By that, I am not referring to the latest escapades in American politics, but when planets reach opposition with Earth. During this time, the planet lies opposite of the Earth from the Sun. Why should we care about this? When opposition occurs, this is a planet’s closest approach to Earth and is the optimal time to observe it. On September 26th, Jupiter was in opposition as you can see below.
Jupiter in opposition on September 26th as seen in Starry Nights
As Jupiter and the Sun are on opposite sides of the Earth, when the Sun set in the west on September 26th, Jupiter rose in the east. The following morning, as the Sun rose in the east, Jupiter set in the west. Hence, Jupiter was visible all night. Also, Jupiter’s day side was facing the Earth, allowing astronomers to capture the shadows of Jupiter’s moons eclipsing the surface of the giant planet.
Three moons eclipsing Jupiter. Image Credit: NASA, ESA, and E. Karkoschka (University of Arizona)
While the optimal time to observe any planet that resides outside of Earth’s orbit is during opposition, historically, the opposition of Mars tends to draw the most anticipation. Today, the approaching opposition of Mars heralds the opening of launch windows to the red planet. During the late 1800’s, some astronomers observed Mars during opposition in the hope of discovering signs of intelligent life.
Before the age of space exploration, astronomers especially anticipated what is referred to as perihelic oppositions of Mars. During these oppositions, which occur every 15 or 17 years, Mars is close to perihelion. That is when Mars is closest to the Sun in its orbit (in Greek, peri means close and helion is the Sun). And if Mars is at its closest point to the Sun, it is also at its closest point to the Earth if this occurs during opposition. During the 19th century, the perihelic opposition of Mars in 1877 and 1892 would alter our perception of Earth’s closest neighbor for decades to come.
In 1877, at the Brera Observatory in Milan, Giovanni Schiaparelli was mapping the surface of Mars with an 8.6 inch refractor. In drawing his maps, Schiaparelli employed the same terminology used for the Moon. Dark areas were referred to as seas and lighter areas as land. This was not meant to be taken literally. For example, the Sea of Tranquility, where Apollo 11 landed, is not actually a sea but a dark area (or mare) of basaltic rock. More important than these distinctions, were the dark lines on Mars that Schiaparelli drew on his maps referred to as canali.
Schiaparalli map of Mars. Credit: Wiki Commons.
Schiaparalli intended the word canali to be interpreted as channel. However, businessman turned astronomer enthusiast Percival Lowell interpreted canali as canal. This preconception influenced Lowell as he made observations of Mars during the next perihelic opposition in 1892. In what is referred today as confirmation bias, Lowell proceeded to take his observations as evidence of an advanced civilization on Mars that built irrigation canals from the polar regions to transport water to the arid mid-latitudes. Lowell would continue to advance his case until he passed away in 1916. While this theory did not pan out, it did inspire quite a bit of science fiction (good and bad) during the following half century.
Lowell announces latest discovery of canals on Mars. New York Times, August 27, 1911. Click on image for full resolution.
Lowell did go on to build the Lowell Observatory, where Pluto was discovered. It is still active with a recently built 4.3 meter telescope. Located in Flagstaff, the observatory offers tours for the public.
In all fairness to Lowell, he was not the only one to postulate that life might exist on Mars. The article below from August 7, 1892, presents a proposal from the Kew Observatory in London to attempt to communicate with beings on Mars via a light beam projected from Earth to Mars. This is a prototype for modern SETI projects.
Credit: New York Times
With rovers on the surface and satellites in orbit around Mars, we no longer rely on opposition events for close up views of the red planet. However, we do rely on opposition to open up launch windows to Mars. As a Mars opposition occurs every 26 months, if a mission is unable to launch due to technical or budgetary issues, it has to wait another two years for the next launch window to open. The video below shows the trajectory of the Mars Science Laboratory which landed the rover Curiosity on the surface.
On August 27, 2003, another perihelic opposition put Mars closer to Earth than at anytime during the past 60,000 years. Actually, the differences in perihelic oppositions are difficult to discern with the naked eye. Nonetheless, the event launched an annual internet meme every August stating that Mars will appear as large as a full Moon. Even in 2003, this did not come close to happening. For Mars to appear as large as the full Moon, it would have to be located about a half million, rather than 34 million, miles from Earth. If Mars was to appear as large as a full Moon, something much more bizarre than opposition would have to be happening. So come August, if you see that meme on social media, it is safe to ignore it.
However, I do not recommend missing the opposition of Mars on December 8th this year. Just have realistic expectations of what to see. If the skies are cloudy on that date, worry not, Mars will be very bright in the skies for weeks to follow. As Mars approaches opposition, you will be able to discern its reddish hue with the naked eye. The next perihelic opposition of Mars will be on September 15, 2035.
2018 perihelic Mars opposition via Starry Night. Click on image for higher resolution.
During the 2020 launch window, the Perseverance mission began its voyage to Mars. The mission, just as in the 1892 opposition, will explore for signs of life on Mars. This time, rather than searching for an advanced civilization, the mission will seek out signs of microbial life during Mars ancient history when water flowed on the surface. While the search for intelligent life has moved beyond the Solar System, the missions launched today will afford us a view of Mars that Giovanni Schiaparelli and Percival Lowell could only dream about.
*Image on top of post is Percival Lowell at the observatory he founded in Flagstaff, Arizona in 1912. Credit: Mary Evans Picture Library.
We tend to think of the Earth as apart from the rest of the universe. That is natural as astronomy is the science of looking away from our home planet. While there are many things in space we do not experience in our daily lives such as relativistic effects and black holes, there are other phenomena in space that are closely related to our day-to-day lives. Some introductory astronomy texts lump the Earth and Moon in a chapter with all the other inner planets. I think this is a mistake. A separate section should be dedicated to the Earth and Moon as a starting point to understanding space.
There are many Earth to space examples to pick from and below I’ll describe a few.
