Asterism "French 20": A toadstool in the sky...
The asterism "French 20" is also called "Toadstool" and is located in the summer sky in the constellation Dolphin. It lies about one and a half degrees
east of the globular cluster "NGC 7006" and has an apparent size of 11'x14'.
The toadstool consists of 10 brighter and some fainter stars, which just happen to be in the same direction and are not gravitationally bound to each other.
The distances vary between 600 and 8,600 light-years. The magnitudes of the individual stars vary between 8.8mag and 12.1mag, so that the asterism is
a nice sight even in a small telescope.
At the base of the mushroom there is a small galaxy named "NGC 7025", which was discovered in 1863 by the German astronomer Albert Marth. It is
230 million light years away from Earth and is a spiral galaxy (type S0Aa). From the apparent magnitude of 12.9mag the absolute magnitude can be
calculated to -21.3mag, which corresponds to a luminosity of about 30 billion suns. With a true diameter of about 130,000 light years NGC 7025 is a
bit larger than our own Milky Way.
----------------------------------------------------------------------------------------------------------------------------------------------
One of the funniest objects ever is in the constellation Dolphin. I don't know when or where I stumbled across this object, but it was in my early days with
8" aperture. All I can remember is that I was looking for NGC 7006. Because I didn't find the globular cluster, I changed my strategy and started sweeping
the area aimlessly. But instead of NGC 7006 I suddenly had this asterism in my eyepiece and was totally perplexed:
In the middle of the eyepiece I saw a "toadstool" and at the foot of the mushroom a small ant in form of a galaxy... This is a good way to describe "French
20" ;) If you look very closely, you can see another tiny galaxy near the center. But this one is quite difficult even with 20 inches at 270x under a superb
sky... The Ant on the other hand can be seen with 8" aperture.
Since this first sighting, the mushroom with the ant is one of my favorite objects and is on the starting line almost every night during the summer.
(If you move the cursor over the drawing, the distance of the stars is displayed.)
