Event Date: April 24th
Time: 8:00 PM
Brief
Let's get back to the planets after a break of a few days. Venus is still the main attraction in the sky as it is about a week away from greatest brilliancy. Do you remember the formula to find out the area of reflected Sunlight to our eyes? I ask, not because the formula is tricky; as a reminder, the date that Venus reflects the greatest amount is the designated date of greatest brilliancy. Ten entries ago, I glazed over a link that I included in the text for Lambert's Law. Without going into detail about it in this entry, letting you read it on your own time, I will mention that greatest brilliancy happens at a smaller phase than maximum brightness.
The first image shown here before the calculation and zoom-in, is a reminder of where Venus is in its orbit, and why we are seeing less and less of it illuminated each day; use the orbit thickness as a reminder for that. The 12% illuminated, waxing crescent Moon about 6º away, is paired nicely with Venus as both set a similar altitude.
Let's get back to the planets after a break of a few days. Venus is still the main attraction in the sky as it is about a week away from greatest brilliancy. Do you remember the formula to find out the area of reflected Sunlight to our eyes? I ask, not because the formula is tricky; as a reminder, the date that Venus reflects the greatest amount is the designated date of greatest brilliancy. Ten entries ago, I glazed over a link that I included in the text for Lambert's Law. Without going into detail about it in this entry, letting you read it on your own time, I will mention that greatest brilliancy happens at a smaller phase than maximum brightness.
The first image shown here before the calculation and zoom-in, is a reminder of where Venus is in its orbit, and why we are seeing less and less of it illuminated each day; use the orbit thickness as a reminder for that. The 12% illuminated, waxing crescent Moon about 6º away, is paired nicely with Venus as both set a similar altitude.
Detailed
Refer back to my entry for April 14th for more information on that, as well as the formula for calculating lit surface area. For this evening, compared to the 276 arc-seconds (") of area on the 14th, Venus is 290". As it continues to approach us, its growth in angular size is still overriding its decreasing percentage illuminated. This continues for awhile longer, yet eventually before inferior conjunction, Venus will wane quickly enough that the area starts to decrease faster. Even so, its apparent magnitude will only decrease slowly, as it approaches us more quickly. At the time listed in the images, Venus is a little over 45 million miles from us.
This second image with a field of 15', shows the planet with an angular size of 17' (radius) in its current waning crescent phase of 32%. At magnitude -4.5, and Jupiter now too low towards the Sun's glare, Venus dominates the western sky in comparison to any other star near it. Many of those stars, just barely visible to the eye alone, are tens of thousands of times dimmer than it in apparent magnitude.
Refer back to my entry for April 14th for more information on that, as well as the formula for calculating lit surface area. For this evening, compared to the 276 arc-seconds (") of area on the 14th, Venus is 290". As it continues to approach us, its growth in angular size is still overriding its decreasing percentage illuminated. This continues for awhile longer, yet eventually before inferior conjunction, Venus will wane quickly enough that the area starts to decrease faster. Even so, its apparent magnitude will only decrease slowly, as it approaches us more quickly. At the time listed in the images, Venus is a little over 45 million miles from us.
This second image with a field of 15', shows the planet with an angular size of 17' (radius) in its current waning crescent phase of 32%. At magnitude -4.5, and Jupiter now too low towards the Sun's glare, Venus dominates the western sky in comparison to any other star near it. Many of those stars, just barely visible to the eye alone, are tens of thousands of times dimmer than it in apparent magnitude.
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*click on images to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp. |
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