Starship Asterisk*

• 1) an annular eclipse happens every 15 months
  2) a total eclipse happens every 19 months
  3) a hybrid eclipse happens every 105 months

• 1) I have cloud filled skies whenever an astronomical event occurs.
  2) I spend a lot of time with my head below the clouds.

Beyond wrote:On average:

• 1) I have cloud filled skies whenever an astronomical event occurs.
  2) I spend a lot of time with my head below the clouds.

ta152h0 wrote:
I am hoping we have a really really cold winter where the skies will be clear for Comet ISON.

And that other comet that is/is not going to hit Mars.

• Which other comet

http://en.wikipedia.org/wiki/Comet_ISON wrote:
<<On its closest approach, C/2012 S1 passed about 0.07248 AU from Mars on 1 October 2013.>>

http://astrobob.areavoices.com/2013/11/03/photos-of-sundays-rare-hybrid-solar-eclipse/ wrote:

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<<Total solar eclipse photographed by Finnish photographer Janne Pyykkö, who traveled to Gulu, Uganda. He befriended a local university student there named Irene who holds two plates of oranges in this photo taken during totality.

Check out Janne’s blog for more information.

Credit: Janne Pyykkö (janne.pyykko@gmail.com)>>

neufer wrote:

ta152h0 wrote:
I am hoping we have a really really cold winter where the skies will be clear for Comet ISON.

And that other comet that is/is not going to hit Mars.

• Which other comet :?:

Chris Peterson wrote:

neufer wrote:

ta152h0 wrote:
I am hoping we have a really really cold winter where the skies will be clear for Comet ISON.

And that other comet that is/is not going to hit Mars.

• Which other comet

I assume he's referring to C/2013 A1 (Siding Spring), which will make an extremely close pass of Mars in October 2014. Colleagues of mine who have analyzed the encounter are predicting that Mars (which will pass through the debris stream) may see a meteor shower with a ZHR exceeding one million events per hour. There is real concern for the safety of our various orbiters around Mars (the rovers should be fine on the ground, but if they lose the communications relays in orbit, their operation will be severely limited).

Chris Peterson wrote:

neufer wrote:

ta152h0 wrote:
I am hoping we have a really really cold winter where the skies will be clear for Comet ISON.

And that other comet that is/is not going to hit Mars.

• Which other comet

I assume he's referring to C/2013 A1 (Siding Spring), which will make an extremely close pass of Mars in October 2014. Colleagues of mine who have analyzed the encounter are predicting that Mars (which will pass through the debris stream) may see a meteor shower with a ZHR exceeding one million events per hour. There is real concern for the safety of our various orbiters around Mars (the rovers should be fine on the ground, but if they lose the communications relays in orbit, their operation will be severely limited).

http://en.wikipedia.org/wiki/C/2013_A1 wrote:
The spacecraft MAVEN & Mangalyaan will arrive at Mars one month before the comet's closest approach. The comet is not expected to create a spectacular meteor shower on Mars or be a threat to the spacecraft in orbit or on the ground. The comet will have to be extremely close to Mars for its debris to pose any real risk. At the time of closest approach, the comet will be ~142,000 km (42 R_M) from the center-point of Mars on the sunward side of the planet. Millimeter-sized grains will be ejected at about 1 m/s, and would take more than a year to travel 100,000 km from the comet.

Code: Select all

Perihelion 	     1.39875 AU
Eccentricity 	   1.00046
Inclination 	    129.0°
Next perihelion 	25 October 2014
Orbital period 	~700,000 yr
(Barycentric solution for epoch 2050)

neufer wrote:

http://en.wikipedia.org/wiki/C/2013_A1 wrote:
The spacecraft MAVEN & Mangalyaan will arrive at Mars one month before the comet's closest approach. The comet is not expected to create a spectacular meteor shower on Mars or be a threat to the spacecraft in orbit or on the ground. The comet will have to be extremely close to Mars for its debris to pose any real risk. At the time of closest approach, the comet will be ~142,000 km (42 R_M) from the center-point of Mars on the sunward side of the planet. Millimeter-sized grains will be ejected at about 1 m/s, and would take more than a year to travel 100,000 km from the comet.

Chris Peterson wrote:

neufer wrote:

http://en.wikipedia.org/wiki/C/2013_A1 wrote:
[Comet ISON] is not expected to create a spectacular meteor shower on Mars or be a threat to the spacecraft in orbit or on the ground. The comet will have to be extremely close to Mars for its debris to pose any real risk. At the time of closest approach, the comet will be ~142,000 km (42 R_M) from the center-point of Mars on the sunward side of the planet. Millimeter-sized grains will be ejected at about 1 m/s, and would take more than a year to travel 100,000 km from the comet.

