Guidance of " Venus-Watch Campaign"
1.Background
Venus is a planet that is often called the morning star or the evening star. It is a brightest star in
the evening and the dawn sky. One of characteristic features of Venus is a waxing and waning.
Furthermore, Venus's apparent size changes. The Moon waxing and waning is well known. TheMoon and Venus are shining only when the Sun illuminates them. Since the relative positions ofEarth, the Moon, and the Sun changes, the shape of the shining part of the Moon changes (asshown in Figure 1). Similar to the Moon, the conﬁguration of Earth, Venus, and the Sun changes,
the shape of the shining part of Venus changes (as shown in Figure 2). This is the reason for thewaxing and waning of them. The apparent size of Venus changes considerably, though that of theMoon changes little. This is because the distance between Venus and Earth changes much morethan that changes of Earth and the Moon. When Venus locates between the Sun and Earth, we cansee a large Venus, while when Venus locates the behind the Sun, we would see a small Venus(see Figure 2).
Figure 1 Earth and Moon

Figure 2 Earth Venus and Sun
Since the distance between Earth and Venus is large,

Sunlight

the apparent size of Venus is small.

VenusThe Moon
Moon's orbit

Earth's orbitSun

daytimeevening

Orbit of Venus

morningnighttime Eartheveningmorning

Earth
Since the distance between Earth and Venus is small,the apparent size of Venus is large

Galileo Galilei, ﬁrst, noticed the waxing and waning of Venus. He looked through his telescope atthe celestial bodies in 1609, and in the next year, he discovered the waxing and waning and theapparent size change of Venus. At that time, the Copernican theory or the Ptolemaic theory had been
the subject of debates. It was not clear which theory is the correct one. Galileo's discovery apparently
supported the Copernican theory. Because the Ptolemaic theory could not explain the waxing andwaning of Venus, it caused a signiﬁcant impact to believers of the Ptolemaic theory.
You can see the waxing and waning of Venus with the 4cm telescope.

2. Purpose
The aim of this activity is that children to experience the feeling of wonder that Galileo had when
he observed Venus the ﬁrst time. Assembling the telescope and ﬁnding the waxing and waning andthe changes of the apparent size of Venus by themselves are an exciting experience. It is importantthat children to understand the reasons behind such phenomena.

3. Observation

Tips

At ﬁrst, it may not be easy acquiring Venus in the telescopeʼ s ﬁeld of view. To help stabilizing thetelescope and to make ease of acquisition, use of tripod is recommended. When Venus enters in theﬁeld of view, tighten the tripod to ﬁx the telescope at once. Then, adjust telescope focus. It isadvisable to have a practice session by using distant scenery in daytime. Children should be
informed that the scenery turn upside down through telescope. You can get information about thepositions of Venus by the following website.
For the 15 power telescope, it is diﬃcult to deﬁne the shape of the Venus in the dark night because
it is too bright. When the sky becomes dawn, the contrast decreases. At that time, it is easier to deﬁne
the shape and size of the Venus.

4. Steps(a) Observation and sketch
First, print out the work-sheet. Then, observe Venus and make a sketch on the work-sheet.
From March to May 2011, Venus can be seen at the eastern sky at dawn.
During this period, you should observe Venus at least once a month (i.e. in total three times).
If it is possible, you may add the sketch column, and recommend children to observe as many
as possible.
Magniﬁcations of the telescopes are as follows:
For Hoshi-no-Techou Inc. telescope kit,
the magniﬁcation is 15 power(Focal length of the telescope is 273mm and focal length of the eye piece is 18.2mm).
For ORBYS Inc. telescopes kit,
it is 35 power (Focal length of the telescope is 420mm and focal length of the eye piece is 12mm).
(b) Write any ﬁndings and/or questions
Write anything you found out and/or question from your observations in your sketch sheet under
the sketch column. It is not easy to recognize the apparent change in size of Venus just from these3 observations. However, children will learn it by working on the workbook.

(c) Conﬁrm how Venus looked from EarthUsing the after observation workbook, explain children to understand how Venus is seen from Earth.
Use the balloon example on the after observation workbook, let children think about a relationshipbetween the apparent size of the balloon and the distance to it. When children understand therelationship well, let them ﬁll the parentheses.

Example of answer

Think about the apparent size of the baloon･･･

If it is close to you･･･

If it is far from you･･･■ How about the Venus size?
When the Venus is large, it is（close to Earth）.

When the Venus is small, it is（ far from Earth）.

Then, move on to the second page of the after observation workbook, consider the distance andthe apparent size from the relative positions of Earth, Venus and the Sun. Draw the shape and thesize of Venus would be seen from the Earth like the example shown in red lines.
Example of answer
The apparent size of Venus

Venus

can be small because Venus

Venus orbit

is far from the Earth.

the Earthʼ s orbit
Eary Jan. 2012
EveningSun

Eary Mar. 2012

Eary Apr. 2011Dawn

Eary Feb. 2011
Dawn

Evening

Late Apr. 2012
Evening

This time, you can observe
the changes of the Venus
around there.

Late Dec. 2010
Dawn

28 Oct. 2010

The apparent size of Venus
can be large because Venus

From March to May, 2012,
you can observe big changesof shape and size of the Venus.

Earthis close to Earth.

(d) Write down what is learned today, and what you want to know more.
A summary should look like: “Venus displays phases like those of the Moon. Venus presentsa small "full" image when it is on the opposite side of the Sun. It shows a "quarter phase" when it isat its maximum elongations from the Sun. It presents a "thin crescent" in views as it comes aroundto the near side between the Earth and the Sun. The apparent size of Venus becomes largest when
it is between the Earth and the Sun.” Also, write down what you want to know more and whatchildren can do further.

5.Notes
It helps that teaching the change in phases of the Moon before observing Venus."
Caution must be given to children that "Never watch the Sun through the telescope!”