get for this brightness peak.
That brightness would place Mira below the brightness of other stars in Cetus.
Mira’s unusual fluctuations were known to modern astronomers as far back as at least the late 16th century. In 1662, German-Polish astronomer Johannes Hevelius named it Mira (meaning wonderful or astonishing in Latin). At its dimmest, Mira falls to 10th magnitude, below the visibility limit of modest binoculars. That’s an overall brightness change of more than 1,500 times. Astonishing, indeed!
Mira varies because it’s past its prime. It has exhausted most of its hydrogen fuel and puffed up to become a red giant. The last gasps of its stellar furnace make the star pulsate and throw off its outer layers. Eventually, most of it will be gone, leaving behind a shell of gas called a planetary nebula that will surround the stellar cinder called a white dwarf.
View larger. | This is what astronomers call a light curve, in this case for the star Mira over the past 2 years, approximately early 2016 to late December 2017. The horizontal axis is time; the vertical axis is Mira’s observed magnitude or brightness. This light curve is made of 1,635 observations of this star, submitted to the AAVSO. You can see the star gets brighter and then fainter as it goes through its regular, 11-month cycle. Light curve via the AAVSO.
As modern astronomers study the star, Mira continues to amaze. In 2007, observations by a satellite viewing in ultraviolet light discovered that Mira has a luminous tail of gas more than a dozen light-years long. This is the material that Mira has shed, leaving it behind as it speeds through the galaxy at some 80 miles per second (130 km per second) – very speedy for a star! The invisible tail spans about 2 degrees in the sky, about four times the diameter of a full moon. See the image at the top of this post.
Bottom line: The star Omicron Ceti – aka Mira – in the constellation Cetus varies in brightness regularly, over about 11 months. In late December 2017, the star might be near its peak brightness. It’s easily bright enough to be viewed with the eye alone.
The star Mira has a comet-like tail, discovered in 2007. The tail stretches 13 light-years in space. Image via NASA’s Galaxy Evolution Explorer.
The star Omicron Ceti – proper name Mira and known to early astronomers as Mira the Wonderful – lies 420 light-years away in the constellation Cetus the Whale. It’s in an unremarkable patch of the night sky along the celestial equator, easily visible from the entire Earth, well to the west in our sky of the hard-to-miss constellation Orion the Hunter. Mira is visible to the unaided eye – except when it isn’t, which is most of the time. And that’s why it earned the name wonderful, in the sense of arousing wonder.
Today we know this star varies in brightness. Its changes happen on a regular schedule of about 11 months. Mira’s last brightness peak was in late January 2017. Its next brightness peak was scheduled for late December 2017, and indeed – according to recent observations from the American Association of Variable Star Observers (AAVSO) – Mira is now easily bright enough to be viewed with the eye alone.
At this writing, the estimates for Mira’s stellar magnitude, or brightness, are ranging up to about magnitude +3.6. That’s in contrast to Polaris, for example – the legendary North Star – whose magnitude holds steady at nearly +2. In other words, Mira isn’t as bright as Polaris now, but it’s easily visible to the eye.
Mira might get brighter in the coming days. How bright Mira will become at this current peak isn’t predictable!
You can spot Mira’s constellation, Cetus, during the evening hours. Even at its brightest, Mira isn’t one of our sky’s brightest stars. But it’s a super interesting star to come to know and to follow.
Throughout the centuries, Mira has sometimes been as bright as 2nd magnitude (approaching the noticeability of Polaris, say, or the stars of the Big Dipper), but it usually peaks at about magnitude +3.5. In other words, it might now be about as bright as it’ll get for this brightness peak.
That brightness would place Mira below the brightness of other stars in Cetus.
Mira’s unusual fluctuations were known to modern astronomers as far back as at least the late 16th century. In 1662, German-Polish astronomer Johannes Hevelius named it Mira (meaning wonderful or astonishing in Latin). At its dimmest, Mira falls to 10th magnitude, below the visibility limit of modest binoculars. That’s an overall brightness change of more than 1,500 times. Astonishing, indeed!
Mira varies because it’s past its prime. It has exhausted most of its hydrogen fuel and puffed up to become a red giant. The last gasps of its stellar furnace make the star pulsate and throw off its outer layers. Eventually, most of it will be gone, leaving behind a shell of gas called a planetary nebula that will surround the stellar cinder called a white dwarf.
