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Katherine Johnson’s mathematical calculations helped guide some of America’s most important early space missions while she confronted the racial and gender barriers faced by Black women in twentieth-century America.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
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| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 11h 53m 49.84732s[1] |
| Declination | +53° 41′ 41.1350″[1] |
| Apparent magnitude (V) | 2.438[2] |
| Characteristics | |
| Spectral type | A0 Ve + K2 V[3] |
| U−B color index | +0.008[2] |
| B−V color index | –0.013[2] |
| Astrometry | |
| Radial velocity (Rv) | −12.6[4] km/s |
| Proper motion (μ) | RA: +107.68[1] mas/yr Dec.: +11.01[1] mas/yr |
| Parallax (π) | 39.21±0.40 mas[1] |
| Distance | 83.2 ± 0.8 ly (25.5 ± 0.3 pc) |
| Absolute magnitude (MV) | 0.4[5] |
| Orbit[5] | |
| Period (P) | 20.5 ± 1 yr |
| Semi-major axis (a) | 0.460″ |
| Eccentricity (e) | 0.3 ± 0.3 |
| Inclination (i) | 51 ± 15° |
| Longitude of the node (Ω) | 6 ± 61° |
| Periastron epoch (T) | B 1984.0 ± 2.0 |
| Argument of periastron (ω) (secondary) | 185 ± 37° |
| Details[6] | |
| γ UMa A | |
| Mass | 2.412+0.053 −0.060 M☉ |
| Radius | 3.385 (equatorial) 2.186 (polar) R☉ |
| Luminosity | 44.57+3.39 −3.61 L☉ |
| Surface gravity (log g) | 3.79[7] cgs |
| Temperature | 6,751 (equatorial) 10,520 (polar) K |
| Rotational velocity (v sin i) | 184.5+32.6 −35.6 km/s |
| Age | 333+43 −83 Myr |
| γ UMa B | |
| Mass | 0.79[3] M☉ |
| Radius | 0.919[3][a] R☉ |
| Luminosity | 0.397[3] L☉ |
| Temperature | 4,780[3] K |
| Other designations | |
| Phad, Phecda, Phekda, Phegda, Phekha, Phacd, Fekda,[8] γ Ursae Majoris, γ UMa, Gamma UMa, 64 Ursae Majoris, BD+54 1475, FK5 447, GC 16268, HD 103287, HIP 58001, HR 4554, PPM 33292, SAO 28179.[9] | |
| Database references | |
| SIMBAD | data |
Phecda /ˈfɛkdə/, also called Gamma Ursae Majoris (γ Ursae Majoris, abbreviated Gamma UMa, γ UMa),[10][11] is a star in the constellation of Ursa Major. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[12] Based upon parallax measurements with the Hipparcos astrometry satellite,[13][14] it is located at a distance of around 83.2 light-years (25.5 parsecs) from the Sun.[1]
It is more familiar to most observers in the Northern Hemisphere as the lower-left star forming the bowl of the Big Dipper, together with Alpha Ursae Majoris (Dubhe, upper-right), Beta Ursae Majoris (Merak, lower-right) and Delta Ursae Majoris (Megrez, upper-left). Along with four other stars in this well-known asterism, Phecda forms a loose association of stars known as the Ursa Major moving group.[7] Like the other stars in the group, it is a main sequence star, as the Sun is, although somewhat hotter, brighter and larger.
Phecda is located in relatively close physical proximity to the prominent Mizar–Alcor star system. The two are separated by an estimated distance of 8.55 ly (2.62 pc); much closer than the two are from the Sun. The star Merak is separated from Phecda by 11.0 ly (3.4 pc).[15]
γ Ursae Majoris (Latinised to Gamma Ursae Majoris) is the star's Bayer designation.
It bore the traditional names Phecda or Phad, derived from the Arabic phrase فخذ الدب fakhth al-dubb ('thigh of the bear').[16] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[17] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[18] included a table of the first two batches of names approved by the WGSN, which included Phecda for Gamma Ursae Majoris A.