I’ll start on the ground level. The Earth experiences plate tectonics along with resultant earthquake and volcanic activity. Lets take a look at shield volcanoes. These volcanoes vent liquid lava rather than explosive pyroclastic material we typically associate with such events as the Mount St. Helens eruption in 1981. Shield volcanoes are gently sloping (Hence, they resemble shields) as liquid lave runs downhill quickly preventing the buildup of steep slopes. A prominent example are the Hawaiian Island chain situated above the Hawaii hot spot. Why is there a chain rather than just one island? As the Earth’s tectonic plate slides over the hot spot, a chain of islands are formed.
Shield volcano of Mauna Kea in Hawaii where the Keck Observatory sits at the summit. Credit: Wiki Commons.
The largest shield volcano in the Solar System is Olympus Mons on Mars. This volcano stands 16 miles high (Mt. Everest is 5.5 miles high) and has a base the size of Arizona. The low gravity of Mars, a third that of Earth, allows for the extreme height of Olympus Mons. And why is Olympus Mons a single volcano rather than a chain like Hawaii? Mars does not have plate tectonics as Earth does. Hence, the crust of Mars never slid across the hot spot as the Hawaiian Islands did on Earth. Understanding the nature of shield volcanoes on Earth can be integrated into an comprehension that Mars has smaller mass, thus, smaller gravity than Earth and no plate tectonic activity either. Land features are not the only place to find planetary similarities.
Computer generated image of Olympus Mons using data from Mars Global Surveyor laser altimeter. Credit: NASA/MOLA Science Team/ O. de Goursac, Adrian Lark.
The rotation of Earth affects air circulation via the Coriolis effect. In the Northern Hemisphere, air movement is deflected to the right. In the Southern Hemisphere, air movement is deflected to the left. What this means is in the Northern Hemisphere, low pressure systems rotate in a counterclockwise pattern. You can see this in radar shots of hurricane systems which are massive regions of low pressure. High pressure systems rotate in a clockwise pattern. The pattern is reversed in the Southern Hemisphere.
Hurricane Mathew circulating in a counterclockwise fashion. Credit: NOAA.
Now lets take a look at Jupiter’s Giant Red Spot from this time lapse video of the approach of Voyager I in 1979.
Jupiter rotates in the same fashion as Earth. That is, counterclockwise if looking down from the North Pole. At first glance, the Giant Red Spot seems to resemble a hurricane and it might be easy to assume it is an area of low pressure. However, it is in the Southern Hemisphere and rotates counterclockwise. By understanding how the Coriolis effect works on Earth, you can deduce the Giant Red Spot is actually an area of high pressure. Beyond this raging centuries old storm, understanding the nature of Earth’s magnetic field will help one understand the space environment surrounding Jupiter.
Most of the matter we encounter is electrically neutral. That is, their constituent atoms contain as many negatively charged electrons as positively charged protons. In space, the Sun is hot enough to break the atomic bonds between electrons and protons. The result is an electrified gas called plasma. Neon lights are filled with plasma. When plasma encounters a magnetic field, it’s electrically charged particles travel along the path of a magnetic field line in helix pattern seen below.
Credit: cnx.org
This can be visualized on the Sun which has a more complex magnetic field than the Earth. The Solar Dynamics Observatory images plasma traveling along the solar magnetic field lines in formations referred to as coronal loops.
Coronal loops. Credit: SDO/NASA
Back on Earth, these charged particles move along the magnetic field lines until they hit the upper atmosphere in the polar regions. Nitrogen and oxygen atoms absorb the kinetic energy of the incoming particles causing electrons to jump to a higher energy orbit. When the electron moves back to its usual lower energy orbit, the absorbed kinetic energy is converted and released as light. This light is known as the aurora. Earth is not the only planet with an aurora, the gas giants have strong magnetic fields that produce the same effect, albeit mostly in ultraviolet. This presents a good opportunity to understand that light and ultraviolet are both electromagnetic radiation. The difference is our eyes are not designed to detect ultraviolet rays, but our skin can in the form of sunburn. The aurora of Saturn as imaged by the Hubble can be seen below.
Credit: NASA/ESA/J. Clarke (Boston University).
Electrons, when accelerated, will emit radio waves. This is the principle behind radio transmitters. Electrons are accelerated up and down a radio tower causing the transmission of a radio broadcast. The same thing happens in space when electrons are accelerated along the path of a magnetic field line. Jupiter emits radio waves in this fashion that can be detected on Earth with ham radio sets. This process plays itself out in the deepest regions of the universe. For one such example, we’ll take a look a the galaxy Centaurus A located 12 million light years away. Below is an optical image of the galaxy.
Credit: ESO
In 1949, it was discovered this galaxy was a strong emitter of radio waves. Below is a radio image of Centaurus A.
Credit: NRAO/AUI
The radio source emanates perpendicular to the mass of the galaxy. Each lobe is a million light years long (10 times the width of the Milky Way) and would appear 20 times the size of a full Moon if we could see radio waves. This suggests a massive stream of plasma being ejected from the galaxy. What could cause this to happen? In the core of Centaurus A resides a black hole 55 million times the mass of the Sun.
It seems counter-intuitive that a black hole could result in such a massive ejection of matter. We think of black holes as objects that suck in everything, including light. However, some of the matter in the accretion disk surrounding the black hole hits a magnetic field before crossing the event horizon. So instead of continuing into the black hole, the plasma is accelerated and ejected violently along the magnetic field line exiting the galaxy. Below is a composite image of Centaurus A with optical, radio, and x-ray imaging.
Credit: ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray)
There is a tendency to think of Earth science and astronomy as separate fields of study, but as we live on Earth we are also living in space – under the protective cover of the atmosphere. The first step in understanding space is to learn the science behind what we experience in our surroundings. From there, we can explore and understand the universe.
*Image atop post – Earth and the Milky Way from the International Space Station. Credit: NASA.
Above is the Halloween radio adaptation of the War of the Worlds by WKBW in Buffalo. WKBW originally broadcasted War of the Worlds in 1968 and updated versions throughout the 1970’s. For myself, it was a Halloween tradition to sit on the front steps, chow down some Halloween candy, and listen to the broadcast. Although the program would start at 11 PM, I had no worries, as going to a Catholic school, the following morning was All Saints Day and that meant an off day. It wasn’t only Western New Yorkers who listened to the dramatization of their city being destroyed by Martians, WKBW’s 50,000 watt transmitter would reach as far into the Carolinas once the Sun set.
