Physics 1051
Astronomy of the Solar System
Observations of the Moon and Planets Laboratory
Objectives:
 Develop expertise using an astronomical telescope.
 View, identify and describe geological features on the surface of the Moon.
 Develop an understanding of the Moon’s orbital properties, and how those properties
are related to its visual appearance, and the pattern of its motion across the sky.
 Locate on the sky and identify the planets within the solar system.
 Describe the planets as they appear through a telescope.
 Develop the skills of an experienced “naturalist”, i.e., a careful observer of nature.
Materials:
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Edmund Mag-5 Star Atlas
Working flashlight with a red filter
Paper and pencil
Scientific calculator
Location: UNT Observatory, North Locust Street, 5 miles north of Denton
Preparation:
These instructions contain two sections: explanatory material and a set of worksheets.
 Read through the introduction.
 Read the discussion entitled “Looking at the Moon” in your Mag-5 Atlas.
 Review your textbook and/or course notes concerning lunar motions, and the lunar
phase cycle.
 Review your textbook and/or course notes concerning the motions of the planets.
 Complete the pre-lab worksheet.
The lab consists of a series of observations using the telescopes at the UNT observatory.
Introduction
In this lab, you will use a telescope to view surface features on the Moon. You will also
locate the Moon on the night sky and relate the Moon’s visual appearance with its orbital
properties. You will also your eyes and a telescope to locate, identify, and describe
additional objects within our solar system. The targets of your investigation will include
those planets visible during your lab session, from Mercury to Neptune, and possibly
bright asteroids or comets. You will carefully record your observations, and also explore
the orbital properties of solar system objects. You will also learn about artificial
satellites, and their appearance in the night sky.
Lunar Orbital Motion
The Moon is Earth’s only natural satellite. It orbits the Earth in an elliptically-shaped
path, taking 27.3 days to complete 1 circuit with respect to the background stars, a
timeframe known as the Moon’s sidereal period. The Moon moves through 360 during
that period, passing through all 12 zodiacal constellations. Why the zodiac? Remember
that the zodiacal constellations lie along the ecliptic plane, which defines the Sun’s path
across the sky. The Moon’s orbital plane is not the same plane as the Earth’s equatorial
plane, as might be expected. Rather, it follows the path of the ecliptic, with the Moon’s
orbit oriented at about an angle of 5 from the ecliptic. The Moon appears in the same
segment of the sky as does the Sun and all of the planets.
The Lunar Phase Cycle
During each orbit, the Moon presents a different appearance to Earth-bound observers.
While we see the same side of the Moon at all times, the illuminated (i.e., visible) portion
of the disk changes in a regular pattern, termed “phases”. The lunar phase cycle, known
as the synodic period, takes 29.5 days to complete, a little over two days longer than the
sidereal period. The phase cycle is defined as the time it takes the moon to complete one
circuit with respect to the Sun, e.g., one new moon to the next. Why aren’t these two
periods exactly the same length ? Earth is not standing still while the Moon completes its
orbit around it. During each month, the Earth/Moon system completes 1/12 of its annual
orbit around the Sun, about 30. When the Moon returns to the same spot in the sky with
respect to the stars, it will not be in exactly the same position with respect to the Sun, due
to this motion, and needs a few more days to reach the same phase.
Lunar Surface Features
With a small telescope and clear, steady skies, a great deal of surface detail can be
discerned on the Moon. The familiar “man-in-the-moon” is revealed as a topography of
dark “seas”, splattered with circular structures termed craters, and lighter-colored
mountainous regions exhibiting a much higher density of craters. You will be asked to
locate, sketch and describe some of these features. Their appearance to an Earth-bound
observer will change markedly with the Sun’s height above the lunar terrain. Remember:
Mostly full moon: the Sun is almost overhead to a lunar observer; shadows are short, the
topography muted.
1st quarter & crescent moon: the Sun is low in the sky to a lunar observer; shadows are
longer, the surface relief more pronounced.
Here are the surface features that you should choose to observe. Some will be more
prominent during a crescent or 1st quarter moon, others are better viewed around the full
Moon.
