Posts Tagged ‘Collision’

10/02/2022 – Ephemeris Extra – NASA goes on the offensive

October 2, 2022 Comments off
Didymus and Dimorphos from DART

DART images of both Didymos, the big one, and Dimorphos, on approach. Credit NASA / JHAPL

This is a slightly revised version of my article in the Stellar Sentinel, the newsletter of the Grand Traverse Astronomical Society. Educators may receive a free PDF copy of this monthly publication via email, which covers astronomical topics and events visible from Northwest Lower Michigan. Send your request, stating your affiliation, to

The score is: Asteroids-billions, NASA-1. It’s a bit unfair, since asteroids have been hitting the Earth for 4.567 billion years or so, and NASA has been around for 64 years before DART spacecraft collided with the asteroid Dimorphos. Hey, this was their first attempt at a small asteroid. As far as the 21st century destructive asteroid score is 1 to NASA’s 1, as far as I know.
That strike was in Chelyabinsk, Russia. That was February 15, 2013. We were all waiting on another asteroid making a close pass of the Earth, when the Chelyabinsk meteoroid exploded 14 miles above the city. Over a thousand people were injured by the blast wave. They saw the bright flash and rushed to the windows to see what it was. Then the blast wave hit, shattering the windows, causing glass cuts for over a thousand people. One building’s wall collapsed, and a fragment fell into a lake outside of town.
NASA’s record in attempting to hit a planetary object dates back to the early 1960s and the nine Pioneer missions to crash a probe on the Moon, sending back pictures all the way down. Back in the early 60s, just hitting a 2,100-mile (3380 kilometer) wide object a quarter of a million miles away was a dicey prospect. It’s one thing to miss the Moon on one side or the other, but to not have enough oomph to even make it all the way is downright embarrassing. NASA did much better by the end of the decade with the Apollo manned landings and bombarding the Moon with used space vehicles for seismic studies of its interior.
NASA actually collided a spacecraft into a comet. That was July 4, 2005, when the impactor part of the Deep Impact spacecraft hit Comet Tempel 1’s nucleus, attempting to study part of its subsurface. The non-impactor part was later renamed EPOXI and went on to fly by the dog-bone shaped Hartley 2 comet nucleus. Another reused comet explorer spacecraft Stardust after collecting cometary dust from Comet Wild 2 (pronounced Vilt 2), and possible interstellar dust penetrating the solar system, and after dropping the sample re-entry capsule back on Earth it ended in solar orbit. Later it was repurposed as the Stardust-NexT mission and flew by Tempel 1 six years later to study the crater the Deep Impact Impactor made in the comet.
To study the effect of a collision of a spacecraft from the Earth despite the fact that Dimorphos cannot be seen is a trick. However, the pair is an eclipsing binary from our point of view, so the brightness of the unresolved pair changes as they eclipse each other.
Before the collision, Dimorphos had an 11.9 hour orbit of Didymos. Dimorphos is a fifth the size of Didymos orbiting it at three times the primary’s radius. If the orbit is near circular, Dimorphos’ orbital velocity is only 0.39 mph (0.63 kph). It should be relatively easy to see a tiny change in Dimorphos’ orbital period.

Last frame Dimorphos fit in from DART

Last frame Dimorphos fit in from DART. Credit NASA / JHAPL.

Two images from the LiciaCube satellite

Two images from the LiciaCube satellite launched from the DART spacecraft 15 days before the impact, and trailing it to record the collision with its wide and narrow angle imagers. Dimorphos does appear to be a rubble pile asteroid from its appearance and the amount of ejecta caused by the impact. The ejecta adds to the effect of the spacecraft’s kinetic energy by pushing away from the asteroid by Newton’s third law of motion. Credit: Italian Space Agency.

Dimorphos ejecta from Atlas

A frame from a time-lapse video taken from the ATLAS Project’s South African observatory of the unresolved Didymos – Dimorphos pair and the expanding ejecta cloud. The asteroid pair developed a dust tail like a comet for a while.
ATLAS is an acronym for a rather apocalyptic title “Asteroid Terrestrial-impact Last Alert System”. Developed by the University of Hawai’i and funded by NASA. It has two telescopes in Hawai’i, one in Chile, and one in South Africa. Credit: NASA/UH.

Days later, Dimorphos was exhibiting a thin dust tail, like a comet.

Now we wait on Earth’s observatories to observe of the period of Dimorphos’ orbit. It should decrease the orbital time.

08/25/2020 – Ephemeris – The Great Andromeda Galaxy will collide with the Milky Way someday

August 25, 2020 Comments off

This is Ephemeris for Tuesday, August 25th. Today the Sun will be up for 13 hours and 33 minutes, setting at 8:30, and it will rise tomorrow at 6:58. The Moon, at first quarter today, will set at 12:26 tomorrow morning.

Stars are at extreme distances compared to their sizes, even if one includes their planetary systems. Galaxies in a galaxy cluster are much closer with respect to their size. Astronomers have determined that our Milky Way galaxy will collide with the Great Andromeda galaxy, some two and a half million light years away, in about four and a half billion years. Don’t worry, it is very unlikely that any stars will collide during the event, though the solar system may be in for a wild ride. As the galaxies approach each other their beautiful spiral structures will begin to distort into tidal tails. Multiple passes of the two will occur before they will coalesce into one large elliptical galaxy. Other galaxies of the Local Group will join in over time.

The event times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


Colliding galaxies. Note the tidal tails. Credit: Hubble Legacy Archive, ESA, NASA.

View from Earth-Andromeda collision

Original caption: This illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. In this image, representing Earth’s night sky in 3.75 billion years, Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull. (Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger)

11/14/2014 – Ephemeris – When Galaxies collide… With ours (Gulp)

November 14, 2014 Comments off

Ephemeris for Friday, November 14th.  The sun will rise at 7:37.  It’ll be up for 9 hours and 37 minutes, setting at 5:15.   The moon, at last quarter today, will rise at 12:33 tomorrow morning.

Yesterday we looked at the closest spiral galaxy to our own Milky Way, the Great Andromeda Galaxy.  I said that it would collide with the Milky Way in about 4 billion years.  Usually no stars are harmed by such a collision.  What does collide are the dust and gasses in each galaxy, that will trigger a burst of star formation.  Over the next several billion years the two galaxies will probably merge into one giant elliptical galaxy.  The sun at that time will see some changes of life the too.  The Earth would by then be uninhabitable because the sun would be too hot, and by then would begin to bloat out into a red giant star.  It would be a great spectacle, but no one would be around  to watch it.  However there are many distant colliding galaxies to watch.

Closer to home, Saturday night there will be a star party at NMC’s Rogers Observatory starting at 9 p.m.

Times are for the Traverse City/Interlochen area of Michigan.  They may be different for your location.


The Great Andromeda Galaxy (M31). Image taken by Scott Anttila.

The Great Andromeda Galaxy (M31). Image taken by Scott Anttila.

Here’s a link to a YouTube video of a computer simulation of the collision of the Andromeda galaxy with our Milky Way galaxy.