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Monday May 1st 2017

Posts Tagged ‘Venus’

The Moons of the Solar System

More Questions Than Answers

Europa Moon of Jupiter Europa – Moon of Jupiter. Credit NASA

Think of our solar system, and for most of us the first thing to come to mind would be the eight planets orbiting our Sun. But perhaps even more interesting are the moons which orbit the planets. Our Moon seems to be a lifeless body, with hardly any atmosphere and no dynamic activity. But the more data we collect, and the more we learn about its formation, the more fascinating it becomes. The same is true of the moons of the outer gas giants, some of which are comparable in size to the Moon. Little was known about these bodies until we began to send spacecraft armed with a host of sensors in order to analyse them in much greater detail. Each has its own uniquely distinctive characteristics in terms of overall composition, and their widely diverse range of surface features give tantalizing clues to what is going on beneath. The image below shows the size of the Earth’s Moon in relation to other moons and planets in the Solar System.

Moons of the Solar System Moons of the Solar System / Credit NASA

Galileo and the Beginning of Modern Astronomy

In 1610 Italian astronomer Galileo Galilei discovered the four largest moons of Jupiter; Io, Europa, Ganymede and Callisto. He used a homemade telescope to observe the motion of these bodies, which he first took to be stars. But after a few weeks he realized that they never left the vicinity of Jupiter, and they changed position in relation to each other and the planet. Galileo therefore concluded that they must be planetary bodies in orbit around Jupiter. This discovery, along with his measurements of the phases of Venus, proved that not everything in the Universe revolves around the Earth, and led to conflict with the Catholic Church by refuting the geocentric view of the Solar System. But importantly for science, his work also marked the beginning of modern astronomy.

Jupiter-moons_475px All that’s required to see the Galilean moons of Jupiter is either a good pair of binoculars or a small telescope. Credit: Jan Sandberg, www.desert-astro.com

The Inner Solar System

Phobos_Deimos_475px Phobos (left) and Deimos (right), Moons of Mars. Credit NASA

Both Mercury and Venus have no moons at all. One theory for this is that if they ever possessed a moon in the past, it would have eventually been stolen by either the gravitational pull of the Sun or the gravitational pull of the host planet. Then there’s Mars which has two moons, Phobos and Deimos. These are very small bodies, with Phobos having a diameter of 22.2 km and Deimos 12.4 km, so they haven’t got enough mass to enable them to form into the roughly spherical shapes that larger bodies are able to do. The orbital radius of Phobos is just 9,377 km, with an orbital period of 0.32 days. It is being pulled 1.8 m closer to Mars every century, and so will eventually either crash into the planet or break up and form a ring of material around it. Deimos, on the other hand, has an orbital radius of 23,460 km, and is gradually moving in the opposite direction, away from Mars, just like our own Moon is moving away from the Earth. So one day both Deimos and the Moon will cease to be influenced by the pull of their host planets and be set free into space.

The Outer Solar System

Io, moon of Jupiter shown with plume. Credit: NASAIt seems reasonable to assume that the further from the Sun the colder the temperature of the bodies that exist there. At Jupiter, which lies five times further from the Sun than the Earth, the average surface temperature of its moons is -170°C. At Saturn the average surface temperature is -200°C, at Uranus -210°C, and at Neptune -235°C. Before it was possible to closely inspect the moons of the outer planets in any great detail, scientists assumed that, due to these low temperatures, they would be cold, lifeless, inactive bodies. But since Voyager 1, launched in 1977, the Galileo mission, launched in 1989, and Cassini-Huygens in 1997, it has become clear that their theories were very far from the truth. Io for example, the innermost of the four Galilean moons of Jupiter, is the most volcanically active body in the solar system. Whilst having an average surface temperature of -130°C, its volcanoes can reach 1,650°C. It is covered in sulfur due to the hundreds of active volcanoes on its surface, and has lava lakes, floodplains of liquid rock and plumes of sulfur reaching as high as 300km. The above image (credit: NASA) of Io showing an active plume from a volcano. Io’s colorful appearance is due to various materials produced by its volcanism, including silicates, sulfur and sulfur dioxide.