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Lunar maria or seas
Mountain ranges
Sharp craters: Copernicus, Kepler, Tycho, Clavius
The “Straight Wall”, a long linear scarp
Walled plains (filled craters): Archimedes, Plato
Planet Basics
Nine planets populate our solar system plus an assorted menagerie of moons, asteroids,
comets, and meteoroids. Four planets are easily visible to the unaided along with Earth's
moon; they are Venus, Mars, Jupiter and Saturn. Mercury can also be observed, but
because it never strays more than 28 from the Sun, an observer must isolate Mercury
from the twilight glare, shortly after sunset or before sunrise. Uranus, Neptune and Pluto,
denizens of the cold outer solar system, are telescopic objects, although Uranus can be
found with a pair of binoculars. Each of the bright planets presents an interesting
appearance through a modest telescope, and many of the basic properties of the solar
system can be discerned with careful observations of these objects.
Visual observations of the planets, without optical aid, are also very instructive. From
ancient times, people have watched the heavens and charted the changing positions of the
planets, with increasing precision. Tycho Brahe and his assistants produced the finest
pre-telescopic positional measurements of planetary motion, permitting Kepler to discern
the true nature of their orbits and to cement acceptance of the heliocentric model of the
solar system. In this lab, weather permitting, you will also place the visible planets on a
sky map, and attempt to visualize their motion across the sky with time.
Small Bodies in our Solar System
Observations of the smaller bodies in the solar system are more difficult, largely because
they are faint, and/or transient and unpredictable phenomena. No asteroid is bright
enough to see without optical aid, and even the largest do not show any surface details to
even the largest Earth-based telescopes. Comets appear in the sky without warning; those
with calculated orbits generally are faint, fuzz-balls, requiring a telescope to see.
Meteoroids enter the Earth's atmosphere every minute, smaller sand-grain sized ones
more frequently, larger, baseball-sized ones less frequently. Heated to incandescence by
friction with atoms and molecules in the atmosphere, they are visible as "shooting stars",
(more properly termed meteors), as they streak across the sky, taking a few seconds to
burn up. Like comets, most meteors are unpredictable; a spectacular meteor may shoot
across the sky behind you, and you miss the show. Several times per year, between 1050 meteors per hour seem to radiate from a particular spot in the sky; these are termed
meteor showers. The origin of meteor showers is linked to comets-- the meteoroids
comprising the shower are the pebble to dust-mote sized remains of old comets. If
possible, you may be asked to view a comet or asteroid during this lab, and if you're
lucky, a meteor or two may streak by.
Planetary Features
With a small telescope and clear, steady skies, a wealth of detail can be discerned on
some of the bright planets. The shape, angular size, surface or atmospheric markings, and
the presence of planetary satellites may all be determined. For almost three hundred
years after the invention of the telescope, visual observations through telescopes of
increasing size were the primary means of astronomical discovery—there were no digital
cameras or photography. The “canals” on Mars were identified through visual
observations; perhaps the observers suffered eye strain, because the canals turned out to
be an illusion. You will be asked to make similar careful visual observations as part of
this lab. Remember that visually the planets will not look like the spectacular pictures
presented in your textbooks. There is an enormous difference between a timed exposure
obtained by a spacecraft orbiting a few thousand kilometers from the planet and a your
eyeball image taken from millions of kilometers distant.
Lunar and Planetary Dimensions
A straightforward measure of the angular size of the Moon or a planet can, with a little
geometry and knowledge of the distance to the Moon or planet, provide an estimate of its
physical dimensions. Remember that angular size is defined as the extent of an object on
the celestial sphere, expressed in units of degrees, minutes of arc, or seconds of arc. How
to measure angular size ?? A sextant would work for the Moon, but since the planets are
just points of light to the unaided eye, we will use a telescope, together with an
understanding of the Earth’s daily motion, to make these measurements. The following
expression can be used to measure the angular size of an object:
angular size = (15 * T) * cosine(declination).
Here T is the time in seconds required for the Moon or planet to drift into or out of the
field of view of the eyepiece when the clock drive is turned off (not the time it takes to
cross the field of view). Declination is one of the coordinates which place the planet on
the celestial sphere. Since the Moon and planets are never located more than about 30
from the celestial equator, the last term in the expression is always number between 1 and
0.88. To make this measurement, position the Moon (planet) so that one edge is just
inside the view of the eyepiece. Then turn the clock drive off. Measure the time, in
seconds, that it takes for the entire Moon (planet) to drift out of the field of view.
Why does this work ? The Earth rotates through 360 in 24 hours. This rotation rate
corresponds to an angular rotation rate of 15 arcseconds on the sky per second of time,
meaning that every second 15 arcseconds sweeps by your view. This rate is maximum at
the celestial equator and of course is zero at the poles. The cosine term takes into account
the angle between the Moon (planet) and the celestial equator.
