Register to reply

Connection between right ascension and time

Share this thread:
Wheelwalker
#1
Sep27-13, 09:04 PM
P: 36
I'm a physics major currently taking my first astro class. We're covering the basics at the moment but I am having trouble visualizing this question from our textbook. To preface this, I understand that declination is to the celestial sphere what latitude is to the Earth and RA is to the celestial sphere what longitude is to the earth. I also know that RA is measured from the vernal equinox. The problem references Hemingway's "The Old Man and the Sea" and describes a man in Cuba lay in his boat shortly after the sun set one September night and saw Rigel rising. I'm supposed to find what is incorrect about this. I'm fairly certain that Rigel wouldn't appear in the night sky until much later than the sun sets. Rigel's RA is 05h 14m. The longitude of Cuba (in a very general sense) is approximately 80 degrees west. But where do I go from here? Do I calculate how many hours away Cuba's longitude is from Rigel's RA? How do I factor in the time?
Phys.Org News Partner Astronomy news on Phys.org
Young binary star system may form planets with weird and wild orbits
Evidence of a local hot bubble carved by a supernova
Astronomers measure weight of galaxies, expansion of universe
Chronos
#2
Sep27-13, 09:35 PM
Sci Advisor
PF Gold
Chronos's Avatar
P: 9,386
You need to determine what 'clock' is used to define RA, and the clock used by the 'Old Man'. The rest is easy.
Wheelwalker
#3
Sep27-13, 09:44 PM
P: 36
So the 'clock' used to define RA is that 0h is at the vernal equinox, and goes up east from there. The clock used by the Old Man allow him to read the time at approximately sunset in Cuba in late September?

Philosophaie
#4
Oct7-13, 07:06 PM
P: 366
Connection between right ascension and time

There is time in the Hour Angle:
[tex]LMST = GMST + time + Longitude/15[/tex][tex]HA = LMST - RA[/tex]where LMST is Local Mean Sidereal Time in Hours. GMST is Greenwich Mean Sidereal time. The Sidereal Time above London, England. And time is in hours also.


Register to reply

Related Discussions
Connection between gravity time dilation and velocity. Special & General Relativity 0
Given Riemann & connection, does time variation nec'ly imply full spacetime metric? Special & General Relativity 2
Is time constant, for capacitors, changed by series/parallel connection? Introductory Physics Homework 1
Connection between fabric of space, max. speed (of light) and time dilation Special & General Relativity 3
UMC Time, Right Ascension and Longitude Astronomy & Astrophysics 12