A visit to the Ďáblice Astronomical Observatory
Ďáblice Astronomical Observatory, located in the north of Prague, has been welcoming stargazers since 1956. Built by local astronomy enthusiasts, it started as a small project and grew into an observatory with two domes. Led for many years by teacher Zdeněk Corn, it became an important place for astronomical observation and education. Today, it operates as part of Prague’s observatory and planetarium network. Dominik Jůn paid a visit.
The Sun is slowly setting, it is a beautiful clear sky, and I am in the northern Prague district of Ďáblice inside a long wooded park called Ďáblický háj, which is approximately 60 hectares in size. And on the north-eastern tip of the park – apart from a wonderful outcropping of rocks, where you can gaze into the distance northward and eastward for many kilometres – there is also an astronomical observatory here, Hvězdárna Ďáblice, which is open to the public. And today, one of the guides that works here, Milan Uhlár, has kindly agreed to show me around. Hopefully, once the Sun sets, we’ll be able to look at some planets and stars.
I’m stepping inside now into the astronomical dome. The dome’s shutter is open, so we can see into the night sky. There is a big stand in the middle holding two telescopes. And I am joined by Milan – hello.
“Hello. Nice to meet you. I am an amateur astronomer and astronomy has been my big passion since childhood.”
And you work as a guide here, don’t you?
“Yes, I am a guide here. My role is to show visitors some interesting objects in the sky both during the night and during the day.”
Can you tell me a little bit about the history of the Ďáblice observatory?
“The observatory was built in 1956, and it was an effort by the local astronomical club, which was coordinated by a local teacher called Zdeněk Corn.”
And this is obviously a perfect spot for astronomy, being up on a hill on the edge of Prague, right?
“Correct. They decided to build the observatory here back in the 1950s – but Prague is growing, and unfortunately we have a problem with light pollution. Nevertheless, when I compare it with the other observatories in Prague, I think this is the best place. Compared to Štefánik’s Observatory in the centre the (light pollution) conditions there are worse.”
Yes, that is the famous observatory on Petřín hill right in the centre of Prague near Prague Castle, so probably most tourists will be walking past that on their excursions.
“Right.”
So is it actually possible to do real science here?
“Not real science. But what we do is that we take certain data measurements, and then we send that to a specific organisation or institution. And later they use this data for their own observations or to implement some kind of specific aspects [of scientific research].”
I see that there are two telescopes here pointing at the sky, sort of clamped next to each other. One is a long and thin telescope and the other one is short and wide. So what is the difference between the two?
“One is old and the other is quite modern. And the construction is different. The long, thin telescope is a very old telescope – more than 122 years old. It is a lens-type telescope with a 19cm diameter. The other more modern one is a Newtonian telescope which has two mirrors inside, the primary one measuring 30cm in diameter. And also as you can see, there is no eyepiece at the end of that telescope and at the top is a kind of big black box, wheresits our astronomical camera. We also use that camera to send images directly to a big screen...”
Pointing to a big screen TV which is here in the observatory...
“And the camera can capture more details. It is also nice for visitors to observe something through one telescope and then compare this with what is on the screen [from the other].”
And right now in the news we are hearing a lot a planetary alignment that is taking place this month. All eyes are on the astronomical community at the moment. So could you explain what this alignment means.
“It means that from the point of view of the Earth, we can see almost all the planets in the sky. We can go from the west, seeing Saturn and Venus, and then continue to the east and see Jupiter and Mars...”
As the Sun is setting, we are now going to look at a couple of planets. What will be the first one?
“The first planet will be Venus. You can see it without a telescope and it is a very bright spot in the sky.”
Oh, yes. Because we are not in complete darkness yet, but we can already see a bright star. So that is Venus. And of course Venus being in a narrower orbit around the Sun is always visible only near the Sun, never far away from the Sun. I remember learning that recently...
“Yes. It’s an inner planet.”
So, I’m just stepping up the ladder now and looking through the eyepiece. Oh, my goodness! I am looking at the planet Venus. Very unexpectedly, I can see a crescent. So it is not fully illuminated, but is partly in shade, just like the moon.
