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## 2012 KT42 will transit the sun

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• Another possibility to observe an NEO crossing the sun? On May 29 about 10:10 UT, the minimum geocentric elongation from the center of the sun will be 0.1
Message 1 of 8 , May 28, 2012
Another possibility to observe an NEO crossing the sun? On May 29 about 10:10 UT, the minimum geocentric elongation from the center of the sun will be 0.1 degrees, so given the parallax there will be a transit across the sun, centered in southern Asia. Could include Europe and eastern Asia, but I won't have time to compute this.

If the diameter is about 5m, then the object could be about 6" across against the solar disk.

Andrew
http://members.shaw.ca/andrewlowe/home.htm
• ... Hi Andrew, Here is the map for the transit: http://www.webalice.it/alvitagl/Figures/KT42Tran.gif Regards Aldo
Message 2 of 8 , May 28, 2012
--- In mpml@yahoogroups.com, "Andrew Lowe" <andrew.lowe@...> wrote:
>
> Another possibility to observe an NEO crossing the sun? On May 29 about 10:10 UT, the minimum geocentric elongation from the center of the sun will be 0.1 degrees, so given the parallax there will be a transit across the sun, centered in southern Asia. Could include Europe and eastern Asia, but I won't have time to compute this.
>
> If the diameter is about 5m, then the object could be about 6" across against the solar disk.
>

Hi Andrew,

Here is the map for the transit:
http://www.webalice.it/alvitagl/Figures/KT42Tran.gif

Regards
Aldo
• The transit will occur at the zenith in Egypt, with a duration of 12 minutes. Since the apparent size could be half that of a Mercury transit, the object may
Message 3 of 8 , May 28, 2012
The transit will occur at the zenith in Egypt, with a duration of 12 minutes. Since the apparent size could be half that of a Mercury transit, the object may be visible with optical aid. Observers in the Middle East take note!

Of course additional astrometry to refine the event would be welcome.

Andrew

> Hi Andrew,
>
> Here is the map for the transit:
> http://www.webalice.it/alvitagl/Figures/KT42Tran.gif
>
> Regards
> Aldo
>
• Ignore my comment about observing the transit. As Aldo points out, the size will be 0.006 , not 6 ... Andrew
Message 4 of 8 , May 28, 2012
Ignore my comment about observing the transit. As Aldo points out, the size will be 0.006", not 6"...

Andrew

--- In mpml@yahoogroups.com, "Andrew Lowe" <andrew.lowe@...> wrote:
>
> The transit will occur at the zenith in Egypt, with a duration of 12 minutes. Since the apparent size could be half that of a Mercury transit, the object may be visible with optical aid. Observers in the Middle East take note!
>
> Of course additional astrometry to refine the event would be welcome.
>
> Andrew
>
> > Hi Andrew,
> >
> > Here is the map for the transit:
> > http://www.webalice.it/alvitagl/Figures/KT42Tran.gif
> >
> > Regards
> > Aldo
> >
>
• ... That s even larger than Apophis will be on 2029 April 13, yet this object is almost two orders of magnitude smaller than Apophis, which means it would have
Message 5 of 8 , May 28, 2012
> If the diameter is about 5m, then the object could be about 6" across
> against the solar disk.

That's even larger than Apophis will be on 2029 April 13, yet this
object is almost two orders of magnitude smaller than Apophis, which
means it would have to get almost two orders of magnitude closer to
subtend an angle as large as Apophis.

A nice number to keep in your head is 206265, the number of arcsec
in a radian.

6" / 206265" = 0.000029

5 m / 0.000029 = 172000 m = 172 km

Because it will pass more like 20,500 km from the center of the Earth,
or about 14,000 km from the surface, that's about a factor of 80 farther
away, so a factor of 80 smaller. Not knowing what the close approach
distance uncertainty is, let's put it in the 0.07 to 0.08 arcsec range.
Then there's the diameter uncertainty stemming from the unknown albedo.
Not sure where the 0.006 arcsec value came from. Maybe somebody felt
that the 6 arcsec figure came from a kilometers versus meters mistake?
• How did the figure of 6 arc sec diameter get derived for a 5m diameter asteroid? At the time of the transit, the geocentric distance is about .0008AU, or about
Message 6 of 8 , May 29, 2012
How did the figure of 6 arc sec diameter get derived for a 5m diameter asteroid?

At the time of the transit, the geocentric distance is about .0008AU, or about 120,000km (about 1/3 of the lunar distance). At that distance, 5 meters equates to about 9mas – far far too small to be visible in transit. If you are in doubt about this – ask yourself whether in your scope you can see things that are 15meters across on the surface of the moon....

May I suggest that someone lost track of powers of 10, and derived the apparent diameter based on the asteroid being 5_km_ in diameter.... oops!

