Add catalog of "Points of special interest"

[apos]

There are a lot for the category "special points of interest" for observation or e.g. aligning a telescope or just show "where things are".
Some of them need to be calculated, because they are "dynamic" ...

Fixed positions

• NCP, SCP
• Galactic Centre (Sagittarius)
• Zodiacal Constellations along the Ecliptic or the Constellations as such
• BIg structures (center of) like "Virgo Cluster"

Dynamic calculated

• Zenith
• Cardinal Points -> Horizon -> North, East, West, South
• Point where Meridian and Dec 0 (celestial equator) meet - important to understand RA/DEC system (also for the Scheiner Method or other polar alignment methods)
• Point where Ecliptic an Meridian meet, Ecliptic starts / end at the horizon
• or something exotic: Vernal and autumn Equinox

Star hopping

• One could also think about a "Star-Hopping" guide, so people learn how to star hop. ... (scripted).
  PiFinder gets a list of Stars, which then, once reached, will automatically lead to the next star until the final object is reached.
  Would be a cool feature ...

[apos]

Fixed Positions (RA, DEC)

North Celestial Pole (NCP):
    RA: 00h 00m 00s (or 0h)
    DEC: +90° 00' 00" (or +90°)

South Celestial Pole (SCP):
    RA: 00h 00m 00s (or 0h)
    DEC: -90° 00' 00" (or -90°)

Galactic Center (Sagittarius A):*
    RA: 17h 45m 40.04s
    DEC: -29° 00' 28.1"

Zodiacal Constellations (Approximate Centers):
    Aries: RA 02h 30m, DEC +20°
    Taurus: RA 04h 30m, DEC +18°
    Gemini: RA 07h 00m, DEC +22°
    Cancer: RA 08h 30m, DEC +20°
    Leo: RA 10h 30m, DEC +15°
    Virgo: RA 13h 20m, DEC -05°
    Libra: RA 15h 15m, DEC -15°
    Scorpius: RA 16h 45m, DEC -30°
    Sagittarius: RA 19h 00m, DEC -25°
    Capricornus: RA 21h 00m, DEC -20°
    Aquarius: RA 22h 30m, DEC -10°
    Pisces: RA 00h 30m, DEC +10°

Virgo Cluster (Center):
    RA: 12h 28m
    DEC: +12° 40'

[apos]

Gemini tells me: "Please give me the locations in RA and DEC for the following fixed positions. Also show me how to calculate in Python the dynamic postitions: [...] TEXT FROM FIRST THREAD HERE"

Dynamic Positions (Python with astropy)

We'll use the astropy library, a powerful tool for astronomical calculations in Python.
Python

from astropy.time import Time
from astropy.coordinates import EarthLocation, AltAz, SkyCoord, get_body
import astropy.units as u

# Define your location (e.g., Heidelberg)
location = EarthLocation(lat=49.4478 * u.deg, lon=8.6833 * u.deg, height=114 * u.m)

# Define the current time
time = Time.now()

# Function to convert AltAz to RA/DEC
def altaz_to_radec(alt, az, location, time):
    altaz = AltAz(alt=alt, az=az, location=location, obstime=time)
    radec = altaz.transform_to(SkyCoord('icrs'))
    return radec

# 1. Zenith
zenith_altaz = AltAz(alt=90 * u.deg, az=0 * u.deg, location=location, obstime=time)
zenith_radec = zenith_altaz.transform_to(SkyCoord('icrs'))
print(f"Zenith (RA, DEC): {zenith_radec.ra}, {zenith_radec.dec}")

# 2. Cardinal Points (Horizon)
horizon_north = altaz_to_radec(alt=0 * u.deg, az=0 * u.deg, location=location, time=time)
horizon_east = altaz_to_radec(alt=0 * u.deg, az=90 * u.deg, location=location, time=time)
horizon_south = altaz_to_radec(alt=0 * u.deg, az=180 * u.deg, location=location, time=time)
horizon_west = altaz_to_radec(alt=0 * u.deg, az=270 * u.deg, location=location, time=time)

print(f"Horizon North (RA, DEC): {horizon_north.ra}, {horizon_north.dec}")
print(f"Horizon East (RA, DEC): {horizon_east.ra}, {horizon_east.dec}")
print(f"Horizon South (RA, DEC): {horizon_south.ra}, {horizon_south.dec}")
print(f"Horizon West (RA, DEC): {horizon_west.ra}, {horizon_west.dec}")

# 3. Meridian and Celestial Equator Intersection
meridian_equator_altaz = AltAz(alt=(90 * u.deg - location.lat), az=180 * u.deg, location=location, obstime=time)
meridian_equator_radec = meridian_equator_altaz.transform_to(SkyCoord('icrs'))
print(f"Meridian/Equator Intersection (RA, DEC): {meridian_equator_radec.ra}, {meridian_equator_radec.dec}")

# 4. Ecliptic and Meridian Intersection (requires more complex calculation)
from astropy.coordinates import get_body_barycentric_posvel
from astropy.coordinates import get_body_barycentric

sun = get_body('sun', time)
sun_earth = get_body_barycentric('earth', time)
earth_sun = get_body_barycentric('sun', time)
ecliptic_coord = SkyCoord(earth_sun, frame='heliocentrictrueecliptic', representation_type='cartesian')
ecliptic_coord_geocentric = ecliptic_coord.transform_to('icrs')

#Find the altaz coordinates of the sun
sun_altaz = SkyCoord(ecliptic_coord_geocentric.ra, ecliptic_coord_geocentric.dec, frame='icrs').transform_to(AltAz(location=location, obstime=time))

#This is a simplified method. A proper calculation requires finding the intersection of the ecliptic plane with the meridian.
print(f"Sun altaz (alt, az): {sun_altaz.alt}, {sun_altaz.az}")

# 5. Vernal and Autumnal Equinox
vernal_equinox = SkyCoord(ra=0 * u.hourangle, dec=0 * u.deg)
autumnal_equinox = SkyCoord(ra=12 * u.hourangle, dec=0 * u.deg)

print(f"Vernal Equinox (RA, DEC): {vernal_equinox.ra}, {vernal_equinox.dec}")
print(f"Autumnal Equinox (RA, DEC): {autumnal_equinox.ra}, {autumnal_equinox.dec}")

Explanation:

• astropy: This library handles coordinate transformations, time calculations, and location information.
• EarthLocation: Defines the observer's location on Earth.
• Time.now(): Gets the current time.
• AltAz: Represents coordinates in altitude and azimuth.
• SkyCoord: Represents coordinates in various celestial systems (ICRS, AltAz, etc.).
• Coordinate Transformations: astropy allows easy conversion between coordinate systems (e.g., AltAz to RA/DEC).
• Cardinal Points: The cardinal points' RA/DEC values change with time and location.
• Meridian/Equator Intersection: The altitude of this point is (90° - latitude).
• Ecliptic/Meridian Intersection: This requires more complex plane intersection calculations. The provided example uses the suns coordinates as a close aproximation.
• Equinoxes: The equinoxes are points where the Sun crosses the celestial equator.

Important Notes:

The dynamic calculations change with time and location.

The Ecliptic/Meridian calculation is simplified. For very high accuracy, the ecliptic plane must be calculated and the intersection with the meridian must be found.

The Astropy library is very powerful, and can be used for many other astronomical calculations.