What is a Coordinate System?

• The Cartesian Coordinate System you have seen in Math Class
• X-axis, Y-axis, Z-axis (x,y,z)
• Tells you where something is located
• Universal, language independent
• Other Coordinate Systems exist:
• Polar
• Spherical
• Curvilinear

Latitude and Longitude

(Lat, Lon)

To the left

• Based on Great Circles
• ‘E’ is center of the sphere
• CDE is a Great Circle
• AB is a small circle
• P is the Zenith (North Pole)

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To the right

• Lat/Lon are Great Circles
• Starting from the Equator, N/S are Latitude
• Starting from Greenwich, England, E/W are Longitude

Celestial Coordinate Systems

• Locate objects in space
• Many different Coordinate Systems exist based on equator location and purpose
• Assume fixed Earth and rotating sky
• Are somewhat analogous to Lat/Lon

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Types of Celestial Coordinate Systems:

• Horizontal Coordinate System
• Equatorial Coordinate System
• Ecliptic Coordinate System
• Galactic Coordinate System
• SuperGalactic Coordinate System

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Horizontal Coordinate System

• Based on the Observer (you)
• The ‘Equator’ is the Horizon
• Straight up from you is the Zenith
• Meridian is where you are facing
• Lat Coor. are measured from the Horizon and are called Altitude
• Lon Coor. are measured from ‘Meridian’ and are called Azimuth
• Primary use: Star-Gazing

Equatorial Coordinate System

• Based on the Earth’s Equator (Geocentric)

or Sun’s Equator (Heliocentric)

• The Zenith is the North Rotational Pole (Axis)
• Meridian is pointed towards Vernal Equinox at a specific time (J2000.0, B1950.0)
• Lat Coor. are measured from the Equator and are called Declination (Dec)
• Lon Coor. are measured from the Meridian and are call Right Ascension (RA)
• Primary use: Astronomy

Equatorial Coordinate System

Ecliptic Coordinate System

• Based on the Ecliptic Plane centered at either the Earth (geocentric) or Sun (heliocentric)
• Zenith is the Ecliptic pole (rotational axis of the Earth-sun system)
• Meridian is pointed towards Vernal Equinox at a specific time (J2000.0, B1950.0)
• Lat Coor. are measured from the Ecliptic Plane and are called Ecliptic Latitude
• Lon Coor. are measured from the Meridian and are call Ecliptic Longitude
• Primary use: Tracking the Zodiac

Galactic Coordinate System

• Based on the Sun as it sits in the Galactic Plane
• Zenith is based on height from the Galactic Plane as seen from Earth
• Meridian points from the Sun to the Galactic Center
• Lat Coor. are measured from the Galactic Plane and are called Galactic Latitude
• Lon Coor. are measured from the Meridian and are call Galactic Longitude
• Primary Use: Astronomy

SuperGalactic Coordinate System

• Based on the Galactic Center
• Zenith is based on height from the Galactic Plane as seen from Earth
• Meridian points from the Sun to the Galactic Center
• Lat Coor. are measured from the SuperGalactic Plane and are called SuperGalactic Latitude
• Lon Coor. are measured from the Galactic/SuperGalactic Intersection and are call Galactic Longitude
• Primary Use: Galaxies and Clusters

HAWC Significance Maps Race Calculations

RA can be written as Hours (HRS), minutes (min) and seconds (s) but can also be written as a Decimal. To convert from HRS, min, s to a Decimal use the following equation:

(HRS +(min/60)+(s/3600))x 15

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For example the Crab Nebula has a RA of 5 HRS 34 min 32 s

The conversion looks like:

(5+(34/60)+(32/3600))x15 = 83.63

HAWC Significance Maps Race Calculations

Declination (Dec) is the degree along the celestial sphere where the celestial equator is zero and the celestial pole is 90 degrees in the Northern Hemisphere. In the Southern Hemisphere the degrees go from zero to -90 degrees.

Dec can be written as degrees (°) minutes (‘) and seconds (“) or as a Decimal. To convert from Degrees, minutes, seconds to Decimal use the following equation:

(Degree + (minute/60)+ (seconds/3600)

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For example, the Crab Nebula has a Dec of 22° 0’ 52”

The conversion looks like:

(22+(0/60)+(52/3600))= 22.01