Arcturus

Definition

Arcturus is a red giant star that is one of the brightest stars in the night sky. It is located in the northern celestial hemisphere and is part of the constellation Boötes, the Herdsman. Arcturus is known for its distinctive orange-red color and is a prominent feature in the evening sky during certain times of the year.

5 Must Know Facts For Your Next Test

1. Arcturus is one of the closest red giant stars to Earth, located approximately 37 light-years away.
2. With an apparent magnitude of -0.05, Arcturus is the fourth-brightest star in the night sky, after Sirius, Canopus, and Alpha Centauri.
3. Arcturus has a mass about 1.08 times that of the Sun and a radius about 25 times larger, making it a typical red giant star.
4. The star's high proper motion, or apparent motion across the sky, is a result of its relatively close proximity to the Sun.
5. Arcturus is a member of the Arcturus moving group, a set of stars that share a common motion through space and are thought to have formed from the same giant molecular cloud.

Review Questions

• Explain how the characteristics of Arcturus, as a red giant star, are related to its position on the Hertzsprung-Russell (H-R) diagram.
  • As a red giant star, Arcturus is located in the upper right region of the H-R diagram, which represents stars with low surface temperatures and high luminosities. This is because red giants have expanded and cooled as they have exhausted the hydrogen in their cores and begun fusing hydrogen in a shell around the core. This expansion has caused the star's radius to increase significantly, resulting in a lower surface temperature but a higher overall luminosity compared to main sequence stars like the Sun.
• Describe how the distance to Arcturus can be determined using the concept of parallax, and how this information is used to calculate the star's absolute magnitude.
  • The distance to Arcturus can be determined using the parallax method, which measures the apparent shift in a star's position relative to more distant background stars as the Earth orbits the Sun. By measuring the parallax angle of Arcturus, astronomers can calculate its distance using the inverse relationship between parallax and distance. Once the distance is known, the star's absolute magnitude, which is a measure of its intrinsic brightness, can be calculated from its apparent magnitude and distance using the distance modulus formula: $M = m - 5 \log_{10}(d) + 5$, where $M$ is the absolute magnitude, $m$ is the apparent magnitude, and $d$ is the distance in parsecs.
• Analyze how the high proper motion of Arcturus, relative to other nearby stars, provides information about its membership in the Arcturus moving group and the overall structure and dynamics of the local stellar neighborhood.
  • The high proper motion of Arcturus, which is the star's apparent angular motion across the sky, indicates that it is moving at a relatively high velocity compared to other nearby stars. This is a characteristic of the Arcturus moving group, a set of stars that share a common motion through space and are believed to have formed from the same giant molecular cloud. By studying the proper motions and other kinematic properties of Arcturus and other members of the Arcturus moving group, astronomers can gain insights into the structure and dynamics of the local stellar neighborhood, including the distribution of matter and the gravitational forces that shape the motions of stars in this region of the Milky Way galaxy.

Related terms

Red Giant:

A large, cool, and luminous star that has exhausted the hydrogen in its core and is fusing hydrogen in a shell around the core, causing the star to expand and cool.

Absolute Magnitude:

A measure of the intrinsic brightness of a star, based on how bright the star would appear if it were located 10 parsecs (32.6 light-years) from Earth.

Parallax:

The apparent shift in the position of an object due to a change in the observer's position, used to measure the distance to nearby stars.