The Haleakala volcano is located on the island of Maui, the second-largest island of Hawaii. On the top of this extinct volcano, at an altitude of 3055 m, an astronomical observatory has been built. One of the telescopes in this observatory is the Pan-STARRS telescope, with a 1.8 m diameter mirror and equipped with the largest digital camera ever built, recording almost 1.4 billion pixels per image
The function of this telescope is to scan the sky, looking for moving astronomical objects, like comets and asteroids. The idea is simple, you take two pictures of a part of the sky, at different times and compare them.
In 1930 the planet Pluto has been discovered this way. Here are the original photographs, taken 6 days apart, the arrows point to Pluto. In those days the astronomer used a gadget, called a blink comparator, which rapidly switched from viewing one photograph to viewing the other. The moving object would stand out by “blinking”.
Nowadays computers can do this much better than humans, and Pan-STARRS is connected to a sophisticated computer system, that not only analyses the images, but also communicates with other observatories all over the world, when moving objects are found.
The interest in these objects is not only scientific. Pan-STARRS is taking part in the NEO Search Program. NEO stands for Near Earth Object, and NEO‘s are objects, mostly asteroids, that could collide with Earth in the future. Readers who have been following my blog from the start, may remember my posts about the asteroid Apophis, published in 2010(!). In 2013 Pan-STARRS had already discovered 10.000 NEO’s
On 19 October 2017 a new moving object was discovered by Pan-STARRS. At first it was assumed to be a comet, and named C/2017 U1 but as it had no characteristic comet tail, it was reclassified one week later as an asteroid : A/2017 U1
A short intermezzo about the classification of comets. The first letter describes the kind of object, P for a periodic comet, C for a comet with unknown period and A for an object that was first classified as a comet but is actually an asteroid. There are a few more categories. The letter is followed by the year of discovery and by a letter that indicates the “half-month” of discovery. A for the first half of January, B for the second half, C for the first half of February, etc. The letter I is not used, so the U means that the object was discovered in the second half of October. It is here followed by the number 1, because it was the first discovery in that half-month.
Further observation of this asteroid, by many other observatories, showed that it came from OUTSIDE our solar system!
So this was an EXTRAORDINARYevent, the first observation of an object that came from another star! On 6 November 2017, less than three weeks after its discovery, it was reclassified again, as 1I/2017 U1 , where a new category was introduced, I, standing for Interstellar object. The number 1 in front of the I was added, because it was the first occurrence of this new category. And it was given a proper name: ʻOumuamua, which in the Hawaiian language means “a messenger from afar arriving first“. The symbol ʻ in front of the name is not a typo, but a ʻokina, a glottal stop.
How do the astronomers know that it comes from outside our solar system? By its speed and its orbit! Here is an animated gif of ʻOumuamua’s orbit.
The orbit is hyperbolic ! From far away it approached the solar system with a velocity of ~26 km/s. Attracted by the Sun, its velocity increased to ~88 km/s at perihelion, on 9 September 2017. When it was discovered by Pan-STARRS, 40 days later, it was already on its way out.
Here is another sketch of ʻOumuamua’s orbit, with dates. Try to view it “3-dimensional”, the orbital plane of ʻOumuamua is tilted with respect to the ecliptic (the orbital plane of the planets).
Is there anything more that we know about this visitor from outer space? For example from which star it started and how long it is underway? It arrived roughly from the direction of the star Vega, 25 lightyear away. In that case, with its velocity it would have taken ~ 600.000 year to reach our solar system. But Vega was not in the same location, that long ago. We just don’t know, ʻOumuamua could have left its star system billions of years ago.
Surprisingly we know a bit more about its shape, its size and its color! The color is dark reddish and the size is roughly 200 x 30 m. A kind of gigantic cigar…:-) Here is an artist impression
You may wonder how anything can be said about the shape, as the image of ʻOumuamua is only a single pixel in even the strongest telescopes! The answer is that the asteroid is “tumbling” with a period of ~ 8 hours. Therefore the amount of light it reflects varies.
Here are the measurements done by several telescopes, with a theoretical fit, assuming a 1:10 ratio between length and width Click to enlarge.
Of course there are people who are wondering if it could be a spaceship…:-). In that case it would probably be out of control or abandoned, because of the tumbling. Anyway, both SETI and Breakthrough have been listening for any signals coming from ʻOumuamua. Without results.
For this blog I have used the very informative Wikipedia article about ʻOumuamua and other Internet sources.
All are retired professors and quite old, not unusual for Nobel Prize winners…:-; More unusual is that this Nobel Prize has been awarded for the observation of gravitational waves in September 2015, only two years ago! The time between a discovery and the Nobel Prize is often 10-20 years and tends to increase
In this case the physics community was pretty sure that the Nobel Prize would go to LIGO, the Laser Interferometer Gravitational-Wave Observatory, where the gravitational waves were observed. Problem is that a Nobel Prize (with the exception of the Peace Prize) can not be awarded to an organisation but only to a maximum of three individuals (and never posthumously). And the article in Physical Review Letters, where the discovery was published in February 2016, has more than 1000(!) authors. Here is the beginning of the author list
In this blog I will explain why these three people were selected. But first I must tell a bit more about gravitational waves, and why physicists are so excited that they have been observed.
Motion takes place in 3-dimensional space as a function of time. Both space and time are absolute concepts, independent of each other.
Newtonian mechanics works extremely well, but there is one disturbing fact, the speed of light c in vacuum turns out to be always the same, no matter how fast the light source is moving itself. Einstein “solved” the problem in 1905 by accepting the constancy of c as a fact, which resulted in his Theory of Special Relativity (TSR)
But it came at a price! Space and time are no longer absolute and independent in this theory, together the three dimensions of space and the single dimension of time form a 4-dimensional continuum, called spacetime .
Gravitation doesn’t play a role in the TSR, but in 1916 Einstein publishes his Theory of General Relativity (TGR). In this theory gravitation is described as a curvature of spacetime. A massive object like the Sun curves the spacetime in its surroundings and a planet like Earth just “follows” this curvature.
