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M81 & M82 : The galaxies wars

M81 and M82 are the 81st and 82nd Charles Messier wrote down in his catalog. They are part of the M81 Group, a local regroupment of galaxies, about 12 millions lightyears away from our galaxy, the Milky Way.

How can we find it ?

M81 ans M82 are included in the Great Bear constellation. This constellation is one of the easiest to recognize in the nothern hemisphere because of its asterism in shape of dipper.

To find the M81 group, you need to follow the imaginary line (in red).

...Congrats! You have spotted M81 and M82! ...

...You can't see them? It's normal, they are tiny and not shining at all: their apparent magnitude are 6.9 and 8.4 respectively (see previous post).

You will at least need binoculars or take a camera with a zoom lense. If you still can't see them, you will need a telescope or make a long time exposure (about 30 seconds) picture so enough light hits you sensor.

The picture


This picture has been realised with an equatorial mount and a zoom lense (Canon 70-200mm f/2.8) on a Canon 70D. It has been then processed and cropped.

It is the result of 55 minutes exposition time at f/2.8, ISO 1600 and 200mm focal lenght.

The equatorial mount allows the camera to stay aligned to M81 (it compensates the earth rotation).

To take this picture, I got lost in the countryside between Paris and Reims, looking for the perfect spot offering the darkest sky possible.

"We meet again, at last"

We can clearly see M81 (the biggest one) and M82 (just above). These two galaxies are still locked in a gravitational fight that which began billion years ago. The gravity from each of them affect the other:

  • M82's gravity raised density waves in M81 arms

  • M81 left M82 with gas clouds and star forming regions (not visible on the picture)

M81 and M82 have already passed by each other in the past and in a few billion years only one galaxy will remain. The same phenomenon will happen to our galaxy (the Milky Way) and our neighbour: the Andromeda galaxy.

Here is the full scope of the picture.

If you have (really) good eyes you will be able to spot the Coddington nebulae (left) and 3 more galaxies: NGC3077 (left of M81), NGC 2959 (right) and NGC2976 (down right)

The picture is not perfect yet: stars are blurry and the background is still very noisy. This could be corrected with a better polar alignment and by doing more pictures (believe me, 55 minutes is long when you are not moving in the cold), but with patience and more experience I hope I will be able to capture sharper details.

The Andromeda & Milky Way collision

As I said before, our galaxy will enter in collision with M31 in about 4 billion years. We are approaching at a speed around 150km/s (ouch!) but the two galaxies are so diffuse their is almost no chance a collision between two stars occur.

Here is a picture I took of M31, way better than the previous one ! It is the result of a 30 minutes exposure with a 70mm focal lenght at f/4 and ISO 1600.

Normally, in about 2 billion years, M31 will be so close we (or other type of living beings) will be able to see the stars ans the dust inside M31 with the naked eye! See examples below:

To conclude

It is incredible to see what photons that have travelled for millions of years do when they hit your camera sensor! I can't wait to have some good conditions (temperature, Moon, clouds,...) to see other objects.

Hope I will get you a little bit more interested in astronomy.

Anyway, if you want to see these galaxies in details, check the amazing Hubble website: M81 and M82.

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