Astro101103 section 5 Lec 2

1
Astro101/103 section 5Lec 2
2
Equatorial coords.

• Right Ascension (RA)
• Equivalent to longitude
• Measured in hours (24 hrs 360 degree
• or 1hr 15
  degree)
• increase from west to east
• zero point is spring equinox (around Pisces)

3
Equatorial coords.

• Declination (Dec)
• Equivalent to latitude
• Measured in degrees
• zero point on the celestial equator
• North pole 90 deg. South pole -90 deg

4
Equatorial coords.

• The coordinate system is fixed on the celestial
  sphere
• The coordinates of stars and constellations dont
  change
• The coordinates of the Sun do change (why?)

5
RA

• Reference date
• RA of the star on the meridian (transit) at
  midnight
• Sep. 21 gt 0 hr
• Dec. 21 gt 6 hr
• Mar. 21 gt 12 hr
• June 21 gt 18 hr
• RA of the Sun on the meridian (at noon, of
  course)
• Sep. 21 gt 12 hr
• Dec. 21 gt 18 hr
• Mar. 21 gt 0 hr
• June 21 gt 6 hr

6
RA

• A star on the east has larger RA.
• large RA -gt East
• small RA -gt West
• During one night, larger RA transits later.

7
Visibility of stars

• Invisible at certain time of the year
• --RA close to the Sun
• --Outshined by the sunlight
• --Wait for a different time

8
Equatorial coords.
9
Visibility of stars

• Invisible at certain location on the Earth
• --Dec is smaller than -(90 your latitude)
• --Blocked by your horizon, never rises
• --move to a different location

10
The Night sky
Horizon
Meridian
11
Acceleration

• The change rate of velocity
• velocity VS speed
• velocity speed direction
• Fma

12
Acceleration

• The acceleration of gravity on Earth is
  approximately 10 m/s2 (more precisely, 9.8
  m/s2). If you drop a rock from a tall building,
  about how fast will it be falling after 3
  seconds?
• A. 10 m/s B. 30 m/s2 C. 30 m/s D. 20 m/s E. 10
  m/s2

13
Acceleration

• The acceleration of gravity on Earth is
  approximately 10 m/s2 (more precisely, 9.8
  m/s2). If you drop a rock from a tall building,
  about how fast will it be falling after 3
  seconds?
• A. 10 m/s B. 30 m/s2 C. 30 m/s D. 20 m/s E. 10
  m/s2