A consequence of this theory is that even light would follow this curved spacetime and will be deflected when it passes close to the Sun. This prediction was successfully confirmed only a few years later. During a solar eclipse the stars near the Sun became visible and their position was shifted in complete agreement with the TGR. It was front page news and made Einstein world famous.
Another prediction of the TGR was that (accelerated) motion of massive objects could produce waves and ripples in this fabric of spacetime. Mind you, in spacetime itself ! However, these waves and ripples were estimated to be very small, maybe only measurable if those objects were extremely massive.
For example, two black holes or neutron stars, orbiting each other.
Here is an artist impression of the gravitational waves caused by two orbiting black holes. I have hesitated to include this image, because I find it very confusing, suggesting that the cells of the spacetime fabric are moving up and down, whereas the cells themselves are changing shape, stretching and contracting. But the image comes from LIGO, so who am I…:-)?
After this long(?) introduction it is time to go back to LIGO and the three Nobel Prize winners.
LIGO has a long and complicated history, starting in the 1960! Here are some important dates. The names of the three Nobel Prize winners in blue. __________________________________________________________________
In 1968, almost 50 (!) years ago, Kip Thorne (Caltech) did calculations about the gravitational waves of black holes. Which, by the way, had not yet been discovered at that time, but their existence followed from the TGR! He came to the conclusion that detection should be possible. Also in the 1960s, Rainer Weis (MIT) proposed to use interferometry to detect the incredibly small variations in the fabric of spacetime. See below for more about interferometry.
In 1980, under pressure of the American National Science Foundation (NSF) , MIT and Caltech joined forces in the LIGO project. But progress was slow and funding not easy.
In 1994, Barry Barish (Caltech) was appointed director of the project. He was a good organiser, proposed to build the LIGO detector in two phases. This proposal was approved by NSF and got a budget of USD 395 million, the largest project in NSF history!
In 2002, the first phase of LIGO became operational, but no gravitational waves were detected.
In 2004, funding and groundwork started for the second phase, “Enhanced LIGO”, four times more sensitive than the first phase.
In September 2015, after a 5 year overhaul of USD 200 million was completed, Enhanced Ligo started operating.
Within days, on 14 September at 9:50:45 UTC, Enhanced LIGO detected gravitational waves for the first time in history. __________________________________________________________________
So, what is an interferometer? Here is a sketch of the LIGO interferometer
And who could better explain how it works than Rainer Weis himself?
What may not be fully clear from the video is the huge scale of this LIGO project.
Two “identical” interferometers have been built in the US, about 3000 km apart
Here is an aerial view of the Hanford interferometer, each of the arms is 4 km long!
Both interferometers can be seen easily on Google Earth. Left Hanford, right Livingston.
As Weis explained, gravitational waves cause small differences in the length of the arms. Very, very small. In the order of 10-19 m, that is about 1/10.000 part of the size of a proton. Read that again and again, I still find it difficult to believe..:-)
The sensitivity must be about 1/10.000 part of the size of a proton.
New technology had to be developed to reach this sensitivity. Ultra-high vacuum, very precise mirrors, extremely stable lasers. Noise reduction (thru seismic vibrations, a passing truck, etc) is the main problem. That is also the main reason that two interferometers were built. Accidental noise should be different in both detectors, but a gravitational wave should reach both (with a slight time difference, because of the distance between the two detectors).
Critical is the suspension of the mirrors. They must be absolutely stable. Here two images of the damping and suspension systems. Click here for details
What kind of signal do we actually expect? Let’s concentrate on orbiting back holes (it is called a binary), like Thorne did. As shown in the earlier image, they produce gravitational waves, but those are way too small to be detected. However, the binary will loose energy sending out these waves, as a result over time the two black holes will get closer and closer. Until they come so close that they will merge into one larger black hole, a cataclysmic process that may take less than a second! It is during this phase that the gravitational waves are much stronger and might be detectable.
Here is a computer simulation of the merger of two black holes. The simualtion has been SLOWED down about 100 times, in reality the merger occurs in a split second. The “moving” background stars are a result of the extreme distortion of spacetime.
Click here to see the gravitational waves, sent out during the merger.
You will notice that before merging the two black holes spin faster and faster, distorting the fabric of spacetime more and more. It is a bit similar to a bird chirp: increasing frequency and loudness. After they merge into one, no more gravitational waves.
So, what happened on 14 September 2015? The two interferometers were to start the first research run on 18 September and were already in fully operational “engineering mode”, when at 9:50:45 UTC both detected the typical “chirp” signal. For testing purposes sometimes “fake” signals were injected, to test the alertness of the system and the scientists. It took a few hours before it became clear that this was a real signal and not a test!
Here is the “Nobel Prize winning” signal. The red graph is from Hanford, the blue one from Livingston (the Hanford signal is also shown, inverted and shifted in time) Notice the time scale, the whole merger takes place in a few tenths of a second!
The lower two graphs show a fit to the data, using Numerical Relativity. It is surprising how much information can be extracted from these two graphs. Here is a (partial) result
Two black holes, with a mass of 35 and 30 M☉. (solar mass) , at a distance of about 1.4 billion lightyear away from Earth, merged into a single black hole of 62 M☉. .
The mass difference of 3 M☉ , was radiated during the merger as gravitational waves. That is an awful lot of energy! The estimated peak emission rate was greater than the combined power of all light radiated by all the stars in the observable universe! If you don’t believe me, click here.
This first event has been named GW150914. GW stands for Gravitational Wave and is followed by the detection date 14-9-2015. In the past two years more gravitational waves have been detected, here is a list
If you look at the location, you see that in the first five events the location of the binary is not well-defined. The reason is that you need more detectors to determine the location accurately, two is not enough.
The sixth event, GW170814 was not only detected by LIGO, but also by Virgo , the European counterpart of LIGO. This interferometer is located near Pisa in Italy. Same setup as LIGO, slightly smaller arms (3 km)
Virgo was also designed in two phases. The first phase did not detect gravitational waves. In 2106 Advanced Virgo became operational and is now cooperating with LIGO. Another interferometer will be built in India: INDIGO .