Dave Herald
Murrumbateman, Australia

From: Aldo Vitagliano
Sent: Tuesday, May 29, 2012 3:10 AM
To: mpml@yahoogroups.com
Subject: {MPML} Re: 2012 KT42 will transit the sun

--- In mpml@yahoogroups.com, "Andrew Lowe" <andrew.lowe@...> wrote:
>
> Another possibility to observe an NEO crossing the sun? On May 29 about 10:10 UT, the minimum geocentric elongation from the center of the sun will be 0.1 degrees, so given the parallax there will be a transit across the sun, centered in southern Asia. Could include Europe and eastern Asia, but I won't have time to compute this.
>
> If the diameter is about 5m, then the object could be about 6" across against the solar disk.
>

Hi Andrew,

Here is the map for the transit:
http://www.webalice.it/alvitagl/Figures/KT42Tran.gif

Regards
Aldo

------------------------------------

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Posts to this list or information found within may be freely used, with the stipulation that MPML and the originating author are cited as the source of the information.Yahoo! Groups Links

[Non-text portions of this message have been removed]
• From: mpml@yahoogroups.com [mailto:mpml@yahoogroups.com] On Behalf Of Dave Herald Sent: Tuesday, May 29, 2012 4:03 AM To: mpml@yahoogroups.com; Aldo Vitagliano
Message 7 of 8 , May 29, 2012
From: mpml@yahoogroups.com [mailto:mpml@yahoogroups.com] On Behalf Of Dave Herald
Sent: Tuesday, May 29, 2012 4:03 AM
To: mpml@yahoogroups.com; Aldo Vitagliano
Subject: Re: {MPML} Re: 2012 KT42 will transit the sun

For a 5 meter asteroid at a distance of 120000 km, its apparent angular diameter would be

calculated as

theta = (5 m / 1.20E8) * 206265 = 0.0086 arcsec

I would think you would need a telescope with a 30 meter primary aperture to see this event.

How did the figure of 6 arc sec diameter get derived for a 5m diameter asteroid?

At the time of the transit, the geocentric distance is about .0008AU, or about 120,000km (about 1/3 of the lunar distance). At that distance, 5 meters equates to about 9mas – far far too small to be visible in transit. If you are in doubt about this – ask yourself whether in your scope you can see things that are 15meters across on the surface of the moon....

May I suggest that someone lost track of powers of 10, and derived the apparent diameter based on the asteroid being 5_km_ in diameter.... oops!

Dave Herald
Murrumbateman, Australia

From: Aldo Vitagliano
Sent: Tuesday, May 29, 2012 3:10 AM
To: mpml@yahoogroups.com <mailto:mpml%40yahoogroups.com>
Subject: {MPML} Re: 2012 KT42 will transit the sun

--- In mpml@yahoogroups.com <mailto:mpml%40yahoogroups.com> , "Andrew Lowe" <andrew.lowe@...> wrote:
>
> Another possibility to observe an NEO crossing the sun? On May 29 about 10:10 UT, the minimum geocentric elongation from the center of the sun will be 0.1 degrees, so given the parallax there will be a transit across the sun, centered in southern Asia. Could include Europe and eastern Asia, but I won't have time to compute this.
>
> If the diameter is about 5m, then the object could be about 6" across against the solar disk.
>

Hi Andrew,

Here is the map for the transit:
http://www.webalice.it/alvitagl/Figures/KT42Tran.gif

Regards
Aldo

------------------------------------

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Posts to this list or information found within may be freely used, with the stipulation that MPML and the originating author are cited as the source of the information.Yahoo! Groups Links

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]
• With a substantial mylar solar filter... :) Alain
Message 8 of 8 , May 29, 2012
With a substantial mylar solar filter... :)
Alain

"Robert M. Elowitz" <elowitzr@...> a écrit :

>
>
>
>
> From: mpml@yahoogroups.com [mailto:mpml@yahoogroups.com] On Behalf
> Of Dave Herald
> Sent: Tuesday, May 29, 2012 4:03 AM
> To: mpml@yahoogroups.com; Aldo Vitagliano
> Subject: Re: {MPML} Re: 2012 KT42 will transit the sun
>
>
>
> For a 5 meter asteroid at a distance of 120000 km, its apparent
> angular diameter would be
>
> calculated as
>
>
>
> theta = (5 m / 1.20E8) * 206265 = 0.0086 arcsec
>
>
>
> I would think you would need a telescope with a 30 meter primary
> aperture to see this event.
>
>
>
> How did the figure of 6 arc sec diameter get derived for a 5m
> diameter asteroid?
>
> At the time of the transit, the geocentric distance is about
> .0008AU, or about 120,000km (about 1/3 of the lunar distance). At
> that distance, 5 meters equates to about 9mas ? far far too small to
> be visible in transit. If you are in doubt about this ? ask yourself
> whether in your scope you can see things that are 15meters across on
> the surface of the moon....
>
> May I suggest that someone lost track of powers of 10, and derived
> the apparent diameter based on the asteroid being 5_km_ in
> diameter.... oops!
>
> Dave Herald
> Murrumbateman, Australia
>
> From: Aldo Vitagliano
> Sent: Tuesday, May 29, 2012 3:10 AM
> To: mpml@yahoogroups.com <mailto:mpml%40yahoogroups.com>
> Subject: {MPML} Re: 2012 KT42 will transit the sun
>
> --- In mpml@yahoogroups.com <mailto:mpml%40yahoogroups.com> ,
> "Andrew Lowe" <andrew.lowe@...> wrote:
>>
>> Another possibility to observe an NEO crossing the sun? On May 29
>> about 10:10 UT, the minimum geocentric elongation from the center
>> of the sun will be 0.1 degrees, so given the parallax there will be
>> a transit across the sun, centered in southern Asia. Could include
>> Europe and eastern Asia, but I won't have time to compute this.
>>
>> If the diameter is about 5m, then the object could be about 6"
>> across against the solar disk.
>>
>
> Hi Andrew,
>
> Here is the map for the transit:
> http://www.webalice.it/alvitagl/Figures/KT42Tran.gif
>
> Regards
> Aldo
>
> ------------------------------------
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Posts to this list or information found within may be freely used,
> with the stipulation that MPML and the originating author are cited
> as the source of the information.Yahoo! Groups Links
>
> [Non-text portions of this message have been removed]
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
>
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