Astronomy 305 Exam Topics Exam I – Star Charts Exam II –Coordinate Systems and Telescopes Exam III – Planets, Comets and Asteroids Exam IV – Stars.

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?