Credit/Permission: For text, © William Amsberry, David Jeffery. For figures etc., as specified with the figure etc. / Only for reading and use by the instructors and students of the UNLV astronomy laboratory course.
This is a lab exercise without observations.
However, for reference, see Sky map: Las Vegas, current time and weather.
Sections
We touch on the following topics:
Some of the
Tasks can be completed ahead of the lab period.
Doing some of them ahead of lab period would be helpful.
However, you can print a copy ahead of time if you like especially if
want to do some parts ahead of time.
You might have to compensate for updates in this case.
The Lab Exercise itself is NOT printed in the lab ever.
That would be killing forests
and the Lab Exercise is designed to be an active web document.
General remarks about quiz prep are given at
Quiz Preparation.
For DavidJ's lab sections, the quiz prep is doing all the items listed here and self-testing with the
Prep Quizzes and Prep Quiz Keys
if they exist.
However to complement and/or supplement the reading, you should at least
read the intro of a sample of the articles
linked
to the following keywords etc.
so that you can define and/or understand some keywords etc. at the level of our class.
A further list of keywords which you are NOT required to look at---but it would be useful to do so---is:
All the Tasks are linked here so that you can find them in the context of
the lab exercise---which should be useful when completing your Report Form.
Sunspots were occasionally
recorded thereafter without their existence becoming common knowledge
(Wikipedia: Sunspots: Early observations;
J.M. Vaquero, 2007,
astro-ph, Historical Sunspot Observations: A Review).
The early, occasional observations were probably mostly done when there was
a large sunspot
and the Sun
was very close to the horizon
(i.e., at sunrise and
sunset)
so that its intensity was strongly reduced by the thicker
air mass
at those times or when the Sun
was viewed through
smoke or mist.
Eventually,
pinhole projection
(see also Wikipedia: Camera obscura)
was used for safe observation.
This seems to have been after the
discovery of the telescope.
Pinhole projection
uses an opaque covering with a small aperature that allows
pinhole projection on a background screen.
A point inverted image of the
object is cast on the screen.
Pinhole projection is easily understood using
light ray tracing.
Benedetto Castelli (1578--1643),
a protege of Galileo, developed
a projection technique for the telescope
to allow safe observation of the
Sun at any time
(see The Galileo Project: Sunspots
(scroll down about 50 % or search on "Castelli")).
Castelli's setup may have been a lot
like the one in the figure below
(local link /
general link: venus_transit.html)---without the wife and kids---he was a
Benedictine monk.
The Sun is a sphere of gas, and NOT
a solid sphere.
Sphere of gas and
liquid
can have differential rotation
and non-rotational motions like
convection and oscillations.
The Sun has these.
The Earth, is in fact,
NOT entirely a solid sphere.
The outer core
(2890--5150 km from the center)
is liquid (primarily
molten iron
and nickel)
(see Wikipedia: Structure of the Earth).
The outer core probably exhibits
both differential rotation
and convection.
Define briefly in your own words:
1. Sunspots:
2. Photosphere:
3. Rotation vs. Revolution:
4. Solar Cycle:
5. Sidereal Rotation Period:
6. Synodic Rotation Period:
We will measure how long it takes a
sunspot to complete one rotation of
the Sun's surface.
This will help us establish the synodic rotation rate of the
Sun. With that information,
we will then be able to calculate the sidereal rotation period.
The easiest way to determine the period of rotation of the
Sun would be to find a
sunspot
and just watch it until it comes back around the
Sun to the same place in the images.
However, due to the nature of the life of
sunspots, there is no guarantee that the
sunspots you choose will survive an entire rotation.
Sub Tasks
We will measure the sunspots
and compare them to the size of the
Earth to get some perspective of these
objects.
Sub Tasks:
NOTE 2: The Sun will have
both negative and positive pixel values. Use the absolute value of
both and add them to get the diameter in pixels.
MATH:
Sunspot diameter
in kilometers (km)
= [(pixel diameter of
sunspot)/(pixel
diameter
of the Sun)]*(diameter of the
Sun in km)
Divide the Sunspots in kilometers
by the diameter
of the Earth in
kilometers (km)
to get the relative size of the
sunspots
in Earth diameters
(i.e., (Sunspots in km)/(diameter of the
Earth in km).
The sunspot is __________ times the
size of the Earth.
The prime meridian of
heliographic
coordinate system
is just "the north-south centerline on the visible solar disk"
(Coordinate System:
Center for Integrated Space Weather Modeling (CISM)).
This prime meridian is always moving because of the
solar rotation and the
Earth orbital motion.
The
solar longitude
is negative/positive to the
Sun's west/east
(east/west on the sky).
Given that the Sun
has no permanent surface features, the
solar longitude
defined as above seems to be convenient.
Then 360° over that synodic rotation rate gives the
synodic period.
Sub Tasks:
Sub Tasks:
In
Task 5: Calculation of the Synodic Period of Rotation,
you measured the observed (synodic) rotation period. Remember that as
the sunspots
are going around the Sun,
we are orbiting the Sun in the same direction. Therefore,
the time in which we see the sunspots
cross the surface is greater than what it really is.
We must correct for the motion of the Earth
in order to determine the
sidereal period: i.e.,
the rotation period relative
to the observable universe
which can be justly called
absolute rotation.
Sub Tasks:
Using these formulae calculate
the synodic periods
and sidereal periods
for the sunspots you
"observed" and enter the values below in
Table: Sunspot Synodic and Sidereal Periods.
Sub Tasks:
Any that are semester-section-specific will have to added as needed.
Comments:
Do the preparation required by your lab instructor.
Keywords:
Julian day,
orbit,
orbital period,
photosphere,
revolution,
rotation,
sidereal period,
sidereal time,
solar cycle,
solar photosphere,
sunspot,
sunspot group,
sunspot number,
synodic period,
etc.
Hm.
Task Master:
In this section, we look at the discovery of sunspots
and their implications.
One should NEVER observe the
Sun this way.
It is damaging to the eyes
although a few such fleeting observations
MAY cause only marginal damage.
The first telescopic observations seem to have been
direct ones with the Sun
very close to the horizon.
This was probably very bad for eyes.
However, Galileo's
blindness late in life
seems to have been unrelated to his solar observations
(see The Enigma of Galileo's Eyesight).
One of the "discoveries" of Lab 7 is that
solar rotation
is differential rotation:
i.e., parts rotate at different rates.
For a further introduction to sunspots,
see the figure below
(local link /
general link: solar_sunspots_granules.html).
NOTE 1: The diameter
of the Sun in pixels is GREATER than the
diameter
of the sunspot in pixels.
Left Pixel X-Value Right Pixel X-Value Size in Pixels Size in km
Sunspot
Sun
By
solar longitude,
we mean what is usually
called
Carrington longitude
in the
heliographic
coordinate system.
End of Task
End of Task
End of Task
SYN(days)=(360°)/[Rate(°/day)] and SID(days)=(SYN*365.25)/(SYN+365.25) .
_______________________________________________________________________________________
Table: Sunspot Synodic and Sidereal Periods
_______________________________________________________________________________________
Sunspot ID Latitude Rate Synodic Period Sidereal Period
(degrees) (degrees/day) (days) (days)
_______________________________________________________________________________________
A
B
C
Average Sidereal Period
_______________________________________________________________________________________
End of Task
Goodnight all.
Below are some generic comments for
Lab 7: Sunspots
that may often apply.