Free Astronomy Magazine July-August 2026

33 JULY-AUGUST 2026 ASTRO PUBLISHING megaparsec — while predictions de- rived from the early Universe yield a lower value, closer to 67 or 68. Al- though the numerical difference is modest, it is far larger than can be explained by statistical uncertainty. This persistent disagreement, known as the Hubble tension, has now been observed across multiple independ- ent studies and techniques. By bringing together decades of in- dependent observations into a sin- gle, unified framework, an interna- tional collaboration of astronomers has achieved the most precise direct measurement to date of the expan- sion rate of the nearby Universe. In a paper published on 10 April in Astronomy & Astrophysics , the H 0 Distance Network (H 0 DN) Collabora- tion reports a value of the Hubble constant of 73.50 ± 0.81 kilometers per second per megaparsec, corre- A rtist’s interpretation of the cosmic distance ladder — a succession of over- lapping methods used to measure distances across the Universe, where each rung of the ladder provides information that can be used to determine the distances at the next higher rung. Methods include observations of pulsat- ing Cepheid variable stars, red giant stars that shine with a known brightness, Type Ia supernovae, and certain types of galaxies. In this illustration, the dis- tance ladder begins at the Coma Cluster, which is the nearest extremely rich galaxy cluster to us. The distance to the Coma Cluster can be measured directly using observations of Type Ia supernovae within the cluster. Type Ia super- novae have a predictable luminosity that makes them reliable objects for dis- tance calculations. [CTIO/NOIRLab/DOE/NSF/AURA/J. Pollard. Image Processing: D. de Martin & M. Zamani (NSF NOIRLab)] sponding to a precision of just over 1%. The study, “The Local Distance Network: a community consensus report on the measurement of the Hubble constant at ~ 1% precision,” is the outcome of a broad commu- nity effort launched at the Interna- tional Space Science Institute (ISSI) Breakthrough Workshop, “What’s under the H 0 od?”, held at ISSI in Bern, Switzerland, in March 2025. “This isn’t just a new value of the Hubble constant, − the collabora- tion notes − it’s a community-built framework that brings decades of independent distance measure- ments together, transparently and accessibly.” NSF NOIRLab contributed both ex- pertise and observational data to this effort. John Blakeslee, as- tronomer and Director of Research and Science Services at NSF NOIRLab, is a member of the collaboration. The study includes data from tele- scopes at NSF Cerro Tololo Inter- American Observatory (CTIO) in Chile and NSF Kitt Peak National Ob- servatory (KPNO) in Arizona, both Programs of NSF NOIRLab. Those data were incorporated into a broader, collaborative framework spanning both ground and space- based observatories, helping to strengthen the overall result. Rather than relying on a single method, the team constructed a “distance network” that links many overlapping techniques for measur- ing distances across the local Uni- verse. These include observations of pulsating Cepheid variable stars, red giant stars that shine with a known brightness, Type Ia supernovae, and certain types of galaxies. This ap- proach enables multiple independ- ent paths to the same final result, and allows for a critical test: is the discrepancy caused by an error within a single method? The results indicate that this is unlikely. Even when individual techniques are re- moved from the analysis, the overall result changes only minimally. Inde- pendent measurements remain con- sistent with one another, reinforcing the robustness of the locally meas- ured expansion rate. “This work effectively rules out ex- planations of the Hubble tension that rely on a single overlooked error in local distance measure- ments,” the authors conclude. “If the tension is real, as the growing body of evidence suggests, it may point to new physics beyond the standard cosmological model.” The implications are significant. The lower expansion rate inferred from the early Universe depends on the standard model of cosmology, which describes how the Universe has evolved since the Big Bang. If that model is incomplete — for ex- ample, if it does not fully account for the behavior of dark energy,