Lecture

The Cosmic Distance Ladder

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In course

PHYS-643: Astrophysics VI : The variable Universe

Introduction to time-variable astrophysical objects and processes, from Space Weather to stars, black holes, and galaxies. Introduction to time-series analysis, instrumentation targeting variability, and the importance of the time domain for astronomy, cos ...

Description

This lecture discusses the recalibration of the cosmic distance ladder using accurate photometry of galactic Cepheids with HST and Gaia EDR3 parallaxes. It explores the challenges of relying on Gaia and HST photometry, the impact of Gaia systematic errors on parallax measurements, and the need for additional offsets in the global fit. The instructor presents conclusions on achieving a 1% determination of the cepheid distance and the potential for further refinement in Gaia DR4.

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Instructor

Richard Irving Anderson

Official source

Ontological neighbourhood

Astronomy

Astrophysics: Stellar astronomy

Related concepts (32)

Cosmic distance ladder

The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A direct distance measurement of an astronomical object is possible only for those objects that are "close enough" (within about a thousand parsecs) to Earth. The techniques for determining distances to more distant objects are all based on various measured correlations between methods that work at close distances and methods that work at larger distances.

Stellar parallax

Stellar parallax is the apparent shift of position (parallax) of any nearby star (or other object) against the background of distant stars. By extension, it is a method for determining the distance to the star through trigonometry, the stellar parallax method. Created by the different orbital positions of Earth, the extremely small observed shift is largest at time intervals of about six months, when Earth arrives at opposite sides of the Sun in its orbit, giving a baseline distance of about two astronomical units between observations.

Stellar kinematics

In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as the internal kinematics of more distant galaxies. Measurement of the kinematics of stars in different subcomponents of the Milky Way including the thin disk, the thick disk, the bulge, and the stellar halo provides important information about the formation and evolutionary history of our Galaxy.

Galactic Center

The Galactic Center is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact radio source which is almost exactly at the galactic rotational center. The Galactic Center is approximately away from Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius, where the Milky Way appears brightest, visually close to the Butterfly Cluster (M6) or the star Shaula, south to the Pipe Nebula.

Galactic coordinate system

The galactic coordinate system is a celestial coordinate system in spherical coordinates, with the Sun as its center, the primary direction aligned with the approximate center of the Milky Way Galaxy, and the fundamental plane parallel to an approximation of the galactic plane but offset to its north. It uses the right-handed convention, meaning that coordinates are positive toward the north and toward the east in the fundamental plane. Longitude (symbol l) measures the angular distance of an object eastward along the galactic equator from the Galactic Center.

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The Cosmic Distance Ladder

Explores the fundamental problem of distance in astronomy and discusses various methods for distance measurement, including wide-angle astrometry and detached eclipsing binary distances.

Stellar Orbits: Understanding Galactic Dynamics

Covers the dynamics of stellar orbits in the Milky Way, focusing on the Sun's neighborhood and the significance of Oort constants and epicyclic frequencies.

Hubble's Universe: Redshift and Distance MOOC: Introduction to Astrophysics

Delves into the universe's evolution using Hubble's observations and concepts like redshift, distance measurement, Cepheid stars, and supernovae.

Stellar & Galactic Dynamics

Series explores the dynamics of stars and galaxies, covering topics such as stellar orbits, collisionless systems, and the Milky Way's structures.

The Cosmic Distance Ladder

Explores the Variable Universe through the Cosmic Distance Ladder, focusing on standard candles and the Hubble constant tension.

Related concepts (32)

Cosmic distance ladder

Stellar parallax

Stellar kinematics

Galactic Center

Galactic coordinate system