View larger. | This is what astronomers call a light curve, in this case for the star Mira over the past 2 years, approximately early 2016 to late December 2017. The horizontal axis is time; the vertical axis is Mira’s observed magnitude or brightness. This light curve is made of 1,635 observations of this star, submitted to the AAVSO. You can see the star gets brighter and then fainter as it goes through its regular, 11-month cycle. Light curve via the AAVSO.
As modern astronomers study the star, Mira continues to amaze. In 2007, observations by a satellite viewing in ultraviolet light discovered that Mira has a luminous tail of gas more than a dozen light-years long. This is the material that Mira has shed, leaving it behind as it speeds through the galaxy at some 80 miles per second (130 km per second) – very speedy for a star! The invisible tail spans about 2 degrees in the sky, about four times the diameter of a full moon. See the image at the top of this post.
Bottom line: The star Omicron Ceti – aka Mira – in the constellation Cetus varies in brightness regularly, over about 11 months. In late December 2017, the star might be near its peak brightness. It’s easily bright enough to be viewed with the eye alone.
December 15, 2017. Image via NASA.
In September 2017, a new iceberg – named B-44 – calved from Pine Island Glacier — one of the main outlets where the West Antarctic Ice Sheet flows into the ocean. Just weeks later, it shattered into more than 20 fragments.
NASAs Landsat 8 satellite captured the above image of the broken iceberg near midnight local time on December 15, 2017.
Scientists say that an area of relatively warm water, known as a polyna, has kept the water between the iceberg chunks and the glacier front ice-free. In fact, NASA glaciologist Chris Shuman suggests that it’s the polynya’s warm water that caused B-44’s rapid breakup.
Scientists used parameters in the satellite’s midnight image to calculate the iceberg’s size. Using the azimuth (an angular measurement) of the sun and its elevation above the horizon, as well as the length of the shadows, Shuman has estimated that the iceberg rises about 49 meters (161 feet) above the water line. That would put the total thickness of the iceberg — above and below the water surface — at about 315 meters (1,033 feet).
This animation combines five Landsat 8 views of B-44 acquired over the past four months (September – December 2017). Image via NASA.
Read more from NASA Earth Observatory
December 15, 2017. Image via NASA.
In September 2017, a new iceberg – named B-44 – calved from Pine Island Glacier — one of the main outlets where the West Antarctic Ice Sheet flows into the ocean. Just weeks later, it shattered into more than 20 fragments.
NASAs Landsat 8 satellite captured the above image of the broken iceberg near midnight local time on December 15, 2017.
Scientists say that an area of relatively warm water, known as a polyna, has kept the water between the iceberg chunks and the glacier front ice-free. In fact, NASA glaciologist Chris Shuman suggests that it’s the polynya’s warm water that caused B-44’s rapid breakup.
Scientists used parameters in the satellite’s midnight image to calculate the iceberg’s size. Using the azimuth (an angular measurement) of the sun and its elevation above the horizon, as well as the length of the shadows, Shuman has estimated that the iceberg rises about 49 meters (161 feet) above the water line. That would put the total thickness of the iceberg — above and below the water surface — at about 315 meters (1,033 feet).
This animation combines five Landsat 8 views of B-44 acquired over the past four months (September – December 2017). Image via NASA.
Read more from NASA Earth Observatory
As 2017 draws to a close, three bright planets are lined up across the eastern sky before sunrise. In their order from the sunrise point upward, these worlds are surprisingly bright Mercury, dazzling Jupiter, and modesty-bright Mars. Draw an imaginary line from the red planet Mars through the king planet Jupiter to find Mercury, the solar system’s innermost planet, near the sunrise point on the horizon.
As Earth spins under the sky, Mercury is the last planet to rise into the morning sky, coming up just above your sunrise point as predawn darkness gives way to morning twilight. In the Northern Hemisphere, Mercury rises better than 90 minutes before the sun in late December. At temperate latitudes in the Southern Hemisphere, Mercury comes up about 70 minutes before sunrise. Although this apparition of Mercury favors the Northern Hemisphere, most everyone worldwide should be in a good position to view Mercury before sunrise for a week or so around the time 2017 ends, and 2018 begins.
Click here for recommended almanacs; they can tell you of Mercury’s rising time into your sky.
Steve Pond captured the planets on December 28 ” … from a very cold and frosty southern England.”
Technically, all 5 of the so-called bright planets – Mercury, Venus, Mars, Jupiter and Saturn – reside in the morning sky right now. By bright planet, we mean any planet that can be seen without an optical aid and which has been observed by our ancestors since time immemorial. Mercury, Jupiter and Mars are easy to see, but Venus and Saturn sit so close to the glare of sunrise that – while technically up before the sun – they aren’t presently visible.