Resonance

The reason for Io’s volcanic activity is due to the orbital resonance of three of the four Galilean moons, meaning that their orbital periods are multiples of each other. Io revolves around Jupiter four times in the same period it takes Europa to revolve twice and Ganymede to revolve once. This regular alignment results in a gravitational pull which has caused their orbital paths around Jupiter to become elliptical. This in turn creates immense tidal forces, causing the physical rock on Io’s surface to rise up and down a hundred meters during the course of each Io day, or about every 42 hours. A huge amount of heat is therefore generated, which is enough to melt a large proportion of Io’s interior and bring about the conditions we have observed on its surface from pictures relayed by Voyager 1 in the late seventies and the Galileo mission in the late 1990’s and early 2000’s. Resonance is common in the solar system, and accounts for the geysers and the jets on Enceladus for example, and the liquid water ocean beneath the surface of Europa.

Cryovolcanism

Image taken by NASA’s Cassini probe of jets of water ice being emitted from the surface of Enceladus. Credit: NASA/JPL/SSI Image taken by NASA’s Cassini probe of jets of water ice being emitted from the surface of Enceladus. Credit: NASA/JPL/SSI

Volcanism does not only occur on rocky bodies like Io. In March 2006 the Cassini probe observed icy jets being emitted from the south pole of Enceladus, a moon of Saturn. The volcanoes erupting these jets were however not spewing out molten rock. When Cassini flew through the plume of one of these emissions, it detected predominantly salty water-ice, with small amounts of carbon dioxide, ammonia, methane and other hydrocarbons. The contaminants lower the melting temperature of the ice on the crust of Enceladus, allowing the generation of cryomagma, which can be erupted in plumes reaching hundreds of kilometers above its surface. Other icy moons exhibiting cryovolcanism include Ariel and Miranda orbiting Uranus, and Triton, the largest moon of Neptune.

Is There Life in the Solar System?

Mars has traditionally been the place to look for alien life in the solar system, but the icy moons of the outer planets are exciting for scientists to study because their surfaces are comprised of large amounts of water ice. Although solid at the surface, it has been proven that vast amounts of liquid water can exist underneath. The Galileo mission to Jupiter gave evidence that Europa has an ocean of water beneath its icy surface totaling more than all the oceans, rivers and lakes existing on the Earth. And where there’s water there’s the potential for life, at least life as we know it. Tidal distortion has created cracks on the surface of Europa, enabling liquid water to escape to the surface. These could be the places where life is most likely to occur, as sunlight could create the conditions for photosynthesis to take place. Other places with the potential for life are Ganymede, Enceladus and Titan, Saturn’s biggest moon.

Plate tectonics on Europa. Image Credit: NASA Plate tectonics on Europa. Image Credit: NASA

But life can also be created without the need for sunlight. At the bottom of our oceans on Earth, hydro-thermal vents exist that harbor microbes which, in a process called chemosynthesis, convert chemicals from the vent into usable energy. So why can’t this same process take place elsewhere in the solar system, or elsewhere in the Universe for that matter?

Future Exploration

NASA’s New Horizons spacecraft is one of the latest ongoing missions to explore the solar system. It is on its way to a rendezvous with the newly termed dwarf planet Pluto and its moon Charon, both members of the vast region beyond Neptune known as the Kuiper Belt. Launched in 2006, and moving at almost one million miles per day, it will reach Pluto in summer 2015, armed with much more state of the art sensors than earlier missions. For instance, it will include LORRI, one of the highest resolution telescopes ever sent into space. Scientists believe that the Kuiper Belt contains a totally different class of world than the rest of the Solar System, so to better understand it, we need to understand worlds like Pluto and Charon.
In 2022 the European Space Agency is planning to launch the Jupiter Icy Moons Explorer (JUICE), which will study Ganymede, Europa and Callisto, and their potential for containing life. NASA too is hoping to launch its own mission to Europa in 2022, called the Europa Clipper. It will fly down to within 25km of its surface, and may even include a lander. So the future of space exploration is alive and well, with plenty of exciting encounters to look forward to.