The 1968 broadcast was an homage to Orson Wells legendary 1938 radio version. The events were transplanted to the Buffalo region. In 1968, KB DJ Danny Neaverth opens up the proceedings with a brief introduction. If you lived in Buffalo during that era, Neaverth’s presence around town seemed ubiquitous. I can remember watching Neaverth’s noon weather report on WKBW-TV, hearing him at an evening’s Braves game handling the PA duties (two for McAdoo!), then being woken up by Neaverth’s morning show at 6 AM so I could deliver the Courier-Express.
The 1971 version has an updated introduction by Jeff Kaye. That intro describes various events caused by the 1968 program. Much like the myth of the 1938 panic, there is some hyperbole involved. The local newspapers did not report anything unusual the following day except for a few calls made into the station. After the intro, the broadcast commences with the real newscast from that day. The first sign of something different is when the news ends with a report from Mt. Palomar Observatory that nuclear sized explosions had been observed on Mars.
The real director of the Mt. Palomar Observatory at the time was Horace Babcock (the broadcast used the name Benjamin Spencer). In 1953, Babcock first proposed the use of adaptive optics to reduce atmospheric interference for astronomical imaging. This technique, which utilizes a laser created guide star and deformable mirrors in a telescope’s instrument package, is standard on all modern observatories. From 1947-93, Mt. Palomar was the largest telescope in the world.
The 200-inch Hale Telescope at Mt. Palomar. Photo: Gregory Pijanowski.
Were the nuclear sized explosions on Mars a realistic plot point? At first glance that might not seem to be the case. However, keep in mind the Martians made it to Earth in a 24-48 hour period. Standard chemical rockets take about 8-10 months to complete a voyage to Mars. What could have propelled the Martians so fast to Earth? One possibility is nuclear pulse propulsion. The concept is targeted nuclear explosions are used to provide impulse to spacecraft. From 1958-63, Project Orion worked on such a propulsion method. Eventually, the project was shut down by the Nuclear Test Ban Treaty which, obviously, would not apply to invading Martians.
To be fair, the folks at WKBW were concerned with providing programming that had a Halloween ambiance rather than scientific rigor. And they accomplished this by letting the invasion gradually slide into the program. It is 20 minutes in until the invasion occupies the show completely. During that first 20 minutes, listeners are treated to a time capsule of 1968 radio. The news of the day opens with the Vietnam War and ongoing peace talks (the 1971 version also would open with news from Vietnam, which gives you an idea how well those talks went), Governor Rockefellar breaking ground on the new UB Amherst campus, and various local police busts. The video removed the music interludes for copyright purposes. Ads include an 8-track stereo player for $49.95 ($345 today) and shoes for $13.00 ($90 today). The broadcast takes a dramatic turn with the announcement of a meteor strike on Grand Island.
When that announcement was made, it could be heard throughout the East Coast. WKBW transmitted with a 50,000 watt tower, the maximum allowed for AM stations. At night, the range of AM stations expand greatly. I can remember listening to Sabre-Bruins hockey games and switching back and forth between the Buffalo and Boston broadcasts. Also, I have tuned into St. Louis’ KMOX in both Buffalo and Houston during the late 70’s when Bob Costas worked there. While FM has advantages in sound quality over AM, it cannot match the range of AM radio. And that is due to the nature of the Earth’s ionosphere.
Credit: NASA
During the day, ultraviolet and x-ray radiation strike atoms in the upper atmosphere. This energy ejects electrons, which carry a negative electric charge and forms the various ionosphere layers. During the day, the lower D and E layers absorb AM radio waves. Here, the atmosphere is still thick enough so electrons that absorb radio waves collide into air molecules dampening the radio signal. At night, these lower layers dissipate as there is no sunlight to continue the ionization process. This leaves radio waves free to reflect off the higher F ionosphere layer. Here, the atmosphere is tenuous enough so collisions with air molecules are rare. As a result, AM radio waves are reflected back to the ground enhancing the station’s range. FM stations do not enjoy this effect as their transmissions are at shorter wavelengths, reducing the collision rate with free ions in the F layer.
For those who heard the original broadcast outside of the Buffalo area, and those listening to it now, here is a map to give you a framework of the events:
Nominally a sleepy rural area outside of Buffalo, Grand Island has had an interesting history. Navy Island, adjacent to NW Grand Island, was once considered a potential site for the United Nations. In 1825, a city on the island called Ararat was proposed as a site for Jewish refugees which never came to fruition. The Niagara River current, as mentioned in the broadcast, is swift at 3 feet per second and would pull anyone trying to swim across away and over the Falls eventually. That, of course, happens when the Grand Island bridges are blown in a vain attempt to trap the Martians on the island.
Grand Island Bridges. Credit: amandabanana87 https://flic.kr/p/6PVNVR
The invading Martians make their way downtown to Niagara Square where Irv Weinstein is stationed atop City Hall. Weinstein started on the radio side of WKBW in the late 50’s, moving over to television in the mid 60’s. For the next next three decades, Weinstein was the most prominent news figure in the Buffalo area. Weinstein did refrain from using his trademark “pistol packing punks” (heat ray packing punks?) in the War of the Worlds. I do not know if there was actually a communications center on top of City Hall back then, but there is an observation platform. You can see Niagara Falls from up there, and on the clearest of clear days, the CN Tower in Toronto.
On top of City Hall. Credit: Gregory Pijanowski
The dramatization concludes where it began, at the WKBW radio station which was at 1430 Main St. a block north of Utica St. The voice of the last surviving news reporter belongs to Jeff Kaye. You may find that voice familiar. During the 1980’s, Jeff Kaye did an admirable job filling the large shoes of John Facenda at NFL Films. Kaye also produced the War of the Worlds broadcast. After the Martian’s poison gas takes out the last of the WKBW team, Dan Neaverth returns to conclude the broadcast noting that H.G. Wells ended the War of the Worlds with the Martians dying off, unable to resist Earth’s microbes. Wrote Wells:
“But there are no bacteria in Mars, and directly these invaders arrived, directly they drank and fed, our microscopic allies began to work their overthrow. Already when I watched them (the Martians) they were irrevocably doomed, dying and rotting even as they went to and fro.”
