Download Lab 7

Astronomy 115
Name:
Lab 7: Building and expanding model of nearby space
Outcomes:
• Build a three-dimensional model of the Sun’s stellar neighbors
• Find databases for obtaining stellar information
• Verify that the information on the model is correct
• Add some new information to the model
Introduction: By looking at an apparently flat background of stars at night or at a
star chart printed on a page, we often forget about the three-dimensional nature
of the universe.
In this exercise, you will construct (with welding rods and Styrofoam balls) a
model of nearby space including many of the nearest stars. Of course, you will
need information on where to place the stars accurately; you will need a
coordinate system to specify the position of an object in space.
Astronomers use the right ascension (RA) to determine the position
along the celestial equator of an object (think of it as sort of a space longitude).
By tradition, the RA is measured counterclockwise in units of hours and minutes,
starting at 0 hours and coming back, after one full circle, to 24 hours. To
determine the angle above or below the celestial equator you will need the
declination (think of this as a space latitude). The declination runs from -90°
(celestial south pole) to +90° (celestial north pole). Both of these coordinates are
laminated to the metal pole bases.
In addition, the stars have been colored according to their spectral
classes; blue balls represent O, B and A type stars; yellow represent F and G
type; orange represents K type and red represents M type. Finally, there are
red giants as well as white dwarf stars (they have a "d" in the star type).
You may also see a luminosity class associated with the stars; main
sequence stars, like the Sun, are class V, whereas supergiants are class IA or IB.
Building the basic model
A. Select a base. We’ll start with the bases with labels printed in black. Note the
coordinates and note the name and stellar spectral type of the star. The Sun is set
up as an example.
B. Using the spectral type, select the appropriate Styrofoam ball (or balls
connected by toothpicks, if you've selected a multiple star system). Remember,
size is a factor, too.
C. Using a scale of 5 centimeters = 1 light year, spindle the ball(s) on a welding
rod. Place the base at the appropriate RA and then adjust the distance and the
ball's height to achieve the correct distance and declination (you have to do these
two together, so a lot of fiddling will be required).
D. Repeat steps A to C for the remaining bases.
The following is to be answered using only the black-label stars.
1. Is there an exaggeration of scale between the diameters of the stars and the
distances between stars?
2. What is the scale of this exaggeration? Use the Sun for your calculation; it is 1.4
million kilometers wide. One light year is 9.5 × 1012 km.
3. If we keep the scale given of the distances between stars (5 cm = 1 ly), what
diameter should the Sun actually be? What object can be used to model the Sun,
in that case?
4. Okay, now to the model itself. Given that the Milky Way (the galaxy in which
these stars reside) is thought to be shaped as flattened disk, is this evident from
the model (in other words, do the stars bunch up along the celestial equator)?
What does this imply about the true thickness of our galaxy?
5. Given that the Milky Way is also thought to be a spiral-armed galaxy, is
there any evidence of these "arms" in the model (in other words, do the model's
stars seem to define an "arm")? What does this imply about the true width of our
spiral arms?
6. How long would it take a message (radio, TV or any other EM wavelength) to
reach the furthest star on this model and return to us? What year would the
message needed to have left earth in order for a reply to reach us today (2013)?
7. The nearest 25 star systems could be contained in a sphere of about how many
light years’ radius? What is the volume of this sphere (in cubic light-years)?
Calculate the stellar density in stars per cubic light year.
Adding on to the basic model
E. Now place the red-label stars onto the model, using the same scale and
procedure as the black-label stars.
8. According to the Observer’s Handbook 2008 (page 236), 85% of all stars are in
binary or multiple systems. Of course, this is a value calculated in the 1700s.
Check the model and calculate the percentage of stars in multiple-star
systems. For this calculation you will need to count stars (even ones in multiplestar systems) separately.
9. So is model consistent with the Handbook? Suggest a reason that this 1700s
value might be off. Hint: what might not have been as visible in the 1700s?
10. How many Sun-like stars (remember, even if it's in the same spectral class as
the Sun, it can't be part of a multiple-star system — except under certain
circumstances!) are there on this model? What percentage of all the stars in the
model are Sun-like?
11. According to the most recent research, 10% of the stars in the Milky Way are
spectral class G. Is this consistent with the model? Is our local space unusual, in
terms of stellar class distribution?
12. The red-label stars are the next nearest 25 star systems; how many more light
years is the model extended outward? How much more volume of space (in cubic
light-years) does this extra spherical shell occupy? Calculate the stellar density
in stars per cubic light year of this spherical shell.
13. Comparing the stellar densities in questions 7 and 12, what conclusion can
you draw about the Sun and its position inside the Milky Way galaxy; for
instance, does the Sun seem to occupy a relatively less densely or more densely
populated patch of space?