Further Sources

NASA JPL Live http://ustre.am/onbo. NASA Scientists discuss the future mission to Europa

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Positions of Planets

Saturn, credit: Nasa
Saturn, image credit: NASA

The tables offer monthly positions of the four brightest planets: Venus, Mars, Jupiter and Saturn. Note, that a constellation may not be visible during the night.  Another good monthly reference is created by the folks of SkyMaps.  It shows monthly events and locations of planets and can be downloaded as pdf for printing.  Also Sky View Cafe and Astronomy Magazine offer very nice online planetaria that show positions of planets and provide a wealth of other information. Both need Java installed on your computer.

2012 Jan Feb Mar Apr May June Jul Aug Sep Oct Nov Dec
Venus AQR PSC ARI TAU TAU TAU TAU GEM CNC LEO VIR LIB
Mars VIR LEO LEO LEO LEO LEO VIR VIR LIB SCO SGR SGR
Jupiter ARI ARI ARI ARI TAU TAU TAU TAU TAU TAU TAU TAU
Saturn VIR VIR VIR VIR VIR VIR VIR VIR VIR VIR VIR VIR
                         
2013 Jan Feb Mar Apr May June Jul Aug Sep Oct Nov Dec
Venus SGR CAP AQR ARI TAU GEM LEO VIR VIR OPH SGR SGR
Mars CAP AQR PSC PSC ARI TAU GEM GEM CNC LEO LEO VIR
Jupiter TAU TAU TAU TAU TAU TAU GEM GEM GEM GEM GEM GEM
Saturn LIB LIB LIB VIR VIR VIR VIR VIR LIB LIB LIB LIB
                         
2014 Jan Feb Mar Apr May June Jul Aug Sep Oct Nov Dec
Venus SGR SGR CAP AQR PSC ARI TAU CNC LEO VIR LIB SGR
Mars VIR VIR VIR VIR VIR VIR VIR LIB SCO OPH SGR CAP
Jupiter GEM GEM GEM GEM GEM GEM CNC CNC CNC LEO LEO LEO
Saturn LIB LIB LIB LIB LIB LIB LIB LIB LIB LIB LIB LIB
                         
2015 Jan Feb Mar Apr May June Jul Aug Sep Oct Nov Dec
Venus CAP AQR PSC TAU GEM CNC LEO LEO CNC LEO VIR LIB
Mars AQR PSC PSC ARI TAU TAU GEM CNC LEO LEO VIR VIR
Jupiter LEO CNC CNC CNC CNC LEO LEO LEO LEO LEO LEO LEO
Saturn SCO SCO SCO SCO SCO LIB LIB LIB LIB SCO SCO OPH
                         
2016 Jan Feb Mar Apr May June Jul Aug Sep Oct Nov Dec
Venus OPH SGR AQR PSC ARI TAU CNC LEO VIR LIB SGR CAP
Mars VIR LIB SCO OPH SCO LIB LIB SCO OPH SGR CAP AQR
Jupiter LEO LEO LEO LEO LEO LEO LEO VIR VIR VIR VIR VIR
Saturn OPH OPH OPH OPH OPH OPH OPH OPH OPH OPH OPH OPH
                         
2017 Jan Feb Mar Apr May June Jul Aug Sep Oct Nov Dec
Venus AQR PSC PSC PSC PSC ARI TAU GEM LEO VIR LIB OPH
Mars AQR PSC ARI TAU TAU GEM GEM CNC LEO VIR VIR VIR
Jupiter VIR VIR VIR VIR VIR VIR VIR VIR VIR VIR LIB LIB
Saturn OPH OPH SGR SGR SGR OPH OPH OPH OPH OPH OPH SGR
                         
2018 Jan Feb Mar Apr May June Jul Aug Sep Oct Nov Dec
Venus SGR AQR PSC ARI TAU CNC LEO VIR VIR VIR VIR LIB
Mars LIB OPH SGR SGR CAP CAP CAP CAP CAP CAP AQR AQR
Jupiter LIB LIB LIB LIB LIB LIB LIB LIB LIB LIB LIB OPH
Saturn SGR SGR SGR SGR SGR SGR SGR SGR SGR SGR SGR SGR
                         
2019 Jan Feb Mar Apr May June Jul Aug Sep Oct Nov Dec
Venus OPH SGR CAP AQR PSC TAU GEM LEO VIR LIB OPH SGR
Mars PSC ARI ARI TAU TAU GEM CNC LEO LEO VIR VIR LIB
Jupiter OPH OPH OPH OPH OPH OPH OPH OPH OPH OPH OPH SGR
Saturn SGR SGR SGR SGR SGR SGR SGR SGR SGR SGR SGR SGR
                         
