clix - Unit 3: The Solar System and Beyond

Role Role play : Revolution of planets
Procedure:

Form groups of nine. One student becomes the Sun, the others become one planet each.
Every student should carefully see and remember the revolution period of the planet she has become.
Fall in the line in the same order as the planets. The Sun, Mercury, Venus,....Neptune. (planets never come in one line like this, we are doing this to understand their order and relative speeds).
Now, first the Earth should make one revolution (ignore the rotation). The Earth’s speed should such that Mercury should be able to perform four revolutions around the Sun by the time the Earth completes one.
After the Earth completes one revolution, rest of the planets can start. Mercury will have to go fast, Venus is little slower, Earth is even more slower. Mars has to go a little slower than the Earth. Jupiter onwards, the planets will have to be very slow. When the Earth completes one revolution, Jupiter should have moved only one-twelfth forward in its orbit and Neptune should move only by one small step.
The revolution period of the planets closer to the Sun is smaller. Their orbits are smaller. As you go away from the Sun, the revolution time increases. In Table 1, you can see that these planets are very far from the Sun. It takes more than 43 minutes for sunlight to reach to Jupiter and more than four hours to reach to Neptune!. Effectively, their orbits are bigger. So they take more time to cover that distance.
Observe that when the Earth is on one side and a planet is on the other side of the Sun, that planet will not be visible. So, on any given night, we see only some planets in the sky.
Notice that every once in awhile you will see Mercury or Venus coming between the Earth and the Sun. This is very similar to the situation of a Solar eclipse. However, the apparent size of the planets being much smaller than the Moon, they do not cover the entire Sun but appear to be moving on the disk of the Sun, when seen from the Earth (Figure 2). Careful observations of the transits are important because they help us determine the size of the planets and the sunspots. The transit of the Earth would be visible from Mars and planets beyond it. Wouldn’t that be interesting?
The planets closer to the Sun are revolving much faster than the planets farther from the Sun. Consequently, when seen from the Earth, some planets are seen at a completely different position after one year and some planets will be almost at the same place. Stars on the other hand, are seen at exactly the same position after one year. That is how we know that one year is complete. Ancient people had noticed that some of the celestial bodies do not follow the pattern that the rest of the stars do. Ancient Greeks named them ‘planētes asteres’, which means ‘wandering stars’, from where their current name ‘planets’ is derived. Ancient people also thought that these planets seemed to be more powerful (most planets look brighter than other stars, and can move differently). So they thought that the planets could influence life on the Earth. This is how astrology developed. But now we know why planets appear to move differently than the stars, and why they look brighter! Besides, how would an inanimate object, which is so far away, have any impact on our lives? And why would it differ from person to person? So in case someone tells you that something happened in your life because of the planets, think a bit before you believe it!

Figure 2: Transits of Mercury and Venus

Figure 2a: Transit of Mercury (captured on 8 Nov. 2006)
(Credit: By NASA - http://www.nasa.gov/images/content/162385main_Merctransit2006_sm.jpg on http://www.nasa.gov/vision/universe/solarsystem/20oct_transitofmercury.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=1355554)

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Figure 2b: Transit of Venus (captured on 8 June 2012)
(Credit: By NASA - https://www.nasa.gov/mission_pages/sdo/multimedia/gallery/venus-transit-2012-first.html)

Draw Draw a diagram of the Solar System as seen from above the North Pole of Sun. Show all the planets and, their orbits and axes of rotations (like the Earth, all the orbits are almost circular). Try to position the planets in such as way that if seen from the Earth,

The transit of Mercury can be seen.
Venus is behind the Sun (this situation is called conjunction).
Mars is in conjunction with the Sun.
Jupiter is visible at zenith at midnight.
Saturn appears to be rising at midnight.
Uranus appears to be setting at midnight.
Neptune appears to be on zenith at the time of sunset.

Use your notebook for drawing. Please write following on page where you are drawing- The Basic Astronomy Module: Unit 3: Lesson 1: Activity 1 & your Login ID

We have gathered information about the planets through the satellites we have sent into space so far. Here is some interesting information. The first four planets, referred to as inner planets (Mercury, Venus, Earth and Mars) have solid surfaces (with or without a fluid layer around it). So they are called rocky planets. The four outer planets (Jupiter, Saturn, Uranus and Neptune) are much bigger than the inner planets, so they are called giant planets. Jupiter and Saturn are made up of gases (mostly Hydrogen and Helium) and Uranus and Neptune are made up of different types of ice.