The last event, detected until now, GW170817 (about three months ago), is an interesting one, because it is not a merger of black holes! For the first time a merger of two orbiting neutron stars has been observed. The masses of the two stars are comparable with the Sun and the binary is closer to Earth, although still a respectable 130 million lightyear! It is not sure if the merger resulted in a neutron star or a black hole. But anyway, a merger of neutron stars should result in visible light coming from the debris after the merger.
Because of the detection with three interferometers, it was possible to narrow the region of space where the gravitational waves came from. The location predicted by LIGO/Virgo was still large, about 150 times the area of a full moon. Within hours after detection, alerts were sent to astronomers all over the world and a massive search started.
A few hours later the Swope telescope in Chili reported they had found the source in galaxy NGC 4993 , 140 million lightyear away. This was soon confirmed by other observatories.
Here is an image of this elliptical galaxy. The inset shows the light coming from the merger, getting weaker and weaker, as expected.
More interesting discoveries can be expected in the future, this is just the beginning.
When you want to learn more about this fascinating new field of astronomy, you should read the book Ripples in Spacetime, written by Govert Schilling
Are you using Whatsapp and did you recently receive this picture? Getting excited already, that in a few weeks time you will observe a unique event?
Sorry to disappoint you, but this is complete nonsense. Yes, on 21 August 2017 there will be a total solar eclipse, and to watch it is an experience of a lifetime. But solar eclipses are common, almost every year there will be a solar eclipse visible, somewhere on Earth..:-)
Here is a list of solar eclipses between 2011 and 2020. In the third column the type of eclipse is given. Twenty four eclipses in total, five of them total. The last column gives the geographic region where the eclipse will be visible.
I do not want this blog to be very technical, but some explanation may be useful..:-)
A solar eclipse occurs when the moon passes between the sun and the earth.
The moon orbits the earth in about 29 days, so you would expect a solar eclipse roughly every month. But the orbital plane of the moon is tilted 5 degrees, therefore the shadow of the moon will not touch the earth every month. Also, because of the (big) size of the sun, the shadow of the moon (the white lines) just reaches a small part of the earth. The pink lines mark the region where the moon blocks the sun only partially.
Another effect is that the orbit of the moon is slightly elliptical, so the distance of the moon to the earth is not always the same. If the moon passes between the sun and earth while it is farther away from the earth, it can not block the sun completely, resulting in an “annular” eclipse.
Let us look in a bit more detail at the 21 August eclipse. The blue band is where you can see the total eclipse. Weather permitting of course…:-) The light blue lines parallel to the blue band indicate the regions where you have a 75%, 50% and 25% partial eclipse.
Is there anything special about this eclipse? Yes..:-) It will only be visible from the Unites States of America and no other country! AMERICA FIRST…:-) Probably Trump will twitter one of these days that it is one of the successes of his administration…;-)
Of course there is a lot of interest in the USA for this Great American Eclipse . Here are a few advertisements, taken from the Internet.
But also for the USA it is not a unique event. The last total eclipse, visible in mainland USA, was on 26 February 1979 and the next one will be on 8 April 2024.
Total eclipses are spectacular. It gets dark, and the solar corona becomes visible. A reason for many people to travel to a region where the total eclipse can be watched.
Actually I was one of them, 8 years ago!
Friends told us about a total eclipse, visible in China on 22 July 2009. Here it is
This post is about the planet Jupiter and the spacecraft Juno, launched in August 2011 and orbiting Jupiter since July 2016. The image shows both the planet and the spacecraft.
But we will start with some Roman (Greek) mythology. Jupiter (Zeus) was the king of the gods and Juno (Hera) his wife. Jupiter was an promiscuous god with numerous extramarital affairs and Juno was a jealous spouse, always keeping a eye on her adulterous husband. Here are a few of his affairs
He lusted for Io, and transformed the girl into a cow, to hide her from his wife. In vain, Juno asked him to give her the cow as a present.
He abducted Europa, disguised as a bull. King Minos of Crete was one of their children
He fell in love with the nymph Callisto and took the shape of virgin goddess(!) Artemis to seduce her.
He was so enchanted of Ganymede, that, in the shape of a raven, he took the beautiful boy(!) to Mount Olympos.
You will understand that as schoolboys we were always happy when our Latin and Greek teachers told us about these myths…:-)
Back to astronomy. Jupiter is the largest planet in our solar system. The planet is so big that all the other planets would fit in it. It is the second-brightest planet (after Venus) in the night sky.
In 1610, Galileo discovered that Jupiter has four moons. In the image you can see their size, compared to Jupiter. They look small beside the planet, but they are actually big. The largest one, Ganymede, is bigger than the planet Mercury!
The four moons were named after the four lovers of Jupiter named above! Below you see a (resized) image of each moon and a painting with Jupiter in action.
Callisto seduced by Jupiter disguised as Artemis. Boucher (1759)
The abuction of Europa Jean François de Troy (1716)
Jupiter and Io Paris Bordone (~1550)
The abduction of Ganymede Eustache Le Sueur (~1650)
Since Galileo observed the four moons, many more (smaller ones) have been discovered. At the moment 67 moons have been observed, of which 53 have been named, often after Jupiter’s girlfriends and boyfriends…:-) Here is the complete list of Jupter’s moons
It may now be clear why the spacecraft has been named Juno 🙂 After the launch of the spacecraft, NASA published a mission statement in which they explained the name of the spacecraft:
“The god Jupiter drew a veil of clouds around himself to hide his mischief, and his wife, the goddess Juno, was able to peer through the clouds and reveal Jupiter’s true nature.”
Actually the mission of Juno is to explore Jupiter and not his moons…:-) Much is still unknown about this gas giant. Does it have a solid core? Does its atmosphere contain water? An important part of the mission will be the study of Jupiter’s gravitational and magnetic fields.
