Did Astrodienst’s DE441 Switch Change Your Saved Synastry Chart?

What did Astrodienst change in May 2026?

Astrodienst changed the ephemeris basis of Swiss Ephemeris. Its technical page says the project used JPL’s DE431 from release 2.00 in February 2014, then moved to DE441 in May 2026. An ephemeris is the position data a chart calculation draws on for a specified time. The announcement identifies a newer basis for calculations through software using updated Swiss Ephemeris data. It doesn’t establish that every chart displayed after May was recalculated, or that an older chart file was edited. That distinction matters: a new calculation can use new inputs, while a saved chart remains the result it captured. Astrodienst says the compressed Swiss files reproduce JPL data to 0.001 arcseconds precision. Its page also describes several calculation paths: compressed Swiss files, original JPL files when available, or the built-in Moshier theory. The package selects among available files according to what an installation contains. So “Swiss Ephemeris” names the calculation toolset, but the label alone may not tell you which data path produced a result. The May date identifies the project’s updated basis. By itself, it doesn’t show that a placement in your synastry chart moved, which file an earlier calculation used, or whether an aspect interpretation should change.

Sources: Swiss Ephemeris - for 8000 years and more

Does an ephemeris update rewrite a chart already saved?

No. A saved chart image, PDF, or written list of placements records the result it captured. Changing the ephemeris used for later calculations does not reach back and edit that file. The distinction matters because “my chart” can mean three different things: the birth details stored in an account, a chart result calculated from those details, or a fresh screen generated when someone opens the record. The first may remain available while the displayed result is produced anew. If a service recalculates on opening, its current output could differ from an older saved copy; if it simply displays the old file, the image remains as it was. The screen alone may not tell you which happened.

Astrodienst’s “Swiss Ephemeris - for 8000 years and more” documents the ephemeris basis and available calculation paths. It says the project has used DE441 since May 2026, after DE431, and explains that software can use compressed Swiss Ephemeris files, original JPL files when available, or the built-in Moshier model. That information helps identify what may underlie a calculation. It does not say whether a particular chart service preserves each previously calculated result, regenerates it when opened, or updates an old display. So the May change alone cannot establish that a chart you saved was rewritten.

JPL’s 2021 announcement, “Updating to DE440/441 Planetary Ephemeris (Horizons),” offers a useful comparison, but only for its own system. JPL said Horizons would replace DE430/431 with DE440/441, and described recalculating its catalog of small-body orbit solutions under the updated model. That is an explicit service update with a stated recalculation step. It shows why an ephemeris change can lead a provider to recalculate outputs; it does not show that Astrodienst, or any other chart service, handles stored charts the same way. Keep the chart file or note the placements you are comparing. If a chart now looks different, first ask whether you are viewing that saved result or a new calculation from stored birth data. Then compare the two outputs. Until that distinction is clear, a changed screen is not proof that an old chart artifact changed, and an unchanged file does not tell you what a fresh calculation would show.

Sources: Swiss Ephemeris - for 8000 years and more; Updating to DE440/441 Planetary Ephemeris (Horizons)

Why can two Swiss Ephemeris calculations use different paths?

Think of Swiss Ephemeris as a calculation library, not a single permanent set of planetary files. The library supplies the methods; the installed data and runtime choice determine which path a particular calculation follows. That distinction matters when you compare a chart made before May 2026 with one made later. A project-wide change in the stated basis does not, on its own, identify the data source behind every earlier or later result. Astrodienst’s “Swiss Ephemeris - for 8000 years and more” describes three routes. The package can use original JPL DE431 or DE441 files when those files are available at the installation, use Astrodienst’s compressed Swiss Ephemeris files, or use its built-in Moshier model. Astrodienst says the compressed files are the default and reproduce the JPL data to 0.001 arcseconds precision. It also says the package automatically chooses the available ephemeris according to the installed files it finds. So two programs carrying the Swiss Ephemeris name may not be using identical underlying files: one may have a JPL file available, another may rely on the compressed data, and a setup without stored ephemeris files may use Moshier. The hierarchy is useful. First comes the library or software that calls Swiss Ephemeris. Next comes the collection of ephemeris files installed with, or made available to, that software. Then comes the runtime selection, which may be automatic or exposed through a setting. The Astrodienst page describes the package’s options and automatic selection, but it does not reveal what files a particular desktop program, app, or hosted chart service has installed. Nor does the May 2026 announcement prove that an older local installation replaced its files or that every service now follows the same path. For a careful comparison, note the program and version shown, along with any ephemeris setting or file detail the software exposes. If the setting is hidden, you can still compare the displayed outputs while being precise about what that comparison establishes: the two results differ, if they do, but the cause has not been isolated to the ephemeris. Keep birth inputs and other chart conventions fixed as well. The goal is to identify a real output difference before changing an interpretation, not to infer the calculation path from the Swiss Ephemeris label alone. That is the soundest way to describe what you know.