And more than likely, Wells was right about the lack of microbes on Mars, at least on the surface anyway. Unlike Earth, Mars does not have an ozone layer to block out ultraviolet radiation from the Sun. Also, Mars lacks a magnetic field. The Earth’s magnetic field shields life from harmful cosmic rays Unabated, this radiation is highly harmful to any life on the Martian surface, whether it be microbes or astronauts in the future. However, the subsurface of Mars may be another story.
One of the key discoveries on Mars the past few decades has been the existence of water below the surface. On the surface, the lack of atmospheric pressure reduces the boiling point of water so that if it does not freeze it will evaporate quickly. However, the subsurface of Mars has been found to have significant amounts of water. Planning for future human exploration of Mars entails utilizing this water for long duration stays on the red planet. Moreover, where there is water, there may be life. And this leads to the issue of planetary protection.
NASA has an Office of Planetary Protection. The goal is to prevent Earth microbes from contaminating Mars and vise versa. This will become a growing concern for the space program when attempts are made to land humans on Mars or if a Mars sample return mission is sent. Drilling for water on Mars may expose an ancient subsurface biosphere, and certainly humans could carry Earth microbes to Mars. While the risks involved are still a matter of scientific debate, Wells was very prescient to include this factor in the War of the Worlds.
Regardless of what we discover about Mars in the next few decades, there was a deeper lesson in the original novel that tends to get lost in modern versions. The WKBW broadcast capped a night of Halloween themed programming and the primary goal was, as Orson Wells said to conclude his 1938 version, “Dressing up in a sheet, jumping out of a bush and saying, ‘Boo!”. H.G Wells had intended War of the Worlds as a critique of colonialism. Wells makes this clear on page three of the novel:
“And before we judge of them (Martians) too harshly we must remember what ruthless and utter destruction our own species has wrought, not only upon animals, such as the vanished bison and the dodo, but upon its inferior races. The Tasmanians, in spite of their human likeness, were entirely swept out of existence in a war of extermination waged by European immigrants, in the space of fifty years. Are we such apostles of mercy as to complain if the Martians warred in the same spirit?”
At the close of WKBW’s The War of the Worlds,Dan Neaverth asks the audience to think about what they would have done if the invasion was real. An equally important question to ask is what you would do if you were on the invading side. Would you join the invasion as the social forces of war coalesced around you, or would you resist the tide, as Bertrand Russell did in World War I:
“I knew it was my business to protest, however futile that protest might be. I felt that for the honour of human nature those who were not swept off their feet should show that they stood firm.”
That question, for those of us of a certain age, is associated most often with the garish 70’s singles scene. For teachers, it represents part of the struggle to educate students new to astronomy to disabuse the relationship between the location of the stars and planets with one’s personal future outlook. While a teacher might recoil in horror when an assignment is turned in with the heading Astrology 101, a student’s interest in astrology can be used to teach certain astronomy concepts. It is somewhat similar using science fiction in the classroom. After all, part of the purpose of education is to enable students to make conceptual leaps from myth to reality. And to do that, you have to meet the student on level ground.
Astrology is where many of us first learn of the constellations. There are 88 constellations that divide the celestial sphere in the same manner states divide a nation. However, astrology focuses on 12 zodiac constellations that lie in the ecliptic and form a background that the Sun and planets move through. The ecliptic is a narrow path in the sky that the Sun and planets travel from our perspective on Earth. As the Solar System formed 4.5 billion years ago, the solar nebula flattened causing the planets and Sun to coalesce in the same disk. Conceptually, it can be difficult to imagine the Sun and planets moving in the same path in the sky as we see them during different times (the Sun during the day and planets at night). A total solar eclipse does allow us to visualize this.
This is a simulation of the total eclipse to occur on April 8, 2024 in Buffalo. With the Sun’s light blocked by the Moon, you can see how the planets (in this case, Mercury, Venus, Mars, & Saturn) and Sun move along in the same path in the sky. And this path is called the ecliptic. You’ll also note two constellations in the ecliptic, Pisces and Aquarius, which correlate to astrological signs. This illustrates how the Sun lies in constellations just as the planets do. We typically do not get to visualize this as the Sun’s brightness does not allow us to see constellations during the day. This image demonstrates how the zodiac constellations align with the Earth and Sun during the year.
Credit: David Darling
The Sun will be located in the constellation opposite from Earth. Some caveats here, the month the Sun is located in a constellation will not match your astrological sign. Also, there actually is another constellation, Ophiuchus, that lies in the ecliptic but the ancient Babylonian astrologers decided to casually toss that one out as they were using a 12 month calendar. Noting that astrology has not kept up with the precession of the Earth’s axis the last few thousand years will hopefully be a first step in cracking any validity astrology may have with a student. Note in the eclipse image above the Sun resides in Pisces, but your astrological sign is Taurus if born on April 8th. Planetarium software such as Starry Night will allow the class to view the changing zodiac throughout time.
Retrograde Motion
Often referred to in astrology, retrograde motion pertains to a “backwards” motion of a planet in the ecliptic. Before the Copernicus revolution putting the Sun, instead of the Earth, at the center of the Solar System, retrograde motions confounded astronomers. Lets take a look at an example, Mars during 2016. The image below tracks Mars motion in the ecliptic from the beginning of 2016 to the end of September, 2016.
The retrograde or backwards motion of Mars occurs from April 17th to June 30th. What’s happening here? Earth and Mars are approaching opposition, an event that will take place on May 22, 2016. At this time, Mars and the Sun are on opposite sides of the Earth. This means on that date, Mars will rise in the east as the Sun sets in the west. As this is Mars closest approach to Earth, Mars is at its brightest. Opposition is the optimal time to observe a planet. In the case of Mars, impending opposition to Mars also represents launch windows for space agencies to send missions there. If the launch window is missed, the mission must wait another 26 months until the next opposition. So how does all this result in retrograde motion? This is when Earth “passes” Mars like a race car with an inside track passes a car on the outside. The resulting retrograde effect is visualized below:
Credit: NASA
Point d is when opposition occurs and is the midway point of the retrograde motion.