So, let us follow Juno on her exploration of Jupiter. It took her five years to reach Jupiter. Why so long? Here is the reason:
To give the spacecraft enough speed at launch to reach Jupiter would cost too much energy. Therefore it is first launched in an (elliptical) orbit around the sun.
The Deep Space Maneuvers one year later will bring it back very close to Earth, which will give it a gravitational slingshot. See my Rosetta blog for an explanation.
As a result the orbit becomes a hyperbole, at the right moment crossing the orbit of Jupiter, where it will be captured by the planet.
Here is a fascinating animation of the whole process.
Jupiter has to be approached carefully because of its intense radiation belts. The magnetic field of a planet traps charged particles like electrons and protons in a doughnut-shaped region around the planet. Earth has these radiation belts, they are called the Van Allen Belts. For Jupiter they are many thousand times stronger and can seriously damage the spacecraft.
To protect the instruments of Juno, the most sensitive ones have been placed in a titanium container with 1 cm thick walls and a weight of 18 kg.
Here is an image of the spacecraft during assembly. The Radiation Vault is the brown box on top of the spacecraft.
Note the size of the human!
To minimise the radiation risk, Juno has to be captured carefully in a polar orbit. Here is a YouTube animation:
The capture orbit is very elliptical with a period of ~ 54 days. The original plan was to reduce the period to 14 days, after two capture orbits (1 and 2). The first reduced orbit (3) would be a clean-up orbit, followed by 32 “science” orbits (4-36), each of them slightly shifted, so the whole surface of Jupiter would be covered.The image gives an impression of these science orbits. Mind you, during each 14 days only a few hours before and after perijove (the point of shortest distance to Jupiter) can be used for science!
However, during the second orbit, a few days before the planned Orbit Reduction Maneuver on 19 October 2016, a problem was found with some helium valves needed to operate the main engine, and a few hours before perijove, the spacecraft went into “safe mode”, because the onboard computer encountered unexpected conditions. The next two orbits were used for testing and diagnostics.
Finally, on 17 February 2017, mission control decided it was too risky to perform the Orbit Reduction Maneuver. So the spacecraft will remain in its 54 day orbit. Totally 12 science orbits will be performed until July 2018. The next perijove (orbit 7) will occur on 11 July.
It must have been quite a disappointment for the scientists, instead of new data every two weeks, they now have to wait almost eight weeks.
Are there results already? The instruments that are measuring the magnetic field of Jupiter and the composition of the Jovian atmosphere are collecting data, it seems the magnetic field is more lumpy than expected.
The most spectacular results come from the on-board camera Junocam. Here is an image of Jupiter’s south pole, not observable from Earth. Amazingly complex and turbulent.
And last week NASA published another picture, taken 19 May, just after Juno passed perijove 7. Keep in mind that these images are color enhanced! Part of the south pole region is visible. The white spots are part of the “String of Pearls”, massive counterclockwise rotating storms.
The next orbit will pass over the famous Great Red Spot, a storm on Jupiter that has lasted already for several hundred years and is so big that Earth would fit inside it. Will be interesting to see images.
At the end of the Juno mission, the spacecraft will be directed into the Jovian atmosphere, where it will be completely destroyed. This will be done to avoid any chance that material of Juno might “contaminate” one of Jupiter’s moons. If ever life forms are found on these moons, there must not be any doubt about its origin.
To end this post in a lighthearted way, the Juno has three passengers on board! Figurines, specially crafted by Lego in the shape of Jupiter (with a lightning bolt), Juno (with a magnifying glass) and Galileo (with a telescope and Jupiter in his hand)
Preparing this post, I have made extensive use of a very informative web page: Juno Mission and Trajectory Design . Very detailed and sometimes quite technical, but worth reading.
Tomorrow, 31 December 2016, just before midnight, an extra second will be added to the Universal Coordinated Time (UTC)! It is called a leap second.
Probably everybody will be familiar with the concept of a leap day . A year in the international calendar has 365 days, but the solar year is a bit longer, 365.25 days. To keep this calendar synchronised with the solar year, every four years an extra day (29 February) is added to the calendar, a leap day. 2016 was a leap year, the next one will be 2020.
The Chinese calendar is based on the motion of the Moon, orbiting the Earth with a period of 29.53 days. A (lunar) year is 12 months = 12 × 29.53 = 354.36 days, about 11 days shorter than the solar year. To keep this calendar synchronised with te solar year, every two/three years an extra month is added, a leap month. Next year will be a leap year in the Chinese calendar, it will have 13 months with one of the months duplicated. Not always the same month, this time the 6th month. More detailed information about calendars can be found on my website
For those not familiar with UTC, it is the primary time standard by which the world regulates clocks and time. It is basically the solar time at 0° longitude, with the solar day as fundamental unit. The 0° meridian passes through Greenwich, therefore UTC is sometimes called Greenwich Mean Time (GMT). The world has been divided into 24 time zones, they are defined as UTC plus or minus a number of hours. For example Malaysian time is UTC + 8.
So, the UTC is based on the (solar) day and a day is 24 x 60 x 60 = 86400 seconds, right? Why do we need to add a leap second? The answer is simple, but may surprise you.
A (solar) day is not exactly 86400 seconds!
Here is a graph of the “extra” length of day over the last few decades. Click to enlarge and see more details
It is only a few milliseconds every day, but it accumulates! Therefore it has been decided, in 1972, to add an extra second to UTC, when this accumulated deviation gets more than 0.9 second. The red graph shows when leap seconds were inserted. As you see, the deviation from 85440 seconds is quite irregular and actually not predictable. That’s why the leap seconds are announced only 6 months in advance.
Why are the deviations always positive? That has an interesting, physical, reason. It is because of the moon! The moon is responsible for the tides, causing friction! This friction slows down the rotation of the Earth! It is a small but real effect, the solar day increases about 1.4–1.7 milliseconds per century. There is geological evidence that about 500 million year ago, the length of the day was shorter, ~ 22 hours.
The leap second will be added to UTC, 31 December at midnight. 23:59.59 will not be followed by 00.00.00 but first by 23.59.60
In Malaysia (UTC + 8) the leap second will be added on 1 January. 07:59:59 should not be followed by 08:00:00 but first by 07:59:60.