Sources: Swiss Ephemeris - for 8000 years and more

How are the old and new JPL solutions related?

Both DE431 and DE441 are long-span JPL ephemerides, but they belong to different generations of the planetary and lunar solutions. DE431 was the extended-time counterpart to DE430. DE441 later took the same broad role beside DE440. That family relationship helps explain what the May 2026 change means: it replaced one calculation basis with a later solution, not simply a differently named copy of the old one. JPL's 2014 record, “The Planetary and Lunar Ephemerides DE430 and DE431,” describes DE431 as similar to DE430 but fitted without a damping term between the Moon's liquid core and solid mantle. That choice matters to the length of the integration. JPL says the damping term gives a better fit to lunar laser-ranging data but is unsuitable for backward integration over more than a few centuries. DE431 therefore spans years -13,200 to +17,191, while DE430 covers 1550 to 2650. The tradeoff is explicit: near the present epoch, DE431's lunar orbit is less accurate than DE430's, while its model suits calculations far deeper into the past. JPL's 2021 “The JPL Planetary and Lunar Ephemerides DE440 and DE441” describes a later generation. DE440 and DE441 were fit to the same data set, with about seven additional years of observations compared with DE430. JPL notes improved models and data calibration, including new information for the orbits of Jupiter, Saturn, and Pluto. DE441 again omits the lunar core-mantle damping term. Its span reaches from year -13,200 to +17,191; DE440 covers 1550 to 2650. JPL's comparison therefore gives DE441 the long historical reach and DE440 the more accurate solution for the current century. The export guidance makes the design choice plainer. “JPL Planetary and Lunar Ephemerides” calls DE440 the fully consistent modern solution, then explains that DE441 was integrated without the lunar damping term to cover a longer span. It reports that planetary positions in DE441 agree with DE440 to within one meter over DE440's time span, while the Moon differs mainly through the estimated tidal damping term. That comparison is specifically DE440 against DE441. It does not tell us how much DE431 and DE441 differ at a person's birth moment. So the versions share a purpose and a lunar-model choice, but that does not make their coordinates interchangeable. DE431 extends DE430; DE441 extends DE440, which incorporates later observations and model work. This lineage confirms that the ephemeris basis changed in a substantive technical sense. It cannot establish whether a given chart's degree, sign, or synastry aspect changed. For that, compare the same birth inputs under both calculation bases. A version history can orient the question. Only matched outputs can answer it for a chart, using the same timestamp and calculation conventions throughout.

Sources: The Planetary and Lunar Ephemerides DE430 and DE431; The JPL Planetary and Lunar Ephemerides DE440 and DE441; JPL Planetary and Lunar Ephemerides

What does JPL's DE440/DE441 comparison actually tell us?

JPL's comparison explains why DE440 and DE441 are related, yet not interchangeable as evidence about the May 2026 Swiss Ephemeris change. The JPL paper, The JPL Planetary and Lunar Ephemerides DE440 and DE441, says both solutions were fitted to the same observations. The work added seven years of data beyond the previous general-purpose ephemerides and improved dynamical models and data calibration. This shows that the newer pair reflects revised inputs and modeling. It does not tell us how much a birth chart's zodiac longitude moved from DE431 to DE441.

The important difference between DE440 and DE441 concerns the Moon's treatment. DE440 includes damping between the Moon's liquid core and solid mantle. DE441 leaves that term out, allowing the integration to run much farther backward without divergence. The paper says DE441 is less accurate than DE440 for the current century, while covering years -13,200 to +17,191; DE440 covers 1550 to 2650. JPL's Planetary and Lunar Ephemerides export guidance gives a useful scale for this specific pair: planetary positions in DE441 agree with DE440 within one meter over DE440's time span. It also says the Moon's along-track position differs by about ten meters a century from the present, with the gap growing farther back in time. This is a DE440-versus-DE441 comparison, not a measurement against DE431.

That distinction sets the limit. A small stated difference between two solutions cannot serve as a numerical stand-in for the difference between one of them and a third solution. DE431 is not DE440, and the JPL pages don't provide a paired DE431/DE441 longitude comparison for a particular birth timestamp. Nor do they translate physical position differences into tropical or sidereal sign labels, synastry aspect separations, or orb classifications.

So use JPL's comparison to understand why DE441 exists and what tradeoff it makes, not to conclude that a synastry placement stayed put or changed. The engineering comparison supports neither blanket claim. To answer the chart question, compare outputs for the same birth inputs and settings, then examine the unrounded longitudes and the astrological categories you actually use. Until that matched comparison exists, JPL's DE440/DE441 figures cannot establish whether a sign or aspect in a DE431-based chart moved.

