M61 DIMENSION AND

BRIGHTNESS

Eduarda Leal

INDEX M61 Image scale Bulge Width Height Ratio 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 52,5 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/pixelDistance 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, we started zooming the image to have more accuracy and traced a line along the bulge.

Bulge = 22,856 arcsec

Bulge = 22,856 / 60 = 0,381 arcmin

Bulge* = 0,381 x 52,5 x 0,3 = 6,0 kly = 6 000 light-years

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

BULGE

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

Width = 322,887 arcsec

Width = 322,887 / 60 = 5,381 arcmin

width* = 5,381 x 52,5 x 0,3 = 84,751 kly = 84 751 light-years

Real width = 5,8 arcmin (Wikipedia)

Real width* = 5,8 x 52,5 x 0,3 = 91,4 kly = 91 400 light-years

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

WIDTH

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

Height = 327,387 arcsec

Height = 327,387 / 60 = 5,456 arcmin

Height* = 5,456 x 52,5 x 0,3 = 85,939 kly = 85 939 light-years

Real height = 6,5 arcmin (Wikipedia)

Real height* = 6,5 x 52,5 x 0,3 = 102,4 kly = 102 400 light-years

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

HEIGHT

RATIORatio width / height = 322,887 / 327,387 = 0,99

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

BRIGHTNESSWe 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