“Yes, exactly. Because it is a matter of geometry in terms of the position of the Sun, Earth and Venus. Again, Venus is an inner planet. So all inner planets, Mercury and Venus, can change phases.”
But I suppose that unlike the Moon, I am not going to see any craters or other surface details on Venus, am I?
“No, that’s not possible. Because Venus is covered by a very thick atmosphere and so we can’t see any surface details. We can only see upper layer of the atmosphere. And it is a really hostile planet! No one could live there, because the surface temperature is more than 400 degrees Celsius, and the pressure is like 80 Earth atmospheres. Hellish!”
So, Milan, what is next?
“We can try Saturn!”
Ok, Saturn. And because we live in the computer age, he is typing in some coordinates into a device, which them helps him to manually move the telescope into position...
We can hear the sound of the dome being turned...
Apparently the position of Saturn is getting worse and worse now with respect to the Earth, moving closer, from our point of view, to the Sun.
Now I am just stepping up the ladder to look through the telescope again. Oh, yes, I can see it. I can see the rings, which I think makes this the most beautiful planet.
“Absolutely.”
If there is one planet you have to see with a telescope, it has to be Saturn. Because those rings are just spectacular. And when our atmosphere is still enough, you get a kind of wonderfully sharp view. And then it is just you and this planet and it is just a fantastic experience. So, Milan, what can you tell me about Saturn?
“The rings are comprised mostly of ice. That’s the reason why we see them so well. Because the ice has very good reflective properties. Of course Jupiter, Uranus and Neptune also have rings. But they are from dust.”
So only Saturn has ice rings, and the other planets have dust rings, and that helps with why we can see these rings so well compared to the others.
“Exactly.”
We’ve repositioned the telescope and now I am looking at the planet Jupiter, which features brown-coloured bands of clouds that swirl around this planet. And around Jupiter I can see several bright specks, which are Jupiter’s moons. Milan, what exactly am I looking at here?
“You can see the four Jovian or Galilean moons. These are Callisto, then we have Io, and the closest moon to Jupiter is Europa. And on the left side you can see Ganymede. Ganymede is the largest moon in the Solar System, even bigger than the planet Mercury. Europa is covered by ice oceans, and Io has volcanic activity on the surface.”
Ok, so we are going to see one more planet...
“Yes, the rusty planet (the Red Planet)! Mars.”
We’ve now repositioned the telescope towards Mars, which is actually in a position right next to the Moon at the moment. And to the right we can see Jupiter visible to the naked eye.
Once again I am stepping up the ladder. I am seeing that it is very red, almost a kind of salmon-like pink-red. Milan, Mars is famous for its polar ice caps. I am trying to figure out if I can see them or not.
“You can see them. The polar caps are made of frozen carbon dioxide and water ice.”
I can see the caps now. The effect of our atmosphere creates a slight shimmering, so sometimes it looks sharper, and sometimes less sharp.”
“Yes, such is the effect of our atmosphere.”
And I am seeing details on the surface apart from the polar ice caps – a slight darker band in the middle of the planet.
“Those areas [reflect the fact that] Mars has the biggest volcano in the Solar System and also the largest canyon.”
Now we are going to look at one last object in the night sky. What have you chosen as the final thing to see?
“It will be a multi-star. Not a double star or a triple star, but a multi-star.”
I am stepping up once again, climbing up the ladder. And we have only moved the telescope a little bit to the left from where Mars and the Moon are. To the naked eye, it looks to me like one star. But when I look through the telescope I see one, two, three...
“You should see three stars. It is Castor, a star in the Gemini constellation. In reality there are six stars, but we can see by telescope only three stars. The two very bright stars are Castor ‘A’ and ‘B’...”
Very close to each other...
“And then there is a really small, fainter star that is Castor ‘C’ and this is a red dwarf star. Its size is half of that of the Sun. And it has half the mass of our Sun as well, with a surface temperature of around 3000 degrees Celsius.”
What better way to end than with a red dwarf star! Milan Uhlár, thank you very much. It has been an absolute pleasure to visit the Ďáblice Astronomical Observatory today.
“I really appreciate that you spent some time with me to explore the night sky. Thank you very much.”
