Big Moon - Small Moon

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Big Moon - Small Moon

Postby Aratus » Tue Nov 15, 2016 8:12 pm

A 20 minute gap in the cloud last night allowed me to quickly record and image of the full moon. For comparison here is the full moon last night which coincided with a close approach, and the full moon last February when it was at its furthest this year.

Image

The distance to the moon varies every month. Catching the full moon when it is at its nearest seems to have become a feature of popular journalism in recent years, although it isn't unusual, or particularly noticable. The photos in newspapers and news websites seem to be taking the moon near to the horizon, and using special lenses to make the moon look big in comparison to some distant object. It is a trick that can be done every full moon, and is not indicative of it being large. With the photo above the difference can be seen straight away, and can be measured.
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, with an 80mm refractor as a guidescope. They are housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC for imaging.
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Re: Big Moon - Small Moon

Postby andrewscomputers » Tue Nov 15, 2016 10:30 pm

Hi Aratus I can see the difference,I tried last night to view but was cloudy all evening.I did manage to see it's brightness through the cloud,it was the first time I heard it on the news for such an event.
Thks
Andy
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Re: Big Moon - Small Moon

Postby Aratus » Fri Nov 18, 2016 7:03 pm

There was a big fuss in September 2015 over what they called 'a super moon'. From an astronomical point of view a large full moon is pretty useless. However a large moon at any other time enables details to be seen that otherwise might be too small. In in any lunar cycle it worth finding out when it is closest and mark it in the diary. For instance on 12th December & 10th January the biggest moons will be nearly full again, but on 6th Feb 2017 the biggest moon will be a waxing gibbous moon. 3rd March 2017 the biggest moon will be a crescent.

If anyone wants to take comparison photos next year the smallest full moon is 8th June, and the largest is on 4th December. You need to decide which telescope and lens combination you are going to use, and then always use that to take the photos. I always use a f6.3 focal reducer so the whole moon fits on to the frame.
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, with an 80mm refractor as a guidescope. They are housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC for imaging.
Aratus
 
Posts: 625
Joined: Tue Jan 12, 2016 2:17 pm
Location: East Lincolnshire

Re: Big Moon - Small Moon

Postby Gfamily2 » Sat Nov 19, 2016 11:13 am

As the moon cleared the clouds on Monday I took a spotting scope on a fixed tripod and timed how long it took for the moon to move completely out of the field of view.
My aim is to repeat the exercise a few days after the next new moon, when hopefully Earthshine will make the whole disc visible. The moon will then be near apogee so should take significantly less time as it'll be smaller in the sky.
The timing I have for the Full Moon is 2'25"
If I manage a second timing I'll report back.
Scopes: Meade 8" SCT, Skywatcher 127mm Mak
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
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Re: Big Moon - Small Moon

Postby Aratus » Sat Nov 19, 2016 12:32 pm

That sounds an interesting way of measuring the angular size of the moon. However, you will have to take into account the declination of the moon when measuring its movement across the field of view. The rotation of the earth moves things more slowly the further away it is from the celestial equator. The equation is, time x cos(d) x 0.25 where 'd' is the declination of the moon at the time of observation. This equation assumes you measure time in seconds and want the angle in arc minutes.

Edit:
To work through your example the time was 145 seconds and the moon was about 16.6 degrees in declination on 18th Nov so the angular size of the moon was 145 x cos(16.6) x 0.25 = 34.7 arc minutes. That is in the right order but it is probably best to do 6 or more readings knock off any extreme values and average the rest. That will give a more accurate result.
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, with an 80mm refractor as a guidescope. They are housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC for imaging.
Aratus
 
Posts: 625
Joined: Tue Jan 12, 2016 2:17 pm
Location: East Lincolnshire


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