Conjunctions
As the planets all orbit the Sun in the same plane, sometimes they align in the same line of view to form a conjunction of planets. One such example will occur in the early morning hours of October 28th when Venus, Mars, or Jupiter will all be within a few degrees of each other. The scene will look like this:
These conjunctions serve as excellent teaching opportunities as it allows students to locate several planets at once quite easily. Below is an inner Solar System view of the event. Jupiter is not in the image but would be aligned right behind Mars if visible in this view:
From an planetary science perspective, conjunctions really do not have much to offer, but for the rest of us they can provide a really neat night time spectacle. These events are an excellent way to introduce the planets to those new to astronomy.
Zodiacal Light
I’ve never heard the zodiacal light mentioned in an astrological context but, while we are learning about the zodiac, now is as good as any time to familiarize ourselves with this. Besides the Sun, planets, and asteroids, the plane of ecliptic is occupied by cosmic dust. This dust is the remnants of comet tails and asteroid collisions. Best seen in dark sky locations, the zodiacal light is visible in the east just before sunrise or in the west just after sunset. This faint glow, which follows the ecliptic in the sky, is usually most observable in the Spring or Fall. During these seasons, the ecliptic has a steeper pitch relative to the horizon. Fainter than the Milky Way, most urban dwellers do not get the opportunity to see it. However, if you find yourself away from the city lights, this is what you can expect to see:
Zodiacal light from VLT in Chile Credit: ESO/Yuri Beletsky
Sagittarius
The Sun enters Sagittarius in mid-December and exits during mid-January. During the Summer months, the classic teapot of Sagittarius lies high in the night sky along with the Milky Way. In fact, the center of the Milky Way lies in Sagittarius. What this means is that each December, both the center of the Milky Way and the Sun are in Sagittarius. You might recall back in 2012, this alignment was, according to some less than reliable sources, going to result in the end of the world. Needless to say, as an annual event, this would have destroyed the Earth a whole lot sooner than 2012. That is the power of a liberal arts education, it clears a lot of silly stuff out of the way.
December 21, 2015 – The Sun and Milky Way center both reside in Sagittarius. Daylight was shut off on Starry Night software so both the Sun and constellation can be seen at the same time.
Speaking of which, although Sagittarian Jim Morrison gets it “right” about astrology here, you really should not need a celebrity to tell you what is useful information and what is not. And the audience is clearly going with whatever Morrison is telling them here. A liberal arts education provides a basic framework of knowledge to make up your own mind and not be concerned with looking cool or not with the results.
*Image on top of post is the painting of the 12 constellations of the Zodiac on the ceiling of the Grand Central Terminal in New York City. Infamously, the designer goofed and placed the constellations backwards. Photo: Gregory Pijanowski.
“No one would have believed in the last years of the nineteenth century that this world was being watched keenly and closely by intellegences greater than man’s…”
So began H.G. Wells’ classic 1898 novel War of the Worlds. Wells, of course, was describing a vision of Mars occupied by an advanced race. That stands in stark contrast to the movie The Martian, which focuses on the isolation of an astronaut left stranded on the red planet. In a sense, that movie completes a transformation of the public’s perception of Mars underway since the Mariner 4 mission transmitted pictures of the Martian surface fifty years ago. While we can say that astronomy and the space age have played a key role in that transformation, it was also astronomers who provided the previous impression that Mars might be inhabited as well.
Prior to the 1990’s, no planets were known to exist outside our Solar System. There was a sense that such planets did exist of course, science fiction like Star Trek is proof of that. Giordano Bruno postulated as far back in the late 1500’s that, “numerable suns exist; innumerable earths revolve around these suns in a manner similar to the way the seven planets revolve around our sun. Living beings inhabit these worlds.” That, along with a lot of other things, did not endear Bruno to the Catholic Church and he was burned at the stake for his troubles in 1600. Nonetheless, without concrete observational proof of these planets, Mars seemed the best known candidate for life to exist beyond Earth.
In 1698, Christiaan Huygens published Cosmotheoros, which speculated about not only life on Mars but on the other planets in the Solar System as well. Of Mars Huygens wrote, “But the inhabitants…our Earth must appear to them almost as Venus doth to us, and by the help of a telescope will be found to have its wane, increase, and full, like the Moon.” Huygens was the first to discern Saturn has rings and discovered the Saturn moon Titan. In 2005, ESA landed a probe on Titan named in Huygens’ honor. It remains the most distant landing attempted in space. While life on Mars was pure speculation on Huygens’ part, he was an accomplished astronomer. And as we can tell by the rover Curiosity image below, his description of what Earth looked like from Mars is close to the mark.
Credit: NASA/JPL-Caltech/MSSS/TAMU
In 1784, William Herschel published On the Remarkable Appearances at the Polar Regions on the Planet Mars. Like Huygens, Herschel ranks as one of the great observational astronomers with the discovery of Uranus among his many accomplishments. And like Huygens, Herschel also speculated on the possibility of life on Mars, stating, ““And the planet (Mars) has a considerable but moderate atmosphere, so that its inhabitants probably enjoy a situation in many respects similar to our own.” Both Huygens and Herschel set the stage for the boldest claim by an astronomer regarding life on Mars.
Percival Lowell was a contemporary of H.G. Wells. Born in 1855, Lowell was a successful businessman who had an interest in astronomy. This interest intensified when Lowell read Giovanni Schiaparelli published maps of Mars with channels across the surface in the 1890’s. Schiaparelli was Italian, and the English version of his work translated the Italian word for channel -canalis – into canals. As Mars headed towards opposition (closest approach to Earth) in 1894, Lowell set off to Arizona to make observations. Perhaps with a strong preconception, or too much desire to make a groundbreaking discovery, Lowell published this drawing of Mars from his telescope.
Credit: Wiki Commons
Lowell speculated that intelligent life on Mars had built a series of canals to draw water from the polar ice caps to the mid-latitudes for irrigation. Lowell’s work was rejected by other astronomers who also observed Mars during opposition but did not note canals. Had Lowell been trained as a scientist, the lack of replication may had given him pause. However, trained as a businessman, Lowell marketed his case directly to the public. At first, through articles written for magazines such as the Atlantic Monthly, then through a series of books and continued defense of the canal theory until his death in 1916*. Though rebuffed by astronomers, Lowell’s work on Mars provided a framework for popular culture during the next half century.
