Free Republic
Browse · Search
General/Chat
Topics · Post Article

Skip to comments.

Astronomy Picture of the Day 05-04-04
NASA ^ | 05-04-04 | Robert Nemiroff and Jerry Bonnell

Posted on 05/04/2004 2:51:40 AM PDT by 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.

2004 May 4
See Explanation.  Clicking on the picture will download
 the highest resolution version available.

Missoula Crater on Mars
Credit: Mars Exploration Rover Mission, JPL, NASA

Explanation: Scroll right to see the rocks, craters, and hills that were in view for the Spirit rover last week as it continued its trek across Mars. Missoula crater, taking up much of the above frame, appeared from orbit to have ejecta from Bonneville crater inside it. Upon closer inspection, however, Spirit finds only evidence for wind-blown drifts. The rocks show numerous blisters and small cavities that may have occurred as ancient water vapor evaporated from hot cooling lava. Columbia Hills in the distance is now planned as the ultimate destination for the Spirit rover. Both of the Mars rovers have now successfully completed their original mission and are now exploring topical opportunities.

Lunar Eclipse Today: Visible from Europe, Asia, Africa. Times | Webcast | Photo Tips


TOPICS: Astronomy; Astronomy Picture of the Day; Science
KEYWORDS: mars; rover; spirit
Galaxy family has close interaction in cosmic tango
EUROPEAN SOUTHERN OBSERVATORY NEWS RELEASE
Posted: May 3, 2004

Stars like our Sun are members of galaxies, and most galaxies are themselves members of clusters of galaxies. In these, they move around among each other in a mostly slow and graceful ballet. But every now and then, two or more of the members may get too close for comfort - the movements become hectic, sometimes indeed dramatic, as when galaxies end up colliding.


A cosmic tango by the triple system NGC 6769-71, located in the southern Pavo constellation (the Peacock) at a distance of 190 million light-years. Credit: ESO
 
This composite image was obtained on April 1, 2004, the day of the Fifth Anniversary of ESO's Very Large Telescope (VLT). It was taken in the imaging mode of the VIsible Multi-Object Spectrograph (VIMOS) on Melipal, one of the four 8.2-m Unit Telescopes of the VLT at the Paranal Observatory (Chile). The two upper galaxies, NGC 6769 (upper right) and NGC 6770 (upper left), are of equal brightness and size, while NGC 6771 (below) is about half as bright and slightly smaller. All three galaxies possess a central bulge of similar brightness. They consist of elderly, reddish stars and that of NGC 6771 is remarkable for its "boxy" shape, a rare occurrence among galaxies.

Gravitational interaction in a small galaxy group

NGC 6769 is a spiral galaxy with very tightly wound spiral arms, while NGC 6770 has two major spiral arms, one of which is rather straight and points towards the outer disc of NGC 6769. NGC 6770 is also peculiar in that it presents two comparatively straight dark lanes and a fainter arc that curves towards the third galaxy, NGC 6771 (below). It is also obvious from this new VLT photo that stars and gas have been stripped off NGC 6769 and NGC 6770, starting to form a common envelope around them, in the shape of a Devil's Mask. There is also a weak hint of a tenuous bridge between NGC 6769 and NGC 6771. All of these features testify to strong gravitational interaction between the three galaxies.

The warped appearance of the dust lane in NGC 6771 might also be interpreted as more evidence of interactions. Moreover, NGC 6769 and NGC 6770 are receding from us at a similar velocity of about 3800 km/s - a redshift just over 0.01 - while that of NGC 6771 is slightly larger, 4200 km/s.

A stellar baby-boom

As dramatic and destructive as this may seem, such an event is also an enrichment, a true baby-star boom. As the Phoenix reborn from its ashes, a cosmic catastrophe like this one normally results in the formation of many new stars. This is obvious from the blueish nature of the spiral arms in NGC 6769 and NGC 6770 and the presence of many sites of star forming regions.

Similarly, the spiral arms of the well-known Whirlpool galaxy (Messier 51) may have been produced by a close encounter with a second galaxy that is now located at the end of one of the spiral arms; the same may be true for the beautiful southern galaxy NGC 1232 depicted in another VLT photo.

Nearer to us, a stream of hydrogen gas, similar to the one seen above, connects our Galaxy with the LMC, a relict of dramatic events in the history of our home Galaxy. And the stormy time is not yet over: now the Andromeda Galaxy, another of the Milky Way neighbours in the Local Group of Galaxies, is approaching us. Still at a distance of over 2 million light-years, calculations predict that it will collide with our galaxy in about 6,000 million years!

1 posted on 05/04/2004 2:51:40 AM PDT by petuniasevan
[ Post Reply | Private Reply | View Replies]

To: MozartLover; Joan912; NovemberCharlie; snowfox; Dawgsquat; Vigilantcitizen; theDentist; ...

YES! You too can be added to the APOD PING list! Just ask!

2 posted on 05/04/2004 2:57:51 AM PDT by petuniasevan (Liberal Rule #1 - When in doubt, tell a lie.)
[ Post Reply | Private Reply | To 1 | View Replies]

To: petuniasevan
BTTT
3 posted on 05/04/2004 4:47:53 AM PDT by GodBlessRonaldReagan (Count Petofi will not be denied!)
[ Post Reply | Private Reply | To 1 | View Replies]

To: petuniasevan
I still get goose bumps every time I see a postcard from Mars.

Thanks, P.
4 posted on 05/04/2004 6:10:52 AM PDT by foolish-one
[ Post Reply | Private Reply | To 2 | View Replies]

To: petuniasevan
Thanks for the ping.
5 posted on 05/04/2004 5:34:37 PM PDT by sistergoldenhair
[ Post Reply | Private Reply | To 2 | View Replies]

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.

Free Republic
Browse · Search
General/Chat
Topics · Post Article

FreeRepublic, LLC, PO BOX 9771, FRESNO, CA 93794
FreeRepublic.com is powered by software copyright 2000-2008 John Robinson