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The cosmic distance ladder 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" 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. Several methods rely on a standard candle, which is an astronomical object that has a known luminosity.
HD 114783 is a star with two exoplanetary companions in the equatorial constellation of Virgo. With an apparent visual magnitude of 7.56 it is too faint to be visible with the unaided eye, but is an easy target for binoculars. Based on parallax measurements, it is located at a distance of 68.7 light years from the Sun, but is drifting closer with a radial velocity of −12 km/s.
R Doradus is a red giant variable star in the far-southern constellation Dorado. Its distance from Earth is 178 light-years. Having a uniform disk diameter of 57±5 mas, it is thought to be the extrasolar star with the largest apparent size as viewed from Earth.
65 Andromedae, abbreviated 65 And, is a single, orange-hued star in the northern constellation of Andromeda. With an apparent magnitude of 4.73, it is visible to the naked eye. The distance to 65 And can be derived from its annual parallax shift of 7.5 mas, which yields a range of around 440 light years. At that distance, its brightness is relatively lowered primarily by the inverse square law but also by an extinction of 0.16 magnitude due to interstellar dust. The star is moving closer to the Earth with a heliocentric radial velocity of −5 km/s.
7 Aquarii, abbreviated 7 Aqr, is a binary star system in the zodiac constellation of Aquarius. 7 Aquarii is the Flamsteed designation. It is visible to the naked eye with an apparent visual magnitude of 5.5; the brighter component is baseline magnitude 5.62 while the faint secondary is magnitude 11.4. As of 2002, the pair had an angular separation of 2.10″ along a position angle of 165°. The distance to this system, based upon an annual parallax shift of 4.9 mas, is around 660 light years. It is moving closer to the Earth with a heliocentric radial velocity of −32 km/s.
66 Aquilae, abbreviated 66 Aql, is a fifth-magnitude star in the constellation of Aquila. 66 Aquilae is its Flamsteed designation. It is visible to the naked eye, having an apparent visual magnitude of 5.44. The star shows an annual parallax shift of 4.4 mas, which provides a distance estimate of around 730 light years. It is moving closer to the Earth with a heliocentric radial velocity of −30 km/s. The motion of the star over time suggests some displacement, which may indicate it is a close binary system.
6 Boötis is a binary star system in the northern constellation of Boötes, located around 460 light years away from the Sun. It has the Bayer designation e Boötis; 6 Boötis is the Flamsteed designation. The system is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.92. It is moving closer to the Earth with a heliocentric radial velocity of −3 km/s.
1 Cancri is a single star in the zodiac constellation of Cancer, positioned near the border with Gemini at a distance of around 470 light years from the Sun. It is barely visible to the naked eye as a dim, orange-hued star with an apparent visual magnitude of 5.97. The object is moving further from the Earth with a heliocentric radial velocity of +14 km/s.
60 Cancri is a star in the zodiac constellation Cancer, located about 850 light years away from the Sun. It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of +5.44. 60 Cancri is situated near the ecliptic, so it is subject to the occasional occultation by the Moon. It is moving away from the Earth with a heliocentric radial velocity of +25 km/s.
Theta Geminorum is a single star in the northern zodiac constellation of Gemini. It is visual to the naked eye with an apparent visual magnitude of 3.59. Based upon an annual parallax shift of 17.25 mas, it is about 189 light years distant from the Sun.
HD 197036 is a single star in the northern constellation Cygnus. It has an absolute magnitude of −1.15 and an apparent magnitude of 6.61, below the max naked eye visibility. Located 1,310 light years away, it is approaching Earth with a heliocentric radial velocity of −15 km/s.
Gliese 42 is a star in the southern constellation of Sculptor. It is too faint to be seen with the naked eye, having an apparent visual magnitude of +7.3. The annual parallax shift of 70.56 mas provides a distance estimate of 46 light years. It has a relatively high proper motion, advancing 0.62 arcseconds across the sky per annum, and is moving closer to the Sun with a radial velocity of −13 km/s.
6 Draconis is a single-lined spectroscopic binary star system in the northern constellation of Draco, located about 430 light years away from the Sun. It is visible to the naked eye as an orange-hued star with an apparent visual magnitude of 4.95. The system is moving further from the Earth with a heliocentric radial velocity of 3 km/s.
Upsilon1 Eridani is a single star in the constellation Eridanus. It has an apparent visual magnitude is 4.51, which is bright enough to be faintly visible to the naked eye on a clear, dark night. The distance to this star, as determined using the parallax method, is around 127 light years.
111 Herculis is a suspected astrometric binary star system located 92 light years from the Sun in the northern constellation Hercules. It is visible to the naked eye as a faint, white-hued point of light with an apparent visual magnitude of 4.34. The system is moving nearer to the Earth with a heliocentric radial velocity of −45 km/s, and may come as close as 37 light-years in 537,000 years.
HD 81799 is a suspected astrometric binary star system in the equatorial constellation of Hydra. It is visible to the naked eye with an apparent visual magnitude of 4.69. The distance to this system, as determined from an annual parallax shift of 19.9 mas, is 164 light years. It is moving further away from the Earth with a heliocentric radial velocity of 29 km/s. The system has a relatively high rate of proper motion, traversing the celestial sphere at the rate of 233±19 mas/yr along a position angle of 136°.
Kappa Pavonis is a variable star in the constellation Pavo. It is the brightest W Virginis variable in the sky.
16 Virginis is a single star in the zodiac constellation of Virgo, located about 308 light years from the Sun. It has the Bayer designation c Virginis; 16 Virginis is the Flamsteed designation. This object is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.96. This is an IAU radial velocity standard star; it is moving further from the Earth with a heliocentric radial velocity of +37 km/s. The star has a relatively high proper motion, traversing the celestial sphere at an angular rate of 0.301″ per year.
3 Piscis Austrini, also known as HD 201901, is a suspected astrometric binary star system that, despite its Flamsteed designation, is actually located in the constellation Microscopium. It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 5.41. The system is moving closer to the Earth with a heliocentric radial velocity of −46 km/s. It is following a highly elliptical orbit around the Galactic Center, moving between a pericenter of 2.6 kpc out to an apocenter of 7.6 kpc, with an orbital eccentricity of 0.49.
Adriaan Jan Wesselink (1909–1995) was a Dutch astronomer who worked successively in the Netherlands, South Africa and the United States. He specialised in observing and understanding the characteristics of stars, particularly variable stars.
References
- ↑ Adriaan Wesselink (1946). "The observations of brightness, colour and radial velocity of δ Cephei and the pulsation hypothesis (Errata: 10 258, 310)". Bulletin of the Astronomical Institutes of the Netherlands . 10: 91–100. Bibcode:1946BAN....10...91W.
- ↑ "Baade–Wesselink method". Oxford Reference. Retrieved 4 February 2019.
- ↑ Kirshner, R. P.; Kwan, J. (1974). "Distances to extragalactic supernovae". The Astrophysical Journal. 193: 27. Bibcode:1974ApJ...193...27K. doi:10.1086/153123.
- ↑ Schmidt, B. P.; Kirshner, R. P.; Eastman, R. G. (1992). "Expanding photospheres of type II supernovae and the extragalactic distance scale". The Astrophysical Journal. 395: 366–386. arXiv: astro-ph/9204004 . Bibcode:1992ApJ...395..366S. doi:10.1086/171659. S2CID 119342854.