Download Orbit of Mercury

Orbit of Mercury
Yeah protractors!
Planetary Orbits
- All planets orbit the Sun
in an ellipse
- Semi-major axis (a) is
half of the long axis
Planetary Orbits
- All planets orbit the Sun
in an ellipse
- Semi-major axis (a) is
half of the long axis
- Period (p) is the time it
takes to go around the
Sun one time
- Eccentricity (e) is how
squished the orbit is
e = 0 is a circle
e = 0.5 looks like an oval
e = 1 is a very squished oval
Mercury's Orbital Parameters
Write these down!
(You need them for the take home.)
- period = 87.9 days
- semi-major axis = 0.387 AU
- eccentricity = 0.21
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Inferior planets
show phases!
Inferior planets always appear close
to the Sun, so it's easy to measure
angular separation (aka elongation angle).
Right after sunset every day for one month!
Which day had the greatest elongation angle...?
“Greatest elongation angle”
means largest angular separation
Greatest elongations are cool because
they tell us exactly where the planet is.
We are going to figure out Mercury’s orbit
using greatest elongations!
First mark Earth’s position for the 13 dates
- “Degrees” column
- Number the positions
- Counter-clockwise!
- Angle is at the Sun
EARTH POSITIONS
•
•
•
Large circle is
orbit of Earth
Arrows on orbit
represent
direction Earth
is moving
around Sun
Sun is the
center dot
EARTH POSITIONS
1.
2.
3.
42°
Draw dashed
line between
Earth (X) and
Sun (center
dot)
Line up
bottom edge
of protractor
on line with
center on Sun
Measure out
calculated
angle (last
column of
Table 7.1)
from previous
Earth position
to get new
Earth position
EARTH POSITIONS
1.
2.
Draw a dotted
line between
the Sun and
your new
Earth position
Label this
position so
you know
what line this
is later
EARTH POSITIONS
1.
2.
3.
72°
4.
Again, line up
the bottom
edge of
protractor on
Earth-Sun line
with Sun at
center and
Earth at 0°
Measure out
calculated
angle and
mark it
Draw dashed
line between
Sun and new
position
Label position
EARTH POSITIONS
•
•
This is what all
13 positions
should look like
All should be
labeled with
dotted lines
between Earth
and Sun
We are going to figure out Mercury’s orbit
using greatest elongations!
First mark Earth’s position for the 13 dates
- “Degrees” column
- Number the positions
- Counter-clockwise!
- Angle is at the Sun
Then mark Mercury’s position for each date
- “Elongation Angle” column
- Number the positions
- EAST : LEFT
WEST : RIGHT
- Angle is at the Earth
- Use correct Earth position
MERCURY POSITIONS
27.2°
Line bottom
edge of
protractor
with EarthSun line
2. Earth at
center of
bottom of
protractor
3. Measure out
given angle
(column 3 in
Table 7.1) –
position #1
has east
angle
East angle: left
of the Sun
West angle:
right of the
Sun
1.
MERCURY POSITIONS
1.
2.
3.
Draw solid line
between Earth
and mark from
measured
angle
Be sure the
line goes past
Earth –
necessary for
the next step
Mercury is
located
somewhere on
this line
MERCURY POSITIONS
1.
2.
3.
Place the
protractor so
that the solid
line goes
between the
center of the
bottom and
the 90° tick
Keeping that
alignment, line
up the bottom
of the
protractor with
the Sun
Where the
protractor
bottom
intersects the
solid line,
place a dot
MERCURY POSITIONS
1.
2.
3.
Place the
protractor so
that the solid
line goes
between the
center of the
bottom and
the 90° tick
Keeping that
alignment, line
up the bottom
of the
protractor with
the Sun
Where the
protractor
bottom
intersects the
solid line,
place a dot
MERCURY POSITIONS
18.1°
1.
2.
3.
Position #2
has a west
angle so
angle must
be measured
to the right of
the Sun
Line up
protractor
and measure
angle to the
left of Sun
Draw solid
line between
Earth position
2 and new
angle mark
MERCURY POSITIONS
1.
2.
3.
4.
Line up
protractor at
90° on
Mercury line
Line bottom
of protractor
on Sun
Mark where
bottom of
protractor
crosses
Mercury line
Label
Mercury
locations
based on
Earth position
#’s
MERCURY POSITIONS
•
•
This is what
all 13 Mercury
positions
should look
like
Each position
should be
labeled same
number as
corresponding
Earth position
(needed for
later question
in lab!)
We are going to figure out Mercury’s orbit
using greatest elongations!
First mark Earth’s position for the 13 dates
- “Degrees” column
- Number the positions
- Counter-clockwise!
- Angle is at the Sun
Then mark Mercury’s
position for each date
- “Elongation Angle”
- Number the positions
- EAST : LEFT
WEST : RIGHT
- Angle is at the Earth
- Use correct Earth
position