Astronomy Picture of the Day 9-25-03

NASA ^ | 9-25-03 | Robert Nemiroff and Jerry Bonnell

[petuniasevan]

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2003 September 25

Logarithmic Spirals Isabel and M51
Credit: Comparison and M51 image copyright Brian Lula; Hurricane Isabel, courtesy GHCC, NASA

Explanation: Uncomfortably close hurricane Isabel (left) and 30 million light-year distant galaxy M51 actually don't have much in common. For starters, Isabel was hundreds of miles across, while M51 (the Whirlpool Galaxy) spans about 50,000 light-years making them vastly dissimilar in scale, not to mention the extremely different physical interactions which control their formation and evolution. But they do look amazingly alike, both exhibiting the shape of a simple and beautiful mathematical curve known as a logarithmic spiral, a spiral whose separation grows in a geometric way with increasing distance from the center. Also known as the equiangular spiral, growth spiral, and Bernoulli's spiral or spira mirabilis, this curve's rich properties have fascinated mathematicians since its discovery by 17th century philosopher Descartes. Intriguingly, this abstract shape is much more abundant in nature than suggested by the striking visual comparison above. Logarithmic spirals also describe, for example, the arrangement of sunflower seeds, the shapes of nautilus shells, and ... cauliflower.

[petuniasevan]

Also integral to spiral structure is the Fibonacci sequence. It's everywhere! Here's a LINK to all sorts of information for the whole family to enjoy.

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M51, the Whirlpool Galaxy, is presently "catching" a smaller barred spiral galaxy (that's the huge bright hazy structure visible at the end of one spiral "arm"). Once the Whirlpool and its smaller companion merge, the resulting galaxy will be distorted.

M51, the Whirlpool Galaxy

Right Ascension	13 : 29.9 (h:m)
Declination	+47 : 12 (deg:m)
Distance	37000 (kly)
Visual Brightness	8.4 (mag)
Apparent Dimension	11x7 (arc min)

NGC 5195, companion to M51

Right Ascension	13 : 30.0 (h:m)
Declination	+47 : 16 (deg:m)
Distance	37000 (kly)
Visual Brightness	9.6 (mag)
Apparent Dimension	6.4x4.6 (arc min)

For the amateur, M51 is easy and a showpiece if the sky is dark, but is quite sensitive for light pollution which easily makes it fade in the background. Under very good conditions, even suggestions of its spiral arms can be glanced with telescopes starting from 4-inch. Low magnification is best for viewing this pair.

Where to look? "Under" the Big Dipper's handle! See below:

Here's a larger overview of the region where M51 is located:

It wouldn't be the same without a Hubble image. So here's a great shot of the inner part of the Whirlpool:

[petuniasevan]

[GodBlessRonaldReagan]

Wow! Love those Hubble shots!

[theDentist]

Not to mention the little foam shape when I pour some milk into my tea.... looks the same.

[RightWhale]

What is the Sagittarius Galaxy that's been in the news the past couple days. It doesn't seem to be a Messier object.

[LiteKeeper]

SPOTREP

[SuziQ]

Love that Hubble shot!! Thanks for the cool link. It's added to our 'Education' favorites!

[GATOR NAVY]

From light years in diameter to inches-the spiral is everywhere.

[petuniasevan]

The Sagittarius Dwarf Elliptical Galaxy was the subject of this thread:

http://www.freerepublic.com/focus/f-news/988893/posts

And it was an APOD subject back in 1998.

http://antwrp.gsfc.nasa.gov/apod/ap980216.html

[RightWhale]

the dwarf Sagittarius -- which is about 10,000 times the mass of the Milky Way

That is the bothersome part. I assume that is an error, that the Milky Way is much more massive, and denser, too, than the Sagittarius Galaxy.

[petuniasevan]

Yes, that's a typo (sloppy editing).

It should be 1/10,000 times the mass of the Milky Way.

These news agencies give stories like this to their flunkies to write. The top reporters want the J. Lo circuit or the political scene, so the low man (or woman) gets the throwaway tabloid angle to cover.

They don't know diddly about the subject matter in most cases, and this is no exception.

[RightWhale]

Good. Then my physics degree wasn't entirely wasted.

[Soaring Feather]

Thank you so much for this lovely thread.