Inner planets

Mercury is the smallest, lightest and fastest planet in our solar system. It has no atmosphere. Being closest to the Sun, the temperature in those parts where is it day, rises very high (~ 427 °C). But due to the absence of atmosphere, it gets very cold at night (-173 °C). So the difference between day-time temperatures and night-time temperatures is highest on Mercury.
Next to it, Venus is covered by clouds. The sunlight gets reflected from these clouds, which is why it looks so bright! The heat gets trapped inside the clouds, which makes Venus the hottest planet in the solar system (maximum temperature 462 °C). Venus is around the same size as the Earth. If seen from above the North pole, all the planets seem to rotate in an anticlockwise direction, except Venus. Imagine how the path of the Sun and the stars would appear from Venus!
Earth is the planet we live on. It has a solid surface with a thin layer of water on a large part of it and an atmosphere of about 100 km around it. Of course, we know a lot more about the Earth than that! But to study the Earth, there is a separate branch of science called ‘Earth Science’ or ‘Geoscience’.
Mars’s surface contains iron oxide (rusted iron) because of which it looks red. It has a layer of ice on both its poles.

Outer Planets

Jupiter is the largest and heaviest planet in our Solar System. When viewed from a telescope, we see a red spot on it. This is a storm that has been going on for the last 350 years. The diameter of this storm is three times the diameter of the Earth. It is known as the ‘Great Red Spot’.
Saturn is famous for its rings. There are nine rings made up of dust and ice. The maximum thickness of these rings is only one km! Saturn also is a gaseous giant. Its density is close to 0.7 gm/cm³ which is less than that of water. Remember, at normal temperature and pressure, the density of pure water is 1 gm/cm³. This makes it the least dense among all planets.
Uranus, being far away from the Sun, is very cold. It is made up of Hydrogen, Helium, and a little bit of Methane and Ammonia. On the Earth, these elements or compounds would be in a gaseous form, but they are frozen on Uranus. The axis of Uranus is so tilted that it is almost in the plane of its orbit. Would day and night occur on Uranus? Would the seasons occur on Uranus? If yes, how would they be?
Neptune has a windy atmosphere. The maximum speed of the wind on Neptune (2,100 kilometres per hour) is the highest in the Solar System. It has a ‘Great Dark Spot’ of a storm just like the Great Red Spot on Jupiter.

Figure 3: Photographs of Planets in our solar system

Figure 3a: Mercury
(Credit: By NASA https://solarsystem.nasa.gov/planets/mercury/galleries)

Figure 3b: Venus
(Credit: By NASA - http://photojournal.jpl.nasa.gov/catalog/PIA00104, Public Domain, https://commons.wikimedia.org/w/index.php?curid=11826)

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Figure 3c: Earth
(Credit: NASA Earth Observatory image by Joshua Stevens, using Suomi NPP VIIRS data from Miguel Román, NASA's Goddard Space Flight Center)

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Figure 3d: Mars
(Credit: By ESA - European Space Agency & Max-PlanckInstitute for Solar System Research for OSIRIS Team ESA/MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA - http://www.esa.int/spaceinimages/Images/2007/02/True-colour_image_of_Mars_seen_by_OSIRIS, CC BY-SA 3.0-igo, https://commons.wikimedia.org/w/index.php?curid=56489423)

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Figure 3e: Jupiter
(Credit: By NASA, ESA, and A. Simon (Goddard Space Flight Center) - http://www.spacetelescope.org/images/heic1410a/ or http://hubblesite.org/newscenter/archive/releases/2014/24/image/b/, Public Domain, https://commons.wikimedia.org/w/index.php?curid=32799232)

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Figure 3f: Saturn
(Credit: By NASA / JPL / Space Science Institute - http://www.ciclops.org/view/5155/Saturn-Four-Years-On http://www.nasa.gov/images/content/365640main_PIA11141_full.jpg http://photojournal.jpl.nasa.gov/catalog/PIA11141, Public Domain, https://commons.wikimedia.org/w/index.php?curid=7228953)

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Figure 3g: Uranus
(Credit: By NASA/JPL-Caltech - http://web.archive.org/web/20090119235457/http://planetquest.jpl.nasa.gov/milestones_show/slide1.html (image link) http://photojournal.jpl.nasa.gov/catalog/PIA18182 (image link), Public Domain, https://commons.wikimedia.org/w/index.php?curid=5649239)

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Figure 3h: Neptune
(Credit: By NASA - JPL image, Public Domain, https://commons.wikimedia.org/w/index.php?curid=640803)

Let's Discuss:

Do you think celestial bodies (e.g. planets, comets) or phenomena (eclipses, meteorite showers) can influence our life? Do you think in might influence lives of animals or trees as well? If yes, give your reasons, if no, give your response.
List the superstitions related to astronomy (Initially limit your response to only one name so that everyone gets a chance. If the list is incomplete after a week name as many as you know, but do not repeat a response).

Select from the following:

1.3 Activity : Revolution of planets (role play)