Sunday, April 19, 2015

M101 and M83

Both pinwheel Galaxies on the same night

M101 and M83 are both spiral Galaxies (M83 is classified as a barred spiral Galaxy) situated at opposite sides of the sky.  Even though they are at different distances from us, 27Mly and 15 Mly respectively, their apparent magnitudes are close to each other: 7.90 and 7.60 respectively. Now, I have also learned that apparent magnitude is not the best way to measure the brightness of some DSOs, so later I will talk about these galaxies’ surface brightness which is a better measurement of brightness in galaxies and others wide “nebulous” objects.

After I had seen M83 for the first time, the 21th of January, I had an itch to sketch both galaxies on the same night. Three days later, I went outside my apartment and spotted what I thought could be M101 (and it was). The very dim spot seemed just like a "presence" in the sky. It was a hard challenge to see it and even more so with the glowing lights around.  I tried to sketch it but my flashlight batteries were dead so it was time to go to bed.

The next day, the 25th, at 3 am I woke up and took the bicycle and my bag packed with binoculars, tripod, sketching stuff and enough flashlights for the night out. On the way out, I put a bamboo chair on the bicycle rack and went south, trying to escape from the city lights. I was riding along the highway so I faced the issue of following the highway street lights. Finally, after almost 40 minutes riding the bike and after trying two or three different spots beside the Highway I found a construction area with no lights, located far enough from the Highway to avoid any intruding lights.

In that place, I could see my hands, but definitely I had to use my flashlight to walk and find my stuff. I was under a Bortle 5 sky with no artificial lights invading my field of view.  The temperature was about 4C (39F), but because I had to ride the bike, I was warm enough to start my journey.

I started with M101. When I had adapted enough to the dark it was easier to see than the previous night. Just about 4 degrees below the stars Mizar/Alcor and Alkaid, there was a faint spot with circular shape. The center, slightly brighter, which was better seen with averted vision. M101 appeared fainter than M83, although the constellation was about 70 degrees over the horizon.  The northern sky was slightly brighter because the biggest part of city was that way. Although both galaxies had similar apparent magnitude, M101 seemed dimmer than M83 due to their surface brightness (15.17 vs. 13.01 respectively) and also because M101 was against a brighter background sky.

I finished with M101 after an hour of sketching then I went for M83. Hydra, the constellation were the Galaxy is located in the sky was at only 30 degrees over the horizon but less affected by light pollution.  I used the Centaurus constellation to guide myself to M83 because its stars were more familiar than the stars in hydra. I started on Menkent (Ɵ Cen) and then I went to above it following star patterns until I found the Galaxy.

M83 seemed similar in size to M101 with a slightly brighter bulge also in its center. The truth is that M101 angular size is bigger than M83 (28.5' x 28.3' vs. 13.1' x 12.2'), but it was improbable that I had been able to differentiate the whole area of the Galaxy with the binoculars under polluted skies. M83 also seemed like a circular shape in the binocular view. I saw no signs of either galaxy’s spiral shape or arms that many pictures on the web had shown.

I just want to say that I feel very thankful with the creator that let us live under this wonderful sky and the possibility to explore it.

Clear skies and warm beds!


Edited by Jennifer Steinberg (editor in chief)



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