Venus at Inferior Conjunction

in steemstem •  26 days ago

3X750.JPG
Venus showing an extreme crescent phase - 2250 exposures were obtained with a Celestron C14 and QHY183c at 1pm in the afternoon, October 20, 2018. A mask with a 4" opening was placed over the telescope to reduce sunlight entering the optical path

On October 26, Venus reaches inferior conjunction which is the point it passes between us and the sun. It is similar to when the moon passes from the morning to the evening sky, and we have "New Moon." As this event approaches, I have been busy getting photos of the planet, one of the latest is this image from the afternoon of October 20. Just as the moon shows a very thin crescent when near new moon, so does Venus near inferior conjunction.
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In the coming days, the planet's crescent becomes even thinner and extends in an almost complete arc around the planet. Unfortunately, observing Venus at this time is not only tricky, but it can also be a little dangerous due to it's proximity to the sun in the sky. Below I describe some of the preparation I had to do to get the above image.

Inferior Conjunction and Atmospheric Scattering

Inferior conjunction refers to when a planet passes between the sun and us. In rare cases, inferior conjunction may in a transit of the sun, as it did in 2012, but generally, Venus will either be due north or south of the sun. For a graphic representation check out the following animation.

inferior-conjunction2.gif
Animation showing the how Venus moves through Superior conjunction (behind the sun) and Inferior Conjunction (in front of the sun). Point's to note are how the phases change, the size changes and the effects of atmospheric scattering of sunlight around inferior conjunction (planet appears as a circle of light)

Venus has an upper atmosphere that scatters light from its sunlit side around into the night time boundary. This same effect causes twilight here on earth, as well as causing the moon to glow a dull orange during a Lunar Eclipse. For earthbound observer's this effect is visible as an extension of Venus's crescent which when close enough to the sun causes it to form a complete circle.

I was curious to see if I could capture the extension of the crescent due to the scattering effect. It seems like Venus was still too far from inferior conjunction to show this effect, but when I enhance the image from above, you can see a small amount of extension to the crescent. Have a look here and see what you think.




Don't Try this at home!

As I mentioned above trying to observe Venus near inferior conjunction is risky because of it's proximity to the sun. Here in this telephoto view, I show Venus with the sun just off the bottom right. Even if the telescope is not pointed at the sun directly, sunlight can enter at an angle and damaged cameras, optics and yes also eyes!

Venus--75mm.JPG

To avoid this, I created a mask to sit in front of the telescope with a 4" diameter opening (the normal aperture is 14"). Although restricting the aperture to 4" reduced theoretical resolution, it also reduced sunlight coming in at an angle. At least that's what I was thinking but still managed to burn a hole in the mask! Luckily the focused light was well outside the focal plane otherwise I might have had a damaged camera.

MASK-WITHHOLE.JPG
Even with the mask to cutdown sunlight entering the telescope tube, this hole was burn't in it by focused sunlight!

What I was missing was an extension tube as shown in the next diagram. I should have realised this initially - there is saying here measure twice and cut once! Here is the corrected mask.

MASK-fixed.JPG

Finally

You should see some quite interesting images in the coming days showing the unusual crescent. It's worth checking out the Spaceweather Gallery as people upload them in almost realtime. Meanwhile if I succeed in getting photo's nearer October 26, I'll will try to post here before the edit option disappears.

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October 21, 2018: After a thunderstorm the sky cleared and managed to get this brief shot of Venus setting over the neighbours roof. 300mm lens OMD EM1mk2

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October 22, 2018: Bat flying past Venus! 300mm lens OMD EM1mk2

October 24, 2018 : Today it was really difficult to find Venus as it is was just too close the sun (about 7 or 8 degrees away) and I abandoned the idea of using the 14 to image the planet, instead I tried to 8" C8 with QHY183m mono camera which I can get in a position at the side of the house to avoid risking sunlight entering the telescope tube. Here is my image, note the crescent is covering an angle perhaps 240 degrees or so. This is actually a monochrome image and I've added a bluish tint to make it look more natural.

References and Further Reading


  1. Earthsky.org . Has some technical details on Venus and conjunction.

  2. Thierry Legault . French amateur astronomer takes some pretty extreme astrophotography. Check out his 2012 Venus transit photos.

NOTE: All Images are the authors, please feel free to use with name credit.



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Thanks to HF20 now I will wait 6 more min before upvoting, because we all know I'm a bot and this is preventing me to abuse whatever I would abuse.

Meanwhile, honourable mentions, why not to shoot long exposures of the Sun

Two more minutes...

Panda vs doughnut

Ok, 15 min. Make Steem 8 again!

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Haha very funny...Hopefully I'll have enough RC to reply to you! Regarding frying cameras with the sun I have heard of somebody Autofocusing on the rising sun, with a Canon 200mm f1.8 lens attached. Left quite a mark....

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Smell of napalm in the morning vs smell of a burning sensor?

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A possible idea for a Youtube channel...telescope/sun vs [insert item] ..what do you think!? Would be more interesting than red-hot knife or hydraulic press vs [item]!

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I've really been enjoying seeing Mars, Saturn, Jupiter and Venus in the early evening sky recently while doing yoga on the roof of my gym. Is this normal that you can see 4 at the same time?

I think Venus is gone now. A building is in the way so no risk of this happening.

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I don't actually think this would be uncommon. However, to have Mars this bright at the same time is rare (i.e every 15 years).

At one point, I was testing new glasses (I'm short sighted) with my daughter and in the late afternoon we had the sun low in the west, and we could not only see the moon, but we could make out Venus, Jupiter (just) and Mars. So that is 5 solar system objects all in a line across the sky - that was a cool sight!

Great read Terry 😊
Sunlight and telescopes are a very dangerous mix. One little carelessness and you're blind or something destroyed.
Btw. With steempeak you can edit posts that are older than 7 days 😉

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Indeed yes they are dangerous! Cool re steempeak, I always assumed it was locked in the blockchain after 7 days.

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This is something new HF20 brought us. Before HF20 it was locked. That’s how I understood it.

Its nice seeing venus from the pictures you captured. Apart from the theories and lectures we had in class, i havent really thought about how it would look like

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Thank you!

@terrylovejoy very interesting topic, enjoying lot

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Much appreciated @dotfee!

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Nice photos as always. I especially like the bat with Venus in the background.