M61 DIMENSION AND

BRIGHTNESS

Eduarda Leal

INDEX M61 Image scale Bulge width M61 width M61 height M61 ratio M61 brightness References

M61M61 was discovered by Barnabus Oriani on May 5, 1779 when following the comet of that year, 6 days before Charles Messier's discovery, who had seen it on the same day as Oriani but mistaken it for the comet, until he realized that it did not move.

It is classified as a spiral galaxy of type SABbc, is 60 million light years away from the Milky Way and is located in the constellation of Virgo (Virgin).

With the program SalsaJ we can analyse and measure images.

In the M61 Image Info we can find the CCDSCALE: 0,3 arcsec/pixel

Image width = 2008 pixels

Real distance = 2008 x 0,3 = 602 arcsec

Image scale = 2008 / 602 == 3,336 pixels/arcsec

Image scale = 3,336 x 60 == 200 pixels/arcmin

IMAGE SCALE

We can calculate the image scale in kly/pixel with this equation:

scale in kly = scale in arcmin / (distance from Earth in Mly x 0.3)

CCDSCALE = 0,3 / 60 = 0,005 arcmin/pixel

Distance from Earth = 52,5 Mly

Image scale = 0,005 / (52,5 x 0,3) = 3,2 x 10-4 kly/pixel

IMAGE SCALE

To measure the bulge width, we started zooming the imageto have more accuracy and traced a line along the bulge.

Bulge width = 23 arcsec

Bulge width = 23 / 60 == 0,4 arcmin

Bulge width* = = 0,38 x 52,5 x 0,3 = 6,3 kly

* size in kly = size in arcmin x distance from Earth in Mly x 0.3

BULGE WIDTH

To measure the M61 width, we traced a line along the galaxy.

M61 width = 323 arcsec

M61 width = 323 / 60 == 5,4 arcmin

Real width = 5,8 arcmin

(Wikipedia)

M61 width* = = 5,4 x 52,5 x 0,3 = 85 kly

* size in kly = size in arcmin x distance from Earth in Mly x 0.3

M61 WIDTH

To measure the M61 height, we traced a line along the galaxy.

M61 height = 327 arcsec

M61 height = 327 / 60 == 5,5 arcmin

Real height = 6,5 arcmin

(Wikipedia)

M61 height* = = 5,5 x 52,5 x 0,3 = 86,6 kly

* size in kly = size in arcmin x distance from Earth in Mly x 0.3

M61 HEIGHT

M61 RATIO

Ratio width / height = 323 / 327 = 0,99

The ratio is near 1, so the galaxy is almost round.

M61 BRIGHTNESS

We made a line along the galaxy to measure the brightness.

Then we analyse the light in that line and SalsaJ plot a graph of light intensity vs distance (arcsec).

The brightness is more intense in the center of the galaxy and the bulge is very bright.

REFERENCES

http://resources.faulkes-telescope.com/course/view.php?id=65 http://lcogt.net/observations/ogg/2m0a/11593/ http://en.wikipedia.org/wiki/Messier_61 http://upload.wikimedia.org/wikipedia/commons/a/a4/Charles_Messier.jpg http://www.euhou.net/index.php/salsaj-software-mainmenu-9