Sources: The JPL Planetary and Lunar Ephemerides DE440 and DE441; JPL Planetary and Lunar Ephemerides

How far can we carry the evidence about changed positions?

The evidence supports a precise conclusion, but not a numerical one. Astrodienst’s “Swiss Ephemeris - for 8000 years and more” says Swiss Ephemeris had been based on DE431 since February 2014 and moved to DE441 in May 2026. That confirms a change in calculation basis. It does not show how far a planet’s zodiac longitude moved for a particular birth date, or whether a synastry category changed. The page gives no before-and-after table for individual charts.

JPL’s “The Planetary and Lunar Ephemerides DE430 and DE431” explains that the pair differs in integration span and lunar modeling. DE431 omits the lunar core-mantle damping term used in DE430 and covers a longer span. “The JPL Planetary and Lunar Ephemerides DE440 and DE441” describes a later pair: both were fit to the same data set, while DE441 omits that damping term and covers a much longer period. JPL says DE441 is less accurate than DE440 for the current century. These sources explain design and lineage. They do not supply a DE431-to-DE441 comparison at ordinary birth timestamps.

That gap rules out two easy answers. We can’t say every chart changed, because the sources report no universal result. We also can’t say positions cannot differ: the basis changed, and the sources do not report identical DE431 and DE441 outputs. Possibility is not proof of a meaningful movement. A raw longitude difference also doesn’t automatically mean a sign, aspect, or reading changed. Those questions require the actual positions and the astrologer’s zodiac, aspect rules, and orbs.

A useful test would calculate the same birth timestamps twice, once with each ephemeris, holding time, location handling, coordinate frame, zodiac, and other settings constant. It would compare unrounded longitudes and angular separations, then check for changed sign or aspect classifications under a stated orb. Repeating the method across a defined set of dates could show how often a boundary is crossed in that sample. It wouldn’t settle an individual chart without its matched outputs.

Until then, the conclusion is narrow: Astrodienst changed the basis used for Swiss Ephemeris calculations, but these sources establish no general DE431-to-DE441 shift in synastry signs or aspects. To see whether your reading changes, compare both outputs for the same chart under matched settings. Revise only if the comparison demonstrates a change in a placement or contact your interpretation uses.

Sources: Swiss Ephemeris - for 8000 years and more; The JPL Planetary and Lunar Ephemerides DE440 and DE441; The Planetary and Lunar Ephemerides DE430 and DE431

When would a changed longitude alter a synastry reading?

A changed coordinate matters to a synastry reading when it changes a layer the astrologer actually uses: a sign boundary, a degree-based contact, or an aspect's separation relative to the chosen orb. If the sign and relevant aspect relationship stay the same, a small numerical difference may leave the practical reading intact. The question is whether the difference crosses an interpretive boundary. Start with each planet's unrounded ecliptic longitude, expressed around the zodiac's full circle. A chart may round the displayed degree, hiding a small difference. Identify the sign from the longitude using the same zodiac in both charts. A sign changes only when the position crosses the boundary between signs. A planet moving from just before that boundary to just after it has changed sign; a movement that stays on the same side has not. Aspect reading asks a separate question. Compare the two planets' longitudes to find their angular separation, then measure how far that separation sits from the exact angle of the aspect being considered. That distance is the orb. Astrodienst’s “Orb” entry defines the permitted deviation from exactness. Neither term gives every astrologer one universal cutoff. The orb, the aspects included, and any rule about aspects across sign boundaries belong to the chosen method. A shift may leave both signs fixed yet move an aspect toward the selected limit. The contact's status changes only if it crosses that limit under the same stated rules. Consider an illustration, not a real chart: two partners' planets sit near the edge of an astrologer's chosen orb for a square. A recalculation nudges their separation across that edge. Under that method, the square enters or leaves the aspect list, which may change how much weight the reader gives that contact. A different astrologer using a wider orb could keep it in view throughout. The classification rule matters. Then rank the result. A changed sign can alter the placement description; a changed aspect category can alter which relationship between the planets is interpreted; a modest shift that changes neither may affect degree-level emphasis without changing the basic reading. For synastry, repeat this check for each relevant cross-chart pair rather than assuming one shift changes every contact. Check the unrounded values, the sign, and the aspect/orb rule in that order. Revise only the layer whose category actually changes.

Which settings must match before you compare two charts?