Against this backdrop, Wells published War of the Worlds four years after Lowell’s first observation of Mars. Often lost in the subsequent radio and movie versions was Wells’ original intent to critique British colonialism, in particular, the concept of Social Darwinism. This concept stated that various nations that are stronger are morally justified in the subjugation of weaker societies in a survival of the fittest competition for resources. Wells’ point was, if that is the case, how could Britain complain if a stronger race colonized them? In America, of course, it is the Orson Wells 1938 radio broadcast version of the story that is most well known.
The legendary broadcast was made so with media reports of panic induced by the realistic reporting of a Martian invasion. However, the extent of the panic, if any existed at all, has been disputed. From Wells’ work on, Martians became a cottage industry in both print and film.
And that cottage industry was all over the map. From the classics such as Ray Bradbury’s The Martian Chronicles and Robert Heinlein’s Red Planet to horrendous efforts such as the movie Santa Claus Conquers the Martians, intelligent life from Mars was a staple in popular culture. Remarkably, astronomers were publishing papers as late as the 1950’s that vegetation might exist on Mars. Gerard Kuiper published a paper in the Astrophysical Journal during 1956 discussing the possibility of greenish moss (to be fair, Kuiper also postulated inorganic causes as well) on Mars during the spring/summer seasons. William Sinton published an article in 1958 suggesting spectroscopic evidence of vegetation on Mars. The concept of life on Mars would take a sobering turn in 1965.
Mariner 4 was launched on November 28, 1964 and begun its seven month journey to flyby Mars. This mission would be the first to bring close up images of another planet back to Earth. Prior to Mariner 4, astronomers had to rely on observatories which lacked digital CCD and adaptive optics technology available today. Below are images of Mars taken from the 100-inch telescope at Mt. Wilson in 1956.
Credit: The Carnegie Institution for Science
What NASA got back from Mariner 4 in July, 1965 were images such as this:
Credit: NASA
The barren, cratered surface of Mars came as a disappointment. Mariner 4 also measured a very thin atmosphere and lack of magnetic field. As such, Mars does not have an ozone layer to protect organic compounds on the surface from ultraviolet radiation. Without a magnetic field, the surface of Mars is also bombarded by a toxic stew of cosmic rays. Quite simply, Mars is not capable of supporting life on a surface constantly exposed to harmful radiation from space. However, future missions to Mars made it clear it is an interesting planet in an all together different way. Much like the planet presented in The Martian.
In 1971, Mariner 9 became the first spacecraft to orbit a planet. As a result, this mission was able to provide a comprehensive map of the Martian surface. Imaging was delayed for two months by a massive dust storm, but once the imaging commenced, planetary scientists were delighted. Among the findings were the largest canyon and volcanic features in the Solar System later named Valles Marineris and Olympic Mons. Most importantly, Mariner 9 imaged ancient dry riverbeds and channels. Water did once flow on the surface of Mars, albeit billions of years ago. The success of Mariner 9 provided the impetus for Vikings 1 & 2, which landed on Mars in 1976 and gave us the first look at the surface. This is how the landing was covered by ABC including an interview with Carl Sagan.
Viking searched for life on Mars and found none at the landing zones. There was a 20 year lull in Mars exploration until 1997 when Pathfinder landed on Mars. Tagging along for the ride was the Sojourner rover, the first of the Mars rovers, named after the 19th century abolitionist Sojourner Truth. By 1997, the public had more access to NASA missions, specifically the mission website that provided updates and images. The original website is still online and can be accessed here.
By this time, it was problematic to present a story with Martians that had serious social commentary a la War of the Worlds. The notion of an advanced race on Mars could not be taken seriously and was reduced to efforts such as the 1996 comedy Mars Attacks. During the course of the 20th century, the public perception of Mars went from a planet that might have an advanced race, to a planet that might have vegetation, to a planet that while geologically interesting, was devoid of life. Conflict is the centerpiece of drama, and without the possibility of life on Mars, the traditional source of conflict had been removed.
Between Pathfinder landing on Mars in 1997 and its use as a plot device in 2015 in The Martian, there have been several orbiter, lander, and rover missions to Mars. Mars Odyssey has been in orbit since 2001 and rover Opportunity has been exploring the surface since 2004. NASA’s Mars Exploration website has images and video from all its active Mars missions. Among the rover images are dust devils which were a feature of the landscape in The Martian.
The results of these missions were used quite effectively to provide a reasonably accurate take on what living on Mars would look like in the movie. Without an alien race to provide drama, the central conflict is the harshness of space itself. The challenges of human travel to Mars include limited availability of launch windows (once every 26 months as Mars approaches opposition), protection from cosmic rays, landing significant tonnage on Mars with very little atmosphere to provide braking, physical deterioration caused by Mars low (30% of Earth’s) gravity, and utilizing recently discovered water resources below the surface. The last point also underscores the need to determine if microbial life exists in the subsurface of Mars where water still exists. Can we avoid contaminating Mars with microbial life from Earth and vise-versa? NASA has an Office of Planetary Protection dedicated to that last issue. Ironically, it was exposure to Earth’s microbes that did in the invading Martians to conclude H. G. Wells’ The War of the Worlds.
The Martian signifies that Hollywood has caught up with science in terms of presenting dramatic stories of Solar System exploration without intelligent life from Mars. The other side of the human vs. harshness of space conflict is the fact that while we may send a handful of astronauts to Mars the next few decades, the vast majority of humanity will remain on Earth. There will not be a mass migration to Mars if we foul things up on our home planet. If space exploration can help discover a means to solve the challenges we face on Earth during the same time we go to Mars, it may be finding the right combination of international competition vs. international cooperation. We can only hope that right mix may be found in reality as readily as it can be found in the movies.
*Percival Lowell’s true legacy to astronomy was founding the Lowell Observatory in Arizona where Pluto was discovered. In 2015, its 4.3 meter telescope became fully operational. You can check that out on the Lowell Observatory website.