I have not made any study myself of this comet at Mars. But several people who are very much experts on this, and whose analyses I do trust, feel that the risk to our assets at Mars has been significantly understated. Whether that is deliberate or not, I can't say (and I'm not one for conspiracy theories). But I do think that this encounter is likely to be an interesting one.

• "Initial observations by Leonid Elenin on 27 February 2013, suggested
  [Comet ISON would probably] pass 41,300 km from the center-point of Mars."

http://www.universetoday.com/102257/astronomers-detect-dust-feature-in-comet-isons-inner-coma/ wrote:
Astronomers Detect Dust Feature in Comet ISON’s Inner [Dust] Coma
by Nancy Atkinson on May 20, 2013

<<Estimates suggest that the nucleus of ISON is no larger than 4-6 km across
while the comet’s dusty coma, or head of the comet is approximately 5,000 km across.>>

neufer wrote:Those analyses might be somewhat outdated by now:

• "Initial observations by Leonid Elenin on 27 February 2013, suggested
  [Comet ISON would probably] pass 41,300 km from the center-point of Mars."

FloridaMike wrote:
Just a wild guess here but I'm thinking Mars will have its own annual meteor shower as a result of the commit fly-by you guys are discussing. True?

MarkBour wrote:

Beyond wrote:On average:

• 1) I have cloud filled skies whenever an astronomical event occurs.
  2) I spend a lot of time with my head below the clouds.

Hear, hear. It seems to happen to me a lot, too. I'm hoping ISON will be good and that I won't have party-spoiling weather.
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I can understand that the angular size of the Moon from Earth's surface is nearly the same as the angular size of the Sun. It seems like an amazing coincidence, but there it is. And I'm guessing that when the Moon is farther away from the Earth during an eclipse, we get an annular eclipse, and when closer, to us, we get a full eclipse. For a hybrid eclipse, then, I guess it has to be at just about the right distance for a minimal full eclipse, and is it correct that lower elevations on the Earth would see the annular eclipse, while higher elevations would get the full eclipse, by being a little closer to the Moon? (They're also closer to the Sun, but the relative distance change to the Moon would be much greater than to the Sun.) And it's a matter of "true elevation" from the center of the Earth, rather than elevation above sea level, which is a bit irregular.

As a rank amateur, I believe I can figure this out, but I'm really just asking if I have this correct ...

Anthony Barreiro wrote:My understanding is that the Earth's total size is a much more significant factor in causing hybrid annular-total eclipses than are variations in elevation. The highest points on Earth are less than 10 km above sea level. With a diameter of about 13,000 km, the surface of the Earth at the noontime meridian is about 6,000 km closer to the Sun than the surface of the Earth at the sunrise and sunset meridians.

Chris Peterson wrote:

Anthony Barreiro wrote:My understanding is that the Earth's total size is a much more significant factor in causing hybrid annular-total eclipses than are variations in elevation. The highest points on Earth are less than 10 km above sea level. With a diameter of about 13,000 km, the surface of the Earth at the noontime meridian is about 6,000 km closer to the Sun than the surface of the Earth at the sunrise and sunset meridians.

While I agree completely with what you are saying, I'd like to point out that "sea level" isn't a very useful metric in this case. What matters is the distance of the observer from the center of the Earth, and in addition to the approximately 10 km variation due to surface roughness, there is also another 20 km because of the oblateness of the mean surface. Still small compared with the radius of the Earth, of course.

Anthony Barreiro wrote:

Chris Peterson wrote:

Anthony Barreiro wrote:My understanding is that the Earth's total size is a much more significant factor in causing hybrid annular-total eclipses than are variations in elevation. The highest points on Earth are less than 10 km above sea level. With a diameter of about 13,000 km, the surface of the Earth at the noontime meridian is about 6,000 km closer to the Sun than the surface of the Earth at the sunrise and sunset meridians.

While I agree completely with what you are saying, I'd like to point out that "sea level" isn't a very useful metric in this case. What matters is the distance of the observer from the center of the Earth, and in addition to the approximately 10 km variation due to surface roughness, there is also another 20 km because of the oblateness of the mean surface. Still small compared with the radius of the Earth, of course.

Thanks Chris.

By the way, this article from earthsky.org has very clear simple diagrams of a hybrid solar eclipse, a cool animation of the eclipse path, and lots of lovely pictures of the eclipse.