2020 Jan Feb Mar Apr May June Jul Aug Sep Oct Nov Dec
Venus AQR PSC ARI TAU TAU TAU TAU GEM CNC LEO VIR LIB
Mars OPH SGR SGR CAP AQR AQR CET PSC PSC PSC PSC PSC
Jupiter SGR SGR SGR SGR SGR SGR SGR SGR SGR SGR SGR SGR
Saturn SGR SGR SGR CAP CAP CAP SGR SGR SGR SGR SGR SGR
                         
2021 Jan Feb Mar Apr May June Jul Aug Sep Oct Nov Dec
Venus SGR CAP AQR ARI TAU GEM LEO VIR VIR OPH SGR SGR
Mars ARI ARI TAU TAU GEM CNC LEO LEO VIR VIR LIB SCO
Jupiter CAP CAP CAP CAP AQR AQR AQR AQR CAP CAP CAP AQR
Saturn CAP CAP CAP CAP CAP CAP CAP CAP CAP CAP CAP CAP
                         
2022 Jan Feb Mar Apr May June Jul Aug Sep Oct Nov Dec
Venus SGR SGR CAP AQR PSC ARI TAU CNC LEO VIR LIB SGR
Mars OPH SGR CAP AQR AQR PSC ARI TAU TAU TAU TAU TAU
Jupiter AQR AQR AQR PSC PSC PSC CET CET PSC PSC PSC PSC
Saturn CAP CAP CAP CAP CAP CAP CAP CAP CAP CAP CAP CAP

 

Constellation Maps

 
AQR- Aquarius ARI – Aries CAP – Capricornus
CET – Cetus CNC – Cancer GEM – Gemini
LEO – Leo LIB – Libra OPH – Ophiuchus
PSC – Pisces SCO – Scorpius SGR – Sagittarius
TAU – Taurus VIR – Virgo  
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Astrophotography – Without a Telescope

Milky Way, Credit: Ralph Clements

By Ralph O. Clements

When I was invited to write about this subject for Astronomysource.com, I must say I was flattered and a bit flabbergasted too, as I do not consider myself an expert on the subject, nor a writer by any means, but just a guy who likes to go out at night and take pictures of the sky. I stumbled into this hobby when my wife brought home an old 4” Meade reflector telescope with a manual equatorial mount from a yard sale that she paid $60 for.

I took that thing out in the country and set it up (completely wrong, I now understand) and as darkness approached, held my point-and-shoot camera up to the eyepiece and took a picture of Venus. Well, now that was very interesting…it was certainly not a very good photo and I have learned it is hard to get a good one of Venus, but I could tell it was not a star, it was not round but had a semi-circular shape. Wow! I took a picture of another planet! That got the gears turning in my head and I just had to do more….I mean who would think I could take a picture of another planet, with a point-n-shoot camera and an old yard sale telescope?

“Camera Only” Images

I do take images with newer telescopes and a decent equatorial mount which I have acquired since. Imaging galaxies and nebulae is an ongoing goal and interest, but I have learned that it is time consuming, tedious and has a fairly steep learning curve. My view of the sky at home is very limited. So for the time it takes to drive out to the country and get all that gear set up and working, I am limited to weekends and then only weekends when the sky is clear. Since clarity of skies does not always happen on Friday or Saturday night, I often image without the telescopes at all. All the tips and advice offered here is just what I have learned and I expect others may have better ways of doing things.

Equipment

My research indicated that Canon cameras are preferred for astrophotography and the T1i is what I use for everything. I also have an older Nikon DLSR with two lenses, a 180mm fixed focal length and a 75-300mm zoom, for which I bought a Canon adaptor, but the 18-55mm “kit lens” that came with the Canon is what I use most often.

If you read up on astronomy and astrophotography equipment you will note it is often said that the mount is every bit as important as the telescope. My camera tripod is my mount and I fully agree that a sturdy tripod is a must. I am fortunate to use a tall Berlebach tripod with hardwood legs. The cheap aluminum department store tripods are not stable enough.

