This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: NASA's Hubble Space Telescope completed its 200,000th orbit around Earth on Sept. 19, marking another milestone for an observatory that continues to transform our understanding of the universe. Hubble has traveled more than 5 billion miles (8 billion kilometers) around Earth over its 36-year lifetime and made more than 1.7 million observations.
An observation made on the day of its 200,000th orbit relates to one of Hubble's defining scientific legacies: measuring the expansion rate of the universe, or the Hubble constant. The image takes advantage of the telescope's ability to return to the same regions of the sky over time to monitor for the reappearance of a supernova, or explosion of a star, called Athena. Massive galaxy cluster MACS J0417, located at the left center of the image, acts as a gravitational lens, bending and magnifying light from objects far behind it.
Light from a supernova can reach Earth along multiple paths, causing the same stellar explosion to appear more than once, with appearances separated by months or even years depending on the paths the light takes. Supernova Athena, discovered by NASA's James Webb Space Telescope in 2025, is predicted to reappear between now and early March 2027. Measuring the timing of Athena's reappearances can help researchers map the mass of MACS J0417, which acts as a magnifying foreground lens for distant objects, and refine our understanding of the expansion rate of the universe.
After more than 36 years in space, Hubble is still reaching new heights of scientific productivity and impact. Hubble's unique ability to observe and analyze ultraviolet and visible light complements the capabilities of NASA's James Webb Space Telescope and the Roman Space Telescope. Demand for Hubble observing time remains high: Each year, astronomers request about seven times as much time as is available.
Hubble continues to observe targets across every area of astronomy around the clock. Real-time tracking of those observations is available on NASA's website. MA in English, copy editor since 2021 with experience in higher education and health content.
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