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 "excerpt": "Mark M. Phillips is an American astronomer whose 1993 Phillips relation made Type Ia supernovae precise distance markers, enabling the 1998 discovery that the universe's expansion is accelerating.",
 "snippet": "Mark M. Phillips is an American astronomer whose 1993 Phillips relation made Type Ia supernovae precise distance markers, enabling the 1998 discovery that the universe's expansion is accelerating.",
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 "markdown": "# Mark M. Phillips\n\n**Mark M. Phillips** is an American astronomer best known for the Phillips relation, the 1993 finding that the peak luminosity of a [Type Ia supernova](https://www.edgepedia.org/type-ia-supernova) is tightly correlated with how fast its brightness declines, which turned these exploding stars into precise cosmic distance markers. He spent most of his career in Chile, first at the [Cerro Tololo Inter-American Observatory](https://www.edgepedia.org/cerro-tololo-inter-american-observatory) and then at the Carnegie Observatories, and was one of the twenty members of the [High-Z Supernova Search Team](https://www.edgepedia.org/high-z-supernova-search-team) whose 1998 measurements showed that the expansion of the universe is accelerating.<sup>[1](https://doi.org/10.1086/186970)</sup><sup> • </sup><sup>[2](https://specialevents.ucsc.edu/events/ucsc-alumni-awards/2023-alumni-award/mark-phillips/)</sup><sup> • </sup><sup>[3](https://www.eurekalert.org/news-releases/566172)</sup>\n\n| Key fact | Detail |\n|---|---|\n| Signature result | 1993 paper showing Type Ia absolute magnitudes correlate with the initial decline rate of the B light curve, the \"Phillips relation\"<sup>[1](https://doi.org/10.1086/186970)</sup><sup> • </sup><sup>[4](https://www.lco.cl/astronomer-mark-phillips-is-named-honorary-foreign-member-of-the-chilean-academy-of-sciences/)</sup> |\n| Why it mattered | Uncorrected Hubble diagrams scatter by ~0.4 mag in B; after decline-rate correction the scatter falls to 0.13–0.17 mag, giving distance precisions of about 7–10%<sup>[5](https://ar5iv.labs.arxiv.org/html/astro-ph/9609062)</sup> |\n| Calán/Tololo survey | Co-founded with Mario Hamuy, José Maza, and Nick Suntzeff; found 50 supernovae in 1990–93, 32 of them Type Ia<sup>[5](https://ar5iv.labs.arxiv.org/html/astro-ph/9609062)</sup><sup> • </sup><sup>[2](https://specialevents.ucsc.edu/events/ucsc-alumni-awards/2023-alumni-award/mark-phillips/)</sup> |\n| High-Z team role | One of twenty members; his distance measurements let the team measure how the expansion rate has evolved, yielding q₀ = −0.75 ± 0.32, an accelerating expansion<sup>[3](https://www.eurekalert.org/news-releases/566172)</sup><sup> • </sup><sup>[6](https://arxiv.org/pdf/astro-ph/9905049)</sup> |\n| Career | CTIO staff from 1982, assistant director 1990–98; Carnegie Observatories from 1998; associate director for Magellan 2006–17; director of Las Campanas Observatory 2014–17, director emeritus since 2017<sup>[2](https://specialevents.ucsc.edu/events/ucsc-alumni-awards/2023-alumni-award/mark-phillips/)</sup><sup> • </sup><sup>[7](https://orcid.org/0000-0003-2734-0796)</sup> |\n| Honors | 2007 Gruber Cosmology Prize, 2015 Breakthrough Prize in Fundamental Physics, AAS Fellow, Medal of the Royal Astronomical Society, Honorary Foreign Member of the Chilean Academy of Sciences<sup>[2](https://specialevents.ucsc.edu/events/ucsc-alumni-awards/2023-alumni-award/mark-phillips/)</sup><sup> • </sup><sup>[4](https://www.lco.cl/astronomer-mark-phillips-is-named-honorary-foreign-member-of-the-chilean-academy-of-sciences/)</sup> |\n| Still active | Co-author of a 2024 ApJS paper on 1991T-like supernovae and a 2025 Carnegie Supernova Project study of fast-declining Type Ia supernovae<sup>[8](https://beta.iopscience.iop.org/article/10.3847/1538-4365/ad4f7e)</sup><sup> • </sup><sup>[9](https://arxiv.org/html/2509.07093)</sup> |\n\n## Education and career\n\nPhillips received a [Bachelor's degree](https://www.edgepedia.org/bachelors-degree) in [Astronomy](https://www.edgepedia.org/astronomy) from [San Diego State University](https://www.edgepedia.org/san-diego-state-university) in 1973 and a Ph.D. in Astronomy from the University of California, Santa Cruz in 1977.