Day by day, Venus will sink sunward while Saturn will climb upward toward Mercury. Venus will transition over to the evening sky on January 9, 2018, to be (again, only technically) the only bright planet in the January 2018 evening sky. Venus will be close to the sunset in January, though, and you might not actually see Venus until February 2018.
Two planetary conjunctions will occur in the January morning sky. For reference, the moon’s diameter spans approximately 1/2o of sky. Watch for Mars to swing less than 1/4o south of Jupiter – half a moon-diameter – on January 7; the moon itself sweeps past these planets a few days later (see chart below). Then Saturn will pass a bit more than 1/2o north of Mercury – about one moon-diameter – on January 13. At that time, Saturn and Mercury will be close to the sunrise and possibly hard to see; binoculars will help.
Yes, the wandering planets will be a sight to behold in the morning sky for the next few weeks!
Let the moon be your guide to the planets Jupiter and Mars on January 10, 11 and 12, 2018.
Around January 11, it’ll be easy to see the moon with Jupiter and Mars, but tougher to catch Mercury, and especially Saturn, closer to the dawn. Binoculars might come in handy! Click here for recommended almanacs; they can give you the rising times of Mercury and Saturn in your sky.
Bottom line: As 2017 draws to a close, and 2018 begins, draw an imaginary line from the red planet Mars through the king planet Jupiter to find elusive Mercury near the sunrise point on your horizon.
As 2017 draws to a close, three bright planets are lined up across the eastern sky before sunrise. In their order from the sunrise point upward, these worlds are surprisingly bright Mercury, dazzling Jupiter, and modesty-bright Mars. Draw an imaginary line from the red planet Mars through the king planet Jupiter to find Mercury, the solar system’s innermost planet, near the sunrise point on the horizon.
As Earth spins under the sky, Mercury is the last planet to rise into the morning sky, coming up just above your sunrise point as predawn darkness gives way to morning twilight. In the Northern Hemisphere, Mercury rises better than 90 minutes before the sun in late December. At temperate latitudes in the Southern Hemisphere, Mercury comes up about 70 minutes before sunrise. Although this apparition of Mercury favors the Northern Hemisphere, most everyone worldwide should be in a good position to view Mercury before sunrise for a week or so around the time 2017 ends, and 2018 begins.
Click here for recommended almanacs; they can tell you of Mercury’s rising time into your sky.
Steve Pond captured the planets on December 28 ” … from a very cold and frosty southern England.”
Technically, all 5 of the so-called bright planets – Mercury, Venus, Mars, Jupiter and Saturn – reside in the morning sky right now. By bright planet, we mean any planet that can be seen without an optical aid and which has been observed by our ancestors since time immemorial. Mercury, Jupiter and Mars are easy to see, but Venus and Saturn sit so close to the glare of sunrise that – while technically up before the sun – they aren’t presently visible.
Day by day, Venus will sink sunward while Saturn will climb upward toward Mercury. Venus will transition over to the evening sky on January 9, 2018, to be (again, only technically) the only bright planet in the January 2018 evening sky. Venus will be close to the sunset in January, though, and you might not actually see Venus until February 2018.
Two planetary conjunctions will occur in the January morning sky. For reference, the moon’s diameter spans approximately 1/2o of sky. Watch for Mars to swing less than 1/4o south of Jupiter – half a moon-diameter – on January 7; the moon itself sweeps past these planets a few days later (see chart below). Then Saturn will pass a bit more than 1/2o north of Mercury – about one moon-diameter – on January 13. At that time, Saturn and Mercury will be close to the sunrise and possibly hard to see; binoculars will help.
Yes, the wandering planets will be a sight to behold in the morning sky for the next few weeks!
Let the moon be your guide to the planets Jupiter and Mars on January 10, 11 and 12, 2018.
Around January 11, it’ll be easy to see the moon with Jupiter and Mars, but tougher to catch Mercury, and especially Saturn, closer to the dawn. Binoculars might come in handy! Click here for recommended almanacs; they can give you the rising times of Mercury and Saturn in your sky.
Bottom line: As 2017 draws to a close, and 2018 begins, draw an imaginary line from the red planet Mars through the king planet Jupiter to find elusive Mercury near the sunrise point on your horizon.
