https://www.khanacademy.org/science/cambridge-o-level-physics-cie/x0e04e0cb682fb793:space-science/x0e04e0cb682fb793:the-universe/v/galaxies-and-gravity 2022-09-10T03:34:09.940758862Z Galaxies and gravity Earth is part of the solar system, which is part of a galaxy, which is part of a galaxy group. All of these systems are held together by gravity, a force that pulls objects with mass toward each other. Khan Academy video https://cdn.kastatic.org/ka_thumbnails_cache/1b98d857-37f2-4764-9e8e-84ae4dab4476_1280_720_base.png Galaxies and gravity Earth is part of the solar system, which is part of a galaxy, which is part of a galaxy group. All of these systems are held together by gravity, a force that pulls objects with mass toward each other. https://cdn.kastatic.org/ka-youtube-converted/tNGVqoOLl-k.mp4/tNGVqoOLl-k.mp4 235 The Universe https://www.khanacademy.org/science/cambridge-o-level-physics-cie/x0e04e0cb682fb793:space-science/x0e04e0cb682fb793:the-universe/a/galaxies-and-gravity 2026-04-26T16:30:39.382257956Z Key points: Galaxies and gravity Review your understanding of galaxies and gravity in this free article aligned to NGSS standards. article https://www.khanacademy.org/science/cambridge-o-level-physics-cie/x0e04e0cb682fb793:space-science/x0e04e0cb682fb793:the-universe/e/understand-galaxies-and-gravity 2026-04-26T16:30:39.382257956Z Understand: Galaxies and gravity Check your understanding of galaxies and gravity in this set of free, standards-aligned practice questions. Lauren Rosebrugh exercise https://www.khanacademy.org/science/cambridge-o-level-physics-cie/x0e04e0cb682fb793:space-science/x0e04e0cb682fb793:the-universe/e/apply-galaxies-and-gravity 2026-04-26T16:30:39.382257956Z Apply: Galaxies and gravity Apply your understanding of galaxies and gravity in this set of free, standards-aligned practice questions. Lauren Rosebrugh exercise https://www.khanacademy.org/science/cosmology-and-astronomy/universe-scale-topic/big-bang-expansion-topic/v/big-bang-introduction 2021-04-04T12:52:27Z Big bang introduction Sal Khan video https://cdn.kastatic.org/googleusercontent/yS3isbJgQeGzBD2vA3nsZb49qvokvWETy54AlwE_N_Jhc0ZJJrs0Wk2zS2ltwo39kCvOIzaKRDsldX2D0Boyr7k Big bang introduction https://cdn.kastatic.org/ka-youtube-converted/eUF59jCFcyQ.mp4/eUF59jCFcyQ.mp4 663 The Universe https://www.khanacademy.org/science/cambridge-o-level-physics-cie/x0e04e0cb682fb793:space-science/x0e04e0cb682fb793:the-universe/a/video-the-big-bang 2026-01-24T14:10:36.770864637Z The Big Bang We may not know everything about the Big Bang, but there’s a lot we do know. Our knowledge of the Universe begins just a fraction of a second after the Big Bang took place. article https://www.khanacademy.org/science/cosmology-and-astronomy/universe-scale-topic/big-bang-expansion-topic/v/radius-of-observable-universe 2021-04-04T12:52:27Z Radius of observable universe Radius of Observable Universe Sal Khan video https://cdn.kastatic.org/googleusercontent/sVQyaTNAayDXAxRdrP4S0vsEAHd8YND1HtlYds0SJa4I_eciVraSZazEKKEJ3KIyabi-5ctpy7n2K8nzdENu6VjHTg Radius of observable universe Radius of Observable Universe https://cdn.kastatic.org/ka-youtube-converted/6nVysrZQnOQ.mp4/6nVysrZQnOQ.mp4 999 The Universe https://www.khanacademy.org/science/cosmology-and-astronomy/universe-scale-topic/big-bang-expansion-topic/v/red-shift 2021-07-06T13:18:38Z Red shift Sal Khan video https://cdn.kastatic.org/googleusercontent/qqAaP_iLY2zBDup91m_GTO5BovIpTu0ef42JQSvX7bmu8szu5QNMMlvU_B5TYavRHE-zfU8qu7X1Q0UWCyrq5Xut Red shift https://cdn.kastatic.org/ka-youtube-converted/mx2M_ZKXM_c.mp4/mx2M_ZKXM_c.mp4 604 The Universe