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No Sign of Venus...


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Last Spring, Venus was high in the evening sky.  Yet this Spring, I couldn't see it at all.  Is it higher in the sky in certain years, more than others?  And yes, I know about it being the "evening star" or "morning star" depending at what time of the year you see it.

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The orbit of Venus is such that as seen from Earth, its evening apparitions are separated by just over 18 months. 

In addition, as  the planets travel along the ecliptic, the height of the planet in the western sky depends on how that is angled in the evening. As it happens, this angle is greatest in the spring, and shallowest in the autumn.

So, two things have come together; firstly, Venus simply wasn't suitably positioned to be visible this spring, and is only just moving away from the sun to allow it to be seen in the evening again. However, because we're later in the year, the angle of the ecliptic to the horizon is less, so Venus will track lower in the sky than last time.

In addition, for those of us in more northern latitudes, the summer night sky doesn't get properly dark until after Venus has set (or at all to be honest), so it'll never stand out as much as in 2020

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26 minutes ago, Ian McCallum said:

Last Spring, Venus was high in the evening sky.  Yet this Spring, I couldn't see it at all.  Is it higher in the sky in certain years, more than others?  And yes, I know about it being the "evening star" or "morning star" depending at what time of the year you see it.

Venus’ position depends on where it is in its orbit around the Sun. When it is leading the Sun it appears as a morning object, when trailing it is an evening object. It is at its highest when at the extreme end of its orbit as seen from the Earth, referred to as maximum elongation.

The timing is not a particular time of year, but where Venus is in its orbit as viewed from Earth. A lot also depends on the angle of the orbit in relation to the horizon as to how high Venus appears at sunset even at maximum elongation. For instance, next maximum elongation is 29th October this year, and Venus will only be 8.7 degrees above the horizon at sunset. The next evening opportunity is June 4th 2023 when it will be 27.8 degrees above the horizon at sunset, much better.

The phases make it interesting too, and actually At maximum elongation it shows half phase, then gradually becomes a finer crescent which is very beautiful as it rounds it’s orbit and gets closer to the sun, eventually becoming too difficult (risky) to observe.

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Was camping in Dorset last weekend and caught a glimpse of Venus shining bright in the red sunset about 30 min after the sun had gone below horizon. It was only about 10 degrees above horizon so not easy to spot but once seen was very bright.

Venus is easier to spot when at greatest elongation (angular separation from the sun as seen from Earth) because it will be shining in darkness. However, greatest elongation needs to coincide with highest elevation of the ecliptic (the plane of the solar system in which all the planets move) for it to be really striking. So it's a combination of the Earth's seasonal tilting (which varies the altitude of the ecliptic) and the relative orbital position of Venus/Earth which together give the most favourable views. You won't see the same exact positioning of planets/moon/sun play out every 365 days. In fact, the venus cycle repeats every 584 days https://en.wikipedia.org/wiki/Venus#Observability - which is not the same as our annual cycle.

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9 minutes ago, Gfamily said:

As it happens, this angle is greatest in the spring, and shallowest in the autumn.

Perfect explanation for the two snapshots in Autumn (October) and Spring (March) respectively. Thanks 👍

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This post by @CentaurZ  plots the position of Venus 30 mins after sunset for the rest of the year. Most of the time is only at 10 degrees altitude rising to about 15 degrees in October/November/December.  That's when it will be larger and best to see this year.

Nik

 

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6 minutes ago, Nik271 said:

This post by @CentaurZ  plots the position of Venus 30 mins after sunset for the rest of the year. Most of the time is only at 10 degrees altitude rising to about 15 degrees in October/November/December.  That's when it will be larger and best to see this year.

Nik

 

Great info, thanks 👍

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Posted (edited)

PS, Just realized that @CentaurZ plot above is for 42 degrees latitude, in the UK it will be even worse  - Venus will not even reach 10 degrees :( 

Edited by Nik271
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Posted (edited)
9 hours ago, Nik271 said:

PS, Just realized that @CentaurZ plot above is for 42 degrees latitude, in the UK it will be even worse  - Venus will not even reach 10 degrees :( 

 

Here's my version for London. 😀

 

Venus-London.JPG.d87b1a2080303584ff28135fb96210a1.JPG

Edited by CentaurZ
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2 minutes ago, CentaurZ said:

 

Here's my version for London. 😀

 

Venus-London.JPG.bfb90fdd68935768ea86797b698cff02.JPG

 

Thank you! A bit more depressing though!! Could I trouble you for one for the following evening apparition from London when it is much higher?

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Posted (edited)
44 minutes ago, Stu said:

Thank you! A bit more depressing though!! Could I trouble you for one for the following evening apparition from London when it is much higher?

 

You're welcome, Stu. Sure, here it is for London 2027-28, which will be similar to 2019-20. 😃

 

Venus-London28.JPG.3e6d6c200ef8f9ed790c170c4aca87e3.JPG

 

 

 

 

Edited by CentaurZ
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