December’s full moon was a supermoon, too. Peter Lowenstein in Mutare, Zimbabwe contributed this composite image of the rising full supermoon on the evening of December 3, 2017.
The first (or second) day of the new year features a full moon and 2018’s largest and closest supermoon. In other words, this full moon will be near perigee, or the closest point of the moon in orbit for this month. Your eye probably can’t detect a difference in size between this supermoon and any ordinary full moon (although experienced observers say they can detect a size difference). But the supermoon is substantially brighter than an ordinary full moon. The moon turns precisely full at the same instant worldwide (January 2, 2018 at 2:24 UTC), the time – and possibly the date – of the full moon varies according to one’s time zone. At North American and U.S. time zones, the full moon happens on the evening of January 1 at these times:
22:24 (10:24 p.m.) Atlantic Standard Time (AST)
21:24 (9:24 p.m.) Eastern Standard Time (EST)
20:24 (8:24 p.m.) Central Standard Time (CST)
19:24 (7:24 p.m.) Mountain Standard Time (MST)
18:24 (6:24 p.m.) Pacific Standard Time (PST)
17:24 (5:24 p.m.) Alaska Standard Time (AKST)
16:24 (4:24 p.m.) Hawaiian Standard Time (HST)
Like every full moon, this one is opposite the sun from Earth. It’ll rise in the east as the sun sets in the west, ascend to its highest point in the sky in the middle of the night, and set in the west around dawn. Clouded out? The Virtual Telescope Project in Rome is offering an online viewing of the January 1 supermoon.
Join the Virtual Telescope Project in Rome for an online viewing of the January 1, 2018 supermoon.
As it happens, January will have two full moons. The second one is a supermoon, too. Some people will call the full moon on January 31 a Blue Moon because it’ll be the second of two full moons in one calendar month.
Moreover, the January 31, 2018 supermoon will stage a total eclipse of the moon: a super Blue Moon eclipse!
Read more: What is a supermoon?
Here’s a comparison between the December 3 full moon at perigree (closest to Earth for the month) and the year’s farthest full moon in June at apogee (farthest from Earth for the month) by Muzamir Mazlan at Telok Kemang Observatory, Port Dickson, Malaysia.
As the moon orbits Earth, it changes phase in an orderly way. Follow these links to understand the various phases of the moon.
Four keys to understanding moon phases
Where’s the moon? Waxing crescent
Where’s the moon? First quarter
Where’s the moon? Waxing gibbous
What’s special about a full moon?
Where’s the moon? Waning gibbous
Where’s the moon? Last quarter
Where’s the moon? Waning crescent
Where’s the moon? New phase
Bottom line: A full moon looks full because it’s opposite Earth from the sun, showing us its fully lighted hemisphere or day side. The January 1-2, 2018 full moon is a supermoon.
Can you tell me the full moon names?
December’s full moon was a supermoon, too. Peter Lowenstein in Mutare, Zimbabwe contributed this composite image of the rising full supermoon on the evening of December 3, 2017.
The first (or second) day of the new year features a full moon and 2018’s largest and closest supermoon. In other words, this full moon will be near perigee, or the closest point of the moon in orbit for this month. Your eye probably can’t detect a difference in size between this supermoon and any ordinary full moon (although experienced observers say they can detect a size difference). But the supermoon is substantially brighter than an ordinary full moon. The moon turns precisely full at the same instant worldwide (January 2, 2018 at 2:24 UTC), the time – and possibly the date – of the full moon varies according to one’s time zone. At North American and U.S. time zones, the full moon happens on the evening of January 1 at these times:
22:24 (10:24 p.m.) Atlantic Standard Time (AST)
21:24 (9:24 p.m.) Eastern Standard Time (EST)
20:24 (8:24 p.m.) Central Standard Time (CST)
19:24 (7:24 p.m.) Mountain Standard Time (MST)
18:24 (6:24 p.m.) Pacific Standard Time (PST)
17:24 (5:24 p.m.) Alaska Standard Time (AKST)
16:24 (4:24 p.m.) Hawaiian Standard Time (HST)
Like every full moon, this one is opposite the sun from Earth. It’ll rise in the east as the sun sets in the west, ascend to its highest point in the sky in the middle of the night, and set in the west around dawn. Clouded out? The Virtual Telescope Project in Rome is offering an online viewing of the January 1 supermoon.
Join the Virtual Telescope Project in Rome for an online viewing of the January 1, 2018 supermoon.
