The Phases of Venus

Venus through telescope on July 10, 2013
Taken by Samer Hariri @ OCC-OR

One of the many observations that Galileo made in support of a heliocentric model of the solar system was on the phases of Venus. One might ask, how can you conclude from observing and recording the phases of Venus over a period of time that the Sun is at the center and that Earth along with all the other planets are orbiting it? Galileo had an understanding of moving bodies, and by using simple geometry he was able to confidently support a heliocentric model once his observations matched his predictions. To truly understand this thought process, one must attempt to draw out what the phases of Venus would look like to Earth in both a heliocentric and a geocentric model. Of course to create such an attempt requires an understanding of how planetary bodies like Venus or the moon can have phases in the first place.

The phases of Venus as drawn by Galileo.
Galileo Galilei, Il Saggiatore [The Assayer] Rome, 1623.
Image obtained from http://brunelleschi.imss.fi.it/

Full Moon during the Oct 18, 2013
partial lunar eclipse. (aka Hunter Moon)
Taken by Samer Hariri

On October 18, 2013, there was a partial lunar eclipse visible here in Michigan. During that eclipse, the Moon was in it's full phase, and was passing through the penumbra of the Earth. The difference in brightness was hard to depict for this partial eclipse but with high quality imaging techniques, one would surely see a difference (click here for example). So why do eclipses happen, and how are they related to the phases of the Moon? When we look at the diagrams showing how the phases of the Moon occur, we notice that during a full phase, the Earth is in between the Sun & Moon. During a new phase, the Moon is directly between the Earth & Sun. When this happens, we are unable to see the moon in the sky because the side that is lit by the Sun is facing away from us. During these two phases (full & new) is when lunar (due to full) & solar (due to new) eclipses are possible. A crescent phase occurs when the Moon is waning into a new phase, or waxing out of a new phase. This occurs when it's location is almost in between the Earth & Sun but not completely. The Moon is either a waning or a waxing gibbous when it is closer to it's full phase location. We know that the Moon orbits the Earth, and by understanding its motion about the Earth we can predict its phases quite accurately.

Diagram showing the location of the Moon and its corresponding phases as it orbits the Earth.
Note how the location of the Moon is different from new phase to new phase (green shaded area).
One would expect it to start and end in the same location as it cycles through its phases but it doesn't. Why?
Image obtained from Wikipedia.

      

Phases of Venus in relation to its orbit
around the Sun as seen from Earth.
Image obtained from Wikipedia.

Similarly, if we were to draw Venus along its orbit about the Sun, we can predict the phases we would see of it. As you look at the diagrams showing the location of Venus in relation to what phase we see of it here on Earth, think about how similar that is to the phases we see of the Moon, but more importantly what difference there are. For example, the possibilities of locations in this case can never have the Earth be in between Venus and the Sun. This means that we can never see a full phase of Venus on Earth. However, if we were to base our prediction on a geocentric model then would we expect to see a full phase of Venus, if any? The answer is yes we would since the orbits would eventually have an order where the Earth is now between the Sun and Venus, and we would be able to see a full phase of Venus, and possibly a Venusian (or Venerian if you'd like) eclipse! When Galileo realized that he is not able to witness a full phase of Venus, he immediately knew that the Sun was at the center of our solar system. In addition, the apparent size of the phases indicated that Venus was indeed orbiting the Sun inside the orbit of the Earth. Think about where Venus is during each phase, and what the size of that phase is as drawn by Galileo and if that makes sense or not.

Images of the phases of Venus taken through the Jaicoa Observatory. The image
shows the phases of Venus over a period of time and depicts nicely how the size and shape changes.
Image was taken by Efrain Morales Rivera and was obtained from http://www.jaicoa-observatory.com

Finally, think about the other planets and what phases of those planets we are able to see. What phases do you think Mercury would exhibit? What about Mars? Would we ever see Mars as a crescent here from Earth? It's amazing how by simply observing the various phases of planetary bodies here from Earth, we are able to explain accurately the location of these planetary bodies with relation to Earth. We were able to construct a fairly accurate representation of our solar system some 400-500 years ago by simply looking up at the night sky and "reverse engineering" what we saw into models and diagrams that make sense. The best out of a lot of these early models of our solar system were the ones that explained a lot of the phenomenon (like phases of Venus, retrograde motion, etc..) in the most simplistic manner possible. I sometimes wonder if I would have had the capacity to come to the same conclusions Galileo, Copernicus, or the various others came to about our solar system simply based on the observations they made. It makes sense to me today, and it seems to be relatively elementary, but I'm not sure if I would be as brilliant to initially think of something that is so simple, yet so profound if I had lived in the times of Galileo Galilei...

SOL

DISCLAIMER: NEVER LOOK AT THE SUN THROUGH A REGULAR TELESCOPE - EVER! Blindess will befall on you in less than a second. Always use a solar telescope designed for solar viewing. Internal blocking filters in such telescopes reject all unwanted and harmful radiation, for completely safe viewing.

