Occulter for a space telescope: what about effects of the Sun ?

I was wondering if it is actually feasible to use an occulter with a
space telescope to watch extrasolar planets by dimming their star. I
think the occulter will be close enough to our Sun so that the
sunlight, dispersed from the edges of the occulter, would completely
drown the faint planets. Am I correct ? Is an occulter even feasible
without moving the telescope / occulter pair many billions kilometers
from the Sun (which is beyond our current propulsion technologies) ?

(ivk) wrote:
I was wondering if it is actually feasible to use an occulter with a
space telescope to watch extrasolar planets by dimming their star. I
think the occulter will be close enough to our Sun so that the
sunlight, dispersed from the edges of the occulter, would completely
drown the faint planets. Am I correct ? Is an occulter even feasible
without moving the telescope / occulter pair many billions kilometers
from the Sun (which is beyond our current propulsion technologies) ?

Sure! This technique is already used on terrestrial telescopes - for
example, here at Subaru, we have HiCIAO, a coronographic imager that
sits behind our 188-element AO system. During _commissioning_ last
year, it found exoplanet GJ 758 B, and there's an ongoing project
(SEEDS - Strategic Exploration of Exoplanets and Disks) to check for
planets around some big number of nearby stars. Other 8-10 meter class
telescopes have similar instruments, or will soon, complementing the
other existing means of finding exoplanets.

Keeping the sun out of your space telescope is pretty much just a
matter of either putting it on the dark side of the Earth or Moon, or
building a nice big sunshade for it.

--
djb@ | Dan Birchall - Observation System Associate - Subaru Telescope.
naoj | Views I express are my own, obviously not those of my employer.
..org | I only wear black so much because I can't find anything darker.

Thanks Dan for your kind reply. But I don't think that hiding the
telescope + occulter behind the Earth shadow will be an option for the
future space telescope missions, because they will be orbiting too far
from the Earth. Also, placing a sunshade behind the telescope won't
work either, because the occulter has to be placed very far from the
telescope (probably millions of telescope mirror's raidii away). Am I
correct ?


On Oct 6, 4:08*am, Dan Birchall wrote:
(ivk) wrote:
*I was wondering if it is actually feasible to use an occulter with a
*space telescope to watch extrasolar planets by dimming their star. I
*think the occulter will be close enough to our Sun so that the
*sunlight, dispersed from the edges of the occulter, would completely
*drown the faint planets. Am I correct ? Is an occulter even feasible
*without moving the telescope / occulter pair many billions kilometers
*from the Sun (which is beyond our current propulsion technologies) ?

Sure! *This technique is already used on terrestrial telescopes - for
example, here at Subaru, we have HiCIAO, a coronographic imager that
sits behind our 188-element AO system. *During _commissioning_ last
year, it found exoplanet GJ 758 B, and there's an ongoing project
(SEEDS - Strategic Exploration of Exoplanets and Disks) to check for
planets around some big number of nearby stars. *Other 8-10 meter class
telescopes have similar instruments, or will soon, complementing the
other existing means of finding exoplanets.

Keeping the sun out of your space telescope is pretty much just a
matter of either putting it on the dark side of the Earth or Moon, or
building a nice big sunshade for it.

--
djb@ | Dan Birchall - Observation System Associate - Subaru Telescope.
naoj | Views I express are my own, obviously not those of my employer.
.org | I only wear black so much because I can't find anything darker.

(ivk) wrote:
placing a sunshade behind the telescope won't work either, because
the occulter has to be placed very far from the telescope (probably
millions of telescope mirror's raidii away). Am I correct ?

I suppose you could do it that way, but most just make the occulter a
lot smaller in diameter than one that you would use for doing
coronographic observations of something nearby like the sun.

--
djb@ | Dan Birchall - Observation System Associate - Subaru Telescope.
naoj | Views I express are my own, obviously not those of my employer.
..org | I only wear black so much because I can't find anything darker.

