Credit/Permission: For text, © 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 with naked-eye observations which are essential.
See Sky map: Las Vegas, current time and weather.
Sections
We will learn how to find some constellations and bright stars both on sky maps and in observations of the night sky, and thus begin to get the basic structure of the night sky in our minds.
We touch on the following topics:
Do the preparation required by your lab
instructor.
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: General Instructions.
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.
You should review the
Observation Safety Rules.
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.
Patchy cloud cover may be OK for this lab exercise.
You will have to make a judgment call based on visual inspection of the
sky.
If the sky is going to be heavily clouded, then
choose an alternative lab exercise without observations (or for which observations are
NOT essential) from the
Introductory Astronomy Laboratory Exercises.
Unfortunately, Lab 2: The Sky is a bit of a long and tedious lab, but
the students do need to cover the topics in it early in the course.
The Tasks recommended for early completion are labeled as such in the
Task Master.
In this section, we find and label
constellations
and
bright stars
on sky maps.
The sky maps
aid in the observations of the
constellations
and
bright stars
which we also do in this section.
The observation Tasks might have be delayed until after other
Tasks are done
depending the observing circumstances of the night.
The celestial sphere
is an imaginary sphere
centered on the Earth and set
at quasi-infinity beyond any actual
astronomical objects.
Taking the Earth as
at rest,
the celestial sphere
rotates once per day
(more precisely, once per
sidereal day = 86164.0905 s
= 1 day - 4 m + 4.0905 s (on average))
around the Earth
turning on the
celestial axis
which is the extension of the
Earth's axis
to the celestial sphere.
We locate
astronomical objects
on the sky
in celestial coordinate systems
(which just require angular positions) by
projection
onto the celestial sphere.
Maps
of celestial sphere
or parts thereof are
sky maps (AKA star charts).
Note there is NO perfect way to
project a curved surface on a flat one.
So flat maps
of the celestial sphere
are always distorted in some way.
Celestial globes
depicting the celestial sphere
have NO distortions, but like
globes
are mostly decorations.
Historically,
the celestial sphere
in Aristotelian cosmology
was a real physical sphere
centered on the Earth
on which the stars were fixed.
This theory
of the celestial sphere
along with the rest of
Aristotelian cosmology
was discarded in the
17th century
in the course of the
Copernican Revolution (c.1543--c.1687).
The instructor
will give some intro to using
TheSky
software if necessary.
Usually, we just do the orientation for
TheSkyX.
There is a self-orientation to
TheSky
at TheSky Orientation.
The instructor
may just direct you to do that orientation.
Sub Tasks:
You will only need one set of sky maps
PER GROUP---unless your
instructor directs otherwise
The set of sky maps
should be appended to the
favorite report form---unless your
instructor
asks for each group member to make a set of sky maps.
RMI Qualification: If you do NOT have a
printer, just sketch the
Unlabeled Sky Maps
by hand with enough detail for your own use.
RMI Qualification: If you do NOT have a
printer,
you will have to write out the
Constellation Tables by hand with enough detail for your own use.
They are part of your
Report Form.
The figure above
(local link /
general link: iau_scorpius_contour.html)
illustrates a tight-fitting red
contour line surrounding
the stick-figure of
a constellation labeled by its abbreviated name.
The 3 unlabeled sky maps
printed out in Task 1: Contouring Constellations
in are shown in the 3 figures below.
This task is to be done DURING observations and SIMULTANEOUSLY with
Task 4: Bright Star Observations.
So you have to wait until you go outside.
Only the favorite report form
requires filled-in tables---unless your
instructor directs otherwise.
Sub Tasks:
Example location specifications:
near zenith,
near nadir,
northern sky, southern sky, eastern sky, western sky, some in-between sky,
etc.
So this task has to be done SIMULTANEOUSLY with
Task 4: Bright Star Observations specified below.
Label the bright stars
shown in Table: Bright Stars
(general link:
Table: Bright Stars)
on the sky maps you printed out.
fill in the Table: Bright Stars now.
The other columns are filled in
in Task 10: Bright Star Data which is usually done
after observations.
This task is to be done DURING observations and SIMULTANEOUSLY with
Task 2: Constellation Observations.
So you have to wait until you go outside.
Only the favorite report form
requires filled-in tables---unless your
instructor directs otherwise.
Sub Tasks:
If there is time DURING the observations, observe
ONE or OTHER of the
Big Dipper
(which is
an asterism in
Ursa Major)
or Cassiopeia
and rank their brightest
stars in order of
apparent brightness
(rank 1, 2, 3, etc.)
in the tables below
(local link /
general link: Table: Big Dipper Stars;
local link /
general link: Table: Cassiopeia Stars).
Any unobservable star, just rank as
unobservable.
