Object: Stephenson 1

Constellation
RA / DEC
Diameter in '
Magnitude
Number of stars
Brightest star (magnitude)
Distance in parsecs (3.26Ly)
: Lyra
: 18 54.5 / +36.54
: 40
: 3.79
: 77
: 4.3
: 315
Details sketch
Date / Time
Observing Location
Seeing / Transparency
Telescope
Eye-piece
Magnification / Field of View '
: 30/08/10 / 22:05
: Landgraaf
: 4 / 3
: Orion Optics UK 350mm
: 22mm Nagler Type 4
: 73 / 68
Stephenson_1
Observing report
This beautiful open cluster around the colorful double star Delta Lyrae can be found very easily. It is already visible at lowest magnification, but the optimum magnification is 73x, which I get with the 22mm Nagler T4. The first impression of Stephenson 1 is a very pleasing one. Two bright stars, one definitely bluish-white, the other bright orange, with a sparkling of fainter stars surrounding the orange-blue double star. Stephenson 1 has no real distinctive shape or form. The stars seem to be more or less randomly scattered over an area of 20’ to 30’.

Stephenson 1 is however well detached from its surroundings. It is a moderately rich cluster with just over 50 stars, with a large range of brightness, from very bright to very faint. There is no real central star. I can see some chains of stars, but these are rather short. Most of them have three or four stars maximum. To the west of the bright orange Delta 2 Lyrae I see I triangle of almost equally bright stars. The star at the soutwestern tip looks definitely yellow-orange. I also see some areas that look empty, without stars. I do not detect any nebulosity or glow from unresolved stars.


stephenson1_finderchart

Image from Voyager by CapellaSoft

Notes
The first thing to be checked are the three colored stars in Stephenson 1. The table below shows some basic data on these three stars.
stephenson1_table1

The data in the table above confirms the visual observation of the three colourful stars in the open cluster Stephenson 1. Delta 1 Lyrae is a hot B2.5V main sequence dwarf, which explains the blue-white color at the eyepiece. Delta 2 Lyrae is a M4II bright (red) giant, which looks orange visually. SAO 67546 is a K0III normal (red) giant, which like Delta 2 Lyrae, also looks orange visually. On the HR diagram below you see the stars plotted at their actual positions in the diagram.

Stephenson1HRDtxt.jpg
Stephenson1_HRD

Move the mouse over the HRD of Stephenson 1 to label the stars.

Delta 1 and 2 Lyrae
The bright blue and orange star in the cluster Stephenson 1, Delta 1 Lyrae and Delta 2 Lyrae, are a visual double star, not a true physical binary. They are actually separated by 50 parsec (almost 200 lightyears). Delta Lyrae 1 is probably a member of Stephenson 1, lying right at the core of this open cluster. The distance to Stephenson 1 and Delta Lyrae 1 is almost equal. Delta Lyrae 2 lies much closer to us, about 50 parsecs.

The size of the three colored stars compared to the Sun.
As you can see from the table above, Delta 2 Lyrae, the red bright giant, has a radius about 200 times that of our Sun, a true giant. On the image below you see the sun as the little white dot on the left, and Delta 2 Lyrae as the red giant on the right. This comparison gives an idea how huge this star actually is. Between the Sun and Delta 2 Lyrae , you see the blue-white main-sequence dwarf Delta 1 Lyrae and the orange K0 giant SAO 67546 with Solar radii of 5.6 and 14.6.


Stacks Image 2389

Resources
Voyager by CarinaSoft
SkySafari by Southern Stars
Star Clusters by Brent and Archinal
The Hundred greatest Stars by James Kaler