By Sarah Wroblewski

BOSTON (CBS) — There was a pretty cool sight in the sky today, a perfect ring around the sun!

This weather phenomenon is not uncommon, but cool to see and is called a halo. It is caused by high thin cirrus clouds about 20,000 ft in the sky. They can be very faint that it still looks mostly sunny! This type of cloud is made up of millions of very tiny, ice crystals. When the sun shines through it at just the right angle, the light splits or refracts and reflects and creates a perfect 22-degree circle or halo. The same thin clouds can cause a ring or halo around the moon at night. Mostly lunar halos are colorless, but at times can seem more red on the inside and blue on the outside. Colors can be more noticeable in halos around the sun like we saw today.

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There is an old saying: Ring around the moon means rain soon!

And sure enough… we have rain moving in tonight!

(WBZ-TV Graphic)

Many times, cirrus clouds move in ahead of a storm system and can signal precipitation with 24 to 48 hours. Well, after a glorious Sunday, rain will be heavy at times overnight.

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(WBZ-TV Graphic)

The steadiest showers move out early Monday with mostly cloudy skies and cooler temperatures.

Sarah Wroblewski