14. The Local Bubble is an area of space, a rough sphere (it’s more of an
hourglass shape) about 500 ly in diameter, which is the result of a supernova that
occurred a few million years ago that “blew away” particles of the interstellar
medium within the Bubble. The lack of what class(es) of star within the model
seems to confirm the existence of the Local Bubble? Why is the lack of that class
of star important for this story (hint: star age)?
Checking the model by accessing stellar databases, and adding some
information
F. Form teams of three or four. Each team will be assigned a sector of the model:
Team 1’s sector includes all stars from RA 0 to 6 hr and dec 0° to +90°
Team 2’s sector includes all stars from RA 6 to 12 hr and dec 0° to +90°
Team 3’s sector includes all stars from RA 12 to 18 hr and dec 0° to +90°
Team 4’s sector includes all stars from RA 18 to 24 hr and dec 0° to +90°
Team 5’s sector includes all stars from RA 0 to 6 hr and dec 0° to –90°
Team 6’s sector includes all stars from RA 6 to 12 hr and dec 0° to –90°
Team 7’s sector includes all stars from RA 12 to 18 hr and dec 0° to –90°
Team 8’s sector includes all stars from RA 18 to 24 hr and dec 0° to –90°
G. Over the weekend, find a recently updated (within the last three years) web
database (or printed database) that contains information about all stars within
about 25 ly of the Sun (they’re usually called “Nearby Star” catalogs). As an
example, the University of Arecibo in Puerto Rico’s Planetary Habitability
Laboratory has a catalog of stars within 10 pc of the Sun
(http://phl.upr.edu/projects/nearby-stars-catalog).
Attached is my list of the 50 or so nearest stars to the Sun, along with their
RA/dec coordinates and stellar spectral type information. The ones in black are
the nearest 25 star systems. The ones in red (which will look medium gray in a
black-and-white printout) are the 25 next furthest star systems.
Note that the luminosity class is missing from each of these entries.
H. Your team’s goal, then, is to update the attached list for your sector:
• to confirm that the nearest star systems I’ve listed are, in fact, the nearest star
systems, and that a) the RA/dec coordinates are more or less correct, b) the
number of stars in the system is correct, c) the distance to the star system
is more or less correct and d) the spectral class(es) is (are) more or less
correct. Update any incorrect information.
• to add the luminosity class of each star. Write this on the list of star systems
that are attached.
• finally, to add more star systems to the model: the current list has only what I
thought were the nearest 50 star systems. For your sector, find the next 10
furthest star systems and write down all the relevant information: name of
the star system, RA/dec coordinates, number of stars and their spectral and
luminosity classes, and the distance (in ly) to the star system. Write this on the
table form that is attached.
Updating the model
In the next class meeting, you will use your newly updated information to update
the model. You may need to change positions, distances, number of stars and so
forth, so there will be sticky notes to allow you to alter the information on the
laminated bases of each star system. You may also have to change the type of star,
and there will be other types of Styrofoam balls available.
As a class, we’ll get a list of the next furthest 25 star systems, so we’ll end up using
some or all of the individual team lists. I will have some blank bases for you to
add these next furthest star systems.
15. What is the name of the star system furthest from the Sun on this model?
How far away is it (in light years)?
16. The Voyager 1 probe, after it completed its “grand tour” of the planets in
1989, was programmed to leave the solar system with whatever fuel it had left on
board. This, and the gravitational assists from the planets, increased its speed to
39000 miles per hour, the fastest speed ever achieved by a human-built vehicle.
That speed is equal to 5.77 × 10-5 light-years/year (remember that light year is a
distance).
How long (in years) will Voyager 1 take in reaching this furthest star system?
Show the calculation below.
17. Are there any recognizable patterns emerging in the distribution of stars yet
(such as spiral arms, flatness of disk, etc.)?
