A Different Voyager Anomaly - Lightday

August 27, 2026 | Self

[Lonesome in Massachussets]

I noticed a discrepancy between a NASA public relations web page and the NASA Horizons App, which models the trajectories of solar system celestial objects. I wrote to NASA twice, once to an online generic "ask NASA" page and once an email to individuals at NASA with cognizance of the issues. I know NASA get a lot of crank emails, and understand why they do not have time to reply to all of them.

I am not convinced my email is a crank missive. Read it and tell me what you think. I am most reluctant to criticize NASA, but this definitely looks like some sort of error.

Note: 1440 minutes equals one day

The email text is below:

Good Morning,

I have been following the progress of Voyager 1 towards the Lightday milestone with some interest. The NASA/JPL Horizons site provides estimates of light time in minutes between an observer and celestial objects, including Voyager 1. I have corresponded with Phil Plait who runs the Bad Astronomy blog and he suggested I contact you.

If I query the NASA JPL/Horizon site for the light time to Voyager 1 at different times expressed in PST (UTC-8) I get the following results:

DATE/TIME (PST) Light Time (Minutes)
------------------------- ------------------
2026-Nov-18 02:16:07.000 1439.91895950

2026-Nov-18 18:16:07.000 1439.99988811

2026-Nov-18 18:17:27.056 1440.00000000

The first line uses the time given by

https://science.nasa.gov/mission/voyager/voyager-1/voyager-1-what-is-a-light-day/

The second line assumes that someone made a sign error converting from PST to UTC and adds 16 hours.

The third line is just successive approximation to find 1440 minutes.

The range differences are simply calculated as:

(1440 - 1439.91895950) x 60 x 299792.458 = 1,457,720 km

(1440 - 1439.99988811) x 60 x 299792.458 = 2,012 km

I assumed Geocentric distance was implied, but subsitutiting the geodetic coordinates of JPL or any place in California only makes it worse.

What am I missing?

Thanks,

[My Legal Name]

Anyone have any suggestions? I have no intention of abusing or ridiculing anyone at NASA, but it would be nice to get to the bottom of the Voyager Anomaly, no matter how inconsequential? Any ideas?

---

TOPICS: Astronomy; Chit/Chat; Hobbies
KEYWORDS: voyageranomaly

[Lonesome in Massachussets]

PST is 8 hours behind UTC, exactly and an astronomical day is exactly 1440 minutes.

Keep it positive, keep it adult. No wisecracks about Herschel's Planet.

[Tell It Right]

Thanks for posting! I had no clue that V’ger was this close to being 16 billion miles away!

[Red Badger]

The Earth is moving too..............

[montag813]

Trust the science

[Lonesome in Massachussets]

The Earth is moving too..............

Thanks for your interest.

Earth's motion is built in to the Horizons App. Voyager I is moving away from the sun at about 16 km/sec. On the date and time specified, the earth's orbit is on the far side of the sun from Voyager. The earth's orbital velocity is about 30 km/sec. The "vector sum" of earth's velocity and Voyagers is about between 25.4071922 and 25.1404967 km/sec on the first and last date in the day posted. The corresponding heliocentric range rates are 16.8815689 and 16.8815679 km/sec.

Voyager will not be one lightday from the sun until 2027-Feb-04 11:58:39.327

[Lonesome in Massachussets]

I think I trust the “science”, not the public relations web page. The data I am presenting were derived from a different NASA web page, which provides a fantastic public service. I suspect that someone at NASA made small error, but I recognize that I could be missing the whole point. That’s why I am humbly asking for help.

[Red Badger]

Plus we are at different points in the Gravity Well, so light travels at a different speeds closer to the Sun than Voyager............

[Lonesome in Massachussets]

The NASA Horizon JPL web page accounts for that. The Horizons database is the result of a massive highly granular calculation of every known body in the solar system, using solar system baricentric dynamical time, which differs from dynamical time (now called Terrestial Time) only by milliseconds due to effects of relativity. Results are translated to Terresital Time or UTC on output.

The results are valid for an observer at the center of the earth who is using a clock beating at the same rate as an ideal atomic clock at sea level. The descrepancy is NOT due to relativistic effects. The measurement is the time measured on the sea level surface of the earth if, in that coordinate frame, a light pulse had been transmitted such that it would arrive at the point where the observer was when it was transmitted.

Voyager tracking is very clever. All communications recieved by Voyager are phase locked and frequency translated and sent back to earth. This removes most of the phase noise and frequency drift from the transponder. The transponder “reply” is recieved by deep space stations in Madrid, California and Canberra. Long baseline interferometry gives excellent angular accuracy and the phase locked transponder gives nearly ideal Doppler and ranging-time performance. The point where Voyager was at the time of reception relative to the receivers is a relatively simple calculation.

[Red Badger]

“...calculation of every known body in the solar system,...”

Then it must be because of Dark Matter.........or Climate Change.........or Trump’s fault......

[Lonesome in Massachussets]

The anomaly is between two NASA sites. JPL has the solar system model and the data, the public relations website probably doesn’t even have Google Sheets.

[Red Badger]

Why don’t they just tell people up front that they use two different methods?...............

[wafflehouse]

so light travels at a different speeds closer to the Sun than Voyager

are you sure about that?

[Red Badger]

Relatively................

[SunkenCiv]

When you put “wisecracks” and “Herschel’s Planet” in the same sentence, you’re askin’ for it. 😁

[muir_redwoods]

Just to be clear, are we discussing +/-35 seconds? Since 1977? Really?

[Lonesome in Massachussets]

Red Badger's first comment is correct, "The Earth is moving too...."

I found the bug, and its all mine. From the horizon app, the description of lighttime:

'1-way_down_LT' = 1-way down-leg light-time from target center to observer. The elapsed time since light (observed at print-time) would have left or reflected off a point at the center of the target. Units: MINUTES

The light time is for the position of where the earth is at the time the pulse is received and where the target was when it was transmitted. The JPL range to the target at the time of receiption is correct to one km, and they do not print any fractional part, no places to the right of the decimal point. My bad. Thank you for all the stimulating comments, which made me rethink my premises.

[Red Badger]

😁........................

[Lonesome in Massachussets]

No the percieved anomaly was on the order of 16 hours. The tracking of the Voyagers is extremely precise (from what I can find out), it has a transponder that is still operating, that is phase-locked to the signal transmitted from earth. The receiving baseline is Madrid, California, Australia, so the measurement error is on the order of kilometers in range and cross range. Since the gravitational attraction of the solar system is known to about 10 decimal places propagation of the orbit and smoothing of errors should be predictable to comparable accuracy. It was a math error on my part.

[Deaf and Discerning]

so light travels at a different speeds closer to the Sun than Voyager

are you sure about that?

That's not true. In vacuum — whether near the Sun, near Earth, or out by Voyager — light always moves at the same speed. The only time light slows down is inside a medium (water, glass, air), but never in empty space. It has nothing to do with gravity.