To measure the physical size of an object, one utilizes the small angle formula:
diameter (in km) = distance (in km) * tangent (angular size),
where the angular size must be expressed in degrees. Remember that 1 = 3600
arcseconds. When you measure the angular size in arcseconds, be sure to divide by 3600
to express that size in degrees.
Useful facts: 1 AU = 149 million kilometers (149 x 106 km)
Average Earth - Moon distance = 384,000 km
Observing Procedure
At the beginning of the lab, the instructor will indicate the observing plan for your
particular lab session. First you will collectively locate the Moon on the sky, then the
visible planets, after which you will proceed to the telescope stations and conduct the
observations as outlined in the worksheets. Following is an outline of the observations;
be sure that you understand each step.
For each object do the following,
Visual (naked eye) Observations of the Moon:
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Locate the Moon and note the constellations and bright stars which surround it.
Orient your Mag-5 to the map which displays the constellations around the Moon.
Mark its position in the Mag-5 Atlas. Estimate the Moon’s current coordinates in
right ascension and declination.
Visual Observations of the Planets:
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Locate the planet on the sky, and note the constellations and bright stars which
surround it.
Orient your Mag-5 to the map which displays the constellations around the planet.
Mark the position of the planet in the Mag-5 Atlas. Estimate its coordinates in right
ascension and declination.
Note the relative brightness and color of each planet with respect to surrounding stars.
At the Telescope:
When you first arrive at the telescope, it is important to refresh your memory about the
operating principles of the telescope. An assistant will guide you; be sure you understand
how to lock and unlock the axes in the scopes, how to enable and disable the tracking,
how to use the fine controls, and the different types of eyepieces. All students are
expected to participate in locating objects with the telescope; students who “hang back”
will lose points. Your grade will be based on the completeness, accuracy, and number of
sketches, and your degree of participation.
Telescopic Observations of the Moon:
1. You may want to use of the gray filters to cut down the intensity. The filters (should)
screw into the eyepiece.
2. Using a low-power eyepiece first, take a good view of the entire Moon, noting
different types of surface features.
3. Select a type of surface feature to be examined.
4. Locate an example of that feature, and carefully view it.
5. Change to a higher-power eyepiece and view the feature again.
6. Sketch it and complete the observing sheet.
7. Repeat 3-6 for at least four different types of surface features.
Telescopic Observations of Planets:
1. Locate the planet on the sky (if it’s a naked-eye planet), then carefully direct the
telescope to it.
2. Using a low-power eyepiece first, center the object in the field-of-view.
3. Make a careful observation and craft a description.
4. Change to a higher-power eyepiece and view the object again.
5. Does it appearance agree with your expectations ?
6. Measure the angular size as described above, using whichever eyepiece works best.
7. Complete your sketch sheet, then proceed to the next target.
Observations of the Moon and Planets Worksheets
Name: _______________________
ID#: ______________________
Date / Time: _____________________
Visual Observations Of The Moon
(1) In which constellation is the Moon located tonight ___________________________?
(2) Mark its position in your star atlas.
(3) Using the coordinate grid in the atlas, estimate RA:___________________________,
and declination: ___________________________.
(4) Sketch the appearance of the Moon on the sky using the square observing box below.
This sketch should be about 60x60 degrees. Include bright stars near the moon,
marked according to their brightness.
(5) Indicate the phase of the Moon on your sketch, by darkening the UN-illuminated
segment.
(6) Which is the current lunar phase?
_______________________________________
(7) The Moon moves through 360 in one sidereal period. How many degrees will the
Moon move per day ? ________________________________
(8) Based on the position for the Moon determined in (3), and the answer to (7), where on
the sky (which constellation) will the Moon appear two nights from now ?
_____________________________________
(9) In which direction is the Moon moving night per night ?
_____________________
(10) What phase will the Moon present one week from today’s date ? ______________
Name: __________________
Date: _____________ Time: _____________________
Feature type: _______________________
Temperature: _______________________
Feature name: ______________________
Sky Conditions: ____________________
Eyepiece in use: ____________________
Wind: ____________________________
Feature type: _______________________
Feature name: ______________________
Eyepiece in use: ____________________
Name: __________________
Date: _____________ Time: _____________________
Feature type: _______________________
Temperature: _______________________
Feature name: ______________________
Sky Conditions: ____________________
Eyepiece in use: ____________________
Wind: ____________________________
Feature type: _______________________
Feature name: ______________________
Eyepiece in use: ____________________
Name: __________________
Date: _____________ Time: _____________________
Venus
(1)
(2)
(3)
(4)
In which constellation is Venus located ? ___________________________________
Mark the position of Venus in your star atlas.