The list of nearby star systems in the current model
Sun Type G2
Proxima Centauri, Alpha Centauri A&B
RA 14.5 h
Dec. -62°
d = 4.4 ly
Type M5, G2, K0
Barnard's Star
RA 18 h
Dec. +4.5°
d = 6.0 ly
Type M5
Wolf 359
RA 11 h
Dec. +7°
d = 7.7 ly
Type M4
Lalande 21185
RA 11 h
Dec. +36°
d = 8.3 ly
Type M2
Sirius A&B
RA 6.5 h
Dec. -16.5°
d = 8.6 ly
Type A1, dA
d = 8.7 ly
Type M6, M6
Luyten 726-8 A&B
RA 1.5 h
Dec. -18°
Ross 154
RA 19 h
d = 9.7 ly
Type M4
d = 10.3 ly
Type M6
Epsilon Eridani
RA 3.5 h
Dec. -9.5°
d = 10.5 ly
Type K2
Lacaille 9352
RA 23 h
Dec. -36°
d = 10.7 ly
Type M2
Ross 128
RA 12 h
Dec. +1°
d = 10.9 ly
Type M4
EZ Aquarii A, B & C
RA 22.5 h
Dec. -15.5°
d = 11.3 ly
Type M5, M6, M7
61 Cygni A&B
RA 21 h
Dec. +38.5°
d = 11.4 ly
Type K5, K7
Procyon A&B
RA 7.5 h
Dec. +5.5°
d = 11.4 ly
Type F5, dA
Gliese 725 A&B
RA 18.5 h
Dec. +59.5°
d = 11.5 ly
Type M4, M4
Groombridge 34 A&B
RA 0 h
Dec. +44°
d = 11.6 ly
Type M1, M4
Epsilon Indi
RA 22 h
Dec. -57°
d = 11.8 ly
Type K5
DX Cancri
RA 8.5 h
Dec +27°
d = 11.8 ly
Type M6
Tau Ceti
RA 2 h
Dec. -16°
d = 11.9 ly
Type G8
Gliese–Jahreiss 1061
RA 3.5 h
Dec. -44.5°
d = 12.1 ly
Type M5
Luyten 725-32
RA 1 h
Dec. -17°
d = 12.0 ly
Type M5
Luyten’s Star
RA 7.5 h
Dec. +5°
d = 12.4 ly
Type M4
Ross 248
RA 23.5 h
Dec. -24°
Dec. +44°
Teegarden’s Star
RA 3 h
Dec. +17°
d = 12.6 ly
Type M7
Kapteyn's Star
RA 5 h
Dec. -45°
d = 12.8 ly
Type M1
SCR 1845
RA 19 h
Dec. –64°
d = 12.8 ly
Type M9
Lacaille 8760
RA 21 h
Dec. -39°
d = 12.9 ly
Type M0
Kruger 60 A&B
RA 22.5 h
Dec. +58°
d = 13.1 ly
Type M3, M5
DENIS 1048–3956
RA 11 h
Dec. –40°
d = 13.1 ly
Type M9
Ross 614 A & B
RA 6.5 h
Dec. –3°
d = 13.3 ly
Type M4, M9
Wolf 1061
RA 16.5 h
Dec. –12.5°
d= 13.9 ly
Type M3
Wolf 424 A & B
RA 12.5 h
Dec. +9°
d = 14.3 ly
Type M5, M7
Gliese 1
RA 0 h
Dec. –37°
d = 14.2 ly
Type M3
van Maanen’s Star
RA 1 h
Dec. +5.5°
d = 14.4 ly
Type dZ
Luyten 1159-16
RA 2 h
Dec. +13°
d = 14.5 ly
Type M6
LHS 288
RA 11 h
Dec. –61°
d = 14.6 ly
Type M5
LHS 292
RA 11 h
Dec. –11.5°
d = 14.8 ly
Type M7
BD +68°946
RA 17.5 h
Dec. +68°
d = 14.8 ly
Type M3
CD –46°11540
RA 17.5 h
Dec. –47°
d = 14.8 ly
Type M3
Luyten 145-141
RA 12 h
Dec. –64.5°
d = 15.1 ly
Type dQ
Gliese 158-27
RA 0 h
Dec. –7.5°
d = 15.3 ly
Type M6
Ross 780
RA 23 h
Dec. –14°
d = 15.3 ly
Type M5
Gliese 208-44 A, B & C
RA 20 h
Dec. +44.5°
d = 15.3 ly
Type M5, M6, M8
Lalande 21258 A&B
RA 11 h
Dec. +43.5°
d = 15.8 ly
Type M2, M6
Groombridge 1618
RA 10 h
Dec. +49.5°
d = 15.9 ly
Type K7
BD +20°2465
RA 10.5 h
Dec. +20°
d = 16.0 ly
Type M3
CD –44°13515
RA 21.5 h
Dec. –49°
d = 16.1 ly
Type M2
CD –44°11909
RA 17.5 h
Dec. –44°
d = 16.4 ly
Type M4
40 Eridani A,B & C
RA 4 h
Dec. –8°
d = 16.4 ly
Type K1, dA, M4
BD +43°4305
RA 23 h
d = 16.5 ly
Type M4
70 Ophiuchus A & B
RA 18 h
Dec. +2.5°
d = 16.6 ly
Type K0, K5
Altair
RA 20 h
d = 16.8 ly
Type A7
Dec. +44.5°
Dec. +9°