As it happens, January will have two full moons. The second one is a supermoon, too. Some people will call the full moon on January 31 a Blue Moon because it’ll be the second of two full moons in one calendar month.
Moreover, the January 31, 2018 supermoon will stage a total eclipse of the moon: a super Blue Moon eclipse!
Read more: What is a supermoon?
Here’s a comparison between the December 3 full moon at perigree (closest to Earth for the month) and the year’s farthest full moon in June at apogee (farthest from Earth for the month) by Muzamir Mazlan at Telok Kemang Observatory, Port Dickson, Malaysia.
As the moon orbits Earth, it changes phase in an orderly way. Follow these links to understand the various phases of the moon.
Four keys to understanding moon phases
Where’s the moon? Waxing crescent
Where’s the moon? First quarter
Where’s the moon? Waxing gibbous
What’s special about a full moon?
Where’s the moon? Waning gibbous
Where’s the moon? Last quarter
Where’s the moon? Waning crescent
Where’s the moon? New phase
Bottom line: A full moon looks full because it’s opposite Earth from the sun, showing us its fully lighted hemisphere or day side. The January 1-2, 2018 full moon is a supermoon.
Can you tell me the full moon names?
We occasionally receive excellent questions and/or comments by email or via our contact form and have then usually corresponded with the emailer directly. But, some of the questions and answers deserve a broader audience, so we decided to highlight some of them in a new series of blog posts.
In Part 1, we learned about carbon isotopes: how 14C forms in the atmosphere, how different isotopes move through the Carbon Cycle, and how isotopic measurements reveal clues about our changing climate. In this post we will look at how measurements of changing isotopic ratios are described.
Here, again, is the IPCC graph (Figure 1) illustrating the rise in atmospheric CO2 (panel a, black saw-toothed line) and the decreasing 13C:12C ratio in the same CO2 (panel b, red line).
Figure 1. Recent CO2 concentrations and emissions. (a) CO2 concentrations over the period 1970 to 2005 from Mauna Loa, Hawaii (black) and Baring Head, New Zealand (blue). In the lower right of the panel, atmospheric oxygen (O2) measurements from flask samples are shown from Alert, Canada (pink) and Cape Grim, Australia (cyan). (b) Annual global CO2 emissions from fossil fuel burning and cement manufacture in GtC yr–1 (black) through 2005. Annual averages of the 13C/12C ratio measured in atmospheric CO2 at Mauna Loa from 1981 to 2002 (red) are also shown. The isotope data are expressed as δ13C(CO2) ‰ (per mil) deviation from a calibration standard. Note that this scale is inverted to improve clarity. (IPCC, AR4)
One of our readers was puzzled by this graph (which appears in our rebuttal "How do human CO2 emissions compare to natural CO2 emissions?") and emailed us these questions about it:
Can you help me interpret the red line? Does it indicate a decline (negative change) in the C13 isotope (i.e. -7.7 = -7.7 parts per thousands) or are the values showing a ratio of C13/C12 because of the delta symbol? If the red values do represent a ratio can you illustrate with a hypothetical example how a negative value was calculated; for instance how do you get a negative value by comparing C13 with C12 (I would have thought a ratio would produce a fraction of some sort)?
The concentration of atmospheric CO2 is most commonly measured in parts per million (ppm) as seen in the top (a) panel of the graph. The current value is about 405 ppm, which means that for every million molecules in a sample of air there are 405 CO2 molecules. This can be shown as a fraction or a ratio:
or as a decimal: 0.000405
We can also turn this into a percentage:
The carbon isotope ratios are measured in something quite different: the δ-value or notation: δ13C(CO2)‰, or "delta 13C (of CO2) per mil". The "per mil" (symbol: ‰) might lead you to think that this too is a measure of concentration, except, instead of a percentage ("per cent" or "per 100") the carbon isotopes might be a measure of "per mil" or "per 1000". But this is not the case. (Or try this link if that last one doesn’t work.)
Here is the equation used to calculate the δ-value:
Notice that this equation contains a multiplication by 1000, which is where the "per mil" comes from. The values are multiplied by 1000 because they are very small numbers and this multiplication trick makes the values more "user-friendly". Look again at the IPCC graph which gives the δ-value in 1981 as -7.6‰, the "per mil" symbol tells us that the original value was multiplied by 1000, thus the original value was -0.0076.
But what does -0.0076 mean? Has the 13C decreased by 0.0076...somethings?