Estimate Venus’ RA:______________, and declination: _______________________
Sketch the appearance of Venus on the sky using the box below. You should be
facing the planet as you sketch. Include all bright stars near Venus, and the horizon, if
Venus is fairly low to the horizon
(5) Using a low power eyepiece, center Venus in the field through the telescope.
(6) Describe its appearance below. Color ? Shape ? Surface markings ? Is the edge
sharp or fuzzy ? Any moons visible ?
____________________________________________________________________
____________________________________________________________________
(7) Measure its angular size, as described above, using the available timers. Repeat the
measurement a few times; each pair of students should make several measures.
The TA will give you the distance to each planet in AU.
Angular size: ________________. Physical size:____________________________
Are the numbers reasonable ? __________________
(8) Sketch the planet carefully in the circle below, switch to a higher power eyepiece,
observe and sketch again. Any differences ?
Name: __________________
Date: _____________ Time: _____________________
Jupiter
(1) In which constellation is Jupiter located ? __________________________________
(2) Mark the position of Jupiter in your star atlas.
(3) Estimate Jupiter’s RA:__________ & declination: ____________________________
(4) Sketch the appearance of Jupiter on the sky using the observing box below. You
should be facing the planet as you sketch. The sketch should be about 40 x 20
(5) Using a low power eyepiece, center Jupiter in the field through the telescope.
(6) Describe its appearance. Color ? Shape ? Surface markings ? Is the edge sharp or
fuzzy ? Any moons visible ? Does Jupiter appear spherical ? Can you see the Red
Spot ?
____________________________________________________________________
____________________________________________________________________
(7) Measure its angular size, as described above, using the available timers. Repeat the
measurement a few times; each pair of students should make several measures.
Angular size: ________________. Physical size:____________________________
(8) Sketch the planet carefully below, then switch to a higher power eyepiece, observe
and sketch again. Any differences ?
Name: __________________
Date: _____________ Time: _____________________
Saturn
(1) In which constellation is Saturn located ? ___________________________________
(2) Mark the position of Saturn in your star atlas.
(3) Estimate Saturn’s RA:_________________ and declination: ____________________
(4) Sketch the appearance of Saturn on the sky using the observing box below.
You should be facing the planet as you sketch. The sketch should be about 40 X 20
(5) Using a low power eyepiece, center Saturn in the field through the telescope.
(6) Describe its appearance. Color ? Shape ? Surface markings ? Is the edge sharp or
fuzzy ? Any moons visible ?
____________________________________________________________________
____________________________________________________________________
Do you see any details in the rings ? Estimate the degree of tilt in the rings ?
_____________________________________________________________________
(7) Measure its angular size, as described above, using the available timers. Repeat the
measurement a few times; each pair of students should make several measures.
Angular size: ________________. Physical size:__________________________
Now repeat the measurement for the planet + the rings:
Angular size: ________________. Physical size:__________________________
(8) Sketch the planet carefully in the circles below
(9) Switch to a higher power eyepiece, observe and sketch again. Any differences ?
Name: __________________
Date: _____________ Time: _____________________
Mars
(1) In which constellation is Mars located ? ___________________________________
(2) Mark the position of Mars in your star atlas.
(3) Estimate Mars’s RA:_________________ and declination: ____________________
(4) Sketch the appearance of Mars on the sky using the observing box below.
You should be facing the planet as you sketch. The sketch should be about 40 X 20
(5) Using a low power eyepiece, center Mars in the field through the telescope.
(6) Describe its appearance. Color ? Shape ? Surface markings ? Is the edge sharp or
fuzzy ? Any moons visible ? Polar caps visible ?
____________________________________________________________________
____________________________________________________________________
(7) Measure its angular size, as described above, using the available timers. Repeat the
measurement a few times; each pair of students should make several measures.
Angular size: ________________. Physical size:__________________________
(8) Sketch the planet carefully in the circles below
(9) Switch to a higher power eyepiece, observe and sketch again. Any differences ?