<sup>[3](https://www.eurekalert.org/news-releases/566172)</sup><sup> • </sup><sup>[7](https://orcid.org/0000-0003-2734-0796)</sup> He arrived in Chile in 1977 and joined the staff of the Cerro Tololo Inter-American Observatory (CTIO) in 1982, serving as CTIO assistant director from 1990 to 1998.<sup>[4](https://www.lco.cl/astronomer-mark-phillips-is-named-honorary-foreign-member-of-the-chilean-academy-of-sciences/)</sup><sup> • </sup><sup>[2](https://specialevents.ucsc.edu/events/ucsc-alumni-awards/2023-alumni-award/mark-phillips/)</sup>\n\nIn 1998 he moved to the Carnegie Observatories. He was associate director for the [Magellan Telescopes](https://www.edgepedia.org/magellan-telescopes) from 2006 to 2017, director of Las Campanas Observatory from 2014 to 2017, and has been director emeritus of Las Campanas since 2017.<sup>[2](https://specialevents.ucsc.edu/events/ucsc-alumni-awards/2023-alumni-award/mark-phillips/)</sup><sup> • </sup><sup>[7](https://orcid.org/0000-0003-2734-0796)</sup> At Carnegie he joined the Carnegie Supernova Program, which obtained optical and infrared light curves of about 100 nearby Type Ia supernovae and near-infrared observations of about 50 high-redshift (0.3 < z < 0.7) supernovae to measure the expansion history of the universe.<sup>[10](https://carnegiescience.edu/bio/dr-mark-phillips)</sup>\n\n## The Phillips relation\n\nBefore 1993, Type Ia supernovae were promising but imperfect [standard candles](https://www.edgepedia.org/standard-candle). Phillips measured a significant intrinsic dispersion in their absolute magnitudes at maximum light, about ±0.8 mag in B, ±0.6 mag in V, and ±0.5 mag in I, and showed that this scatter was tightly correlated with the initial rate of decline of the B light curve.<sup>[1](https://doi.org/10.1086/186970)</sup> He quantified the effect with a parameter Δm15(B), the drop in B magnitudes from maximum to 15 days after B maximum.<sup>[6](https://arxiv.org/pdf/astro-ph/9905049)</sup>\n\nThe practical consequence was large. In the Calán/Tololo sample, uncorrected Hubble diagrams show dispersions ranging from about 0.4 mag in B to about 0.2 mag in I; applying the peak luminosity–decline rate relation reduced these to 0.17 mag in B, 0.14 in V, and 0.13 in I, corresponding to relative distance precisions of roughly 7–10%.<sup>[5](https://ar5iv.labs.arxiv.org/html/astro-ph/9609062)</sup> The method also estimates host-galaxy extinction, combined with the Lira relation, the observation that the B−V color evolution from 30 to 90 days after V maximum is remarkably similar for all events regardless of light-curve shape.<sup>[11](https://iopscience.iop.org/article/10.1086/301032/fulltext/990035.text.html)</sup>\n\n**Antecedents and refinements.** The Soviet astronomer Pskovskii had argued in papers of 1967, 1977, and 1984 that Type Ia supernovae display a continuous range of decline rates correlated with absolute magnitude, but the luminosity–decline rate relation was confirmed quantitatively in 1993.<sup>[12](https://ogle25.astrouw.edu.pl/presentations/OGLE25_MarkPhillips.pdf)</sup> The original relation was trained on only nine nearby supernovae with uncertain extinction estimates; Riess and colleagues' Multicolor Light Curve Shapes (MLCS) method later reanalyzed essentially the same training set and weakened the initial light-curve-shape–B−V color relation.<sup>[11](https://iopscience.iop.org/article/10.1086/301032/fulltext/990035.text.html)</sup>\n\nPhillips and collaborators also extended the calibration to the infrared, where Type Ia supernovae show a much smaller range of luminosities and dust absorption is negligible, making them nearly perfect standard candles at those wavelengths.<sup>[10](https://carnegiescience.edu/bio/dr-mark-phillips)</sup>\n\n## The Calán/Tololo survey\n\nIn mid-1990, Phillips together with [Mario Hamuy](https://www.edgepedia.org/mario-hamuy), José Maza, and Nick Suntzeff founded the Calán/Tololo Supernova Survey, a collaboration between CTIO and the [University of Chile](https://www.edgepedia.org/university-of-chile).<sup>[5](https://ar5iv.labs.arxiv.org/html/astro-ph/9609062)</sup><sup> • </sup><sup>[2](https://specialevents.ucsc.edu/events/ucsc-alumni-awards/2023-alumni-award/mark-phillips/)</sup> Over 1990–93 the survey discovered 50 supernovae, about one third of all supernovae discovered worldwide in that period, and follow-up spectroscopy showed 32 were Type Ia.