**Image on top of post is Mars Pathfinder landing site in 1997, to be visited by Mark Watney in the future. Credit: NASA/JPL
Located about 100 miles west of London, the city of Bath is known for the ancient Roman Baths that attract 1 million visitors each year. One half mile west from the baths is the Herschel Museum of Astronomy, the 18th century residence of William Herschel. As an observational astronomer, William Herschel tends to get overlooked by the great theorists such as Issac Newton. Nonetheless, the work Herschel did in Bath greatly expanded our knowledge of the universe and remains topical in astronomy research.
In contemporary parlance, Herschel was a career changer. Originally a musician by trade, Herschel took an interest in astronomy in 1773 at the age of 35. Herschel was a self-made man. He had no formal training in astronomy and taught himself the art of telescope making. What had perked Herschel’s interest in astronomy was a book on musical mathematics called Harmonics by Robert Smith. Herschel enjoyed the book so much he sought out other books by Smith and found one titled Opticks. This book, along with Astronomy by James Ferguson, formed the basis of Herschel’s training in the field. Herschel remained a music teacher during the the day and astronomer at night. In his endeavors he was joined by his sister, Caroline Herschel, who became his lifelong assistant.
Above: Herschel’s Symphony No. 8 in C minor by London Mozart Players. Written in 1761, it is one of 24 symphonies composed by William Herschel.
Herschel was unable to buy a telescope suitable for his ambitions. As a result, along with his sister Caroline, he took to the task of making his own telescopes. Astronomers today do not need to do this obviously, but this is similar to the manner many astronomers write their own computer codes for their work. This type of specialized software is not available at a store in your local shopping mall. Over his lifetime, Herschel would grind and polish hundreds of mirrors, some of which he sold to help fund his work.
Herschel’s primary goal was quite formidable, to conduct an all-sky survey. Motorized drives to track objects as they moved in the night sky were not available in the 19th century, so Herschel would observe at a fixed angle on the meridian and logged objects as they crossed the field of view. The next evening, Herschel would lower or raise the telescope to a different angle for complete coverage of the night sky. This effort resulted in the publication of the Catalogue of Nebulae and Clusters of Stars (CN) in 1786, the forerunner of the New General Catalouge (NGC). Along the way, Herschel would make quite a few interesting discoveries.
On the night of March 13, 1781, from his residence in Bath, Herschel observed in his 6-inch telescope what he thought was a comet. Herschel noted:
“On Tuesday, the 13th of March, 1781, between ten and eleven in the evening, while I was examining the small stars in the neighborhood of H Geminorum, I perceived one that appeared visibly larger than the rest: being struck with its uncommon magnitude, I compared it to H Geminorum and the small star in the quartile between Auriga and Gemini, and finding it so much larger than either of them, suspected it to be a comet.”
Measurements of the orbit of this object revealed it to be not a comet, but a planet, the first planet discovered since the ancient astronomers categorized the five naked eye planets of Mercury, Venus, Mars, Jupiter, and Saturn. Below is an image of how the night sky appeared in Bath as Herschel made his first observation of this planet.
Herschel wanted to call this planet Georgium Sidus (The Georgian Star) to honor King George III. Others sought a less English-centric name. Uranus was proposed as in Greek mythology, Uranus is the father of Saturn. It was not until 1850 that the planet was officially designated as Uranus. As Uranus is twice the distance (1,783,939,400 miles or 2,870,972,200 km) to the Sun as Saturn, this discovery doubled the size of the known Solar System. It takes 84 years for Uranus to orbit the Sun. Thus, Uranus has only made 2.8 revolutions of the Sun since its discovery. In 1986, Voyager II would become the only spacecraft to date to pay a visit to Uranus. A view of Uranus from Voyager II is below:
Uranus on January 1986. Image on right is false color to enhance color differentials. The South Pole (red) is darker than equatorial regions. Credit: NASA/JPL.
Uranus’ South Pole was facing Voyager II as it is inclined 98 degrees compared to Earth’s 23.5 degree axial tilt. If Earth had the same axial tilt as Uranus, the Northern Hemisphere would face the Sun in June while the entire Southern Hemisphere would be in darkness. The situation would be reversed in December. When Voyager II flew past Uranus, the Northern Hemisphere was shrouded in darkness. If NASA’s plans to send an orbiter around Uranus comes to fruition in the 2030’s, the Northern Hemisphere would then be visible.
This discovery was a game changer for Herschel. King George III, as the Revolutionary War raged in the American colonies, provided Herschel with a salary to pursue astronomy on a full-time basis. This would launch Herschel on a decade of discovery.
Among the conclusions Herschel came to from these observations are:
The axial tilt of Mars is 280 42′, reasonably close to the now established value of 25 degrees.
The length of the Martian day as 24 hours, 39 minutes, and 21 seconds. This measurement was off by only 2 minutes.
The luminous areas at the polar regions were ice caps, which like Earth, would vary in size on a seasonal basis. Today, we know the northern ice cap has a permanent layer of water ice. The southern ice cap has a permanent top layer of 8 meters of carbon dioxide ice and a much larger layer of water ice below. The seasonal variations of the ice caps are due to the freezing and evaporation of carbon dioxide ice.
Herschel concluded his paper by stating, “And the planet has a considerable but moderate atmosphere, so that its inhabitants probably enjoy a situation in many respects similar to our own.” Ok, this one didn’t quite pan out as we know Mars’ mostly carbon dioxide atmosphere is much thinner than Earth’s and life does not exist on the surface. However, Mars atmosphere in its ancient past must have been warmer and more substantial for water to have been present on the surface, of which the evidence is now pretty conclusive. The search for life in Mars’ past and microbial life in the Martian sub-surface, which still has water, is a major component in NASA’s Mars Exploration Program.
While several rovers and orbiters have provided thousands of high resolution images of Mars, Earth bound telescopes still acquire key data on Mars past and present:
Herschel would also discover two moons of both Saturn and Uranus.
