I have been trying to create a graph which shows the distances between the stars and the earth, yet I could not obtain the desired graph as seen below (click to zoom in):
My graph:
As @uhoh suggested, I overlaid one graph on top of the other.
I apologize for posting this confusing graph
The combined graph denotes that the positions of the curves in my graph totally differ from those in the expected graph.
I followed this guide to calculate the position functions of the stars.
My Question: Did I made any mistakes that resulted in the anomalies?
Thanks in advance.
Annotations for the Code:
Name - Name of the star
RA - Right Ascension in degrees, ICRS coord. (J2000)
Dec - Declination in degrees, ICRS coord. (J2000)
pm_mRA - Proper motion in right ascension, in miliarcseconds per year
pm_mdec - Proper motion in declination, in miliarcseconds per year
vr - radial velocity in kilometers per second, a positive value means that the star is moving away from us
mparallax - parallax of the star in miliarcseconds
d - distance between the star and the earth
My Code:
def parseTextFile(file_name, delimiter=",", header=0):
""" Parse a text file to a list. The file contents are delimited and have a header. """
with open(file_name) as f:
# Skip the header
for i in range(header):
next(f)
data = []
# Parse file contents
for line in f:
# Remove the newline char
line = line.replace('\n', '').replace('\r', '')
# Split the line by the delimiter
line = line.split(delimiter)
# Strip whitespaces from individual entries in the line
for i, entry in enumerate(line):
line[i] = entry.strip()
# Add the contents of the line to the data list
data.append(line)
return data
fig = plt.figure()
ax = fig.add_subplot()
#time span
time = np.arange(-60000,100000,10)
count = 1
xdic = {}
ydic = {}
zdic = {}
#multiple lines of data
for star in parseTextFile(file_name, header=1):
name = str(star[0])
RA = float(star[1])
Dec = float(star[2])
pm_mRA = float(star[3])
pm_mDec = float(star[4])
vr = float(star[5])
mparallax = float(star[6])
pm_RA = pm_mRA * 0.001
pm_Dec = pm_mDec * 0.001
d = 1 / (mparallax * 0.001)
#Transverse velocities
vta = pm_RA * d * 4.740
vtd = pm_Dec * d * 4.740
#Linear velocities
vx = vr * np.cos(Dec) * np.cos(RA) - vta * np.sin(RA) - vtd * np.sin(Dec) * np.cos(RA)
vy = vr * np.cos(Dec) * np.sin(RA) + vta * np.cos(RA) - vtd * np.sin(Dec) * np.sin(RA)
vz = vr * np.sin(Dec) + vtd * np.cos(Dec)
#unit conversion from km/s to pc/year
vx_pcyr = vx / 977780
vy_pcyr = vy / 977780
vz_pcyr = vz / 977780
#initial positions
xi = d * np.cos(Dec) * np.cos(RA)
yi = d * np.cos(Dec) * np.sin(RA)
zi = d * np.sin(Dec)
#position functions
x = xi + vx_pcyr * time
y = yi + vy_pcyr * time
z = zi + vz_pcyr * time
distance = np.sqrt(x ** 2 + y ** 2 + z ** 2)
ax.plot(time,distance,label=name)
ax.set_xlabel('Time (Year)')
ax.set_ylabel('Distance (pc)')
ax.legend()
plt.show()
ax.set_ylim(0.0, 10.0)then save a copy with a transparent background withplt.savefig('mytransparentplot', transparent=True)and overlay it on the original (in powerpoint or any image manipulating tool) and stretch it and see if it overlays perfectly. Or print out some distances numerically and ask how to check those $\endgroup$