Look again at the δ-value equation. You can see that the top part of the fraction within the bracket is the ratio of 13C:12C from some sample containing carbon. The bottom part of the fraction is another 13C:12C ratio from a standard sample which has a known, unchanging ratio of 13C:12C. For carbon isotopes, the standard used is a limestone formation from South Carolina called the Pee Dee Belemnite (or PDB)1, which has an unusually high amount of 13C.
The δ-value is basically a ratio of ratios and can be thought of as a scale to compare different isotope ratios (Figure 2). The standard sample is the zero point of this scale. If there is more 13C in our sample than in the standard, then the δ-value will be positive; if there is less 13C in our sample than in the standard, then the δ-value will be negative. The δ-value doesn't give us a specific number about our sample, as in x ppm of 13C, rather it tells us the relative difference between the sample and the standard.
Figure 2. Isotopic ratios of samples are compared to an unchanging isotopic ratio of a standard. The standard defines the zero point of the scale. Samples with more 13C than the standard will have positive δ13C values, while samples with less 13C than the standard will have negative δ13C values.
Why not just give us the specific numbers of carbon isotopes? (Show me the data!) Isotope ratios are measured by mass spectrometers but it is impossible for these devices to perfectly measure the 13C to 12C ratio in a sample. Lauren Shoemaker, in her in-depth NOAA website on isotopes, explains:
Isotope ratio mass spectrometers measure relative isotopic ratios much better than actual ratios. By comparing to a standard, the precision of the data values are much, much better since all values are relative to a given standard.
She also points out that δ-values make it "easier to compare results both among isotope laboratories and within a single laboratory over a long time period".
Delta-values also make the numbers associated with isotopic ratios much more "user-friendly". To see this let's work through some examples using the δ-value formula. The IPCC graph shows that in 1981 the δ-value for atmospheric CO2 was -7.6‰. The PDB standard ratio is 0.011237. With these two numbers we have enough information to calculate what the 13C:12C ratio was in 1981:
This works out to a ratio of 0.0111516 for the 1981 sample. For 2002 the δ-value was -8.1‰, which gives a ratio of 0.0111459.
Let’s broaden our view out a bit further than that twenty year time span. This graph in Figure 3 (from CSIRO, the Australian agency for scientific research) shows that before the Industrial Revolution the δ-value was -6.5‰. In today's atmosphere, the 13C:12C ratios give a δ-value of -8.5‰.
Figure 3. There has been an increase in the atmospheric concentration of CO2 (in red), as identified by the trend in the ratio of different types (isotopes) of carbon in atmospheric CO2 (in black, from the year 1000). CO2 and the carbon-13 isotope ratio in CO2 (δ13C) are measured from air in Antarctic ice and firn (compacted snow) samples from the Australian Antarctic Science Program, and at Cape Grim (northwest Tasmania). (Copyright CSIRO Australia).
The table below shows the δ-values for various times along with the corresponding isotopic ratios, expressed both as decimals and as percentages of 13C and 12C in the atmospheric samples. You can see why scientists use δ-values rather than the actual 13C:12C ratio numbers, which only show changes far to the right of the decimal points! These ratios change by very small amounts over time, but they clearly illustrate big changes in the atmosphere's composition of 13C and 12C, pointing to the fossil fuel origins of more and more of the atmosphere's CO2.
Here is one final comparison to help make the δ-values more understandable. Annual global average temperatures are usually presented as anomalies with reference to some "base period". Figure 4 is a familiar graph of this from NASA-GISS with data from 1880 to 2016. The "base period" for this graph is 1951-19802, the annual temperatures for these thirty years are averaged together and this is set as the zero point of the anomaly scale. So, the base period is like the standard sample used as the zero point in the δ-notation scale. Then, each individual year's data point is compared to that zero point. If a year's temperature was warmer than the base period, then the anomaly for that year is positive, such as 2016's record high anomaly of 0.99°C. This is comparable to positive δ-values. Years with colder values than the base period would be negative, like 1904's record low value of -0.5°C. This is similar to the negative δ-values described above.
Figure 4. Land-ocean temperature index, 1880 to present, with base period 1951-1980. The solid black line is the global annual mean and the solid red line is the five-year lowess smooth. The blue uncertainty bars (95% confidence limit) account only for incomplete spatial sampling. (NASA-GISS).
In both instances, δ-values and temperature anomalies, cumbersome numbers are converted into more meaningful and useful values. In the case of δ-values, very very small changes in isotopic ratios in the natural environment are more easily described, and we can see more clearly how the Earth's climate system works and changes over time.