<sup>[5](https://ar5iv.labs.arxiv.org/html/astro-ph/9609062)</sup>\n\nThe survey's method was photographic: about 25 fields of 5°×5° each were observed with the Curtis Schmidt telescope twice per month, and the plates were blinked at Cerro Calán to find the variable objects. Follow-up CCD imaging in BVI used the CTIO 0.9 m telescope, and classification spectra came from the 1.5 m and 4.0 m telescopes.<sup>[13](https://noirlab.edu/science/sites/default/files/media/archives/presentations/scipresentation0613-en.pdf)</sup> The resulting decline-rate-corrected [Hubble diagram](https://www.edgepedia.org/hubble-diagram) gave H₀ = 63.1 ± 3.4 (internal) ± 2.9 (external) km s⁻¹ Mpc⁻¹, and showed that ignoring the relation would underestimate the [Hubble constant](https://www.edgepedia.org/hubble-constant) by about 10–15%.<sup>[5](https://ar5iv.labs.arxiv.org/html/astro-ph/9609062)</sup> This sample, with scatter lowered to about 0.15 mag in V after correction, became the local foundation for the high-redshift cosmology programs.<sup>[14](https://ar5iv.labs.arxiv.org/html/astro-ph/9805200)</sup>\n\n## The High-Z Supernova Search Team and the accelerating universe\n\nPhillips was one of twenty members of the High-Z Supernova Search Team, led by [Brian Schmidt](https://www.edgepedia.org/brian-schmidt), which used distant Type Ia supernovae as standard candles to measure distances to galaxies halfway across the universe.<sup>[3](https://www.eurekalert.org/news-releases/566172)</sup> His specific contribution was determining accurate distances to the supernovae, which allowed the team to measure how the expansion rate has evolved since the universe was half its present age.<sup>[3](https://www.eurekalert.org/news-releases/566172)</sup>\n\nThe team's first set of 16 high-redshift supernovae proved on average 10–15% farther than expected in a low mass-density universe without a cosmological constant, and the derived deceleration parameter was q₀ = −0.75 ± 0.32, implying that the expansion of the universe is accelerating.<sup>[6](https://arxiv.org/pdf/astro-ph/9905049)</sup> The Supernova Cosmology Project independently confirmed the finding, and Science magazine named it the Scientific Breakthrough of the Year in 1998.<sup>[3](https://www.eurekalert.org/news-releases/566172)</sup><sup> • </sup><sup>[15](https://mintaka.sdsu.edu/schopp/2008/phillips-bio.html)</sup>\n\n## Honors and recognition\n\nPhillips shared the 2007 Cosmology Prize of the Peter and Patricia Gruber Foundation for his role in the discovery of the accelerating expansion, and shared the 2015 [Breakthrough Prize in Fundamental Physics](https://www.edgepedia.org/breakthrough-prize-in-fundamental-physics) with the High-Z team.<sup>[3](https://www.eurekalert.org/news-releases/566172)</sup><sup> • </sup><sup>[2](https://specialevents.ucsc.edu/events/ucsc-alumni-awards/2023-alumni-award/mark-phillips/)</sup> The American Astronomical Society named him a Fellow for his research on supernova physics and for establishing the relationship, informally named after him, that allows Type Ia supernovae to be used as standard candles.<sup>[16](https://carnegiescience.edu/news/mulchaey-and-phillips-named-aas-fellows)</sup> He has also received the Medal of the [Royal Astronomical Society](https://www.edgepedia.org/royal-astronomical-society) and was named an Honorary Foreign Member of the Chilean Academy of Sciences in recognition of nearly five decades of collaboration with the Chilean scientific community.<sup>[4](https://www.lco.cl/astronomer-mark-phillips-is-named-honorary-foreign-member-of-the-chilean-academy-of-sciences/)</sup> In 2023 he received the UC Santa Cruz Alumni Achievement Award, presented on October 27, 2023.<sup>[17](https://news.ucsc.edu/2023/11/mark-phillips-alumni-awards/)</sup>\n\n## By the numbers, how the Phillips relation changed cosmology\n\nThe relation's effect can be stated as a before-and-after. Without correction, the Calán/Tololo Hubble diagrams scatter by about 0.4 mag in B; with correction, 0.13–0.17 mag in BVI.