Results 1 to 11 of 11

Thread: The Big Day: which day of the year is the most time dilated for the distant observer?

  1. #1
    Join Date
    Dec 2004
    Location
    UK
    Posts
    8,716

    The Big Day: which day of the year is the most time dilated for the distant observer?

    Say for someone watching Earth from a half a light year away, which day of the orbit lasts the longest?

    The orbit of Earth is slightly elliptical, so would the day when it was closest to the Sun be the most time dilated, in terms of speed dilation, and being deeper in the Sun's gravity well?
    Formerly Frog march.

    Newscaster: ... But I've just had a report that a representative of Disaster Area met with the environmentalists this morning and had them all shot, so now nothing stands in the way of the concert going ahead this afternoon on this beautiful sunny day.

  2. #2
    Join Date
    Dec 2016
    Posts
    274
    Quote Originally Posted by Mudskipper View Post
    Say for someone watching Earth from a half a light year away, which day of the orbit lasts the longest?

    The orbit of Earth is slightly elliptical, so would the day when it was closest to the Sun be the most time dilated, in terms of speed dilation, and being deeper in the Sun's gravity well?
    Whats our viewpoint? Are we looking down from the north poles or are we looking from along earths orbital plane?
    I know that I know nothing, so I question everything. - Socrates/Descartes

  3. #3
    Join Date
    Dec 2004
    Location
    UK
    Posts
    8,716
    Quote Originally Posted by DaCaptain View Post
    Whats our viewpoint? Are we looking down from the north poles or are we looking from along earths orbital plane?
    I'm not sure it matters. At half a light years distance, if in fairly flat space, the Earth's revolution should appear to slow down a smidgen(unmeasurable amount)..I think.
    Formerly Frog march.

    Newscaster: ... But I've just had a report that a representative of Disaster Area met with the environmentalists this morning and had them all shot, so now nothing stands in the way of the concert going ahead this afternoon on this beautiful sunny day.

  4. #4
    Join Date
    Jun 2006
    Posts
    4,669

    Wha?

    Quote Originally Posted by Mudskipper View Post
    Say for someone watching Earth from a half a light year away, which day of the orbit lasts the longest?

    The orbit of Earth is slightly elliptical, so would the day when it was closest to the Sun be the most time dilated, in terms of speed dilation, and being deeper in the Sun's gravity well?
    Time dilation is a function of relative velocities, not of distance.

  5. #5
    Join Date
    Mar 2007
    Location
    Falls Church, VA (near Washington, DC)
    Posts
    8,195
    Any time dilation of a clock on Earth as observed from afar should be maximum at perihelion. That is where it is deepest in the Sun's gravitational well and also moving fastest. If I am not mistaken, both of those effects act in the same direction.

  6. #6
    Join Date
    Sep 2003
    Posts
    12,329
    Quote Originally Posted by Hornblower View Post
    Any time dilation of a clock on Earth as observed from afar should be maximum at perihelion. That is where it is deepest in the Sun's gravitational well and also moving fastest. If I am not mistaken, both of those effects act in the same direction.
    Yes, both would be additive to the time dilation, though they oppose each other for orbiting satellites above. I would assume the variation in the Earth-Moon barycenter could also be included, but are these gravity time effects extra tiny compared to the tiny time dilation due to orbital speed?
    We know time flies, we just can't see its wings.

  7. #7
    Join Date
    Aug 2005
    Location
    location
    Posts
    12,410
    It also depends on how you're measuring the duration of "day" - tropical or sidereal. At perihelion, the planet is moving the fastest in its orbit, which also means it has to turn further to put the sun in the same position in the sky as it was the day before (tropical day). This is the source of the Analemma.
    Et tu BAUT? Quantum mutatus ab illo.

  8. #8
    Join Date
    May 2004
    Posts
    1,713
    IIRC Perihelion occurs in January. I forget the exact day.

  9. #9
    Join Date
    Jul 2005
    Posts
    16,487
    Quote Originally Posted by Tom Mazanec View Post
    IIRC Perihelion occurs in January. I forget the exact day.
    It varies from year to year. In the current epoch, either the 2nd, 3rd or 4th of January.

    Grant Hutchison
    Blog

    Note:
    During life, we all develop attitudes and strategies to make our interactions with others more pleasant and useful. If I mention mine here, those comments can apply only to myself, my experiences and my situation. Such remarks cannot and should not be construed as dismissing, denigrating, devaluing or criticizing any different attitudes and strategies that other people have evolved as a result of their different situation and different experiences.

  10. #10
    Join Date
    Dec 2006
    Posts
    2,130
    Quote Originally Posted by grant hutchison View Post
    It varies from year to year. In the current epoch, either the 2nd, 3rd or 4th of January. Grant Hutchison
    Last year in Australia perihelion was on 5 Jan, but in 2018 it retreats to 3 Jan. I can get why it would change after a leap day, but not why it retreats without a leap day.

    https://www.timeanddate.com/astronom...-solstice.html will vary by your longitude. For me it gives this table
    Year Perihelion Distance Aphelion Distance
    2017 5 January 2017 1:17 am 147,100,998 km 4 July 2017 6:11 am 152,092,504 km
    2018 3 January 2018 4:34 pm 147,097,233 km 7 July 2018 2:46 am 152,095,566 km
    2019 3 January 2019 4:19 pm 147,099,760 km 5 July 2019 8:10 am 152,104,285 km
    2020 5 January 2020 6:47 pm 147,091,144 km 4 July 2020 9:34 pm 152,095,295 km
    2021 3 January 2021 12:50 am 147,093,163 km 6 July 2021 8:27 am 152,100,527 km
    * All aphelion/perihelion times are in local Sydney time.
    On average perihelion advances by one day every 59 years. It is a primary marker of Milankovic Climate Cycles.

  11. #11
    Join Date
    May 2005
    Posts
    8,070
    Quote Originally Posted by Robert Tulip View Post
    Last year in Australia perihelion was on 5 Jan, but in 2018 it retreats to 3 Jan. I can get why it would change after a leap day, but not why it retreats without a leap day.

    https://www.timeanddate.com/astronom...-solstice.html will vary by your longitude. For me it gives this table


    On average perihelion advances by one day every 59 years. It is a primary marker of Milankovic Climate Cycles.
    It'll vary because of the time zone differences, but also by the day of the lunar month. During a full moon, it's closer to the sun, and during a new moon, the earth is farther away from the sun--and there are smaller perturbations from the other planets.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •