Why can't Venus cause a solar eclipse

Astronomy: Venus brings us rare mini solar eclipses

Our neighboring planet Venus brings earthly observers to a very rare mini solar eclipse at the beginning of June: At sunrise on June 6th, Venus passes in front of the solar disk. The next so-called Venus transit will only take place again in the year 2117.

Not only amateur astronomers, but also professional researchers should carefully observe the rare event, writes Jay Pasachoff of the International Astronomical Union (IAU) in a comment in the British journal "Nature". Because the data could also help in the search for planets of other stars.

Venus is the inner neighbor of the earth, the second planet as seen from the sun. A transit occurs when it overtakes Earth, the third planet, on the inner orbit and pushes itself exactly between us and the sun.

It is true that Venus regularly laps the earth. However, since the orbits of both planets are slightly tilted against each other, Venus almost always moves north or south of the solar disk in the earthly sky. Only if the overtaking maneuver happens to take place at the intersection of the two orbit levels, Venus moves in front of the sun.

But if you don't know anything about the rare spectacle, you won't even notice it. Only those who look at the sun at the right time and above all with suitable eye protection can recognize the neighboring planet as a small, dark disc in front of the blazing sun, as the Stuttgart astronomy professor Hans-Ulrich Keller in his starry sky guide "Das Kosmos Himmelsjahr" (Kosmos Verlag ) writes.

Without protection there is a risk of serious eye damage

Keller warns observers not to look into the sun without special eye protection. The glaring light threatens serious eye damage and even blindness. This applies in particular to the unprotected view through binoculars or telescopes.

For centuries, Venus has passed by in front of the sun unnoticed by earthly inhabitants. The transit of 1631 was the first to be correctly predicted, but remained largely unobservable due to the weather, as Pasachoff reports.

There have only been six other opportunities to see the drama since then. Hundreds of expeditions were equipped to follow the event in 1761 and 1769. The distance between Venus and the sun can be determined from the observation times from different points on the earth's surface.

Today, the distances in the solar system are measured much more precisely using other methods. Nevertheless, the Venus transit is more than a heavenly spectacle for the interested general public, says Pasachoff.

Observation can be of use to modern research because such planetary transits are one of the methods that astronomers use today to search for distant planets of other stars.

Special satellites peek for the very slight darkening of stars caused by such a transit. With the passage of Venus in front of the solar disk, there is a unique opportunity to observe such a transit up close.

This is particularly useful because our sun is currently going through a particularly active phase with many sunspots. Pasachoff explains that it is possible to check how sunspots can be distinguished from planets passing by.

If you want to watch the Venus transit yourself, you have to get up early, because Europe is not in a favorable position for this year's show.

Mini-eclipse can be observed for an hour and a half

When the sun rises above the horizon shortly after 5 a.m., most of the 6.5-hour mini-eclipse is already over. We can only observe about the last hour and a half.

When the sky is clear, you can see how Venus detaches itself from the solar disk. A strange phenomenon will also be seen that has caused headaches for generations of astronomers: When the Venus disk approaches the edge of the sun, it forms a drop shape as if it wanted to flow out towards the edge.

One of the reasons for this black drop is the limited sharpness of detail (resolution) of all telescopes, explains Pasachoff. On the other hand, the fact that the sun gets darker extremely quickly towards the edge.

The last time Venus passed in front of the solar disk was in 2004, the transit was easy to follow from all of Central Europe. Because of the geometry of the orbit, a first Venus transit is usually followed by a second after eight years, so the spectacle is repeated this year.

After that, however, it always takes 105.5 or even 121.5 years for the position in the sky to repeat itself. Therefore, anyone who misses the show will probably not get a second chance during their lifetime.

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