The Sun through a solar telescope.
Note the prominence loop.

This evening during study group we went outside to safely view the Sun. We used a Meade Coronado Personal Solar Telescope with an H-Alpha filter that allowed us to see amazing prominences and surface features of the Sun. In addition, we used the 4.25 inch AstroScan with a screen to view the reflection of the Sun. The sunspots were evident and it was a great experience for those that have never seen the Sun through a solar telescope before.

A prominence is a loop of plasma that extends out of the Sun and back. It is often very large in size, and you could probably fit dozens of Earths within it. We were lucky to not only witness a prominence in our Sun today, but to actually watch it change. Initially, the prominence had a complete loop which later on broke, and minutes after that faded away entirely. Prominences are actually plasma ejections from the Sun that get trapped within the magnetic field lines (which is why it loops around and spirals back towards the surface of the Sun). 

Astronomy students safely viewing the Sun through a solar scope and a screen.

The reflection of the Sun on a screen.
Note the sunspots.

We also witnessed a few sunspots both in the solarscope and the reflection from the Astroscan. Sunspots are regions that are relatively "cooler" in temperature than the rest of the surface of the Sun. Prominences are actually associated with sunspots except we don't see the prominences in this case because the surface is facing us directly. Both these phenomenon are driven by magnetic field activity from the Sun, and both are associated with solar flares and coronal mass ejections, two primary events responsible for auroras. As a matter of fact, there was a solar flare earlier today that will reach the Earth later tonight and will cause auroral activity for regions in Northern latitudes and possibly low on the horizon in the Upper Peninsula of Michigan. Astronomers usually use an index to determine the strength of an auroral activity called the Kp. For us in Michigan, a Kp of 7 means northern lights will be visible at our latitude.

Astronomy students and Marc viewing the Sun through a solarscope.

Angela looking at the reflection of the Sun from the Astroscan.
The color is green because we were using an O-III filter with a polarizer.

Our Sun is a very dynamic star, and to be able to witness all the activities that occur on its surface is quite the experience. That ball of gas is the reason we exist on this planet. Without it, we would be one lonely and cold planet that has nothing but ice covering its surface. We are in mid October and yet all of us who shared this experience today felt the warmth of this star and embraced it. There are many mechanisms responsible for Earth being the way it is (sustaining life and what not), and without SOL, none of those mechanisms would even matter.

De Systematis Solaris

Neptune group doing a puppet show.

This past week, we had our planetary presentations for Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Overall, the presentations were informative and filled with unique characteristics about each planet. The Mercury group did a news broadcast (the weather part was funny),  Venus did a game show called The Galactic Games (Spock on), Earth did a spinnoff of Family Feud (Survey Says), Mars did a jeopardy game with their host Marvin the Martian,  and Jupiter did a dating game were the lord of the planets is also the lord of the ladies! Saturn did a spin off of Jerry Springer (smh) called Wednesdays with Jeff (I couldn't stop laughing), Uranus did a nice video with awesome music and narration, and finally Neptune did a puppet show of "The Bachelorette" (tell me more!). The two groups that remain (presentations on Monday) are Pluto and Solar Debris. Can't wait to see those!

Sunset - Oct 9, 2013.

After both days of presentations, we did the Solar System Event. This would be my 12th time going through this event, and I should say that it never fails to amaze me how massive the universe in which we live in is, and how small and insignificant I feel on my drive back home after those nights. We go about our day without putting much thought into what our place in space is, but once we start thinking about it, we realize that there seems to be much bigger and important things in this universe than what most people here on Earth occupy their time with.

At SOL on Wed, Oct 9, 2013

It was nice when we were able to see how SOL looked liked from each stop of the terrestrial planets,  but once we got to Jupiter (and no longer were able to see SOL because of the buildings in between us), we were still able to maintain a perspective because we all have good imaginations. To recap, Mercury was 58 steps from SOL, Venus was 108, Earth was 150, and Mars was 245. Jupiter was half a mile at M building, Saturn would end up at Orchard Lake Rd, Uranus at Middle Belt, Neptune at Inkster, and Pluto at Franklin.

At Mercury on our scale model. Monday Oct 7, 2013

At Mars on our scale model. Monday, Oct 7, 2013

We don't think of this much, but the size of the Sun's disk in our sky is smaller than what we perceive, and yet this planet is at the right distance away with the right conditions for life to exist on it. 

Size of the Sun to our scale model from Earth.

Size of the Sun's disk in our sky from Earth.
Picture taken on Sept 30, 2013 in Northville, MI.
NOTE: NEVER LOOK DIRECTLY AT THE SUN. EVER!

Walking to Jupiter - Oct 7, 2013

It's all good up until we realize how far away the closest star to our Sun is. What's more intriguing is to know that we barely scratched the surface in terms of how far we have traveled. Voyager 1 on our scale model is 12.5 miles away from SOL on Farmington Rd. That would put it at Main Street in Royal Oak! If you remember, the closest star was a trip from Farmington Rd heading East, all the way around the world and ending up in Las Vegas after traveling ~25,000 miles (Really it would be the border between Oregon and Idaho if we continue on the same latitude, but that's boring so we decided Las Vegas would be cooler).