The sky maps below
(local link /
general link: iau_ursa_major_ekrem.html;
local link /
general link: iau_cassiopeia.html)
will allow you to identify the
stars in the
constellations.
Print both sky maps.
To print go right click on image/print preview/adjust size/print.
If the task CANNOT be done, say why NOT. Reason why NOT: _____________________________________________
In this section,
we do some tasks concerning the north celestial pole (NCP).
The NCP is the
location where the celestial axis
intersects the celestial sphere---which is the
imaginary, infinitely remote sphere on which we project
astronomical objects in order to locate them
on the sky.
From the Earth's perspective, the
celestial sphere rotates around once
per day (more exactly once per
sidereal day)
on the celestial axis.
We will NOT concern ourselves with the
south celestial pole (SCP), but it is
easy to deal with since every thing is just mirror imaged from the
NCP.
Sub Tasks:
Hint: A regular sentence
begins with a capital letter,
ends with a period.
It usually has a subject
and a verb. NOT always.
The circumpolar circle angular radius (CCAR)
for the NCP
for a given location in the Northern Hemisphere
is the angle measured
from the NCP
within which astronomical objects are
circumpolar for that location
and above the horizon.
Recall circumpolar astronomical objects
are astronomical objects that NEVER rise or set---they
are always above or below the horizon.
Sub Tasks:
Polaris is a particularly interesting
bright star
because it is within 1° of the
NCP, and so to
casual observation does NOT seem to move at all---it actually
revolves in a very small
small circle
on the celestial sphere every day.
Because it is so close to the NCP,
Polaris
is the Northern Hemisphere
pole star of our historical period.
Polaris makes the
NCP easy to find---find
Polaris and you've found the
NCP to within 1°.
See the figure below
(local link /
general link: sky_swirl_polaris_ehrenbuerg.html)
illustrating the daily motion of
stars around the
NCP.
What is the
altitude of
Polaris for
the Northern Hemisphere in general and for
Las Vegas, Nevada in particular?
Answer in sentence form.
Finding Polaris is NOT so hard,
but it takes a bit of know-how.
It's a reasonably obvious
naked-eye star,
but there are many naked-eye stars
as bright or brighter.
So brightness alone won't find Polaris for you.
It is the brightest
star in
Ursa Minor,
and the end of the handle of the
Little Dipper
asterism in
Ursa Minor.
But the other Ursa Minor
stars are much harder to find especially
in bright sky conditions as in modern cities.
So finding Ursa Minor
is NOT the usual strategy for finding
Polaris.
There are two tricks for finding Polaris.
One we leave for another day.
The other is to look due north
and use spread hands to measure out the
angle
of the NCP
above the horizon
(i.e., the altitude
of the NCP from
due north).
The hand and angle diagram in the figure below
(local link /
general link: alien_angular.html)
shows how to use your hand
to make angular measurements.
Sub Tasks:
In this section,
we investigate bright stars
as seen in the sky: i.e.,
stars of high apparent brightness.
Note that in astronomy,
"apparent" does NOT mean "false" or "seeming".
It means "as seen from the Earth".
So stars of high apparent brightness
are bright as seen from Earth.
They are NOT necessarily
stars of high intrinsic
brightness: i.e., high luminosity
(energy output per unit time).
They could just be very close to the
Earth, and so have high apparent brightness.
The stars of highest apparent brightness
usually have traditional names mostly derived from
Latin
(e.g., Polaris which means of/near
the North Pole: see
Wikipedia: Polaris: Names)
or
Arabic
(e.g.,
Algol which means the
Ghoul:
see Wikipedia: Algol: Names).
The bright stars
with traditional names are
the named stars.
For examples of named stars,
see the sky map
of Ursa Major below.
Stars often have multiple names.
The bright stars
as well as often having traditional names
(see Wikipedia: Named stars)
also often have
Bayer designations.
Bayer designation
is explicated as follows:
In fact, the assignment of
Greek letters
is NOT always in the correct order of decreasing apparent brightness.
Johann Bayer (1572--1625)
who developed the
Bayer designation
had NO way of doing exact brightness measurements and, in fact, it was
NOT part of his program to get the right order
(see Wikipedia:
Bayer designation: Is Alpha always the brightest star?).
Nevertheless,
in most constellation,
the α star
is the brightest and the
β star the 2nd brightest.
For reference, the Greek alphabet
in order is given in the diagam below
(local link /
general link: greek_alphabet.html).
The
named stars
and the stars
with a Bayer designation
are only a tiny fraction of all
stars even just
in our local part of the
Milky Way.
And no one is giving any more such special names nowadays.
To accommodate the millions of
stars that are
observed, other
nomenclatures have been
developed.
Surveys of stars
produce catalogs of stars
and the stars
are just named by their catalog number---it does NOT matter if
a star has other names.
