Why are planets visible in a telescope in the daylight?

[truffaldino]

Why are planets visible in telescope in daylight?

As far as I understand both 1) total light flux from the planet 2) and that from the atmosphere receved by scope are proportional to the aperture area. So why then we can see the planets?

And I have realted question. I am my city humidity and light polution are very high, so that one can see only stars with apparent magnitude less than 3 in zenith. Is it possible to see Andromeda galaxy in small telescope (8cm aperture) when it will be close to zenith.

 

[davenn]

Why are planets visible in telescope in daylight?

Because they are very bright objects

Maybe you didn't know that Venus is visible in daytime WITHOUT a telescope ... just your eyes

Is it possible to see Andromeda galaxy in small telescope (8cm aperture) when it will be close to zenith.

possibly, with difficulty ... I cannot try that at home, Andromeda only gets around 15 deg above the horizon

 

[George Jones]

Im my city humidity and light polution are very high, so that one can see only stars with apparent magnitude less than 3 in zenith. Is it possible to see Andromeda galaxy in small telescope (8cm aperture) when it will be close to zenith.

Can you find the constellation Cassiopeia? If you can, I think that you should be able to the see the Andromeda galaxy as a grey smudge fairly easily with 8 cm. My sky is a little better than yours, and I can easily see Andromeda with 5 cm binoculars.

 

[truffaldino]

Because they are very bright objects

Maybe you didn't know that Venus is visible in daytime WITHOUT a telescope ... just your eyes

As far as I understand one can see objects that are not, in principle, visible with naked eyes (eg Jupiter at noon). It is a known fact that telescope does not amplify surface brightness. So I can understand why one can see stars in telescope at the noon, (angular size of a star is practically zero). But it is a different story for an extended object.

 

[davenn]

So I can understand why one can see stars in telescope at the noon, (angular size of a star is practically zero). But it is a different story for an extended object.

yeah but for practical viewing purposes, Venus, Jupiter and Saturn can be regarded at close to point sources
But again, you just don't seem to realize how bright those 3 planets are ...

over the years, ( lots of them, I'm 60 now), I have seen Venus in the daytime sky and often quite close to the sun. Have had to block the sun out with the side of a building or something.
I have never seen Jupiter in day time naked eye, only through a scope

 

[mfb]

Your eyes have a finite resolution - larger than the angular diameter of Jupiter. With the naked eye you compare "a lot of sky" with "a lot of sky with a small bright object in it" - and don't see a difference (at least not enough to find Jupiter). With a telescope you can actually resolve Jupiter and compare "some sky" with "Jupiter's surface brightness". And then Jupiter wins.

 

[DaveC426913]

Can you find the constellation Cassiopeia? If you can, I think that you should be able to the see the Andromeda galaxy as a grey smudge fairly easily with 8 cm. My sky is a little better than yours, and I can easily see Andromeda with 5 cm binoculars.

I was under the impression that Andromeda is potentially visible to the naked eye.
I've tried many times over the years to spot it, but have never done so. (and now my eyes are too old).

 

[George Jones]

I was under the impression that Andromeda is potentially visible to the naked eye.
I've tried many times over the years to spot it, but have never done so. (and now my eyes are too old).

Yes, I have seen it many,many times without aid. The light pollution in the city where the OP lives makes the sky too bright to see Andromeda unaided.

 

[davenn]

I was under the impression that Andromeda is potentially visible to the naked eye.

It is, very easy, but not in daytime

It only gets around 15 deg above the northern horizon for me in Sydney, Australia. I cannot see it from home
too much city light pollution but it is easily seen from one of my darker sites to the north of the city

M33 a large face on spiral galaxy, not far from Andromeda (a handspan) is a much more difficult object to pick out naked eye.Dave

 

[OmCheeto]

Your eyes have a finite resolution - larger than the angular diameter of Jupiter. With the naked eye you compare "a lot of sky" with "a lot of sky with a small bright object in it" - and don't see a difference (at least not enough to find Jupiter). With a telescope you can actually resolve Jupiter and compare "some sky" with "Jupiter's surface brightness". And then Jupiter wins.

Here's an example I just found comparing the moon and Jupiter during the day.

Published on Jun 11, 2016​

Conjunção Lua - Júpiter vista durante o dia em Fortaleza-CE 11/06/2016​

The photographer also caught the ISS fly by the moon during the day.

Published on Aug 24, 2016​

Transit from the International Space Station (ISS) through the unlit part of the moon. Canon SX40 without tripod. Calsky Stats: ISS - Crosses the disk of Moon. Separation = 0.208 ° Position Angle = 302.7 °, Position Angle vertex = 182.0 °. Transit duration = 0.38s Angular diameter = 58.1 "size = 109.0mx 73.0mx 27.5m Satellite at Azimuth = 303.1 ° WNW Altitude = 57.5 ° Distance = 475.7 km Magnitude = -3.8mag​

credits: Christine Leão, Fortaleza, Brazil