Monday, March 20, 2017

The colors in the night sky

Mirach and its Ghost

Click to enlarge


This is a frequently asked question and the cause of many disappointments among newbie stargazers: why can’t color be seen in this or that object? It is not the telescope’s fault but actually our own eyes. The few amount of light we get to hunt down from DSOs is not strong enough to activate the perception of color performed by our cones photoreceptors. Yet there have been reports of seeing color in Orion Nebula or specks of blue and red in the edges of  Ring Nebula. I personally had the feeling of seeing some color in Ring Nebula, but other than that, I can’t recall seeing color in other deep sky objects.

On the other hand, stars are bright and concentrated enough to trigger the sense of color in our cones. Some of the best views are provided by red stars like Antares or Arcturus, blue stars like The Pleiades or Rigel and even double colorful systems like Albireo in Cygnus.

This time lets look at Mirach, the beta star in the constellation of Andromeda. We have used this star before to find the way to the Andromeda Galaxy (M31). Apart from M31, Mirach has a closer friend:  the galaxy NGC404 also known as the Ghost of Mirach.  

While one is enjoying the bronze shine of Mirach, it is possible with the use of averted vision to catch a glimpse of its ghost.  I have to admit that I hadn’t seen the galaxy till I started to look for it. It was not hard to find though. The trick here is to avoid seeing directly to Mirach and start to look for an smudge in its periphery. In fact, some stargazers advice trying to take out Mirach from the FOV as it is a distractor of the peripheric vision, but the problem comes if the view in the eyepiece suffers from vignetting. The few 6 arc minutes that separate the star from the galaxy could not be enough to get a decent view outside the dark edge of a regular eyepiece. In my case, the Luminos 15mm does not show image aberrations at the edge (or at least very noticeable) so I could move away the star and its glance far enough to detect the galactic smudge.

I think the color of Mirach plus the ghosty image make a good couple. It is definitely one of the targets worth keeping the eyes to the eyepiece for a couple of minutes and if one is looking for color in the sky, the stars are there to show us the color of their skin.


Clear skies,


LG

Edited by Jennifer Steinberg (editor in chief)

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