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Why Does The Data For Near-Earth object (NEO) Asteroid 99942 "Apophis" Keep Changing In SN8? (Answer: Read On!)

The Asteroid 99942 "Apophis" is a near-Earth object (NEO) which according to NASA will be 32,000 kilometers of earth's surface on April 13, 2029.

https://science.nasa.gov/solar-system/asteroids/apophis/ 

Using Starry Night Enthusiast to follow the asteroid for that date, I see the closest to earth it will be is: 0.010564924 astronomical units (au).

1 au = about 150 million km. (0.010564924 x 150) x (10^6) = 1584738.6 or about 1.58 million kilometers, not 32 thousand kilometers.

My apologies if I've made an error. If not, does anyone have an idea what's going on?

 

6 comments

  • 0
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    Raymond de Groat

    Adding to my confusion, Starry Night gives different distance from earth data on subsequent launches. Instead of 0.010564924 au, as in my initial post, quitting and relaunching Starry Night now gives me different data for the asteroid. Apophis' distance from earth is now 0.010564759.

    Of course, this difference seems negligible.It's still about 0.10564 AU, but it seemed worth a mention.

  • 0
    Avatar
    Raymond de Groat

    Each day Starry Night reports a different "Distance from Earth" for the Apophis asteroid for April 13, 2029.

    On May 5, when I first posted my question to this forum, Starry night reported Apophis will be 0.010564924 au from Earth on April 13, 2029.

    On May 6 Starry Night reported that Apophis will be 0.010564759 au from earth on April 13, 2029.

    Today on May 7 Starry Night shows that Apophis will be 0.010564274 au on April 13, 2029.

    If I were to set my computer clock for some date in the future, what will Starry Night tell me about Apophis then?

  • 1
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    Keiron Smith

    The trajectory of Near-Earth Object (NEO) Asteroid 99942 "Apophis" and all other asteroids is included in the Asteroids.txt file.

    The Asteroids.txt file, along with Comets.txt and Satellites.txt, are part of the Daily Data that Starry Night will download upon startup each day.

    These files have to be updated each day because the trajectories continue to change quickly over time.

    You can find these text files in the Sky Data folder, see here:

    When you start SN8 and it downloads NEW daily data, those files are updated and overwritten.

    Open the Asteroids.txt file and look at the orbital data for Apophis.  Make a copy of the data or the file.

    Next time you check Apophis in SN8 and find the data has changed, open the Asteroids.txt file and compare it to the previous data/file.

    Did the file data get updated?  If so, there is your answer as to why the data is changing.

    Thanks!

  • 0
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    Raymond de Groat

    Interestingly no, the Asteroids.txt file hasn't been updated since yesterday even though the "Distance from Earth" numbers do change almost every time I restart the application and enter 4/13/2029 as the date and 13:55:00 UT as the time in the toolbar. The location, Stockholm, is the same for all the observations. I've provided some screenshots files which are named with the system date and time.

    But it's not so much the minute changes in Starry Nights own numbers which concern me. I'm impressed with the software regardless. Rather it's the discrepancy between 30 thousand km, or 0.0002 au (NASA), and 1.496 million km, or 0.01 au (Starry Night), which has me scratching my head.

    It's also worth noting, at least from my novice point of view, that if the trajectories are changing then perhaps NASA's should update it's numbers as well.

    It's quite likely I'm simply out of my depth here, but thank you for helping me to understand!

  • 1
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    Keiron Smith

    This is a curiosity, I am not sure what is happening.  Please save an SNF file, attach it here for my review (or share with Dropbox link).

    Please also compare these changes to other asteroids.  Is this Position in Space data only changing for Apophis?

    Also, on the Position in Sky panel, is the Alt/Az RA/Dec changing from day to day as well?

    Thanks!

  • 0
    Avatar
    Raymond de Groat

    Here is link to a zip file containing 4 SNF files for Apophis on 2029-04-13 13:55:00 UTC. Also contained are 2 SNF files for Psyche on 2029-01-13 at 10:00:00 UTC. Each file is accompanied by a screenshot. Also included is the Asteroids.txt file, which you will see has a creation date of May 7. All files were created while disconnected from Internet. Connecting to Internet and launching Starry Night does not update the Asteroids.txt file nor do I see any change in behavior.

    The one consistent thing in all this, is that reopening any of the Apophis SNF files will show me a Distance to Earth of 0.009332833, despite the screenshot taken at the time of the SNF showing a different number. Perhaps this provides a clue as to what I am experiencing.

    https://drive.google.com/file/d/1PWcNZFGdfX1HPIy-gtu4zY3zf6mCUEDM/view?usp=sharing 

     

     

     

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