For example,
Algol (AKA β PER)
is also
HD 19356
(in the Henry Draper Catalog)
and
SAO 45864
(Smithsonian
Astrophysical Observatory Star Catalog).
The simplest way of naming a star is just to name it by
its equatorial coordinates:
i.e., its right ascension (RA)
and declination (Dec or δ).
The meridian
in astro jargon
is a great circle than
passes through the
NCP,
SCP,
and the zenith---the point directly overhead wherever you are.
The meridian is illustrated in the
figure below
(local link /
general link: horizontal_coordinates.html).
Hence, at least in NOT so long ago days,
the local time for a
transit
(i.e., transit time)
was a very important
datum.
It still is for a lot of purposes.
Astronomical objects
move 15° west on the sky per sidereal hour
(which is slightly shorter than a standard hour)
along small circles
of constant declination
just due to the eastward rotation of the
Earth---or from a geocentric
perspective, the westward rotation of the
celestial sphere.
15° is 1 hour of right ascension.
So if you know today's
transit time for
an astronomical object
and its declination,
you can estimate where it will be any observing time.
The importance of
transit times
is the reason for including them in
Table: Bright Stars above
(local link /
general link: Table: Bright Stars).
Making use of TheSky,
complete the data in
Table: Bright Stars above
(local link /
general link: Table: Bright Stars)
in the
favorite report form only---unless directed otherwise
by your instructor.
Note the column "Above Horizon at 9:00 Today" makes use of the "visibility" row in the
TheSky6 information box
which gives rise and set times on the
24-hour clock.
If the rise time is after the set time, then the
star set and then rose during today's date
(see Date & Time if needed).
The apparent
rotation of the sky is NOT
a big part of this lab since is hard to observe in our short period of observations.
The sky does an apparent rotation
about the celestial axis every
sidereal day = 86164.0905 s
= 1 day - 4 m + 4.0905s (on average)
(which is a little shorter than a
metric day
=24 h = 86400 s).
The celestial axis is just
an extension to the celestial sphere of the
Earth's axis.
The apparent rotation is caused by the physical rotation of
the Earth relative to
the fixed stars to very high
accuracy/precision.
During tonight's observations (which are described above in
section Constellations, Bright Stars, Observations),
did you notice the
apparent rotation of the sky?
Complete this task using the
Rotating Sky Explorer
displayed in the figure below
(local link /
general link: naap_rotating_sky_explorer.html).
in the group must do the task for themselves.
Sub Tasks:
Since we love nothing more than a tedious, finicky task at the end of a long night.
On the 3
Unlabeled Sky Maps
given in section
Constellations, Bright Stars, Observations
(local link /
general link: Unlabeled Sky Maps)
mark approximately with a contour line
the horizon
for our location
for today's date
(see Date & Time if needed) for 9:00 pm.
See the below subsection
Finding the Horizon
(local link /
general link: Finding the Horizon)
for help in finding the
horizon.
This task
takes about 15 minutes or so which may be too much time at the end of the night.
So it is omittable at the discretion of the
instructor.
The
TheSky6
should just show the horizon
on its sky map.
The horizon is the boundary
between night (dark on the sky map)
and day (green on the sky map).
For TheSky6,
List of Tricks for TheSky
shows you how to get the horizon
marked on TheSky6
sky map
including the one in
Mercator projection.
Another way to find the approximate
horizon is to make use of a
planisphere
(see the figure below:
local link /
general link: planisphere.html)
Set a planisphere
for today's date at 9:00 pm
(see Date & Time as needed).
The sky above our horizon
is approximately seen in the oval window.
The window border marks our horizon
approximately.
Locate the
horizon by finding what
constellations
the window border crosses or goes between and then use that information
to locate the
horizon
on sky maps.
Goodnight all.
Keywords:
Keywords:
Bayer designation,
bright stars,
celestial globe,
celestial meridian
(AKA the meridian),
celestial sphere,
constellations,
equatorial coordinate system
(AKA celestial coordinates),
declination (Dec),
horizon,
list of brightest stars,
list of constellations,
meridian,
Milky Way,
nadir,
planisphere,
Polaris,
right ascension (RA),
sky map,
TheSky
(TheSky6,
TheSkyX,
List of Tricks for TheSky,
TheSky Orientation),
transit,
zenith,
zodiac,
zodiac constellations.
Task Master:
EOF
Note there are orientations for both
TheSkyX
(TheSkyX Orientation: under construction)
and TheSky6
(TheSky6 Orientation).
There is also a
a href="/~jeffery/course/c_astlab/000_thesky.html">List of Tricks for TheSky
With TheSkyX,
there is NO need to set the date and time.
With TheSky6 there is:
go Toolbar/Data/Time
and set to today's date and time: see
Date & Time.
RMI Qualification:
Since the TheSky
is NOT available, you will have to use
Your Sky
sky maps:
the Jan01 sky map
for the winter
night sky
and
the Jul01 sky map
for the summer
night sky.
