Final answer:
Sirius, with a parallax angle of 0.38 arcsec, is the closest star to us from the given options. The distance to a star in parsecs is the reciprocal of its parallax in arcseconds, and a larger parallax angle indicates that the star is closer.
Step-by-step explanation:
The star that is closest to us can be determined by looking at the provided parallax angles. The parallax angle helps us calculate the distance of a star from Earth, as it gives the angular measurement of the star's shift against the background celestial sphere as viewed from opposite sides of the Earth's orbit. The distance (D) to a star in parsecs can be found using the reciprocal of its parallax angle (p) in arcseconds. Therefore, a larger parallax angle indicates a closer star.
Given the parallax angles:
- A. Procyon = 0.29 arcsec
- B. Ross 780 = 0.21 arcsec
- C. Regulus = 0.04 arcsec
- D. Sirius = 0.38 arcsec
Applying the reciprocal rule, we find the distances as follows:
- Procyon: 1/0.29 parsecs
- Ross 780: 1/0.21 parsecs
- Regulus: 1/0.04 parsecs
- Sirius: 1/0.38 parsecs
Among the given options, Sirius has the largest parallax angle, which results in the shortest distance in parsecs, making it the closest star to us among the ones listed.