<sup>[5](https://ar5iv.labs.arxiv.org/html/astro-ph/9609062)</sup> In one comparison, applying the decline-rate relation to the V-band Hubble diagram cut the scatter from 0.50 to 0.21 mag and raised the derived Hubble constant from 53 ± 11 to 67 ± 7 km s⁻¹ Mpc⁻¹.<sup>[6](https://arxiv.org/pdf/astro-ph/9905049)</sup> Two closely contemporaneous calibrations of H₀ from corrected nearby samples agree closely: 63.1 ± 3.4 (internal) ± 2.9 (external) km s⁻¹ Mpc⁻¹ from the Calán/Tololo sample,<sup>[5](https://ar5iv.labs.arxiv.org/html/astro-ph/9609062)</sup> and 63.3 ± 2.2 (internal) ± 3.5 (external) km s⁻¹ Mpc⁻¹ from six well-observed nearby supernovae (1937C, 1972E, 1981B, 1989B, 1990N, and 1998bu) with HST Cepheid distances.<sup>[11](https://iopscience.iop.org/article/10.1086/301032/fulltext/990035.text.html)</sup> Phillips summarizes the mature capability this way: Type Ia supernovae can measure distances to a precision of 5% or better, and were the tools behind the discovery of dark energy and a Hubble constant measured to better than 5%.<sup>[12](https://ogle25.astrouw.edu.pl/presentations/OGLE25_MarkPhillips.pdf)</sup>\n\n## References\n\n1. [The absolute magnitudes of Type IA supernovae (Phillips 1993), summary](https://doi.org/10.1086/186970)\n2. [Mark Phillips, UCSC 2023 Alumni Award citation](https://specialevents.ucsc.edu/events/ucsc-alumni-awards/2023-alumni-award/mark-phillips/)\n3. [Carnegie's Mark Phillips to share Gruber Prize for Cosmology (2007), EurekAlert](https://www.eurekalert.org/news-releases/566172)\n4. [Astronomer Mark Phillips is named Honorary Foreign Member of the Chilean Academy of Sciences, Las Campanas Observatory](https://www.lco.cl/astronomer-mark-phillips-is-named-honorary-foreign-member-of-the-chilean-academy-of-sciences/)\n5. [Hamuy et al. 1996, The Hubble Diagram of Type Ia Supernovae (Calán/Tololo survey)](https://ar5iv.labs.arxiv.org/html/astro-ph/9609062)\n6. [Riess et al. 1999, Type Ia Supernova Distance Measurements (High-Z Team)](https://arxiv.org/pdf/astro-ph/9905049)\n7. [Mark Phillips, ORCID 0000-0003-2734-0796](https://orcid.org/0000-0003-2734-0796)\n8. [M. M. Phillips et al. 2024, 1991T-like Supernovae, ApJS 273, 16](https://beta.iopscience.iop.org/article/10.3847/1538-4365/ad4f7e)\n9. [Carnegie Supernova Project: Fast-Declining Type Ia Supernovae as Cosmological Distance Indicators (2025)](https://arxiv.org/html/2509.07093)\n10. [Dr. Mark Phillips, Carnegie Science biography](https://carnegiescience.edu/bio/dr-mark-phillips)\n11. [Phillips et al., The SN Decline Rate versus Luminosity Relationship, ApJ](https://iopscience.iop.org/article/10.1086/301032/fulltext/990035.text.html)\n12. [Mark Phillips presentation, OGLE 25th anniversary (July 2015)](https://ogle25.astrouw.edu.pl/presentations/OGLE25_MarkPhillips.pdf)\n13. [The Calán/Tololo Supernova Survey, NOIRLab presentation](https://noirlab.edu/science/sites/default/files/media/archives/presentations/scipresentation0613-en.pdf)\n14. [The High-Z Supernova Search (1998), ApJ](https://ar5iv.labs.arxiv.org/html/astro-ph/9805200)\n15. [Dr. Mark Phillips biography, SDSU lecture page](https://mintaka.sdsu.edu/schopp/2008/phillips-bio.html)\n16. [Mulchaey and Phillips named AAS Fellows, Carnegie Science](https://carnegiescience.edu/news/mulchaey-and-phillips-named-aas-fellows)\n17. [World-renowned supernova expert honored, UCSC News (2023)](https://news.ucsc.edu/2023/11/mark-phillips-alumni-awards/)\n\n---\n*Topic: Encyclopedia › Physical world and mathematics › Physical and mathematical scientists › Physicists and astronomers › Researchers in astrophysics, cosmology, and gravitational-wave science › Stellar explosions and nucleosynthesis*\n\n*Initially written Oct 10, 2026 · Edited: Oct 11, 2026; Oct 15, 2026*\n\n*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*\n\nLicense: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license\n",
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 "credit": "\"Mark M. Phillips\", Edgepedia (EdgeChat), https://www.edgepedia.org/mark-m-phillips. Edgepedia Community License 1.0.",
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 "speakable": "Mark M. Phillips is an American astronomer whose 1993 Phillips relation made Type Ia supernovae precise distance markers, enabling the 1998 discovery that the universe's expansion is accelerating."
}