1. "The original PDB sample was a sample of fossilized shells of an extinct organism called a belemnite (something like a shelled squid) collected decades ago from the banks of the Pee Dee River in South Carolina. The original sample was used up long ago, but other reference standards were calibrated to that original sample. We still report carbon isotope values relative to PDB but now use the term "VPDB" ["Vienna Pee Dee Belemnite"] to indicate that the data are normalized to the values of that standard." (USGS).
2. Any time period, and any length of time, may be used. A thirty year period is often used because thirty years is a long enough time to describe "average" climate variables.
We occasionally receive excellent questions and/or comments by email or via our contact form and have then usually corresponded with the emailer directly. But, some of the questions and answers deserve a broader audience, so we decided to highlight some of them in a new series of blog posts.
In Part 1, we learned about carbon isotopes: how 14C forms in the atmosphere, how different isotopes move through the Carbon Cycle, and how isotopic measurements reveal clues about our changing climate. In this post we will look at how measurements of changing isotopic ratios are described.
Here, again, is the IPCC graph (Figure 1) illustrating the rise in atmospheric CO2 (panel a, black saw-toothed line) and the decreasing 13C:12C ratio in the same CO2 (panel b, red line).
Figure 1. Recent CO2 concentrations and emissions. (a) CO2 concentrations over the period 1970 to 2005 from Mauna Loa, Hawaii (black) and Baring Head, New Zealand (blue). In the lower right of the panel, atmospheric oxygen (O2) measurements from flask samples are shown from Alert, Canada (pink) and Cape Grim, Australia (cyan). (b) Annual global CO2 emissions from fossil fuel burning and cement manufacture in GtC yr–1 (black) through 2005. Annual averages of the 13C/12C ratio measured in atmospheric CO2 at Mauna Loa from 1981 to 2002 (red) are also shown. The isotope data are expressed as δ13C(CO2) ‰ (per mil) deviation from a calibration standard. Note that this scale is inverted to improve clarity. (IPCC, AR4)
One of our readers was puzzled by this graph (which appears in our rebuttal "How do human CO2 emissions compare to natural CO2 emissions?") and emailed us these questions about it:
Can you help me interpret the red line? Does it indicate a decline (negative change) in the C13 isotope (i.e. -7.7 = -7.7 parts per thousands) or are the values showing a ratio of C13/C12 because of the delta symbol? If the red values do represent a ratio can you illustrate with a hypothetical example how a negative value was calculated; for instance how do you get a negative value by comparing C13 with C12 (I would have thought a ratio would produce a fraction of some sort)?
The concentration of atmospheric CO2 is most commonly measured in parts per million (ppm) as seen in the top (a) panel of the graph. The current value is about 405 ppm, which means that for every million molecules in a sample of air there are 405 CO2 molecules. This can be shown as a fraction or a ratio:
or as a decimal: 0.000405
We can also turn this into a percentage:
The carbon isotope ratios are measured in something quite different: the δ-value or notation: δ13C(CO2)‰, or "delta 13C (of CO2) per mil". The "per mil" (symbol: ‰) might lead you to think that this too is a measure of concentration, except, instead of a percentage ("per cent" or "per 100") the carbon isotopes might be a measure of "per mil" or "per 1000". But this is not the case. (Or try this link if that last one doesn’t work.)
Here is the equation used to calculate the δ-value:
Notice that this equation contains a multiplication by 1000, which is where the "per mil" comes from. The values are multiplied by 1000 because they are very small numbers and this multiplication trick makes the values more "user-friendly". Look again at the IPCC graph which gives the δ-value in 1981 as -7.6‰, the "per mil" symbol tells us that the original value was multiplied by 1000, thus the original value was -0.0076.
But what does -0.0076 mean? Has the 13C decreased by 0.0076...somethings?
Look again at the δ-value equation. You can see that the top part of the fraction within the bracket is the ratio of 13C:12C from some sample containing carbon. The bottom part of the fraction is another 13C:12C ratio from a standard sample which has a known, unchanging ratio of 13C:12C. For carbon isotopes, the standard used is a limestone formation from South Carolina called the Pee Dee Belemnite (or PDB)1, which has an unusually high amount of 13C.
The δ-value is basically a ratio of ratios and can be thought of as a scale to compare different isotope ratios (Figure 2). The standard sample is the zero point of this scale. If there is more 13C in our sample than in the standard, then the δ-value will be positive; if there is less 13C in our sample than in the standard, then the δ-value will be negative. The δ-value doesn't give us a specific number about our sample, as in x ppm of 13C, rather it tells us the relative difference between the sample and the standard.