Neptune being perturbed at M-Building. Monday, Oct 7, 2013

On our scale model, Voyager 1 is traveling at 7 cm per hour (or 0.4 miles per year!). At this rate, it would take ~60,000 years to reach the closest star! [Marc check my math!]  So the fastest thing we built is 1,500 times slower than a cosmic snail. We have a long ways to go, but at least we are on our way and are reaching out.

Bottom line, we are tiny! Earth is merely a small little ripple in space and time, and we are but an insignificant species that exists on this little speckle of dust. Despite our insignificance, I take solace in the fact that, after all - and in the famous words of Carl Sagan, we are a way for the universe to know itself.

Tea Time

Astronomy students doing their
sky journals outside of A-Building.

Last night we started off our viewing session by looking at Venus in the western sky. It seems like starting our viewing sessions on top of the hill in front of A-Building to view Venus and then heading off to the soccer field works quite nicely since we aren't able to see Venus from the soccer field due to the trees. The Tea Pot however was clearly visible to us in the southern sky along with the star Antares in the constellation Scorpio. It turns out Sagittarius and Scorpio are located close to the Milky Way in our sky, but because of the amount of light pollution we are unable to see the numerous amounts of stars and dust clouds in that region of our sky. (Click here to see that image).

The Tea Pot and Scorpius (Antares)  (and an Airplanius Flybyus)

Though most of the light pollution seems to linger around in the eastern and southern sky, Pegasus and Andromeda are becoming easier to see as they continue to rise higher in the sky. With binoculars, we can easily see the Andromeda Galaxy if we know where to look.

The Andromeda Constellation. Also visible is the Andromeda Galaxy a little to the left of center in this photo. 
The streak of light is a plane moving.

Above is a picture I took that night which shows the constellation of Andromeda, and what appears to be a faint smudge above some of the stars in this constellation. That smudge is the Andromeda Galaxy! Though this picture doesn't do it justice, it is quite amazing that we are able to capture it with a few seconds of exposure. We'll try to photograph it through a telescope one of these nights. 

A longer exposure time that shows Cygnus (Deneb), Lyra (Vega), and a plane.

The Summer Triangle has also been quite the prominent feature that is among the first things to jump at us when we start our viewing sessions. Deneb and Vega are very close to the zenith, while Altair is a little lower and to the south. Cygnus lies on the plane of the Milky Way, so we expect to see a lot of stars when taking a long exposure photo. (Click here to see such a photo)

Capella rising in the northeast at the very bottom center of the photo. Also visible is a portion of Perseus.

We are also starting to witness the rise of some new objects like Capella from the northeast, and Aries from the East. This is a sign that autumn is here, and winter is right behind it. Brace yourselves, the snow is coming!



SHH

Despite the clouds...

Pointing out Vega and Lyra with an imaginary green light
while everyone jots down info into their sky journals.
Notice Arcturus in the background!

When we checked the sky after class tonight, it was not looking promising given the amount of clouds that were present at that time. However, a meteor in the west that lasted about 4 seconds was the omen we needed to assure us that it was going to be a great night. So we decided to do a viewing, but opted to leave the telescopes behind on this one and focus on the stars and their constellations instead.

Students gathering at the soccer field.

We conglomerated at the entrance of A-Building to look at Venus first, since it was the only planet visible for us at that current time. After that, we headed out to the soccer field and looked at the few stars and constellations that were bright enough to be seen through the haze and broken clouds. The Summer Triangle was the most obvious one right over our heads, a few stars in the handle of the Big Dipper, and Arcturus were among the very few things we could see at first. But it didn't take long for the sky to clear up and for the brilliant constellations to become easily visible. Cygnus, Lyra, Aquila, Big Dipper, Little Dipper, Draco, Hercules, Pegasus, Andromeda, Cassiopeia, Cepheus, and even the Tea Pot were among the constellations present, that most of us are familiar (or should be) at this point in the class. We brought out 6 or 7 binoculars for students to use and some were astonished at how many more stars can be seen simply by looking through a pair of binoculars.

The changes in our night sky are starting to become noticeable, Arcturus is

Students measuring altitude and azimuth of the Big Dipper
later in the night as the sky cleared up.

sinking in the West behind the trees sooner than earlier in the semester, and over in the Eastern sky new objects, like the star Capella of the constellation Auriga are starting to rise. Keep in mind that everything in our sky rotates around Polaris so things appear to rise in the East and set in the West. This of course is an apparent motion of the sky due to the Earth's rotation about its axis and its orbit around the Sun.


Overall, tonight was one of those nights that started off looking not so promising due to some clouds that rolled in from the West, but ended up being a night with a brilliant sky that cleared up quite nicely. Perhaps it was a little reminder that things aren't always the way they seem, and that having a little bit of hope and patience can be rewarding at the end. Let's hope for more clear skies on Wednesday!
-
SHH