Astronomy 305 Exam Topics
Exam I – Star Charts
Exam II –Coordinate Systems and Telescopes
Exam III – Planets, Comets and Asteroids
Exam IV – Stars and Deep Sky Objects
Coordinate Systems
17 - Horizontal Coordinates 18 - Equatorial Coordinates 19 - Ecliptic Coordinates 20 - Galactic Coordinates 21 - Converting decimal degrees to °, ’, ” 22 - Converting Degrees to Hours 23 - Converting between Coordinate Systems 24 - Converting Right Ascension to Hour Angle 25 – Equatorial to Horizontal Coordinate Conversation
Celestial Coordinate Systems
These are coordinate systems with two angular measurements:
• Geographical
• Horizontal
• Equatorial
• Ecliptic
• Galactic
Geographical System
Latitude () –the angle of a city above the
equator
Longitude (L)–the angle around the equator from
the Prime Meridian
17 - Horizontal System
Altitude (a) –the angle of a star above the
horizonAzimuth (A)
–the angle around the horizon from the north point; measured eastward
18 - Equatorial System
Declination () Right Ascension ()Hour Angle (H)
– the difference between the right ascension of your meridian and the right ascension an object
24 – Converting between and H
LST = Local Sidereal Time– LST is the same as the right ascension of the
meridian on your star chartsH = LST – Examples:
– What is the hour angle of Regulus at 11:00 PM tonight?
– What is the hour angle of Sirius at 8:00PM tonight?
H O R I Z O N
S
Celestial Equator
Celestial Meridian
H
90°-
H O R I Z O N
S
Celestial Equator
Celestial Meridian
90°-
19 - Ecliptic System
Ecliptic Latitude () – the angle of a star above the ecliptic
Ecliptic Longitude ()– the angle around the ecliptic from the vernal equinox
– measured eastward
– labeled along the ecliptic on the star charts
Obliquity ()– the angle between the ecliptic and the celestial equator
and is approximately 23.5 degrees
20 - Galactic System
Galactic Latitude (b) – the angle of a star above the galactic plane
Galactic Longitude (l)– the angle around the galactic plane – measured eastward from the galactic center
Examples Problem
For all of the planets find…– their ecliptic longitudes– the host constellation– their equatorial coordinates
Hint: Use Appendix 11
Planet Positions
Planet Constellation
MercuryVenusMarsJupiterSaturnUranus
Planet Positions
Planet Visible? Rise Time Set Time
MercuryVenusMarsJupiterSaturnUranus
Example Problems
Calculate the altitude and azimuth of Capella for 11:00PM tonight.
25 - Equatorial to Horizontal
Step 1Find , LST and H is decimal hours.
Step 2Convert H to degrees.
Step 3Convert to decimal degrees.
Step 4Find sin a = sin sin + cos cos cos H
Step 5Find a
Step 6Find
acoscos
asinsinsinAcos
Step 7Find A’
Step 8If sin H is negative, A = A’
If sin H is positive, A = 360° – A’
Step 9Find a and A in degrees, minutes and seconds.
acoscos
asinsinsinAcos
More Examples
What are the coordinates of Jupiter on May 5, 2005 at 8:00PM?
LST H a A
Reading Assignment
Chapter 2– A Tour of the Sky
Chapter 3– The Monthly Sky Maps
Chapter 16– Telescopes and Binoculars
More Examples
What are the coordinates of Venus tonight at 7:00pm? LST H a A
25 - Equatorial to Horizontal
Step 1Find , LST and H is decimal hours.
Step 2Convert H to degrees.
Step 3Convert to decimal degrees.
Step 4Find sin a = sin sin + cos cos cos H
Step 5Find a
Step 6Find
acoscos
asinsinsinAcos
Step 7Find A’
Step 8If sin H is negative, A = A’
If sin H is positive, A = 360° – A’
Step 9Find a and A in degrees, minutes and seconds.
acoscos
asinsinsinAcos
More Examples
Suppose that the Moon occults the star Antares on Feb 6th. Find the following for the Moon:
Ecliptic Coordinates
Step 1Find and .
Step 2Find and in decimal degrees.
Step 3Find sin= sin cos – cos sin sin
Step 4Find
Step 5Find y = sin cos + tan sin
Step 6Find x = cos
Step 7Find
x
ytan' 1
More Examples
On what day does Vega cross the meridian at 8:00 PM?
What is the maximum altitude of the Sun for today in Nacogdoches?
At approximately what time does the Sun cross the meridian today?
What is the maximum altitude of the Sun over one year?