The Uranus moons were discovered on the same day in 1787 and were named Titania and Oberon. Both moons were imaged by Voyager II on its flyby of Uranus. Titania featured fault valleys as long as 1,500 km and Oberon has a mountain 4 miles high.
Titania taken by Voyager II 369,000 km (229,000 miles). Credit: NASA/JPL
Two years later, Herschel would discover the Saturn moons Mimas and Enceladus. Both these moons have been imaged by the Cassini orbiter mission. Mimas features a large impact crater that has given it the nickname “Death Star”.
Mimas, whose crater gives it a resemblance to the Star Wars Death Star. Credit: NASA/JPL/SSI
The crater has been named in Herschel’s honor. The crater itself is 140 km (88 miles) wide and the outer walls are 5 km high with a central peak 6 km high. An impact just a bit larger would have most likely destroyed Mimas. As interesting as this is, it is Enceladus that has proven to be one of the biggest surprises of the Cassini mission.
Only 500 km wide, Enceladus is very bright as it reflects almost 100% of the sunlight it receives. Thought to be too small for geologic activity, Enceladus provided an unexpected finding when Cassini imaged geysers spraying ice and water vapor into space. Further gravity analysis indicates an ocean 10 km deep underneath a ice shell 30-40 km deep. Recently, it has been determined the geysers are more akin to curtain eruptions seen in volcanic activity in Hawaii and Iceland. Still, this water is thought to be at least 194 degrees Fahrenheit at the ocean floor, the heat generated by gravitational flexing from Saturn. Where there is heat and water, there may be life. Cassini has flown through the geysers but its instrument package was not specifically designed for this task. As such, Enceladus is a priority for NASA exploration in the next decade. Unlike the subsurface ocean of Europa, the ocean of Enceladus could be sampled without having to bore down through several kilometers of ice.
Plumes of water ice emanating from the south pole of Enceladus. Credit: NASA/JPL/Space Science Institute.
As impressive as Herschel’s Solar System discoveries were, the task to complete an all-sky survey meant he studied deep space objects moreso than planets and their satellites. Herschel would discover numerous nebulae and binary stars that prior to his telescope, were not resolvable. By 1785, with the salary granted by King George III, Herschel had moved from Bath to London and was using a 19-inch aperture telescope to map the Milky Way. The results were published as On the Construction of the Heavens.
Credit: Royal Astronomical Society.
The bright spot in the center is the Sun. Herschel was operating under the handicap of observing in visible light only, which is extinguished by the interstellar medium. This gave the illusion the Sun was located in the center of the Milky Way as the interstellar medium dampened optical light in all directions equally. It is like trying to map trees in a foggy forest. There may be more trees in one direction than the other, but the fog cuts down on your vision at equal depths in all directions. In fact, it was not until the 1920’s when Harlow Shapley determined the Sun was located in a spiral arm of the Milky Way and not in the center was this problem resolved. For astronomers to obtain a comprehensive view of the universe, the entire electromagnetic spectrum had to be employed. And it was Herschel who provided the first step in that direction.
In 1800, Herschel was measuring the temperatures of the different colors of sunlight separated by a prism. As Herschel took temperatures from the violet end of the spectrum to the red he discovered an increase in temperature as the thermometer was moved towards the red. Finally, the thermometer was placed just beyond the red light, and the temperature increased even more. It was apparent the Sun was emitting some form of radiation beyond the furthest end of the visible spectrum. More experiments revealed this invisible radiation had the same properties as visible light, it could be reflected and refracted. Herschel published this result in the paper titled, Experiments on the Refrangibility of the Invisible Rays of the Sun. Herschel referred to this radiation as calorific (heat) rays, today we call it infrared light.
Credit: NASA
Optical light is just a small part of the electromagnetic spectrum. Among the other parts we are unable to detect with our eyes, we can detect radio waves with radio receivers, ultraviolet waves with our skin when we get sunburn, and x-rays with film when we go to the doctor. Those forms of radiation only differ from light in the size of their respective wavelengths and consequently, their energy. Infrared is used for remote control and night vision technology. Most of the heat we feel in our day-to-day activities is the result of infrared light and our bodies emit infrared radiation in the form of body heat which is detected in night vision sensors.
Cat in infrared. Eyes appear warmer than body as cat’s fur traps heat, not allowing it to escape into surrounding air to be detected by infrared camera. Credit: NASA/IPAC
Planets radiate mostly in the infrared, as do cool galactic gas clouds. Certain wavelengths of infrared radiation has the ability to pass through dust clouds. Thus, infrared observations can peer into dusty regions in space and see what lies behind the shroud of dust. As a result, infrared astronomy is used for planetary observations, to detect protostars inside of nebulae, and to peer into the galactic center behind the wall of interstellar dust. In other words, the form of radiation Herschel discovered is now used to better understand the very objects Herschel observed.
The video below is a montage of 2.5 million images of the Milky Way taken by the Spitzer Infrared Space Telescope. As certain wavelengths of infrared are not absorbed by the interstellar medium as optical light is, the Spitzer images provide us with the true shape of our home galaxy including the central bulge that contains a massive black hole.
The Spitzer GLIMPSE360 website has an interactive where you can explore different regions of the Milky Way or select objects to view. The Milky Way is not the only region that can be explored in infrared. In 2014, the Keck Observatory imaged Uranus with infrared.
Images of Uranus, such as the ones taken by Voyager, tend to reveal a featureless planetary disk. However, the Keck infrared image revealed storm activity to an extent not seen before on Uranus. This might be indicative of an internal heat source that was not thought to exist previously on the gas giant. Astronomers will need to revise current theories on the interior of Uranus as a result of this work.
Left-Uranus at 1.6 microns. White spots are storms below upper cloud layer. Right-Uranus as 2.2 microns. White spots are storm activity just below tropopause. Uranus ring system is visible in this image. Credit: Imke de Pater (UC Berkeley) & W. M. Keck Observatory images.
As one would expect, many honors have been accorded upon the Herschel name. This would include the 3.5 meter infrared Herschel Space Observatory and the 4.2 meter William Herschel Telescope in the Canary Islands. However, the highest honor we can bestow upon William Herschel is the continued exploration of the celestial bodies he discovered, using the infrared radiation that he also discovered.