Before comparing two synastry calculations, keep every input and convention the same except the ephemeris path you are investigating. Match each person's birth date, recorded time, birthplace, time-zone handling, zodiac, and coordinate settings. Use the same software options where possible. Then a difference has fewer possible causes: you can ask whether the ephemeris explains it, rather than confusing it with a changed birth record or chart method. Start with the two birth records. Confirm the time as entered, including whether it is exact or approximate, and check how the software handles local time and historical time-zone settings. A different conversion can change the moment being calculated. If an input is uncertain, note that before comparing. A comparison can isolate only the variables you held steady. Next, match the coordinate framework. Keep tropical or sidereal zodiac choice constant, along with the same reference conventions and options that affect planetary positions. Astrodienst's “Swiss Ephemeris - for 8000 years and more” explains that Swiss Ephemeris may use compressed Swiss files, original JPL files when available, or the Moshier model; installed files affect the selected path. “Swiss Ephemeris” names a toolkit, then, not proof that two runs used identical data. Record the ephemeris setting or file if the program shows it. If it doesn't, compare the outputs without claiming that DE441 alone caused any difference. With the settings matched, compare unrounded ecliptic longitudes for the same planets, if available. Rounded displays can hide a small movement. Then compare the synastry layer: measure the angular separation for the same planet pairs using the same aspect set and orb rule. Check sign labels, aspect names, and orbs separately. A longitude can shift while its sign and aspect category stay the same; a placement near a boundary deserves closer review. A changed decimal alone doesn't require a materially changed interpretation. This method gives you a controlled output comparison, though hidden settings can leave its cause unresolved. Preserve both outputs and note which inputs and settings you could verify. If a relevant sign or aspect classification differs, revise that part of the reading. If it doesn't, the version change gives you no specific reason to recast the comparison.

Sources: Swiss Ephemeris - for 8000 years and more

What should you do with your current synastry chart?

Keep the chart you already have if it records the placements you chose to compare. Astrodienst's Swiss Ephemeris page says its basis changed from DE431 to DE441 in May 2026, but that announcement alone doesn't show that a saved chart was rewritten. The page describes possible data paths, but not which one a particular chart used or whether a website stores a result or generates a fresh display. Treat those as separate questions. Recalculate only when you have a concrete reason: perhaps you corrected a birth time, received a different placement table, or need a fresh result for a comparison. Before interpreting any difference, check that both charts use the same birth date, time, place, time-zone handling, zodiac, and relevant calculation settings. If the program shows its ephemeris setting, record it. If it doesn't, you can still compare the two outputs, but you can't attribute a difference to DE441 alone. Compare the unrounded longitudes if available, then check sign labels, the angular separation between the two planets, and the aspect and orb rules you chose. A changed number on screen matters to the reading only when it changes a layer your method uses. This order keeps the work proportionate: preserve the chart artifact, investigate a specific discrepancy, match the inputs and settings, and make a targeted revision only if a relevant placement or aspect classification changes. The announcement alone isn't a reason to discard your chart or redo your reading. The Synastry Comparison Report reads Moon, Venus, and Mars placements you supply, with optional degrees. It can help you interpret those inputs together. It doesn't calculate natal charts from birth details, identify which ephemeris produced an outside chart, or verify whether a fresh output differs from an older one. If you want to use it, first decide which set of placements you mean to compare, then enter those placements as they appear in the chart you trust. Keep the source chart and fresh comparison distinct in your notes. Your interpretation stays tied to clear inputs, and any later update gives you a specific result to assess.

Sources: Swiss Ephemeris - for 8000 years and more

The verdict: what changed, and what would change your conclusion?

Astrodienst changed Swiss Ephemeris’s calculation basis in May 2026, moving from DE431 to DE441. Its page, “Swiss Ephemeris - for 8000 years and more,” says what underpins a fresh calculation. It does not say a PDF, screenshot, or recorded placements already in your hands were rewritten. JPL’s “DE440 and DE441” comparison describes those solutions, not the DE431-to-DE441 difference for your birth dates. The sources establish an update, but not a general claim that signs or synastry aspects changed.

The strongest exception is a regenerated chart with a position near a boundary. A coordinate difference could matter if it changes a sign, moves a planet across an aspect threshold under your chosen orb, or alters an angular separation you use to interpret a contact. Changed birth inputs or settings could also produce a different display, so the difference alone doesn’t identify its cause. Compare matched outputs: same birth records and chart conventions, checking unrounded positions where available.

Keep the chart version you used unless a specific discrepancy gives you reason to investigate. If a matched comparison changes a placement or aspect category, revise that part of the reading. If those categories remain the same, the version announcement alone gives you no reason to discard your interpretation. The conclusion changes when a demonstrated before-and-after difference affects a layer you actually use.

Sources: Swiss Ephemeris - for 8000 years and more; The JPL Planetary and Lunar Ephemerides DE440 and DE441

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