Computer guys are not happy with an insertion of an extra second. It may cause computer failure. The Google engineers will just slow down the system clock slightly, from 10 hours before, until 10 hours after midnight, resulting in 1 second extra…:-) Technical details here
Time reckoning is a complicated topic. I have simplified it here…:-)
In a recent blog, Our nearest neighbour? , I reported about the discovery of the planet Proxima b, orbiting around a star, “only” 4.22 lightyear away from Earth. In several media it was suggested that within a few decades a spaceship could be launched to reach this planet. A spaceship is science-fiction, but there exists an ambitious plan to send a swarm of space-chips to Proxima b within a few decades. I promised to write a separate blog about this Breakthrough Starshot Here it is.
In 1865 the French novelist Jules Verne wrote De la Terre à la Lune (From the Earth to the Moon), in which he describes how three adventurers travel to the moon in a projectile, shot from the earth by a large cannon. I have read it spellbound when I was a teenager. You can read it online here , it is fascinating (and hilarious too).
The illustrations are beautiful. Here are some. From left to right the three adventurers climbing into the projectile, the comfortable interior and the firing of the canon.
Why this introduction? We know now that this method is not used in our space age. We don’t shoot our spacecraft to the moon or other planets, we use rocket propulsion. The Voyager 1 (825 kg) was launched by a Titan-Centaur rocket (600.000 kg). The images show the launch, the Voyager spacecraft and a structure diagram of the rocket. The Centaur is mounted on top of the Titan. A huge amount of fuel is needed to launch a “tiny” payload!
After completing its mission, the Voyager is now leaving our Solar System with a speed of more than 60.000 km/h That is fast but it would still take about 75.000 year to reach Proxima b, if it was going in that direction (which is not the case).
So we can forget about space travel to the stars, using rocket propulsion, at least in the foreseeable future. Is there another option, more in the style of Jules Verne?
Actually there may be one…:-)
One year ago Travis Brashears, a graduate student at the University of Santa Barbara in California, and his supervisor, Philip Lubin, professor of astrophysics and cosmology at the same university, published a paper Directed Energy Interstellar Propulsion of WaferSats in which powerful lasers “shoot” miniature (~ 1 gram only!) electronic chips away from earth in the direction of a nearby star, with a speed approaching the speed of light! Here are the (main) writers , Brashears left and Lubin right.
Does this sound as science fiction? For me it does. But apparently not for these guys.
Sure, light exerts pressure, there are several projects going on, using sunlight propelling a solar sail , a bit similar to the sail of a sailing boat being blown by the wind. One successful project is IKAROS, a solar sail of 196 m2 (!) , launched in 2010 by Japan. Here an artist impression of the sail, with Venus, its destination. The sail is so big. because the thrust of the sunlight is only small.
Next year March the LightSail 2 will be launched. To the left the actual spacecraft, a so-called cubesat. To the right an artist impression of the LightSail in space, with a deployed sail. Notice how small the cubesat is compared to the sail!
These projects are using sunlight. The project of Brashears and Lubin is futuristiic.
A ground-based laser will be used as a “shotgun” Estimated power needed 100 GW. That is a lot! The Three Gorges Dam in China, the largest power plant in the world, generates 22.5 GW.
The spacecraft will be a chip with a mass of about 1 gram, with a light sail of ~ 1 m2 . The plan is to prepare about 1000 of these miniature “spacechips” and launch them simultaneously in a mothership, orbiting the earth. From there the starchips will be shot, one after another on a daily basis, during 3 year.
The laser will give a spacechip in about 10 minutes a speed of 20% of the speed of light. That is fast , 60.000 km/s
The spacechips will reach Proxima b in about 20 year. Hopefully at least a few of them will have survived the journey.
They will send back pictures to earth.
Estimated cost of the project US$ 5-10 billion.
Proposed launch date about 20-30 years from now.
Here is an artist impression of the launch. Mind you, the spacechip is the tiny dot in the center of the light sail!
Futuristic indeed. The time span of 20-30 year is because much of the technology still has to be developed. Designing a spacecraft on a centimeter-size, gram-scale chip, developing a light sail with a thickness of 1 micron or less, building a 100 GW laser and many more challenges.
Here another artist impression. The plan is to build a so-called “phased” array of smaller lasers, with a combined power of 100 GW. If you use 100 kW lasers ( at the moment the maximum power available), you need a staggering 1 million of them.
I am skeptic, as usual…:-) But not everybody is. Yuri Milner, for example is optimistic. This Russian/American tech entrepreneur and multi-billionaire, started as a physicist and is very interested in the big question “Are we alone in the universe“. In July 2015 he announced, together with the British physicist Stephen Hawking, the Breakthrough Initiatives , a program to search for extraterrestrial intelligence. At that time the program consisted of two parts.
Breakthrough Message. A prize pool of 1 US$ 1 million for the best (digital) messages that could be sent out into deep space. No concrete plan to actually send these messages, because for example Hawking thinks it might not be advisable to do that. See my blog Anybody Out There?
In April 2016, part 3, Breakthrough Starshot, was announced by Milner and Hawking. Milner and Mark Zuckerberg (FaceBook) will contribute another US$ 100 million to explore the technological feasibility of the program outlined above.
From left to right Yuri Milner (holding a protoype of a spacechip in his hand), Stephen Hawking and “eminence grise” Freeman Dyson, a physicist and cosmologist, now 93 year old. If you are interested in really futuristic ideas, have a look at his Dyson Sphere 🙂
Below is an animation of the process. A few comments may be useful.
There are 135 lasers in the array. You need at least 1 million.
The spacechips are launched simultaneously in a container, but released and shot one after another.
When they reach Proxima b after ~ 20 years, they will pass the planet at full speed (60.000 km/s). So fast that the camera on board can only take a few pictures. Also data will be collected about magnetic fields etc.
These data will be sent back to earth, using miniature lasers on the spacechip, focused with the help of the light-sail.
