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Tuesday, August 26, 2008

 

How Soon After Sunset can You See Jupiter?

11 minutes .... before sunset! Yes, before Sunset. Mind you, it took me a while to set this up, but over the past few days the horizon has been finally clear. I was able to see Jupiter clearly 10 minutes after sunset, and I lined up a post with a pointy bit on it as a reference point (the point seems to help, having a post like object very close to where the planet, be it Jupiter or Venus, should appear makes it very much easier to find).

The next day I was able to look earlier (due to a lack of clouds), and saw Jupiter clearly 4 minutes after Sunset. I used this view to refine my viewing post location.

By making sure my outlook was a fixed number of paces form the post, and making sure I was facing the right orientation by lining up a couple of landmarks, then carefully counting the number of handspans from the top of the post to Jupiter, I prepared for my "daylight Jupiter" assault.

So this afternoon everything was perfect, clear horizon and no clouds at all. I positioned myself at the observing point, lined up my post and "bang", there was Jupiter. A full 11 minutes before Sunset. I was impressed, I expected to have to wait a bit longer, but Jupiter was quite clear (so long as I had it in sight of my referents, if I move to a large patch of sky with no reference objects it disappeared).

It also helped that although the Sun had not set, it was only 2 degrees above the horizon, and hidden by trees and houses, and Jupiter was almost on the other side of the sky from the Sun, where the sky was relatively dark (The Jupiter image above was taken 10 minutes after Sunset, the automatic exposure on the Olympus mu 300 overbrightens the sky washing the planet out if taken earlier).

So what is the earliest you can see Jupiter in the daytime with the unaided eye? I found an article from 1917 that says you can see Jupiter only when the Sun is 5 degrees or less above the horizon. The Sun is 5 degrees above the horizon around 30 minutes before Sunset now at my location (and Jupiter 43 degrees above the horizon). So I will have a go at it on the weekend if the weather is kind. I've had a look around for other reports of Jupiter seen unaided, but haven't seen any that are not telescopic (see images here) or binocular views (see my report here of trying to see Jupiter in daylight back in 2005).

A good aid to seeing planets in the daylight is the Moon. The Moon is quite visible in daylight when it is more than 2 days old, and once you have the Moon in sight locating the planet is easier. The next good daytime Moon encounter for Jupiter is 7 October when Jupiter is one degree north of the Moon (around one fingerwith, so very easy to locate), on this date the Sun is 5 degrees above the horizon at 5:50 pm.

The next good Moon - Venus encounter in Daylight is 1 November when Venus is two degrees from the Moon (earlier than this the Moon is too far away or too thin to be easily seen in daylight).

So why not have a go at seeing Jupiter in the daylight? How far from Sunset can you get and still see it?

(Oh, and the Venus, Mercury, Mars image was taken 35 minutes after Sunset, facing west from my backyard)

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Comments:
Greetings. I found that given minimum conditions, Jupiter is relatively easy to spot at daylight. During my University years, I found it quite easy to spot Jupiter up to half an hour after sunrise with humidity below 25%, clear sky and it laying more than 120° from the sun. I did my observations from Northwest Mexico City (2250 meters ASL) between 1990 and 1995.
 
Is it possible to see any planets located near the sun shortly before sunset? Not necessarily with the naked eye, but say you're taking a picture. Is it likely that a planet in orbit passing the sun would be visible? If so, what planets could they be? And how large might they appear?
 
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