Figure 2. Isotopic ratios of samples are compared to an unchanging isotopic ratio of a standard. The standard defines the zero point of the scale. Samples with more 13C than the standard will have positive δ13C values, while samples with less 13C than the standard will have negative δ13C values.
Why not just give us the specific numbers of carbon isotopes? (Show me the data!) Isotope ratios are measured by mass spectrometers but it is impossible for these devices to perfectly measure the 13C to 12C ratio in a sample. Lauren Shoemaker, in her in-depth NOAA website on isotopes, explains:
Isotope ratio mass spectrometers measure relative isotopic ratios much better than actual ratios. By comparing to a standard, the precision of the data values are much, much better since all values are relative to a given standard.
She also points out that δ-values make it "easier to compare results both among isotope laboratories and within a single laboratory over a long time period".
Delta-values also make the numbers associated with isotopic ratios much more "user-friendly". To see this let's work through some examples using the δ-value formula. The IPCC graph shows that in 1981 the δ-value for atmospheric CO2 was -7.6‰. The PDB standard ratio is 0.011237. With these two numbers we have enough information to calculate what the 13C:12C ratio was in 1981:
This works out to a ratio of 0.0111516 for the 1981 sample. For 2002 the δ-value was -8.1‰, which gives a ratio of 0.0111459.
Let’s broaden our view out a bit further than that twenty year time span. This graph in Figure 3 (from CSIRO, the Australian agency for scientific research) shows that before the Industrial Revolution the δ-value was -6.5‰. In today's atmosphere, the 13C:12C ratios give a δ-value of -8.5‰.
Figure 3. There has been an increase in the atmospheric concentration of CO2 (in red), as identified by the trend in the ratio of different types (isotopes) of carbon in atmospheric CO2 (in black, from the year 1000). CO2 and the carbon-13 isotope ratio in CO2 (δ13C) are measured from air in Antarctic ice and firn (compacted snow) samples from the Australian Antarctic Science Program, and at Cape Grim (northwest Tasmania). (Copyright CSIRO Australia).
The table below shows the δ-values for various times along with the corresponding isotopic ratios, expressed both as decimals and as percentages of 13C and 12C in the atmospheric samples. You can see why scientists use δ-values rather than the actual 13C:12C ratio numbers, which only show changes far to the right of the decimal points! These ratios change by very small amounts over time, but they clearly illustrate big changes in the atmosphere's composition of 13C and 12C, pointing to the fossil fuel origins of more and more of the atmosphere's CO2.
Here is one final comparison to help make the δ-values more understandable. Annual global average temperatures are usually presented as anomalies with reference to some "base period". Figure 4 is a familiar graph of this from NASA-GISS with data from 1880 to 2016. The "base period" for this graph is 1951-19802, the annual temperatures for these thirty years are averaged together and this is set as the zero point of the anomaly scale. So, the base period is like the standard sample used as the zero point in the δ-notation scale. Then, each individual year's data point is compared to that zero point. If a year's temperature was warmer than the base period, then the anomaly for that year is positive, such as 2016's record high anomaly of 0.99°C. This is comparable to positive δ-values. Years with colder values than the base period would be negative, like 1904's record low value of -0.5°C. This is similar to the negative δ-values described above.
Figure 4. Land-ocean temperature index, 1880 to present, with base period 1951-1980. The solid black line is the global annual mean and the solid red line is the five-year lowess smooth. The blue uncertainty bars (95% confidence limit) account only for incomplete spatial sampling. (NASA-GISS).
In both instances, δ-values and temperature anomalies, cumbersome numbers are converted into more meaningful and useful values. In the case of δ-values, very very small changes in isotopic ratios in the natural environment are more easily described, and we can see more clearly how the Earth's climate system works and changes over time.
1. "The original PDB sample was a sample of fossilized shells of an extinct organism called a belemnite (something like a shelled squid) collected decades ago from the banks of the Pee Dee River in South Carolina. The original sample was used up long ago, but other reference standards were calibrated to that original sample. We still report carbon isotope values relative to PDB but now use the term "VPDB" ["Vienna Pee Dee Belemnite"] to indicate that the data are normalized to the values of that standard." (USGS).
2. Any time period, and any length of time, may be used. A thirty year period is often used because thirty years is a long enough time to describe "average" climate variables.
