Showing posts from July, 2020

Telescope magnification

I get asked a lot of questions from a lot of people. All of these questions are good, but some are so good they get asked a lot. This is one of those questions. The magnification of a telescope is how much bigger your target looks compared to looking at it without the telescope. If you like, it's how much closer the target is going to look. Magnification is expressed in multiples, so if your telescope has a magnification of "50 times", it means that whatever you're looking at will look 50 times closer, or will appear 50 times bigger than without the scope. Remember that your telescope can have several eyepieces. Changing eyepieces changes the magnification. So, for watching the Moon, your 25mm eyepiece might give you just the view you want. However, if you want to look at Jupiter, all you get with a 25 is a dot, so you need more magnification. The 10mm eyepiece will give you a much closer image. But to calculate it, there's some mathematics involved. Your telescop

Getting a better Moon photo

Getting a better Moon photo? Easy!   In nearly every case, your first photo through the telescope is going to be the Moon. That's because the Moon is awesome. You know that it's something you absolutely have to do. I've written about attaching your mobile phone or DSLR to a scope before, and how you can get a single shot. But people often ask me how to get a better photo. Using video You use lots of shots. Here's my effort. A while back, there was a bit of sun, and the Moon was visible high in the blue sky when I got back from walking the dog. I fetched my camera and birding lens and put it on a tripod. I didn't want to get more sophisticated than that. I set the camera to manual, and focused carefully using the live view on the back of the camera. I set a 1/1000 second with ISO 200, and set the aperture to underexpose slightly. I didn't want any part of the Moon overexposed. Then I switched to video mode and shot for about a minute - during which a plane passed

Wishing Well cluster

A while back I posted a photo of the Jewel Box star cluster , NGC 4755. I did this for two reasons. First, I wanted to show you something you could reasonably expect to see using a small telescope in the suburbs (say, when you're in lockdown). Second, I wanted to show how large a field of view you'd get. I used two popular focal lengths, 650mm and 900mm, and the two eyepieces commonly supplied with our scopes, 25mm and 10mm. Then I said I'd post a few more of these clusters, hopefully to give you an idea of what you might be able to see with your own telescope. This has the somewhat curious name of the "Wishing Well Cluster", properly known as NGC 3532. It's also known as the Pincushion Cluster. Here it is: To find it, start from the Southern Cross and its pointers. This is high in the Southern sky in the early evening at this time of year (July). With your hand, measure the distance between the right hand pointer (Hadar) and the left hand Cross star (Mimosa)

Park birds and Ivanhoe Powerful Owl

The Wilson reserve is right on the Yarra, and opposite the reserve is a large golf course. Being part of the flood plain, there are not many buildings in the area, leaving some space for the birds. There’s a couple of billabongs as well, with plenty of undergrowth to attract small birds.  For many years there was a Powerful Owl roost here. Several years ago I found the local one in an uncomfortable way. I'd ventured out into a meander of the Yarra, where the owl was roosting. It was just after sunset, and I didn't know exactly which tree it used, so I wandered about aimlessly for a while. Eventually I heard the small sounds of the owl as it began moving about. I spotted a shadow in the lower canopy back away from the peninsula, and realised the owl had me cornered with water on three sides. This owl - it had been claimed - had removed the eye of a golfer on the other side of the river a year or two back, so I was a little nervous. As I watched it, the owl flew to a closer tree,

Noctilucent clouds

Fragile, ethereal and mysterious, they're being seen more in the last couple of decades. Could these wraiths be a portent of doom? Image of Noctilucent clouds over Uppsala, Sweden : Wikipedia Noctilucent clouds are thin, filament-shaped clouds that form in deep twilight. They look very beautiful, light against a deep blue background. But, yes, it looks like they have a dark side. They form in the coldest parts of the atmosphere, at an altitude of about 83,000 metres called the mesopause where the temperature is around -140°C. They're normally restricted to a circular area around the North pole, specifically between 55 and 65 degrees. What's more, they tend to happen only in Summer. They have been seen in the south, but very rarely. They were first reported in the late 1880s. Probably because this was soon after the eruption of Krakatoa, it was initially thought they were associated with volcanic activity, or with dust injected into the upper atmosphere by meteors. But ther