southern Cross
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Southern Cross constellation |
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|---|---|
  |
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| Latin name | Crux |
| Latin genitive | Crucis |
| Abbreviation | Cru |
| Right ascension | 11 h 56 m 14 s to 12 h 57 m 45 s |
| declination | −64 ° 41 ′ 46 ″ to −55 ° 40 ′ 38 ″ |
| surface | 68,447 deg² rank 88 |
| Completely visible | 25.5 ° N to 90 ° S |
| Observation time for Central Europe | not observable |
| Number of stars brighter than 3 mag | 4th |
| Brightest star (size) | Acrux (0.77) |
| Meteor streams |
Crucids |
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Neighboring constellations ( clockwise from north ) |
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| swell | IAU , |
The Southern Cross ( Latin crux ) is a small but distinctive constellation in the southern sky. Due to its four bright stars and the proximity to those of the centaur , it is a very noticeable constellation that is also used for approximate orientation to the south.
description
The Southern Cross is one of the smallest constellations, but very noticeable and well known. The four brightest stars (three of the first magnitude , which are also easily observable double stars ) form a striking cross in the sky. It lies in the middle of the bright band of the Milky Way . To the south a clear dark cloud, the " coal sack ", can already be seen with bare eyes .
Alpha, Beta and Gamma Crucis are easily observable binary stars, three other bright ones are Iota, My and Chi Crucis.
A bright fourth magnitude star cluster , NGC 4755 , was called "jewelry box" by John Herschel. Other star clusters already visible in binoculars are NGC 4349 , NGC 4439 , NGC 4463 as well as NGC 4052 , NGC 4103 and H5 .
The constellation is surrounded in the east, west and north by the extensive constellation Centaur , in the south by the fly (Musca). It cannot be seen from Europe, but only near the equator . The elongated cross axis Alpha - Gamma Crucis shows, extended 5 times, approximately to the southern celestial pole , which is why the constellation was previously important for navigation at sea.
history
The Southern Cross is not one of the 48 classic constellations of antiquity . At the time of ancient Greece, the constellation could still be seen from the Mediterranean area, but was assigned to the centaur. Due to the precession movement of the earth, the visible position of the constellation has meanwhile shifted to the south. However, Dante seems to have already known the southern cross as a distinct constellation.
When the European seafarers crossed the southern seas in the 16th century, they became aware of the constellation again, seeing in it the cross of the Christian faith . The cross also served them for orientation, as the vertical axis points to the southern celestial pole . The stars of the cross as a guide were already known to Amerigo Vespucci in 1501 ; the positions were described in more detail by Andrea Corsali in 1515. As a constellation in its current form, it was drawn for the first time in 1589 by Petrus Plancius on a celestial globe (it is located on a globe from 1589 wrong with Eridanus ). Hevelius was the next to include it in his atlas Firmamentum Sobiescianum (Uranographia) .
Celestial objects
Stars
| B. | F. | Names or other designations | size | Lj | Spectral class |
|---|---|---|---|---|---|
| α | Acrux , Trishanku | 0.77 m | 321 | B0 IV + B1V | |
| β | Becrux , Mimosa | 1.25 m | 353 | B0 III + G ? | |
| γ | Gacrux | 1.59 m | 87.9 | M4 III + A3 | |
| δ | Decrux , Delcrux | 2.79 m | 364 | B2 IV | |
| ε | Epsilon Crucis | 3.4 to 4.0 m | 228 | K3 III | |
| μ 1 | 4.03 m | 378 | B1 IV | ||
| ζ | 4.06 m | 361 | B2 V | ||
| η | 4.14 m | 64.2 | F2 III | ||
| θ 1 | 4.32 m | 230 | A. | ||
| λ | 4.62 m | 360 | B4 V | ||
| ι | 4.68 m | 125 | K1 III + V | ||
| θ 2 | 4.72 m | 753 | B2 IV | ||
| μ 2 | 5.08 m | 378 | B5 V | ||
| κ | 5.89 m | 1700 | B5 Ia | ||
| HD 108147 | 6.99 m | 127 | F8 / G0 V | ||
| HD 106906 | 7.90 m | 340 | F5 V |
The brightest stars are named Acrux , Becrux , Gacrux and Decrux . These are simply abbreviations for alpha, beta, gamma and delta in connection with the Latin name Crux.
Double stars
| system | Sizes | distance |
|---|---|---|
| α | 1.3 m / 1.7 m / 4.8 m | 4.0 / 90 " |
| β | 1.3 m / 11.2 m | 44 " |
| γ | 1.6 m / 6.4 m | 128 " |
| ι | 4.7 m / 7.8 m | 26.4 " |
| μ | 4.03 m / 5.08 m | 34.9 " |
Acrux is a triple star, consisting of two extremely bright stars of the spectral classes B1 and B2 and a slightly weaker component of the spectral class B4. Even in a small telescope , three white stars can be seen.
Gacrux is a double star , consisting of a very bright red giant star of the spectral class M4 and a weaker, whitish companion of the spectral class A3. Due to its wide angular distance of 128 arcseconds , the system can already be separated in the binoculars .
Variable stars
| star | size | period | Type |
|---|---|---|---|
| β | 1.25 m | Beta Cephei star | |
| ε | 3.4 to 4.0 m | irregular | irregularly variable star |
Becrux (also called Mimosa) is a variable star of the Beta-Cephei type, 353 light-years away .
ε Crucis is an irregularly variable star, the brightness of which fluctuates between 3.4 and 4.0 m with no discernible period . It is 150 light years away and belongs to the spectral class K3.
NGC objects
| NGC | other | size | Type | Surname |
|---|---|---|---|---|
| 4349 | 7.4 m | Open star cluster | ||
| 4755 | 4.2 m | Open star cluster | Jewelbox (jewel box), jewelry box | |
| Dark fog | Coal sack |
The open star cluster Herschel's jewelry box is about 5,000 light years away. A concentration of stars can be seen with the naked eye. In the binoculars and in the telescope there is a magnificent sight of bluish and orange-red stars.
To the southwest of the Southern Cross is a conspicuous dark nebula called the Coal Sack . It is a matter of gas and dust 2,000 light years away that absorbs the light from the stars behind it. Interesting structures can be seen in the binoculars.
Determination of the geographic south pole
When determining the geographic South Pole, the Southern Cross helps to find the North Star, similar to the Big Dipper in the northern hemisphere. Extend the major axis of the cross in the direction where it is longer by about 4.5 times. The south celestial pole is thus determined. The geographic south pole is located from there to the horizon.
"False Cross of the South"
The stars δ and κ Velorum together with ι and ε Carinae , which can also be seen in the sky of the southern hemisphere, form a similar shape and are therefore also referred to as the "false cross of the south", which must not be used as a reference for the south direction. The false cross also has three white and one reddish star, but this is the lower one in the false cross and the upper one in the real one. The crossbar of the false cross runs downwards to the right, and upwards in the real cross.
Representations of the Southern Cross
The Southern Cross is a popular motif for flags in the southern hemisphere. This is how it is depicted on the national flags of Australia , Brazil , New Zealand , Papua New Guinea, and Samoas . The flags of many regions and cities, as well as government organizations from South America and Oceania, also show the Southern Cross.
See also
Individual evidence
- ↑ cf. Divine Comedy , Purgatorio, Canto I, verses 22ff.
- ↑ Ridpath: Star Tales.
- ↑ J. Herrmann Astronomie, dtv 2005
Web links
Historical images:
- Hevelius: Uranographia 1690 - Emisfero Sud , Museo Astronomico di Brera
- Johann Bode: Uranographia 1801 - illustration in Ridpath: Startales.