Rukbat al Rami - Pern's sun

Rukbat is known as the sun of Anne McCaffrey's World of Pern (also here). It is located in the constellation Sagittarius, the Archer, and the translation of the Arabic name "Rukbat al Rami" is "Archer's Knee".

Some astronomical data about Rukbat:
Designation:alpha Sagittarii, HD181869, Hipparcos H95347
Position:RA 19h 23m 53.18s, DE -40deg 36m 57.4s
Distance:169.88 lightyears, or 1.607 quadrillion kilometers
Apparent magnitude:3.95m
Absolute magnitude:0.38M
Spectral class:B8V (unfortunately not a G-type star)
Brightness:about 53x our sun
Diameter:approx. 2.6 million km (1.9x our sun)
Surface temperature:12000K

Rukbat's position as alpha Sagittarii

Rukbat al Rami is in the center of the image (263 kB),
at the upper end of this scissors like figure.
To the right ist the Scorpion's tail, in the upper left is Capricornus.
The hook-like constellation right next to Rukbat is the Corona Australis.
The diffuse, bright spot in the upper right
is roughly the direction of the center of our galaxy.

Flying from Earth to Pern, looking at...

...our Sun (894 kB)
...Rukbat (822 kB).
...Orion (1.07 MB).
...the Big Dipper (975 kB).
...the Scorpion (956 kB).

The night sky, as seen from Pern

The following images comprise a star map of the stars that can be seen by somebody living on the planet Pern.
Each vertical line represents one hour (=15 degrees) of right ascension (0h..24h, counterclockwise), each horizontal line represents 10 degrees of declination (-90..90). The view angle of all images is 60 degrees.
Note that of course the grid orientation is chosen arbitrarily - we do not know the orientation of Rukbat's solar system, nor do we know the direction of Pern's north-south axis.
In fact, I used the same coordinate system as for our earth - this way you can compare the maps with standard star maps, to see how much the star's positions have shifted.

So, who can find a constellation that resembles a dragon? :-)

RA 0h, DE 90N

(bottom: 0h, left: 6h, top: 12h, right: 18h. largest circle: 60N)
This is the direction where we would usually see the polar star right in the center. However, since our distance to this star is about 430 ly, its position does not shift very much. It can now be found at 7h15 76N.
The brighter, more reddish star in the top left is tau Sgr. In the bottom left we can find the blue-white gamma Cas, and right below it the two open clusters chi and h Persei. Their positions did not change noticeably, due to the huge distance of more than 7000 ly.

RA 2h, DE 45N

(top left corner: 6h 60N, top right corner: 22h 60N)
Slightly overlapping with the 90N image, chi and h Persei are in the upper half of the image. Right below them is the deep red beta Pegasi. The bright stars to the left belong to Perseus and Andromeda. The two bright stars near the center are barely visible from earth - they are very close to Rukbat (29 and 16 ly).

RA 2h, DE 0N

(bottom: 30S, left: 4h, top: 30N, right: 0h)
The two bright stars are beta and gamma Grus.

RA 2h, DE 45S

(bottom left corner: 6h 60S, bottom right corner: 22h 60S)
The very bright, blue star to the left is alpha Pavo, 60ly. It is almost as bright as our Sirius.

RA 6h, DE 45N

(top left corner: 10h 60N, top right corner: 2h 60N)
Our Sun is in this image! But since it is much less powerful than Rukbat, its apparent brightness is just 7.9m - it is not visible for the naked eye. Its location is the inverse of Rukbat's: 7h23m, 40deg36m. The cluster of blue stars in the lower right are the Pleiades (500 ly, half as bright as seen from Earth).

RA 6h, DE 0N

(bottom: 30S, left: 8h, top: 30N, right: 4h)
The rather distorted Orion constellation (compare to the Orion movie above).

RA 6h, DE 45S

(bottom left corner: 10h 60S, bottom right corner: 2h 60S)
Canopus, our second brightest star. A bit on the yellowish side, and only slightly darker when looking at it from Rukbat (345 ly, -0.4m). To the right is once more alpha Pavo.

RA 10h, DE 45N

(top left corner: 14h 60N, top right corner: 6h 60N)
Again two stars belonging to the Sagittarius constellation: the white epsilon and the red eta, both at 43 ly distance.

RA 10h, DE 0N

RA 10h, DE 45S

(bottom left corner: 14h 60S, bottom right corner: 6h 60S)
This cloud of intensely blue stars apparently all belong to the same group, between 300 and 400 ly from Rukbat. The three brightest ones in the center are the main stars of the sourthern cross. In the lower left is beta Centaurus.

RA 14h, DE 45N

(top left corner: 18h 60N, top right corner: 10h 60N)
The stars to the right are the same as in the image above.

RA 14h, DE 0N

(bottom: 30S, left: 16h, top: 30N, right: 12h)
This chart contains the brightest - and also the closest - star that can be seen from Rukbat. Its distance is 10 ly, and it is slightly brighter (-1.62m) than our brightest star Sirius. Its designation is delta Corona Australis. The red star right next to it is Antares (480 ly 0.6m).

RA 14h, DE 45S

(bottom left corner: 18h 60S, bottom right corner: 10h 60S)
To the left is the white zeta Corona Australis (19 ly, -0.2m), and the yellow theta Scorpii (126 ly, 0.2m). Most of the blue stars belong to a densely populated area in Centaurus, the bright one to the right (beta Centaurus, 440 ly) being one of them.

RA 18h, DE 45N

RA 18h, DE 0N

(bottom: 30S, left: 20h, top: 30N, right: 16h)
The blue sigma Sgr (44ly, -0.3m), and its smaller companion phi (42ly, 0.9m). They are 11 ly apart.

RA 18h, DE 45S

RA 22h, DE 45N

(top left corner: 2h 60N, top right corner: 18h 60N)
The white star to the right is Deneb, about 200000x brighter than our Sun! Its distance is 3220 ly, and it is the most luminous known star.

RA 22h, DE 0N

RA 22h, DE 45S

RA 0h, DE 90S

More information

A few years ago the astrometrical satellite Hipparcos surveyed several million stars and generated high quality measurements of positions, colors, brightnesses, and distances. The 118000 stars of the Hipparcos catalogue are used in a 3D model to create the above images. An additional number of 935000 stars from the Tycho I catalogue is used as an underlying texture.
The images and movies were rendered on SGI workstations in realtime using our visualization software Genesis2, and the rendering system VirtualDesign2.

All images and movies © 2000 by Wolfram Kresse.