Constellation Tables
_________________________________________________________________________________________
_________________________________________________________________________________________
Table: North Polar Sky Constellations
_________________________________________________________________________________________
Constellation Observed Location in Sky Why Not Observed?
(Done in observations
task below)
_________________________________________________________________________________________
Camelopardalis, CAM
Cassiopeia, CAS
Cepheus, CEP
Draco, DRA
Perseus, PER
Ursa Major, UMA
Ursa Minor, UMI
_________________________________________________________________________________________
_________________________________________________________________________________________
Table: Summer Sky Constellations
_________________________________________________________________________________________
Constellation Observed Location in Sky Why Not Observed?
(Done in observations
task below)
_________________________________________________________________________________________
Aquila, AQL
Bootes, BOO
Corona Borealis, CRB
Cygnus, CYG
Draco, DRA
Hercules
Lyra, LYR
Ophiuchus, OPH
Pegasus, PEG
Sagittarius, SGR
Scorpius, SCO
Virgo, VIR
_________________________________________________________________________________________
_________________________________________________________________________________________
Table: Winter Sky Constellations
_________________________________________________________________________________________
Constellation Observed Location in Sky Why Not Observed?
(Done in observations
task below)
_________________________________________________________________________________________
Andromeda, AND
Auriga, AUR
Canis Major, CMA
Canis Minor, CMI
Gemini, GEM
Leo, LEO
Orion, ORI
Perseus, PER
Taurus, TAU
Ursa Major, UMA
_________________________________________________________________________________________
End of Task
Nota bene:
Some bright stars
will appear on 2 sky maps:
the polar sky map
and one of the other
2 sky maps.
Label such bright stars
on both sky maps they appear on.
Click on the name of the
bright star
to see a sky map
locating it in its parent constellation.
The column "Observed Today" is filled in in
Task 4: Bright Star Observations when
you are outside observing.
____________________________________________________________________________________________________________
Table: Bright Stars
____________________________________________________________________________________________________________
Bright Star Bayer RA DEC Transit Above Horizon Observed Why Not Observed?
Desig- (h m) (deg Time at 9:00 pm Today
tion arcmin) Today (Y/N)
(Y/N)
____________________________________________________________________________________________________________
Aldebaran α TAU 4h 36m +16°31'
Algol
Altair
Antares
Arcturus
Betelgeuse
Capella
Castor
Deneb
Polaris
Pollux
Procyon
Regulus
Rigel
Sirius
Spica
Vega
____________________________________________________________________________________________________________
End of Task
RMI Qualification: If you do NOT have a
printer,
you will have to hand sketch the maps in sufficient
detail for your own use.
Of course, neither
the Big Dipper
nor Cassiopeia
may be observable in which this task CANNOT be done.
_______________________________________________________________________
Table: Big Dipper Stars
_______________________________________________________________________
Star Apparent Brightness Order
_______________________________________________________________________
Alioth (ε UMA)
Alkaid (η UMA)
Dubhe (α UMA)
Megrez (δ UMA)
Merak (β UMA)
Mizar (Mizar-Alcor system)
Phecda (γ UMA)
_______________________________________________________________________
_______________________________________________________________________
Table: Cassiopeia Stars
_______________________________________________________________________
Star Apparent Brightness Order
_______________________________________________________________________
α CAS (Schedar)
β CAS (Caph)
γ CAS (Tsih, Navi)
δ CAS (Ksora, Ruchbah)
ε CAS (Segin)
η CAS (Achird)
_______________________________________________________________________
The south celestial pole (SCP) is the southern
counterpart to the NCP.
It is best to do the tasks below before observations, but that may NOT be possible.
End of Task
Stars
in a given constellation
are labeled by small Greek letters
roughly in order of decreasing
apparent brightness in the visible
followed by the
constellation name
in abbreviation (by the most of us)
or
in the Latin
genitive case
(by those who are Latin
devils).
For an example of a star
with a Bayer designation
consider
Mizar in
Ursa Major.
It is also
ζ UMA
(as shown in the sky map above).
The ζ
(spelt out and vocalized zeta) means that
Mizar (AKA ζ UMA) is
about the 6th apparent brighest star in the
constellation.
Precise positional observations of
astronomical objects
transiting
(i.e., crossing) the meridian
are very easy to make.
You should have already set the date and time for
TheSky6
if you are using TheSky6.
If NOT, go Toolbar/Data/Time
and set to today's date (see Date & Time if needed)
and to time 9:00 pm (unless the
instructor
says use another time) using the buttons.
The columns "Observed Today" and "Why Not Observed?" should be filled out in
Task 4: Bright Star Observations during the observations.
Post mortem comments that may often apply specifically to
Lab 1: Constellations: