Could someone explain opposition to me (BBC's The Sky At Night)

[doubledoubleswifty]

Hello,

I'm just watching BBC's Sky At Night right now - 6 minutes in. (https://www.bbc.co.uk/iplayer/episode/m000db8r/the-sky-at-night-a-beginners-guide).

The presenter is explaining opposition.  "But you'll ever hear that Mercury or Venus are at opposition....have orbits which are smaller than the Earth's so they can't appear in the night sky".

Could someone explain the above to me in very simple terms?

[andrew s]

Wiki gives a good discription.  Google "opposition astronomy "

Then we can't see Mercury or Venus in opposition to the Sun as they are inside our orbit. You can't get the Sun, Earth and Mercury (or Venus) in a straight line and in that order.

Regards Andrew 

Edited April 13, 2020 by andrew s

[adyj1]

1 hour ago, doubledoubleswifty said:

they can't appear in the night sky

This is the misleading bit, I think...Venus is currently very much visible in the night sky. I wonder what they meant? 

[bingevader]

For a planet to be in opposition, we (the earth) have to be directly between a planet and the sun.

That can't possibly happen with a planet that has a smaller orbit than ours.

We can be in conjunction and line up, either with the other planet in the middle or the sun in the middle.

When the planet is in the middle, we are at opposition to the planet, but that will only happen in day time, not at night, so we will only ever see it through a solar 'scope.

Edited April 13, 2020 by bingevader
a

[bingevader]

11 minutes ago, adyj1 said:

This is the misleading bit, I think...Venus is currently very much visible in the night sky. I wonder what they meant? 

You can see the planet at night because we are not in opposition.

The 'Who is in opposition with whom?' is the confusing bit, I think.  

Edited April 13, 2020 by bingevader
at

[david_taurus83]

13 minutes ago, adyj1 said:

This is the misleading bit, I think...Venus is currently very much visible in the night sky. I wonder what they meant? 

Correct. Can also see Mercury as long as its behind the sun and trailing on the left as viewed from the northern hemisphere. In fact, 22nd of May after 9pm, both Mercury and Venus will be close together from our perspective here in the UK. Approx 10° above horizon so good western view needed.

[Louis D]

5 hours ago, doubledoubleswifty said:

The presenter is explaining opposition.  "But you'll ever hear that Mercury or Venus are at opposition....have orbits which are smaller than the Earth's so they can't appear in the night sky".

Opposition: When a planet that orbits further from the sun than the Earth (Mars/Jupiter/Saturn/Uranus/Neptune) is exactly on a line with the Earth and sun so it rises as the sun sets and sets as the sun rises, just like a full moon is the moon at "opposition".  It's on the opposite side of the Earth from the sun, so it's visible all night long.

Mercury and Venus orbit between the Earth and Sun, and as such, can only be visible for short periods of time after sunset and before sunrise.  I think that's what the presenter meant by "can't appear in the night sky".  They can only appear during twilight and shortly before and after twilight.  You'll never be able to see Mercury or Venus at midnight because the night side of the Earth at that time is facing toward the outer solar system, not the inner solar system where those two planets orbit.

[Nicola Hannah Butterfield]

21 hours ago, Louis D said:

  You'll never be able to see Mercury or Venus at midnight because the night side of the Earth at that time is facing toward the outer solar system, not the inner solar system where those two planets orbit.

If Stellarium is right 31/5/2023 Venus is 5°39'41" degrees above the horizon at midnight from my location, though it's still not opposition.

Edited April 14, 2020 by Nicola Hannah Butterfield

[Louis D]

23 minutes ago, Nicola Hannah Butterfield said:

If Stellarium is right 31/5/2023 Venus is 5°39'41" degrees above the horizon at midnight from my location, though it's still not opposition.

It is possible that at greatest elongation and at high observing latitudes, it is possible for Venus to be visible many hours after sunset (or hours before sunrise).  However, it will never be on the meridian at astronomical midnight like a superior planet at opposition.

[Filroden]

So any planet, whether an inferior or exterior, can be see at midnight at very high latitudes during winter because it's also possible to see the Sun at midnight at those latitudes!

I think the BBC have over simplified something to the point that it's now actually more confusing.

As Louis just posted: 

2 minutes ago, Louis D said:

it will never be on the meridian at astronomical midnight like a superior planet at opposition

 

[Louis D]

2 hours ago, Filroden said:

So any planet, whether an inferior or exterior, can be see at midnight at very high latitudes during winter because it's also possible to see the Sun at midnight at those latitudes!

I think the BBC have over simplified something to the point that it's now actually more confusing.

Which goes to prove that given the right circumstances, just about anything is possible.  I suppose if a small black hole or group of them wandered into the inner solar system, it or they could make Venus visible at midnight on the meridian given the proper alignment to warp space-time just right.  I don't think I'd want to be around to witness it, though.

[doubledoubleswifty]

Thank you all for your replies.

It makes sense we can never seen Mercury or Venus at midnight as we're facing towards the outer solar system 🙂

Is there a reason why Venus is normally found in the Western sky?  Sorry for the silly question!

 

 

[Marvin Jenkins]

Don’t you dare apologise, no such thing as a silly question. Problem is I have been reading through all the posts and in relation to your original question, what a lot of confusing info, which could be described as something else.

This is supposed to be in beginners and there is whole load of contradictions. How is this supposed to help? How did black holes get in here?

Just goes to show that the easiest questions are the hardest to answer. Sorry I don’t have an answer to your question as after this I am equally confused. Probably better off taking up AP, less confusion there😂
 

Marv

[andrew s]

2 hours ago, doubledoubleswifty said:

Thank you all for your replies.

It makes sense we can never seen Mercury or Venus at midnight as we're facing towards the outer solar system 🙂

Is there a reason why Venus is normally found in the Western sky?  Sorry for the silly question!

 

 

Venus is never far from the Sun so you can see it in the evening in the West as the Sun sets and in the East before and as the Sun rises.

Regards Andrew 

[Louis D]

3 hours ago, doubledoubleswifty said:

Is there a reason why Venus is normally found in the Western sky?

Because it's just as often in the eastern sky before sunrise, but many fewer people are up and about that early to notice it compared to its evening appearances.

[Louis D]

2 hours ago, Marvin Jenkins said:

How did black holes get in here?

Because @Nicola Hannah Butterfield proved me wrong that Venus can never be seen at midnight under the right circumstances.  I was only thinking of my own circumstances in Texas where that can never happen.  I then wanted to head off someone else trying to disprove my supposition that Venus would never be visible on the meridian at midnight from anywhere on earth by claiming that if space-time were bent sufficiently, it could be visible there.  Sorry for adding to the confusion.

[barkis]

Loads of Info here. Read at your leisure of course there is a lot of it.
Pictures do speak a lot more clearly than words.
Ron.

     https://www.google.com/search?q=difference+between+superior+and+inferior+conjunction&safe=strict&rlz=1C1CHBF_en-GBGB876GB876&sxsrf=ALeKk013HnV0hc5UiYWBNy6Flo8nTXd6LA:1587374153365&tbm=isch&source=iu&ictx=1&fir=k6eogyHKlXyOkM%3A%2C-tVVqg8o8chQnM%2C_&vet=1&usg=AI4_-kQqNTfXto04z3ZaeG23WODzRb4Svg&sa=X&ved=2ahUKEwjUvaXE1fboAhUBThUIHUxEAZIQ_h0wAHoECAoQBA#imgrc=k6eogyHKlXyOkM:

[bingevader]

14 hours ago, Marvin Jenkins said:

Don’t you dare apologise, no such thing as a silly question. Problem is I have been reading through all the posts and in relation to your original question, what a lot of confusing info, which could be described as something else.

This is supposed to be in beginners and there is whole load of contradictions. How is this supposed to help? How did black holes get in here?

Just goes to show that the easiest questions are the hardest to answer. Sorry I don’t have an answer to your question as after this I am equally confused. Probably better off taking up AP, less confusion there😂
 

Marv

It got confusing when people started talking about seeing Venus in a more general setting.

The article is about Opposition.

Yes we can see Venus in the night, but we are not at opposition.

We are at opposition to Venus (or Mercury), only at day time, we cannot be at opposition (to Venus or Mercury) in the night time and see Venus (or Mercury).

Edited April 20, 2020 by bingevader

[Waddensky]

Here's a nice drawing from Wikipedia that explains oppositions, greatest elongations and conjunctions very well. As you can see, at opposition a planet is placed on the opposite sides of the celestial sphere as observed from Earth. This can only happen for planets that have orbits farther from the Sun than the Earth. The 'inferior planets' (Mercury and Venus) can never be between the Earth and the Sun, because they are always closer to the Sun than Earth. That's why they always appear close to the Sun as seen from Earth and in most cases are visible only in twilight. The fact that Venus can currently be observed during astronomical darkness is because of the favourable elongation and the large angle the ecliptic makes with the horizon this time of year.

Venus is just as much in the eastern morning sky as it is in the western evening sky, but I guess people are more familiar with the evening sky.

Edit: the skin of SGL renders the image invisible due to the transparent background. Here's a link to the image.

Edited April 20, 2020 by Waddensky