A pre-lit Christmas tree might not have all of the lights working because of a broken wire. There is also the chance that on the pre-lit tree if one bulb is burned out the entire string will not work. Check the bulbs in other working sockets by exchanging bulbs to find the one not working.
The Northern Lights occur in the ionosphere, the highest level of the atmosphere, so all the others layer usually do NOT contain the Northern Lights.
The Thermosphere
The Earth's spheres that produce Southern Lights is the Thermosphere. This layer of air is hot and thin. The Aurora Borealis also occurs in this layer.
The ionosphere is responsible for the northern light. The ionosphere is the outermost layer of the thermosphere.
The Inosphere
Thermosphere (Ionosphere).
This layer contains the ionosphere, which causes the northern lights and the reflection of radio waves. APEX
Node
The "Northern Lights" (or Aurora Borealis) and their southern counterpart the Aurora Australis are formed high in the atmosphere in the ionosphere, which is sometimes considered as part of the thermosphere, the outermost actual atmospheric layer. Above this layer, the exosphere has so few molecules that they can escape into space.(see the related question below)
Router is a Layer 3 (Network Layer)device that checks packet's IP Address at input interface & routes them to interface connected to destination network if available.
Skin is connected to the body by a layer of connective tissue called fascia.
Christmas light hooks can be nailed or hooked onto a thin layer. The best placed to hang a Christmas light hook include the edge of the roof and the porch.