Figure 1: Orion at Peaks of Otter, Credit: Ralph Clements

Widefield & Star Trails

Camera only astrophotos with a static tripod fall into these three general categories:

Widefield – Single Shot

These include what would be considered “scenic” or “landscapes” in daytime photography, that is, including some portion of the Earth, as well as constellations and shot of the Moon (See Figure 1). I try to shoot as long as possible without having oblong or streaked stars. A high ISO setting helps with this and I often use 3200 ISO unless it is twilight or too much man made light is around. Figure 1, Orion and the Peaks of Otter, is a 10 second exposure and the stars are a bit oblong but not too bad.

Widefield – Stacked Images

Images that are composed of multiple single exposures, stacked and aligned in the computer to reveal much more of the faint light features than what is visible to the naked eye. Sagittarius (Figure 2) was taken as series of short, 6 second shots and stacked in the computer using Deep Sky Stacker. The exposure time for shot like this can vary depending on the target, its location in the sky and ambient light conditions. I find that targets nearer the poles may allow a little longer exposure than those on or near the celestial equator, which appear to move more due to their location.

Figure 2: Sagittarius, Credit: Ralph Clements

Star Trails Shots

Long Exposures or combined multiple exposures that show the apparent rotation of the stars above the Earth. Of course, the stars just appear to rotate because we are riding on the Earth which is really doing the rotating (Figure 3).

Taking star trails images is fun, easy and I like the look of them. Although a star trails image of say 40 minutes can be done on the “bulb” setting with a single exposure, this requires a remote timer and more importantly, a very, very dark site as the least ambient light will over expose the shot during that time. So I just take a series of 30 second shots and combine them using “Startrails” software, another useful and free program. This software is definitely easy to use and produces good results, although I do not notice much improvement when I use dark frames with it. For noise reduction I use “Noiseware Community Edition” in the final images instead. I recently became aware of another free software to do this, “Starstax”, and will be trying it soon as it offers more features.

On these star trails shots, sometimes it is good to have some moonlight on the subject and I will go out under a quarter to half moon and shoot them. I find a full moon makes it too much like daylight for my taste and if I lower the ISO under a full moon the stars don’t show up much. So depending on the amount of moonlight, artificial light and desire ground detail, I take these star trails shots at ISO setting of 800, 1600 or 3200. Generally, I try to get 40 to 60 minutes total exposure. Less than that and the trails are too short, more than that and chances are airplane will mess it up.

Figure 3: Startrails, Credit: Ralph Clements

Foreground and Framing

I try to pick a good site with some interesting foreground , although “fore-ground” in this case doesn’t mean close to the camera, rather, it means the part of the Earth that is shown.  I try to frame the shots so that the sky covers roughly ¾ of the frame, since the sky is the real subject and the foreground is really just a reference or point of interest.

Focusing

To get crisp focus on the stars and the ground, anything in the image needs to be as far away as your camera’s “infinity” focus distance, which varies with the lens. So I try to take scenes that I would focus to infinity on if I were shooting them in daylight, such as the farm you see in Figure 3.  For all my images I use the camera’s “live view “. This feature lets me zoom in on a bright star, or the moon and focus. If your target is too dim, aim at a brighter one or an artificial light a long way off and focus on it and re-aim at your target. Make sure your camera is not set to “auto-focus”, use “manual”. The Nikon I was using did not have “live view” but I used the same method, only I looked through the view finder at a bright star or light. Sometimes a few test shots were needed to get it right.   

Getting Started

As for general advice for other beginners, I offer the following

  • Read your camera’s instructions, particularly the section on manual control.
  • Learn to work your camera’s controls in the dark, the corollary of which is….
  • Don’t be afraid to experiment. I use the trial and error method, with lots of trial and plenty of errors. That’s okay though as I am having fun and try to learn from my mistakes, and I don’t have to buy film for a digital camera, so I don’t mind deleting the ones that didn’t come out. 

….just do it! Have fun with it.

 

Further Reading

 

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Helio Now

Solar Dynamics Observatory

Solar Dynamics Observatory 2017-05-01T06:08:18Z
Observatory: SDO
Instrument: AIA
Detector: AIA
Measurement: 171

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