About 4.22 year later, the ground-based laser array will receive these data. Hopefully…:-)
I have been working about two weeks on this blog, reading and collecting as much information as I could find. To be honest, I became more and more skeptic.
A few days ago Scientific American has published a very informative article about the Starshot Program: Inside the Breakthrough Starshot Mission to Alpha Centauri. Many scientists were asked for their opinion about the project. There is respect for the technological challenge, but scepsis about the scientific value.
Just a short post about the Supermoon of 14 November, widely publicised by the media the last few weeks as a not to be missed, once in a lifetime event. For example on Facebook
It’s a hype.
Supermoons are not rare, they occur regularly, on average every 14 months. The last one was 28 September 2015, the next one will be 4 December 2017.
Full moons have different sizes because the orbit of the moon is slightly elliptical. The image shows the moon orbit, exaggerated. The average distance to Earth is 385.000 km, but the moon can come as close as 356.500 km (perigee) and as far as 406.700 km (apogee). The moon orbit also rotates itself with a period of 8.85 year
As a result of these two effects, a full moon can sometimes occur when the moon is in or near its perigee. An observer on Earth will then see this full moon brighter and larger, than when it occurs in its apogee. Dividing the apogee distance by the perigee distance, we find 406.700 / 356.500 = ~ 1.14, so the moon will look ~14 % brighter and ~ 30 % larger. This effect is easily observable, as you can see in the image below. By the way, the name Supermoon has been introduced by astrologers, the correct name is Perigee Full Moon.
So, why this sudden interest in this particular Perigee Full Moon of 14 November?
The values given for apogee and perigee are actually averages. Because of the influence of sun and planets they vary slightly in time. Here are the perigee distances during the Supermoons of 2015 and 2016 :
356.876 km in 2015
356.511 km in 2016
The perigee distance on 14 November is a little bit smaller! To be precise , 365 km smaller, ~0.1%. So the Supermoon of 14 November will be 0.1% brighter and 0.2% larger. Observable for the unaided eye? Not at all, believe me…:-)!
Why the hype? When you look at the Perigee Full Moons in the past and future, you have to go back to 1948 to find an even smaller full moon perigee: 356.462 km (49 km smaller). And from now on you have to wait until 2034 to find a smaller one: 356.447 km (64 km smaller). These Supermoons will be ~0.02 % brighter.
That’s why it is said: the brightest Supermoon in 86 year…:-). Technically correct, but…. a hype.
My suggestion, try to observe the moon tomorrow, when it is rising, just after sunset. The moon looks always larger when close to the horizon! This is an optical illusion, the Moon Illusion. Combined with the Perigee Full Moon it will be beautiful
And when you are not free tomorrow, it is not that critical. One or two days later you can still admire the Supermoon.
Numerous extrasolar planets have been found by now, as of 1 September 2016 the count was 3518. A few dozen of them might be able to support life (rocky, similar size to Earth, orbiting in the habitable zone of their star).
The answer is simple: Proxima Centauri is not just one of the hundreds of billion stars in our galaxy. It is the star closest to our Sun, at a distance of 4.22 lightyear “only“,
Let’s have a closer look at this nearest neighbour of the Sun. Where can we find it in the night sky? And can we see it with unaided eyes or binoculars?
Here is the night sky (in Malaysia) in March, south-eastern direction. You will notice three constellations, dominated by Centaurus. The name comes from Greek mythology, where a Centaur is a half-horse half-man creature
Here is how the Greek saw a Centaur in the stars.
You may find it difficult to see a centaur, but the two bright stars in his left leg are conspicuous. Rigel Kent, better known as α Centauri, is the third-brightest star in the sky, after Sirius and Canopus.
Hadar (β Centauri) is also a bright star.
α Centauri is actually a star system, consisting of three stars. Two of them, α Centauri A and B are so close that they can not be separated by the unaided eye. Here is an image taken by the Hubble telescope.
α Centauri A (to the left) is slightly larger than the Sun, while B is a bit smaller. They orbit around each other with a period of 80 years.
The third component, α Centauri C is a red dwarf, much smaller and cooler (more reddish) than the Sun. Very far away (about 0.21 ly) from the other two. If it is bound by gravitation to A and B (not 100% sure), the estimated orbiting period is ~ 500.000 year. Here are A and B (seen as one star here) and C (in the center of the red circle). The other stars are Milky Way stars, much farther away.
The α Centauri system is closer to the Sun than any other star, about 4.35 ly away, and of the three components, α Centauri C is a bit closer (4.22 ly) and therefore it has been named Proxima Centauri.
Now a planet has been found, orbiting the red dwarf in the α Centauri system. It has been called Proxima b. Very close to the star, orbiting it in about 11 days only. Compare this with Mercury’s period of 88 days. But because the star is less bright than the Sun, the planet is still in the habitable zone. Here is an artist impression how the planet could look like. α Centauri A and B are also shown, as bright stars.
Our closest neighbour! But a distance of 4.22 light-year means that Proxima b is still 40 trillion km away from Earth. At this moment spacecraft New Horizon, after taking spectacular pictures of dwarf planet Pluto, is leaving our solar system with a respectable speed of ~ 60.000 km/h. That is fast, but it would take ~ 80.000 year to reach Proxima b.
Here is what the Mail Online reported on 24/8. “The second Earth that we could visit in our lifetime” and “just four light years away”
Actually there is an audacious plan to send a probe to Proxima b. Not a spaceship but a space-chip! Not one probe, but a swarm of them. Interested? The project is called .Breakthrough Starshot and it deserves a separate blog post.
Here only a few comments on the idea of a “second Earth”.
As the planet orbits very closely to its Sun, it will probably be tidally locked, like Mercury. In that case the sun side will be scorching hot, the other side dark and freezing cold. Only the twilight zone might be able to support life
Proxima Centauri is a flare star, with occasional eruptions of radiation, comparable but much stronger than the solar flares. Not very suitable for the development of life.