"Dan Birchall" wrote in message
...
| (ivk) wrote:
| placing a sunshade behind the telescope won't work either, because
| the occulter has to be placed very far from the telescope (probably
| millions of telescope mirror's raidii away). Am I correct ?
|
| I suppose you could do it that way, but most just make the occulter a
| lot smaller in diameter than one that you would use for doing
| coronographic observations of something nearby like the sun.

As in hold a penny at arm's length...

ics_aa (Androcles) wrote:

"Dan Birchall" wrote in message
...
| (ivk) wrote:
| placing a sunshade behind the telescope won't work either, because
| the occulter has to be placed very far from the telescope (probably
| millions of telescope mirror's raidii away). Am I correct ?
|
| I suppose you could do it that way, but most just make the occulter a
| lot smaller in diameter than one that you would use for doing
| coronographic observations of something nearby like the sun.

As in hold a penny at arm's length...

Precisely. Instead of holding a penny, hold a pinhead[1], or whatever.
I don't know the precise dimensions of the occulter in HiCIAO, or even
the one in the first-generation CIAO before it.

-Dan

[1] This is not a reference to any astro-group posters, honest! Let go
of each other!

--
djb@ | Dan Birchall - Observation System Associate - Subaru Telescope.
naoj | Views I express are my own, obviously not those of my employer.
..org | I only wear black so much because I can't find anything darker.

On 11 Okt, 13:39, "Androcles" wrote:
"Dan Birchall" wrote in message

...| (Androcles) wrote:

|
| *"Dan Birchall" wrote in message
| ...
| | (ivk) wrote:
| | *placing a sunshade behind the telescope won't work either, because
| | *the occulter has to be placed very far from the telescope (probably
| | *millions of telescope mirror's raidii away). Am I correct ?
| |
| | I suppose you could do it that way, but most just make the occulter a
| | lot smaller in diameter than one that you would use for doing
| | coronographic observations of something nearby like the sun.
|
| *As in hold a penny at arm's length...
|
| Precisely. *Instead of holding a penny, hold a pinhead[1], or whatever.

On 11 Okt, 13:39, "Androcles" wrote:
"Dan Birchall" wrote in message

...| (Androcles) wrote:

|
| *"Dan Birchall" wrote in message
| ...
| | (ivk) wrote:
| | *placing a sunshade behind the telescope won't work either, because
| | *the occulter has to be placed very far from the telescope (probably
| | *millions of telescope mirror's raidii away). Am I correct ?
| |
| | I suppose you could do it that way, but most just make the occulter a
| | lot smaller in diameter than one that you would use for doing
| | coronographic observations of something nearby like the sun.
|
| *As in hold a penny at arm's length...
|
| Precisely. *Instead of holding a penny, hold a pinhead[1], or whatever.

On 11 Okt, 13:39, "Androcles" wrote:
"Dan Birchall" wrote in message

...| (Androcles) wrote:

|
| *"Dan Birchall" wrote in message
| ...
| | (ivk) wrote:
| | *placing a sunshade behind the telescope won't work either, because
| | *the occulter has to be placed very far from the telescope (probably
| | *millions of telescope mirror's raidii away). Am I correct ?
| |
| | I suppose you could do it that way, but most just make the occulter a
| | lot smaller in diameter than one that you would use for doing
| | coronographic observations of something nearby like the sun.
|
| *As in hold a penny at arm's length...
|
| Precisely. *Instead of holding a penny, hold a pinhead[1], or whatever.

On 11 Okt, 13:39, "Androcles" wrote:
"Dan Birchall" wrote in message

...| (Androcles) wrote:

|
| *"Dan Birchall" wrote in message
| ...
| | (ivk) wrote:
| | *placing a sunshade behind the telescope won't work either, because
| | *the occulter has to be placed very far from the telescope (probably
| | *millions of telescope mirror's raidii away). Am I correct ?
| |
| | I suppose you could do it that way, but most just make the occulter a
| | lot smaller in diameter than one that you would use for doing
| | coronographic observations of something nearby like the sun.
|
| *As in hold a penny at arm's length...
|
| Precisely. *Instead of holding a penny, hold a pinhead[1], or whatever.