Tuesday, January 10, 2006

Naked Eye: Crescent Venus Redux

Venus_20060110_w140p.jpg Date: 10-Jan-2006 @ 12:50p EST
Magnitude/Size: —4.1 / 63"
Alt./Az. (Venus): 32.5° / 188.0°
Elongation: 7.0° East
Illumination/Phase: 0.7% / 170.4°
Alt./Az. (Sun): 26.4° / 192.0°

Click image for U.S. Naval Observatory's ‘Apparent Disk of Solar System Object’. The image was created for the time of the sighting. Click here for a full list of ‘Data Services’ from the USNO.

Conditions for viewing Venus in full daylight, naked eye or with binoculars, were less than ideal. High haze and thin clouds were getting in the way.

At 12:35p I arrived at Bryant Park looking to spot Venus in binoculars and was making little headway. Glare from sunlight illuminating the surrounding haze was a problem.

After 10 minutes I moved to a spot where I could determine the azimuth of the Sun. Where the Sun was spotted Venus would arrive above the same point 14 minutes later and approximately 6 degrees higher. This would help pinpoint where Venus should be.

A location was picked so that the Sun, after a few minutes, would be safely tucked away behind a building reducing the glare near the planet's location. It took around 5 minutes to finally see Venus' thin crescent shining weakly through haze and thin clouds.

Looking at the image above produced at the USNO site I can see why a typically brilliant Venus seemed somewhat subdued. This and the haze combined to make this attempt more difficult than usual. This was no six second sighting!

Question: What is the surface brightness of a crescent this size compared to the surface brightness of a gibbous Venus near opposition where it was a relatively easy object (less that 4° from the Sun) in a pair of 10×70's?

Relocating Venus with the 8.5×42 binoculars after taking some notes wasn't easy even though I knew the exact position. A minute or two was spent glassing the area before recovering it again. The last time Venus was spotted was around 12:55p.

Viewing the planet naked eye was attempted but without success.


Tag said...

Hi Ben,

Had a great time at lunch and waltzing to Bryant Park for an opportunity to observe crescent Venus - with your optics :~D

SBr = m_v + 2.5 log(2827ab)

where m_v is visual magnitude and a & b are the dimensions of the object.

Don't know what the weather is for tomorrow but would like to try again. I haven't checked to see if it is possible, would you know off hand?

Thanks for making my first obseving session for the new year.


Ben C. said...


Lunch and the trip to Bryant Park work out nicely. Thanks for the invite!

I worked out the surface brightness for Venus at inferior conjunction and superior conjunction. The numbers work out to 7.9 mag/sq" and 9.4 mag/sq" respectively. I added 8.89 to covert from arcminutes to arcseconds.

Does this seem right?

Thanks again.