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Astronomers

A group for people who enjoy the stars. :)

Members: 165
Latest Activity: Mar 18

Discussion Forum

Possible shape of the universe

Started by Donald L. Engel. Last reply by Kiljoy616 Mar 18. 9 Replies

All things Pluto

Started by Joan Denoo. Last reply by Gerald Payne Sep 17, 2015. 2 Replies

The Five Planets in the Sky.

Started by Visvakarman Svetasvatara-Upanish Jun 17, 2015. 0 Replies

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Comment by Gerald Payne on April 24, 2015 at 7:12pm

A doublet.

Comment by Mick Ohrberg on April 24, 2015 at 7:06pm

Gerald - the Newtonians have one big drawback: The eyepiece can end up in really backbreaking positions, depending on if you have an alt-az mount. If you have a GEQ mount you can normally rotate the scope in the mounting rings to get the ep in a good spot for you. 

Is your refractor a doublet or a triplet? A 150mm refractor scope could command a fair price, depending on the optics configuration.

Comment by Gerald Payne on April 24, 2015 at 6:57pm

I own a 150 refractor. Due to back problems I can no longer comfortably access the eyepiece. I've been thinking of trading it in for a Newtonian. I wonder if anyone's got any experience with the comfort of a Newtonian. Their lining up for a swap but I don't want to end up in the same boat with a lesser scope.

Comment by Gerald Payne on April 24, 2015 at 5:54pm

Fantastic close up of comet 67P on ESA's flicker. No news about Philae sadly.

Comment by Idaho Spud on March 22, 2015 at 2:06pm

Beautiful Aurora light shows Patricia.  I think the one like a rainbow is especially gorgeous.  Yellow, green, purple, and blue.

I've never seen any, but would love to.

Comment by Joan Denoo on March 21, 2015 at 7:05pm

Patricia, these are beautiful computer wallpapers. They make me want to dance to their rhythms. 

Comment by Joan Denoo on March 21, 2015 at 7:00pm

Gerald, I like your description of the challenges facing Philae. What an adventure that has been. When I was a kid camping out on the St. Joe River, in northern Idaho, the nights were so clear of dust and light pollution, we thought we could see forever. 

Comment by Joan Denoo on March 21, 2015 at 6:53pm

I saw them the two years I lived on the Kenai Peninsula, Alaska. They are beautiful and in some instances, we could read a newspaper or book by their brightness. The brightest I ever saw them was on a camping trip near Fairbanks. They take my breath away. I wonder what it was like to the ancient native population when they saw such sights?

Comment by Gerald Payne on March 21, 2015 at 6:26pm

Your not alone in wishing to see the northern lights first hand Patricia. I believe Copernicus never got to see Mercury. And of course Edmond Halley never witnessed the eponymous comet. I wonder if Jesus witnessed the resurrection?

Comment by Gerald Payne on March 19, 2015 at 3:13pm

With Philae now receiving twice as much solar energy as it did last November when it finally came to rest in a shaded spot on Comet 67P, the communication unit on the Rosetta orbiter has now been switched on to call the lander. Although it is probably still too cold for the lander to wake up, the prospects will improve with each passing day.

Waking up at the right temperature and energy

Several conditions must be met for Philae to start operating again. First, the interior of the lander must be at least at –45ºC before Philae can wake up from its winter sleep. At its new landing site – Abydos – only a little sunlight reaches Philae, and the temperatures are significantly lower than at the originally planned landing location. In addition, the lander must be able to generate at least 5.5 watts using its solar panels to wake up.

As soon as Philae ‘realises’ that it is receiving more than 5.5 watts of power and its internal temperature is above –45ºC, it will turn on, heat up further and attempt to charge its battery.

Contact during comet daytime

Once awakened, Philae switches on its receiver every 30 minutes and listens for a signal from the Rosetta orbiter. This, too, can be performed in a very low power state.

It could be that the lander has already woken up from its winter sleep some 500 million kilometres away from Earth, but does not yet have sufficient power to communicate with Rosetta, which relays Philae’s signal back to Earth. Philae needs a total of 19 watts to begin operating and allow two-way communication. Between 12 and 20 March, the Rosetta orbiter is transmitting to the lander and listening for a response. The most likely time for contact is during the 11 flybys where the orbiter’s path puts it in a particularly favourable position with respect to the lander during comet ‘daytime’ – when Philae is in sunlight and being supplied with power by its solar panels. Communication will be attempted continuously because Philae’s environment could have changed since landing in November 2014.

 

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