To the Hindus this star was known as Pulastya, one of the seven rishis.[8]
In Chinese, 北斗 (Běi Dǒu), meaning Northern Dipper, refers to an asterism equivalent to the Big Dipper. Consequently, the Chinese name for Gamma Ursae Majoris itself is 北斗三 (Běi Dǒu sān, English: the Third Star of Northern Dipper) and 天璣 (Tiān Jī, English: Star of Celestial Shining Pearl).[19]
Phecda is an Ae star, which is surrounded by an envelope of gas that is adding emission lines to the spectrum of the star;[20] hence the 'e' suffix in the stellar classification of A0 Ve.[15] It is 2.4 times more massive than the Sun and is 333 million years old. It rotates rapidly with a rotational velocity of 386 km/s at its equator, which causes it to have an oblate shape. The equatorial radius measures 3.39 R☉, while the polar radius measures 2.19 R☉. The effective temperature varies as well, from 6,750 K in the equator to 10,520 K in the poles.[6]
Phecda is also an astrometric binary: the companion star regularly perturbs the Ae-type primary star, causing the primary to wobble around the barycenter. From this, an orbital period of 20.5 years has been calculated.[5] The secondary star is a K-type main-sequence star that is 0.79 times as massive as the Sun, and with a surface temperature of 4,780 K.[3]
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
Phecda , also called Gamma Ursae Majoris (γ Ursae Majoris, abbreviated Gamma UMa, γ UMa), is a star in the constellation of Ursa Major. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. Based upon parallax measurements with the Hipparcos astrometry satellite, it is located at a distance of around 83.2 light-years (25.5 parsecs) from the Sun. It is more familiar to most observers in the Northern Hemisphere as the lower-left star forming the bowl of the Big Dipper, together with Alpha Ursae Majoris (Dubhe, upper-right), Beta Ursae Majoris (Merak, lower-right) and Delta Ursae Majoris (Megrez, upper-left). Along with four other stars in this well-known asterism, Phecda forms a loose association of stars known as the Ursa Major moving group. Like the other stars in the group, it is a main sequence star, as the Sun is, although somewhat hotter, brighter and larger. Phecda is located in relatively close physical proximity to the prominent Mizar–Alcor star system. The two are separated by an estimated distance of 8.55 ly (2.62 pc); much closer than the two are from the Sun. The star Merak is separated from Phecda by 11.0 ly (3.4 pc).
Messier 109 (also known as NGC 3992 or the Vacuum Cleaner Galaxy) is a barred spiral galaxy approximately 67.2 ± 23 million light-years away in the northern constellation Ursa Major. M109 can be seen south-east of the star Phecda (γ UMa, Gamma Ursa Majoris).
This is a list of stars arranged by their apparent magnitude – their brightness as observed from Earth. It includes all stars brighter than magnitude +2.50 in visible light, measured using a V-band filter in the UBV photometric system. Stars in binary systems (or other multiples) are listed by their total or combined brightness if they appear as a single star to the naked eye, or listed separately if they do not. As with all magnitude systems in astronomy, the scale is logarithmic and inverted, i.e., lower/more negative numbers are brighter. Most stars on this list appear bright from Earth because they are nearby, not because they are intrinsically luminous (a factor measured in terms of absolute magnitude).
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines. Each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere, although in some cases there are true abundance differences. The spectral class of a star is a short code primarily summarizing the ionization state, giving an objective measure of the photosphere's temperature. Most stars are currently classified under the Morgan–Keenan (MK) system using the letters O, B, A, F, G, K, and M, a sequence from the hottest (O-type) to the coolest (M-type). Each letter class is then subdivided using a numeric digit with 0 being hottest and 9 being coolest (e.g., A8, A9, F0, and F1 form a sequence from hotter to cooler). The sequence has been expanded with three classes for other stars that do not fit in the classical system: W, S and C. Some stellar remnants or objects of deviating mass have also been assigned letters: D for white dwarfs and L, T and Y for brown dwarfs (and exoplanets). In the MK system, a luminosity class is added to the spectral class using Roman numerals. This is based on the width of certain absorption lines in the star's spectrum, which vary with the density of the atmosphere and so distinguish giant stars from dwarfs. Luminosity class 0 or Ia+ is used for hypergiants, class I for supergiants, class II for bright giants, class III for regular giants, class IV for subgiants, class V for main-sequence stars, class sd (or VI) for subdwarfs, and class D (or VII) for white dwarfs. The full spectral class for the Sun is then G2V, indicating a main-sequence star with a surface temperature around 5,800 K.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Madam C.J. Walker
