ASTR 310: Lecture 3
● First tutorial is this week ● Hennings 312, on third floor, DON'T BE LATE ● Go up main staircase (facing Barber), turn right.
● Mastering Astronomy review. ● Those first two were far longer than the average! ● we are 'caught up' now... ● Assignments 2 and 3 past due date now. ● Assignment 4 due 6 AM Wednesday ● only 5 pages of reading MasteringMastering AstronomyAstronomy feedbackfeedback MasteringMastering AstronomyAstronomy feedbackfeedback
2/3 got it wrong the first time MasteringMastering AstronomyAstronomy feedbackfeedback
Only 6 got it wrong first time Star trails, looking North
Taken from the northern United States A. circumpolar stars (which never set). B. you see the NCP C. you see Polaris
Right ascension and Declination
• Declination is from -90° S to +90° N. Easy. • Right Ascension (RA) run around celestial equator. RA=0 at spring equinox • (we'll come back to this) RA goes from zero hours to 24h, increasing east. Each hour divided into 60 minutes (min) of time and each min into 60 seconds. Remember ; Stars have FIXED RA and DEC !!! Where are the celestial pole and celestial equator located in your local sky?
• This is a VERY important concept • • Requires some three-dimensional thinking Paths of stars : View 1 An easy one first: The north pole. An easy one first: The north pole.
- What is the altitude of the NCP? - Where is the celestial equator? Next, from the Equator Next, from the Equator
• Are there any circumpolar stars? Next, from the Equator
• Are there any circumpolar stars? • Where does the celestial equator cut the local meridian? Star trails to South, from Kilimanjaro
• circumpolar stars near SCP also. • There is no star near the SCP. • Where can you see both celestial poles at the same time? Q: Where can you see both celestial poles at the same time? A) From the Earth's north pole B) From the Earth's south pole C) From anywhere on the equator D) From no place on Earth. Star trails to South, from Kilimanjaro
• careful...this is the SOUTH celestial pole Star trails to South, from Kilimanjaro
• careful...this is the SOUTH celestial pole • red line: local meridian • rotating clockwise because east is to the LEFT. Star trails to South, from Kilimanjaro
• careful...this is the SOUTH celestial pole • red line: local meridian • rotating clockwise W because east is to S the LEFT. Now, from the northern hemisphere Now, from the northern hemisphere
• In this example, latitude = 40° • How high is NCP above N horizon? • How high is celest. equator above S?
For an observer at 60 deg N latitude For an observer at 60 deg N latitude For an observer at 60 deg N latitude The stars rotate as a superb clock
●We could thus use SIDEREAL TIME
• The RA of stars on the meridian is called the local sidereal time. • One hour later, the RA of stars on the meridian goes up by 1 hour of RA. For an observer at 60 deg N latitude Facing south, watching the celestial sphere rotate, January in Vancouver (animated....see course web site) Why DON'T we use sidereal time ? Because we days tied to the SUN. • The Sun is NOT fixed The path of the Sun on the celestial sphere. = The Ecliptic It moves! • The path it appears to follow around the sky is called the ecliptic. • Ecliptic is tilted 23.5° to the celestial equator. • Definition of equinox : where Sun crosses the celestial equator • One problem: how do you see it? The Sun follows a well-defined path
OriginOrigin ofof time-keeping.time-keeping. Sun's apparent motion across the sky just caused by Earth's orbit. • Sun 'moves' in front of 12 constellations; the zodiac. TheThe Sun'sSun's movementmovement Because it moves N and S in declination.
ArcArc ofof thethe Sun'sSun's pathpath changeschanges eacheach day,day, withinwithin limitslimits
Sunrise/sunsetSunrise/sunset LocationLocation Although the angle of the celestial equator on each observer's local sky varies (depending on ______), ...
...on the equinoxes ALL observers on Earth see the Sun rise and set due East and West HomeworkHomework 11
Distributed in class
Print and do AS SOON AS POSSIBLE.