Copernicus

It doesn't take many lunar observing sessions before ending up with a picture of Copernicus. Here's a picture I took during an observing session in March. It was a near full moon so the surface is looking rather flat.


I got the webcam orientation a bit wonky so north is roughly pointing towards 4 o-clock. Copernicus is a relatively new crater being around 800 million years old. Typical of many Copernican period craters it has a prominent ray system and the crater hasn't been flooded with lava - some of the features inside the crater are obvious even with this little shadow.

The relatively bright crater in the bottom-right corner is Pytheas, a crater of similar age to Copernicus and located in the southern part of Mare Imbrium. To the right of Copernicus in this picture is the mountain range Montes Carpatus which is 2-3 billion years older than the two craters just mentioned.

The two medium-sized craters situated at 11 o'clock are Reinhold and Reinhold B, both of which are much older craters than Copernicus.

It's a shame I didn't pick a slightly shifted field of view - a little more towards the top-right would have given a better view of Montes Carpatus, but just out of shot in the bottom-left is Eratosthenes which would have made a great target alongside Copernicus. Maybe next time.

Mersenius and Gassendi

Mersenius and Gassendi are two large craters in the southwestern part of the Moon and are the next step in my quest to image the entire lunar surface.


Of the two large craters in the middle of the picture, Mersenius is on the left and Gassendi on the right. The large, smooth, dark region at the bottom of the picture is Mare Humorum and North is roughly towards one o'clock.

Mersenius is 84km in diameter, 2.3km deep and was formed nearly 4 billion years ago. The interior of the crater has been flooded by basaltic lava which has solidified into a central dome shape and covered many other features. The rim of the crater is heavily worn particularly at the northern edge. The small crater Mersenius N can be seen lying across the southwestern rim.

Gassendi is a larger and apparently shallower crater. Similarly to Mersenius, Gassendi has been filled with lava but some of the multiple central peaks are still visible. The crater situated on the northern rim is Gassendi A and the appearance of the two craters has been likened to a diamond ring.

Spectroscopy

At the beginning of this year I added a new toy to my stargazing kit - the Star Analyser 100 from Paton Hawksley. I'd always had a hankering for getting into stellar spectroscopy and this looked like the perfect starting point - spectrometers are VERY expensive, the Star Analyser could get me started for under £100.

Spectroscopy is essentially analysing the light from an object and seeing how the intensity of the light varies as a function of wavelength (i.e. looking at the spectrum of the object). This can reveal all manner of things such as the temperature of the object, what it is made of and how fast it is moving. This is detailed analysis that needs finely tuned equipment and the Star Analyser tries to fill a gap in the low end of the market - it won't show the detail but it's fun, easy to use and informative.

The Star Analyser is just like a standard filter - it screws into any eyepiece and off you go. When combined with my webcam it means I can take pictures of stellar spectra for further analysis. Here are some spectra I took of Arcturus:



As you can see, the results are very consistent and show some detail - the red appearance of Arcturus is obvious and the dark line on the middle-right is one of the Fraunhofer absorption lines due to oxygen in the Earth's atmosphere.

To show the difference between a relatively cool K-type star like Arcturus and something a bit hotter, here's a spectrum taken of Sirius an A-type star:



The spectrum is much more green/blue and other features are visible such as the H-Beta line in the light-blue section.

Another interesting use of the Star Analyser is to compare stellar magnitude. I find it much easier to compare the brightness of two spectra rather than looking directly at the stars. Providing I keep the webcam settings the same and compare stars of the same spectral type then I get a decent comparison of magnitude. I tried this with the main stars in the Plough (which are mostly A-type stars) and got a magnitude comparison and therefore distance approximation. I haven't had much chance to play around with this yet and feel it needs a new post anyway! I'll also follow this post with a description of how to get a spectrum from using the Star Analyser.