Will there be water on Proxima b? Earth got its water during the Late Heavy Bombardment. when numerous comets and asteroids, disturbed in their orbit by the giant planets, collided wit Earth.
My last blog about the Rosetta, Dawn and New Horizon missions was posted in July last year. Before I give an update, let’s first have a look at our Sun. Here is a recent graph of the number of sunspots. Cycle 24 has reached a maximum in April 2014 and is coming to an end.
As you will notice, cycle 24 has a double peak, in itself not unusual, but this time the second peak is higher than the first one. The maximum of cycle 24 is much smaller than that of cycle 23, and the prediction for cycle 25 is that it will be similar to cycle 24 or even smaller.
Here is a graph of the sunspot cycles, recorded until now. It looks like we have passed the Modern Maximum and are going to a minimum. Are we heading to a new “Little Ice Age“? As I wrote in an earlier post, this is a sensitive issue, and I will not comment on it..:-). Be very wary when you search the Internet for info about a relation between solar activity and global warming. Always check the credentials of the report. You might try this site: Skeptical Science
Rosetta is still orbiting comet 67P, which has passed its perihelion and is now on its way out into deep space. Here is the position of Rosetta and the comet, end of last year, the comet has passed already the orbit of Mars. No signals of the comet lander Philae have been received anymore, but Rosetta itself is still active.
Here is a recent image of 67P, taken on 27 March, when Rosetta was 329 km away from the comet nucleus. The Sun is behind the comet, with a spectacular result.
The scientists are planning to let Rosetta make a controlled landing on 67P in September 2016, which will be the end of the mission. You can find the latest news on Rosetta’s blog
Dawn is still in orbit around dwarf planet Ceres. Slowly getting closer, resulting in more detailed pictures. You may remember the excitement about the bright white spots. Now we know that they are located in the center of a crater, which has been given a name: Occator. More (smaller) white spots have been found
Here is the most recent picture (in false color), taken 30-3-2016 from an altitude of 385 km. . Spectacular. Scientists now think that the white spots are formed by highly reflective material, possibly ice or salt.
Actually Dawn is taking pictures of the whole surface of Ceres. Scientists have been busy giving names to the various features..:-)
For more information about Dawn, read this detailed blog So.Much.Ceres, published a few weeks ago
On 14 July 2015, the New Horizons spacecraft passed Pluto at an altitude of 12.500 km above its surface. It took as many pictures during the fly-by (of only a few minutes!) as possible and it still has not finished transmitting all the data to Earth!
Here is one of the images, released a few days ago. It shows numerous “haloed” craters. The false-color image gives the composition: purple is methane ice, blue is water ice. Why the crater rims and walls consist of methane ice has not yet been explained.
New Horizons is now on its way to the Kuiper Belt, where it is supposed to flyby one of the Kuiper Belt objects, 2014 MU69 , on 1-1-2019. Here are the present locations of the New Horizons spacecraft and 2014 MU69
We have reached the outskirts of our Solar System. Pluto, once the 9th planet, has been demoted and is now considered a dwarf planet belonging to the Kuiper belt. Recently more dwarf planets have been discovered in the region beyond Neptune, Eris ( in 2005) , Haumea (in 2004) and Makemake (in 2005) Like Pluto they have quite elliptical orbits and periods in the range of a few hundred years. Pluto for example has a period of 248 year and its distance to the Sun varies between 30 and 49 AU, where 1 AU (the average distance between Earth and Sun) = 150 million km. The orbits of these dwarf planets have been strongly influenced by big neighbour Neptune.
In 2003 dwarf planet Sedna was discovered with an estimated period of 11.400 year and a distance to the sun varying between 76 and 936 (!) AU. Here is the orbit of Sedna. Pluto’s orbit is purple.
What could have caused such an extremely elliptical orbit? It can not have been gravitational disturbance by Neptune, because it never comes close to Neptune (distance of Neptune to the Sun is 30 AU).
In the last decade more of these “strange” objects have been discovered. For example in 2012 2012 VP113, estimated period 4200 year, distance to the Sun between 80 and 438 AU, also very elliptical. Here the orbits of six of them are given.
Could these orbits be gravitationally disturbed by an UNKNOWN planet in the outer reaches of the Solar system?
On 20 January 2016 astronomers Brown and Batygin published an article in the Astronomical Journal: Evidence for a distant giant planet in the Solar System (abstract). Using computer models, they find that a planet with a mass about 10 times the mass of Earth, a period of 10.000-20.000 year, and a distance to the Sun varying between 200 and 1200 AU, could explain the orbits. Tentatively this planet is named Planet Nine .
Here is a sketch with the position of this Planet Nine.
Of course this is a hypothesis until now. Other explanations are possible. Next step is to try and find Planet Nine. That will not be easy, even for the most powerful telescopes. And where to look for it?
Here is a picture of the two authors, both astronomers from Caltech. By the way, Brown (left) is the guy who discovered Eris, which started the demotion process for Pluto!
They have started a website The Search for Planet Nine and just submitted a (highly technical) paper in which they discuss where to search for this planet.
If Planet Nine is ever found, I will not be surprised if they get a Nobel Prize for their research.
On 7 January 2016 a “new” large prime number was discovered, with more than 22 million digits. Time for a blog about these numbers, which have fascinated mathematicians from Greek antiquity until present times.
Prime numbers are numbers that can only be divided by 1 and itself. For example 7 is a prime number, but 6 is not because it can be divided by 2 and 3. . Here is a list of the 168 prime numbers smaller than 1000. The number 2 is the only even prime, all others are odd.
How many prime numbers are there?
Euclides, the famous Greek mathematician, living in present-day Egypt around 300 BC, already proved that their number is infinite, and his proof is so elementary, that I often presented it to my students when I was a teacher, as an example of what is called Reductio ad Absurdum.
Euclides’ proof: Assume that you have a complete list of all prime numbers.
Multiply them together and add 1. Call this number X.
Because of the added 1, this number X can not be divided by any prime number in your list (there will always be a reminder 1)!
So there are only two possibilities, either X is prime itself, or it can be divided by a prime number outside your list. In both cases it shows your list was incomplete.
