Why is Venus so bright?
Tim Jones of Chelford, Cheshire, UK, takes a large group photo of Jupiter (left), Saturn (center) and Venus (right) on November 27, 2021. Do you see how bright Venus is, even though it's close to sunset? If you're interested, look for these three planets after sunset and enjoy the brightest Venus in early December 2021 Thank you, Tim.
Why is Venus so bright?
Jupiter is a bright planet, and Mars can sometimes become bright. But Neither Jupiter nor Mars is bright enough to have Venus at its brightest. So why?
Our cosmic nearest neighbor, Venus, orbits the Sun one more closely than Earth — it's the third brightest object in the sky after the Sun and Moon.
As an adjacent planet in earth's orbit, Venus is relatively close to us, but proximity is not the only reason it is so bright. Think of Mars, which orbits next to each other outside the Earth's orbit around the Sun, and which appears sometimes bright and sometimes dim in our skies. Mars is particularly bright only during the period between Mars and the Sun, and it is closest to the Sun. The last time this happened was in 2018, and the next time it will be in 2035.
There is another reason for the brightness of Venus. Astronomers use the term albedo to describe the absolute brightness of a planet. When sunlight hits a planet, the surface of the planet absorbs some sunlight and the rest is reflected out. The albedo is the ratio of the total amount of incident sunlight to the amount of light reflected out.
As you can guess, Venus has the highest star albedo among the major planets in the solar system.
This is when Venus is at its brightest, which is when it reaches the so-called maximum illumination range, or maximum brightness. At this point in time, Venus is relatively close to Earth. When the telescope shows that it is in the crescent phase, it looks like a mini moon. At this time, you can even see Venus during the day.
This is a telescope view of Venus (l) and the Moon during the daytime, in the crescent phase Image Source: NASA.
Venus shines with albedo
Venus' albedo is close to 0.7, meaning it is able to reflect nearly 70% of sunlight. When the full moon appears above Earth, it reflects only about 10 percent of the sunlight, but it looks much brighter than Venus. The moon's low albedo is due to the fact that it is made of black volcanic rock, which looks bright in our eyes only because it is close to Earth. The Moon is only about a light second away from us and Venus is a few light minutes.
Venus is bright because it is wrapped in a highly reflective atmosphere (hence its high albedo). Venus' atmosphere contains droplets of sulfuric acid and acidic crystals suspended in a gas mixture. Sunlight is extremely easily reflected back from these smooth droplets and crystal surfaces, and the sunlight reflected by the atmosphere constitutes an important reason why Venus is so bright.
By the way, Venus is not the most reflective object in our solar system, a privilege that belongs to Saturn's moon, Enceladus, whose icy surface reflects about 90 percent of the sun.'s rays.
Since late October 2018, Venus passed between the Sun and the Earth, and its bright half-day surface is still mostly facing the Sun. Interestingly, this crescent-shaped Venus may be brighter than the full Venus we've seen before. On November 20, 2018, Prabhakaran A photographed the crescent venus in Mleiha, UNITED Arab Emirates. Device: Edge HD 11''Alt Az - Discovery Science 3x Extender - ZWO 290MC. Post-processing: 9000 frames stacked in AS and processed in Registax.
The apparent size of Venus
As mentioned above, the brightest Mars can be observed as the Earth passes between Mars and the Sun. At this point, Mars is closest to us, so he is the brightest in the sky. The same is true of Venus: the planet is brightest in the sky as it passes between the Earth and the Sun, though not necessarily at that time.
Because Venus orbits the Sun in Earth's orbit, when it travels between us and the Sun, its bright hemisphere, or dayface, is facing away from us. At this point, it is almost impossible to see Venus.
Because Venus is an inner planet (a planet orbiting the Sun in Earth's orbit). As it approaches the Earth and the Sun, we can have Venus take on the shape of a crescent moon. As Venus approaches Earth in orbit — and prepares to "overtake" us in the planetary race — observers on Earth can see Venus's phase weaken. At the same time, as the phase of the new moon Venus gradually weakens, the overall size of Venus in the disk of the Earth's sky gradually increases, because Venus is getting closer to the Earth and moving between the Earth and the Sun.
Venus is brightest when these two factors (the shape of the remnant moon and the largest disk of Venus) are superimposed, when it shows the largest surface area in our sky, which astronomers call the maximum illumination range.
Brett Joseph's photo of Venus in the east taken by Brett Joseph on October 31, 2018, is very close to the sunrise point. This point in time is less than a week after the planet passed between us and the sun, thus entering the morning sky. Venus is so bright that even though it is so close to the sunrise point, photographers can still see the planet
Summary: Venus is the third brightest object in the sky, after the Sun and Moon. Part of the reason is that sunlight is easily reflected by acidic clouds in Venus' atmosphere.
Related knowledge
Venus is a planet close to the sun. Its English name "Venus" is derived from the Roman mythology of Venus, the goddess of love and beauty (Greek counterpart: Aphrodite). As a natural object in the Earth's night sky that is second only to the Moon, Venus can illuminate shadows and, in some rare cases, it can be seen even by the naked eye during the day. Venus is within the orbit of the Earth, so from Earth it does not look too far from the Sun, and it either falls from the west after dusk or rises from the east before dawn. Venus orbits the Sun every 224.7 Earth days, with an rotation period of 243 Earth days and 117 Earth days per day. It has the longest rotation time among the planets in the Solar System and is only in the same direction as Uranus, as opposed to other planets, meaning that the Sun rises west and sets east on Venus. Venus has no moons, in fact, of all the planets in the solar system, only Venus and Mercury have no moons.
BY：earthsky
FY：Astronomical volunteer team
If there is any infringement of the relevant content, please contact the author to delete it after the work is published
Please also obtain authorization to reprint, and pay attention to maintaining completeness and indicating source