Conversation so far:
When was Sirius released?
Between 1988 and 1991, Clannad were involved in side projects including Atlantic Realm (1989) and The Angel and the Soldier Boy (1990).
What singles were from the Atlantic Realm album?
"Something to Believe In" features Hornsby on vocals and keyboards.
Were there any other singles from this album?
The title track was Pol's encouraging call to the environmental movement, and to the Greenpeace ship of the same name.
Did this album receive any awards?
Received with critical apprehension.
Why was the album received with critical apprehension?
Sirius was another different creation, just like their previous 3 albums.
What singles were from The Angel?
CANNOTANSWER.
How did the albums do on music charts?
Both albums proved to be a minor success, and also demonstrated once again that Clannad were one of the most acclaimed soundtrack artists in the music industry.
Did they go on tour during this time?
In 1989, Clannad embarked on their first worldwide tour.
Where did they go while on tour?
CANNOTANSWER.
What was a career highlight during this time?
Two greatest hits albums were released at around this time.

Question: What were the names of the greatest hits albums?
Self-contained rewrite: What were the names of Clannad's greatest hits albums?