Therefore our assumption was wrong and the list of prime numbers is infinite!
How to find out if a number X is prime? Do we have to check whether X is divisible by any number, smaller than X ? That would be a tedious job. Fortunately it is not as bad as that…:-). Because it is easy to see that we only have to check whether X is divisible by any prime number, smaller than the square root of X.
For example X=283, is it prime? The square root of 283 = 16.82…, so we have only to check division by 2,3,5,7,11 and 13.
283 / 2 = 141 rest 1
283 / 3 = 94 rest 1
283 / 5 = 56 rest 3
283 / 7 = 40 rest 3
283 / 11 = 25 rest 8
283 / 13 = 21 rest 10
So 283 is a prime number!
This procedure is called Trial Division. For large numbers it becomes time consuming. For example, we want to check if 1000.003 is prime. There are 168 prime numbers smaller than 1000, so we have to do 168 divisions to finally conclude that, yes, 1000.003 is prime. Repeating this procedure for 999.997, you will find that this number is not prime, it can be divided by 757.
Imagine that you have to do these divisions with only pen and paper!
Back to the recently discovered large mega-prime. It is a so-called Mersenne prime, one less than a power of 2: Mp = 2p − 1 with p itself a prime number.
M2 = 22 − 1 = 4 – 1 = 3 prime!
M3 = 23 − 1 = 8 – 1 = 7 prime!
M5 = 25 − 1 = 32 – 1 = 31 prime!
M7 = 27 − 1 = 128 – 1 = 127 prime!
Could this be a rule to create prime numbers? Unfortunately that is not the case. M11 = 211 − 1 = 2048 – 1 = 2047 = 23 * 89 , not prime!
However the next one M13 = 213 − 1 = 8192 – 1 = 8191 is again prime.
As are M17 = 131.071 and M19 = 524.287. The last two are already quite large, in 1588 the Italian mathematician Cataldi had proven by trial division that they were prime.
Why are these numbers called Mersenne primes?
Marin Mersenne was a French priest with an interest in mathematics, theology and philosophy.
He published in 1644 a list of these numbers 2p − 1, stating that they were prime for p = 2, 3, 5, 7, 13, 17, 19, 31, 67, 127 and 257, and not for any other p below 257.
His list was incomplete and incorrect, but still these prime numbers carry his name…:-)
Incorrect, because M67 and M257 are composite Incomplete, because M61 , M89 and M107 are prime
Mersenne was correct that M31 = 2.147.483.647 is prime, but how could he know? This is a big number, the square root is ~ 46.340, so he should first determine all prime numbers smaller than 46.340 (there are 4792) and then perform trial division for all those 4792 numbers. It must have been a lucky guess. And certainly it was a guess for M127 = 220.127.116.110.469.231.731.687.303.715.884.105.727 🙂
It was only in 1772, more than a century later, that the great mathematician Leonhard Euler proved the primality of M31.
By a clever analysis of the general structure of Mersenne numbers, he managed to reduce the number of trial divisions to 84 !
Still a big job (pen and paper), the story is that he had a team of helpers to do the actual calculations.
This was the last result using trial division. For more than a century no developments regarding Mersenne primes took place.
Until 1857, when Édouard Lucas, a young French boy (15 years old), gets interested to prove that M127 is prime.
As trial division is not feasible for these large numbers, he studies the structure of the Mersenne numbers and develops a method to check the primality without trial divisions.
After 19 (!) years of testing his methods, he is convinced and announces in 1876 that M127 is prime. The 9th Mersenne prime!
His approach, later refined by others, is still used in the search for new Mersenne primes. Characteristic for this Lucas–Lehmer primality test is that it can decide that a Mersenne number is NOT prime, without finding the factors of this number. For example, using this test, we find that M257 = 231.584.178.474.632.390.847.141.970.017.375.815.706.539.969.331.281.128.078.915.168.015.826.259.279.871 is composite, but we don’t know its factors…:-)
With Lucas’ method, in the following years/decades the primality of M61 , M89 and M107 is proven. Still using pen and paper!
New activity starts only in the 20th century when the first computers are built.
One of them is the famous SWAC computer, built in 1950. Nowadays a PC or even a tablet would be more powerful.
In 1952 it was used to check new Mersenne primes. Within one year 5 new ones were found, for p = 521, 607, 1279, 2203 and 2281. Still using the methods developed by Lucas
Very large numbers! Here is prime number M2281 with 687 digits. To make it more readable, spaces have been inserted after three digits.
Computers became more powerful, and new Mersenne primes were discovered. In 1961 the first Mersenne prime with more than 1000 digits was found, M4253, using an IBM 7090 mainframe computer (pic left)
And in 1979 the first Mersenne prime with more than 10.000 digits was found, M44.497, using a Cray supercomputer.
You might expect that the recently discovered Mersenne prime M74.207.281 with more than 22 million digits has been found using a super-super computer…:-) But that is not the case! Actually PC’s were used, not one but many, working together!
In 1996 the Great Internet Mersenne Prime Search ( GIMPS) project was started. It is an example of what is called distributed computing. A PC will often be idle, so why not let it work during that time for a project such as GIMPS. Just download some software and your PC will try to find a new Mersenne Prime. Many thousands of volunteers are doing this. And with success
Since 1996, 15 new Mersenne primes have been found, all of them using GIMPS!
Of course finding a new Mersenne prime has no scientific value, it is just an intellectual challenge. But you might win a prize!
When in 1999 the first Mersenne prime was found with more than 1 million digits,M6.972.593 , the Electronic Frontier Foundation awarded this result with a prize of 50.000 US$. In 2008 M37.156.667 was found, with more than 10 million digits. The award was 100.000 US$
Two more prizes have not yet been awarded
150.000 US$ to the first individual or group who discovers a prime number with at least 100 million digits
250.000 US$ to the first individual or group who discovers a prime number with at least 1 billion digits
The latest Mersenne prime M74.207.281 has 22.338.618 digits, not yet enough for the next reward